Geobiological Aspects of the Southeast Florida Continental Reef Tract

Karl-Franzens-Universitaet Graz

Kenneth Banks

A thesis Submitted to the Faculty of Graduate Studies and Research in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy

Institut fuer Erdwissenschaften

Graz, Austria

2007

Table of Contents LIST OF FIGURES ...... 5 LIST OF TABLES ...... 11 LIST OF APPENDICES ...... 13

ABSTRACT...... 14

1 INTRODUCTION...... 16 INTRODUCTION...... 16

RATIONALE FOR THE STUDY OF THE SOUTHEAST FLORIDA REEF TRACT...... 17 GEOBIOLOGICAL APPROACH TO REEF STUDIES ...... 18 THESIS OBJECTIVES...... 18 REFERENCES...... 19

2 ACTIVE OPTICAL AND ACOUSTIC REMOTE SENSING METHODS OF CORAL REEF GEOMORPHOLOGY ...... 21 INTRODUCTION...... 21 REEF MAPPING...... 23

SIDESCAN SONAR...... 24 ACOUSTIC ECHO ANALYSIS...... 28 RoxAann...... 30 QTC View...... 33 Echoplus...... 35 BATHYMETRIC MAPPING...... 36

SINGLE-BEAM ECHOSOUNDERS...... 37 MULTI-BEAM ECHOSOUNDERS...... 38 ACTIVE OPTICAL METHODS (LASER) ...... 42 COMBINED METHODS...... 45 CONCLUSIONS ...... 45 REFERENCES...... 46

3 GEOMORPHOLOGY OF THE SOUTHEAST FLORIDA CONTINENTAL REEF TRACT (MIAMI-DADE, BROWARD, AND PALM BEACH COUNTIES, USA) ...... 52 INTRODUCTION...... 52 MATERIALS AND METHODS ...... 54

2 BATHYMETRIC DATA COLLECTION AND ANALYSIS ...... 55 SUBBOTTOM PROFILING...... 56 CORING ...... 56 ANALYSIS OF GEOMORPHOLOGY ...... 57 RESULTS ...... 57

OVERALL MORPHOLOGY ...... 58 THE OUTER REEF ...... 60 THE MIDDLE REEF...... 65 THE INNER REEF ...... 70 RIDGE COMPLEX...... 74 DISCUSSION ...... 75

SURFICIAL GEOLOGY ...... 75 DEPOSITIONAL FRAMEWORK ...... 78 RECONSTRUCTED GROWTH HISTORY ...... 79 ACKNOWLEDGMENTS ...... 82 REFERENCES...... 82

4 ENVIRONMENTAL GEOLOGY OF THE CONTINENTAL SOUTHEAST FLORIDA REEF TRACT (MIAMI-DADE, BROWARD AND PALM BEACH COUNTIES, USA) ...... 86 INTRODUCTION...... 86

REGIONAL SETTING ...... 90 Climatology...... 91 Hurricanes ...... 93 Regional Physical Oceanographic Processes...... 95 HOLOCENE CLIMATE...... 100 ENVIRONMENTAL RECORDS IN CORAL SKELETONS ...... 106 CHARACTERIZATION OF SOUTHEAST FLORIDA REEFS ...... 110

GEOMORPHOLOGY...... 110 BENTHIC HABITAT MAPPING...... 115 BIOGEOGRAPHY OF SOUTHEAST FLORIDA REEFS...... 120 PATTERNS IN REEF COMMUNITY STRUCTURE...... 126

REGION-WIDE BENTHIC COMMUNITY STRUCTURE ...... 126 CROSS-SHELF PATTERNS IN BENTHIC COMMUNITY STRUCTURE...... 131 FISH COMMUNITY STRUCTURE...... 137 Miami-Dade and Broward Counties...... 137 Palm Beach County...... 143 HUMAN IMPACTS AND CONSERVATION ISSUES ...... 147

WATER QUALITY...... 148 COASTAL CONSTRUCTION ...... 149 SHIP GROUNDINGS AND ANCHOR DAMAGE ON REEFS ...... 152 CLIMATE CHANGE...... 154 PRESENT STATUS OF REEF HEALTH ...... 155

3 CONCLUSIONS ...... 157 ACKNOWLEDGEMENTS ...... 158 REFERENCES...... 158

5 A SYNOPSIS OF THE GEOBIOLOGY OF THE SOUTHEAST FLORIDA CONTINENTAL REEF TRACT ...... 172 INTRODUCTION...... 172 BIOLOGICAL ASPECTS OF THE SOUTHEAST FLORIDA REEF TRACT.... 172 GEOLOGICAL ASPECTS OF THE SOUTHEAST FLORIDA REEF TRACT .. 180 OCEANOGRAPHIC INFLUENCES ON THE SOUTHEAST FLORIDA REEF TRACT...... 182 STATUS OF THE SOUTHEAST FLORIDA REEF TRACT AND PREDICTION OF NEAR-FUTURE TRENDS...... 185 REFERENCES...... 189

4 List of Figures

Fig 2.1: (a) Sidescan sonar systems can be operated simultaneously with multibeam sonar systems to obtain depth and bottom characteristics. (b) Sidescan transmits two acoustic beams (broad in the vertical plane; narrow in the horizontal plane), one to each side of the survey track line. (c) The transducers are mounted on a towfish pulled behind the survey boat ...... 25 Fig 2.2: Diagrammatic representation of first and second sonar returns (from Chivers et al, 1990)...... 30 Fig 2.3: First (E1) and second (E2) sonar return waveforms (from Schlagintweit 1995). RoxAnn integrates all of E2 and a portion of E1 (in blue)...... 31 Fig 2.4: QTC View Screen Display (from Quester Tangent, 1997)...... 35 Fig 2.5: Geomorphological studies can be greatly facilitated by the use of high- resolution XYZ data which can be used to create (a) surface images, (b) shaded relief images, and (c) depth contour plots...... 37 Fig 2.6: Multi-beam depth sounders, as their name implies, acquire bathymetric soundings across a swath of seabed using a collection of acoustic beams. Backscatter values of multi-beam bathymetry data can be used to characterize bottom types...... 39 Fig 2.7: SHOALS LIDAR system uses a laser to obtain depth measurements. A blue- green laser (532 nm) is used to optimize penetration depth. SHOALS references each depth measurement to a horizontal position accurate to 3 m and a vertical position accurate to 15 cm...... 43 Fig. 3.1: Study area in SE Florida, USA. (a) The red band offshore indicates the position of the SE Florida reef tract. (b) The reef tract borders three counties. Place names used in the text are shown. The Florida Keys reef tract is located south of Biscayne Bay. A patch of LIDAR bathymetry shows the gross morphology of the reef lines of Broward County. White lines show locations of the sub-bottom profiles...... 54 Fig. 3.2: (a) The north end of known Holocene reef framework in Palm Beach County is located at 26º43’N. (b) Bathymetric block diagram shows final stretch of recurved north section of the outer reef terminating immediately adjacent to outermost set of beach ridges that make up a large complex in northern Palm Beach County. Depth in m below sea level, northings and eastings are in Florida State Plane, US survey feet, NAD83...... 58 Fig. 3.3: (a) Location of the bathymetric block diagram (b), which shows clearly that neither the inner nor middle (which terminates further north) reefs correspond to the shelf-edge or outlier reefs of the Florida Keys. (c) Lower insert shows a terrace arching inward just north of the beginning of the Florida Keys reefs. It is not clearly resolved whether this inward-arching terrace on which the outer reef is located is the same terrace on which the shelf-edge reefs of the Florida Keys reef tract are located. The Fowey outlier reef is named after Shinn et al. (1991)...... 59 Fig. 3.4: (a) Inset shows the location of (b) subbottom profile and bathymetry of the outer reef...... 60 Fig. 3.5: (a) North part of the reef tract showing direction of dominant sand transport due to longshore drift. Throughout most of Palm Beach County, no inner or middle reefs are found. (b) Middle part of the reef tract, where all three reef lines, as well as the

5 ridge complex, are well-developed.(c) South part of the reef tract. The middle reef terminates before the inner and outer reef. (d) Maps show location of the bathymetric blocks...... 61 Fig.3.6: (a) Geomorphologic zonation of the outer reef. (b) Inset map shows location of bathymetric block diagram and depth transect...... 62 Fig. 3.7: Common geomorphic features on the outer reef. Bathymetry and subbottom profile show topographic low in outer reef framework. (a) Bathymetry and spur-and- groove structures are clearly visible. White line shows location of (b) subbottom profile. (c) Acropora cervicornis framework with collapsed rubble. Image was taken on the dropoff within the white square in (a). (d) Continuity in the northern part of the outer reef is lost and the reef breaks up into numerous individual reefs (a) or reef patches (d). (e) Map shows locations of (a), (b), (c), and (d)...... 64 Fig. 3.8: (a) Bathymetry and (b) subbottom profile of an outer reef gap, indicating that the gaps are due to antecedent topography...... 65 Fig. 3.9: (a) North and (b) south termini of the middle reef as detected by bathymetry. Spur-and-groove structures on the outer reef are clearly visible...... 66 Fig. 3.10: (a) Map shows locations of (b) bathymetry and subbottom profile of middle reef. The data indicate that the reef may be a shoreline deposit overlain by patchy coral frameworks. Subbottom resolution did not allow clear differentiation of coral framework versus other types of limestones. Dashed line indicates presumed Pleistocene/Holocene contact...... 67 Fig. 3.11: (a) Map shows location of (b) paleo-erosional features cross-cutting the inner and middle reefs...... 68 Fig. 3.12: Bathymetry shows intermediate ridge between (a) inner reef and middle reef and (b) outer reef (with collapse features) and middle reef. (c) The outcrop drawing is modified from Shinn et al. (1977). (d) Map shows location of features...... 69 Fig. 3.13: (a) Bathymetry and (b) subbottom profile of middle and inner reef. Middle reef seems to be a shoreface with patchy reef development. The inner reef at this location seems to have a similar structure. (c) Map shows location of bathymetry and seismic line...... 71 Fig. 3.14: Two different cores through the inner reef off Broward County. (a) shows the entire core. Between “top” and “3 m”, all fragments are Acropora palmata. Above the hatched line, indicating contact between reef and underlying Anastasia Formation, is a Diploria strigosa. Note that both top and bottom of the Diploria specimen are eroded and covered with a gray cement crust, indicating specimen is likely not in growth position. (b) Reef core is arranged horizontally. All fragments are of Acropora palmata...... 72 Fig. 3.15: (a) Bathymetric block diagram of ridge-complex showing purported wave-cut cliff. The cliff could have been a shoreline during the time when the inner reef was alive (until about 3.4 ka, see Table 1). (b) Map shows location of block diagram... 75 Fig. 3.16: Windroses throughout the study region show increasing northerly component of fetch and wind, which would result in higher-energy wave conditions in the northern counties. WIS=wave information system. Axes are relative contribution of wind magnitude to the illustrated sectors. Dominant sector is colored gray. Black lines represent relative fetch (distance over which wind generates waves). Arrows show infinite fetch in the N and NNE due to exposure to open ocean...... 76

6 Fig. 3.17: (a-c) Interpreted sediment cores from sand deposits between SE Florida middle and outer reefs. The sand is a mixture of quartz and carbonate. (d) Map shows location of (e) bathymetry on which core locations are noted (white dots)... 79 Fig. 3.18: Proposed sequence of development of the SE Florida reef system. BP = before present. (a) In the late Pleistocene/early Holocene, sand ridges were indurated during lowstands. (b) During early Holocene sea-level rise, the outer reef initiated growth and accreted. The ridge underlying the middle reef may have been a shoreline. (c) With increasing sea-level rise, outer-reef accretion ceased, and massive corals settled on the previous shoreline to form the middle reef. The inner reef initiated as a backstepped Acropora palmata reef. The sea cliff on the ridge complex (arrow) may have been the locus of a temporary shoreline during the growth phase of the inner reef. (d) Sea-level reached its present level, and middle and inner reefs ceased growth at about 3.6 and 3.4 ka...... 80 Fig. 4.1: Location map of Southeast Florida with key geographic features...... 87 Fig. 4.2: The continental Southeast Florida reef tract extends from Biscayne Bay in Miami-Dade County (N25o35’) northward to West Palm Beach in northern Palm Beach County (N26o43’). It is composed of a complex of limestone ridges and shelf- edge and mid-shelf reefs.Rohmann et al. (2005) estimated that 30,801 km2 of inshore areas situated in less than 18.3 m depth around South Florida could potentially support shallow-water coral reef ecosystems. An area of 19,653 km2 remains outside the Florida Keys and Dry Tortugas and is discussed here with regard to SE Florida and in chapter 4 by Hine et al. with regard to the West Florida shelf. In comparison, estimates for other areas capable of providing habitat for reefs and reef-associated fauna in the United States are 108 km2 in Guam, 1,231 km2 in the Main Hawaiian Islands and 2,302 km2 in Puerto Rico...... 88 Fig. 4.4: Monthly average, minimum, and maximum water temperatures from data collected hourly on the seafloor of the: a ridge complex; b inner reef; c middle reef; d outer reef offshore central and south Broward County from July, 2000, to December, 2003. Cross-shelf variations in water temperature are illustrated by comparing ridge complex and outer reef water temperatures: e minimum water temperature on ridge complex are lower that the outer reef; f maximum temperatures are higher on the ridge complex...... 96 Fig. 4.5: Wave conditions throughout the Southeast Florida region show increasing northerly component of wave energy flux in the northern part of the region. Information based on US Army Corps of Engineers Wave Information System (WIS) hindcast data (http: frf.usace.army.mil/cgi-bin/wis/atl_main.html). WIS data is hindcast at 3-hour time steps for 1956-1975: a mean and maximum wave height (Ho) and period (Tp) increase with latitude (large maximum wave heights and periods at N25.5o are due to the passage of Hurricane Andrew in 1992); b vector plot of average wave direction and relative magnitude shows that average wave direction trends more northerly with increasing latitude and wave magnitude increases with latitude...... 99 Fig 4.6: Data and coral-peat Holocene sea-level curve. MWP 1A and 1B refer to periods of very rapid deglacial sea-level rise dring which A. palmata reefs could not keep up with rise. Overlap between two solid lines indicates a progressively larger depth offset over that time frame (modified from Toscano and Macintyre 2003)...... 103

7 Fig. 4.7: a) Montastraea faveolata coral head 2.5 m in height with core X-radiograph on right dating this coral back to 1694. b) M. faveolata coral head 2 m in height and dating back to the early 1800’s...... 108 Fig. 4.8: Canal discharge data from North New River Canal illustrating high levels of discharge from 1940 to 1970. Arrows indicate 1940, 1970, and 2000 on coral core X-radiograph below. Note high density skeleton (dark) and low extension rate from 1940 to 1970 compared with 1970 to 2000...... 109 Fig. 4.9: Bathymetric block diagrams showing representative samples of morphology of a) the ridge complex, inner and middle reef, b) the outer reef. Inset map shows location of bathymetry blocks (modified from Banks et al. 2007 by permission of Springer)...... 111 Fig. 4.10: Cross-sections of the ridge complex and reef tracts offshore of Southeast Florida. Bathymetry is extracted from a Lidar dataset of Broward County (Banks et al. 2007)...... 115 Fig. 4.11a: Habitat maps for the Continental SE Florida reef tract (Palm Beach County) based on a combined method approach using laser bathymetry, acoustic ground discrimination, visual groundtruthing (Walker et al. 2007). (modified from Walker et al. 2008 by permission of Journal of Coastal Research)...... 117 Fig. 4.11b: Habitat maps for the Continental SE Florida reef tract (Broward County) based on a combined method approach using laser bathymetry, acoustic ground discrimination, visual groundtruthing (Walker et al. 2007). (modified from Walker et al. 2008 by permission of Journal of Coastal Research)...... 118 Fig. 4.11c: Habitat maps for the Continental SE Florida reef tract (Miami-Dade County) based on a combined method approach using laser bathymetry, acoustic ground discrimination, visual groundtruthing (Walker et al. 2007). (modified from Walker et al. 2008 by permission of Journal of Coastal Research)...... 119 Fig. 4.12: Map showing individual collection sites for the study of genetic connectivity along the SE Florida coastline (color scheme corresponds to Fig. 4.14.). Blue arrows depict a counter current flowing through Hawk Channel (after Yeung & Lee 2002). Inset shows the four major collection locations relative to the collection site in Belize: PB, Palm Beach; FT, Ft Lauderdale; LK, Long Key; KW, Key West; GVS, Glover’s Reef. Depth contour data from http://www.ngdc.noaa.gov/mgg/ibcca. .. 121 Fig. 4.13: Richards et al. (2007) used the amphipods: a Leucothoe kensleyi; b L. ashleyae; c brittle star, Ophiothrix lineata, which are all commensals with: d the sponge, Callyspongia vaginalis, to study gene flow among reefs in the Southeast Florida biogeographic region. (photos by: a, b Vince Richards; c scanned with permission from Hendler et al. (1995))...... 122 Fig. 4.14: Statistical Parsimony networks depicting the relationship among different mitochondrial COI haplotypes for (A) Leucothoe kensleyi, (B) Leucothoe ashleyae, and (C) Ophiothrix lineata. Colored circles = individual haplotypes; small black circles = haplotypes that hypothetically should exist in the population, but were not sampled; connecting lines = one base pair mutation. Circle size for each haplotype is proportional to its frequency of occurrence and all three networks have the same scale. Different colors correspond to the five major geographic sampling regions (see Fig. 4.12). Due to the large genetic distance between the Florida and Belize L. ashleyae haplotypes (79 base pair mutations), there is no statistical support for any

8 connection point between them. Consequently, connection of these haplotypes in the same network is precluded. Networks were created using the software package TCS version 1.13 (Clement et al. 2000)...... 125 Fig. 4.15: a, b) The cyanobacteria, Lyngbya confervoides and L. polychroa formed persistent blooms on the reefs in 2003 and smothered many reef organisms, particularly branching octocorals, such as Pseudopterogorgia spp. c Extensive blooms of Cladophora liniformis, Enteromorpha prolifera, Centroceras clavulatum, and others bloomed on inter-reef sand plains and reef tracts of northern Broward County and southern Palm Beach County in the spring of 2007. (photos by: a, b Karen Lane; c )...... 129 Table 4.6: Average relative faunal cover for ridge complex and reef tracts of Southeast Florida. FWCC (2006) data averaged over 2003-2004 and based on 3 sites per county (4th site in Broward is large stand of Acropora cervicornis). Two Broward sites have unusually high stony coral cover (one, 40% cover A. cervicornis and one, 12% cover of massive corals on ridge complex sites). Values in parentheses do not include these high cover sites. Data from other studies are averaged over all sites for each county...... 130 Fig. 4.16: Photos of ridge complex communities illustrate: a) and b) typical flat pavement-like substrate and abundance of octocorals; c) the encrusting zoanthid, Palythoa caribaeorum, is common on the ridge complex and inner reef; d) patches of relatively high stony coral cover are occasionally found on back- and foreslopes; e) and f) relatively large, monotypic patches of Acropora cervicornis are found offshore central Broward County (photos by: a,e,f, Kenneth Banks; b, c, d, David Gilliam, Susan Devictor)...... 133 Fig. 4.17: Photos of the outer reef illustrate: a) typical diversity of sponges, octocorals and scleractinians; b) the massive sponge, Xestospongia muta, is common on all reef tracts in Southeast Florida; c) the alcyonacean, Icilligorgia schrammi is common on the outer reef and areas of high rugosity on the middle reef; d) reef-perpendicular sand channels commonly incise the outer reef (photos by David Gilliam, Susan Devictor)...... 134 Fig. 4.18: a)...... 141 Fig. 4.19: Persistent deposits of silt/clay size sediments were found in sediment depressions and topographic lows on the a reef tract and b inter-reef sand plains following the passages of hurricanes, Charley, Frances, Ivan, and Jeanne, in 2004 (photos by: a Vladimir Kosmynin; b,c Kenneth Banks)...... 147 Fig. 4.20: General location of treated human wastewater outfall pipes in Southeast Florida that discharge effluent on lower foreslope of the outer reef...... 150 Fig. 4.21: Position of shipgroundings near Port Everglades, Broward County. Most groundings are due to ships breaking anchor and drifting from the anchorage during onshore winds...... 153 Fig. 4.22: a) The boring sponge, Cliona delitrix, occurs extensively offshore Southeast Florida and may indicate human sewage contamination of the coastal waters (Ward- Paige et al. 2005). b) Aerial photo of the hardbottom adjacent to the north jetty at Hillsboro Inlet shows high coverage of C. delitrix that may correlate with tidal plume contamination. (photos by: a K. Banks; b D. Behringer)...... 156

9 Fig. 5.1a: Habitat maps for the Continental SE Florida Reef Tract based on a combined method approach using laser bathymetry, acoustic ground discrimination, visual groundtruthing; Palm Beach County (modified from Walker et al. in press)...... 175 Fig. 5.1b: Habitat maps for the Continental SE Florida Reef Tract based on a combined method approach using laser bathymetry, acoustic ground discrimination, visual groundtruthing; Broward County (modified from Walker et al. in press)...... 176 Fig. 5.1c: Habitat maps for the Continental SE Florida Reef Tract based on a combined method approach using laser bathymetry, acoustic ground discrimination, visual groundtruthing; Miami-Dade County (modified from Walker et al. in press)...... 177 Fig. 5.2: Average minimum air temperatures during the period of 1948 to 2004 for Miami, Florida (NOAA 2005)...... 179 Fig 5.3: Advanced very high resolution radiometer (AVHRR)-based sea surface temperature estimates for the (a) Gulf of Mexico and (b) Western Atlantic, 13-14 March 1996, illustrating the location and spatial relationship of the Loop Current, Florida Current and Gulf Stream (modified from Ocean Remote Sensing Group, John Hopkins University Applied Physics Laboratory)...... 183

10 List of Tables

Table 3.1: A comparison of reef zonation and depth between the reef tract of the Florida Keys and southeast Florida shows similar morphology. When depths for the southeast Florida reef tract are normalized (adjusted) to the Keys reef flat depth, zone depths are also similar...... 62 Table 3.2: Reef surface radiocarbon ages for the relict coral reef tracts offshore Broward County, Florida. Reference 1: Lighty et al. (1982), calibrations in Toscano and Macintyre (2003); 2: Precht et al., unpublished data, calibrations in Toscano and Macintyre (2003)...... 70 Table 4.1: Climate data for West Palm Beach and Miami, Florida (Palm Beach County, upper number ; Miami-Dade County, lower number). Temperatures (Co) are based on means from 1971-2000. West Palm Beach and Miami wind data are based on means from 1942-2005 and 1949-2005, respectively (Tave=average monthly temperature, Tmax=maximum monthly temperature, Tmin=minimum monthly temperature, Wave=average monthly wind speed (m/s), Wdir=average monthly wind direction) (NOAA 2005)...... 92 Table 4.2: Storm frequencies for Southeast Florida (USACE 1996). Number of tropical storms or hurricanes passing within a 50-mi radius of Palm Beach, Broward, and Miami-Dade Counties (a single storm may affect more than one county)...... 94 Table 4.3: Southeast Florida tidal inlet characteristics (Stauble 1993, Powell et al. 2006)...... 97 Table 4.4: Growth Correlations for Montastraea faveolata (M.f.) for mid (9m) and deep (18 m) depths...... 110 Table 4.5: Average relative bottom cover for ridge complex and reef tracts of Southeast Florida. FWCC (2006) data averaged over 2003-2004 and based on 3 sites per county (4th site in Broward is large stand of Acropora cervicornis). Two Broward sites have unusually high stony coral cover (one, 40% cover A. cervicornis and one, 12% cover of massive corals on ridge complex sites). Values in parentheses do not include these high cover sites. Data from other studies are averaged over all sites for each county...... 127 Table 4.7: Average relative bottom cover for ridge complex and reef tracts of Broward County. FWCC (2006) data averaged over 2003-2004 and based on 3 sites per county (4th site in Broward is large stand of Acropora cervicornis). Two Broward sites have unusually high stony coral cover (one, 40% cover A. cervicornis and one, 12% cover of massive corals on ridge complex sites) and are not included in the average values...... 135 Table 4.8. Average faunal density for ridge complex and reef tracts of Broward County. Gilliam et al. (2007) data averaged over 2003-2004 and based on 3 sites per county (4th site in Broward is large stand of Acropora cervicornis). Two Broward sites have unusually high stony coral cover (one, 40% cover A. cervicornis and one, 12% cover of massive corals on ridge complex sites) and are not included in the average values...... 136 Table 4.10: Grouper (Serranidae) abundances from point-count surveys in Broward County, Florida and Dixie Shoals (Florida Keys)...... 139

11 Table 4.11: Top 20 nearshore species listed for both N and S Palm Beach County with sighting frequencies. “N FREQ” is the sighting frequency for north Palm Beach County. “S FREQ” is the sighting frequency for south Palm Beach County...... 142 Table 4.12: Top 20 nearshore species listed for both N and S Palm Beach County with sighting frequencies. “N FREQ” is the sighting frequency for north Palm Beach County. “S FREQ” is the sighting frequency for south Palm Beach County...... 144

12 List of Appendices

Appendix 4.1: List of species reported for Southeast Florida ridge complex and reefs170

13 Abstract

The SE Florida continental reef tract consists of shore-parallel, non-accreting, Holocene reefs (mid-shelf and shelf-edge), inshore of which are lithified carbonate sand ridges. The reefs extend along the continental coast of SE Florida from Biscayne Bay (N25o35’) in Miami-Dade County northward to offshore of Riviera Beach (N26o43’) in northern Palm Beach County, a distance of 128 km. The reef developmental history appears to be one of backstepping in response to sea-level rise, contemporaneously with other back-stepped reefs in the Caribbean.

The outer reef (shelf-edge) is of Acropora palmata framework and is a linear structure that is more or less continuous from Miami-Dade to Palm Beach County and, as such, is one of the longest continuous reef structures in the Western Atlantic. It is co-linear with the modern Florida Keys reef tract but its structural relationship cannot be clearly resolved without further study. The upward growth of the outer reef ceased approximately 8,000 cal BP (calibrated 14C age before present).

A middle reef (mid-shelf) may represent a remnant shoreface with continuous reef framework. Its growth ceased approximately 3,700 cal BP.

An inner reef (mid-shelf) of Acropora palmata framework is perched on shoreline deposits. It ceased growth approximately 6,000 cal BP.

Inshore of the inner reef are several nearshore ridges composed of coquina or carbonate/quartz sandstone.

The continental SE Florida reefs have a fauna similar to the Florida Keys, Bahamas and Caribbean, although community structure is different. The only major reef building coral missing from SE Florida is Acropora palmata, although isolated colonies do exist. The middle and outer reefs generally harbor denser benthic cover, dominated by sponges and alcyonacean soft corals. The inner reef is generally more sparsely settled, but has some large patches of dense Acropora cervicornis growth, which represents the northern latitudinal distributional limit for these corals.

14 Recent applications of high resolution hydrographic survey technology have allowed the examination of meso- and micro-scale (regional and local) geomorphology of the SE Florida reef tract and limestone ridge complex. Expansion of reef community structure studies via fixed study sites, landscape analysis, and acoustic ground discrimination methods are, for the first time, allowing the integration of regional reef geomorphology and ecology.

1 Introduction

Introduction

A complex of relict early Holocene shelf-edge and mid-shelf reefs as well as limestone ridges extends along the continental coast of Southeast Florida from offshore south Miami (N25º34’) northward to offshore West Palm Beach (N26º43’). The reefs are arranged linearly and parallel to the trend of the shoreline. They are separated by sandy sedimentary deposits of varying thicknesses that overly erosional hardground surfaces (Duane and Meisburger 1969a, b; Raymond 1972; Shinn et al. 1977, Banks et al. 2007). The reefs themselves are presently not framebuilding but are colonized by a rich tropical fauna otherwise characteristic of the West Atlantic/Caribbean reef systems. A number of variations on the definition of a reef exist and are discussed by Riegl and Piller (2000). The key points shared in several definitions, i.e., reef-associated biota colonizing biogenic (coral) framework of significant vertical relief apply to the Southeast Florida reefs.

It was long held that the shelf-margin coral reefs of the Florida Keys ended offshore of south Miami because of lower temperatures and the southward transport of siliceous sand (Vaughan 1910, Goldberg 1973). Even recently, Spalding et al. (2001) stated that the Florida Reef Tract begins offshore of Miami Beach and extends southward. Banks et al. (2007) proposed the terms, “SE Florida Reef Tract” to represent the continental portion of SE Florida and “Florida Keys” for the insular portion of SE Florida, south of Biscayne Bay (greater Miami area). This distinction is important because the Florida Keys reef tract is situated at the margin of a much wider shelf and is influenced by waters from Florida Bay as well as by the oceanic waters of the Florida Current (Ginsburg and Shinn 1993; Shinn et al. 1989; Lidz and Hallock 2000; Lidz et al. 2003). The continental reefs

16 to the north are situated on a much narrower shelf and are under greater influence of hinterland drainage but are lacking the effects of Biscayne Bay (except at the southern extreme) and Florida Bay.

Rationale for the study of the Southeast Florida Reef Tract Coral reefs and reef-associated biological communities are generally confined to low latitudes and the western coastlines of the world’s ocean basins. Warm equatorial surface currents deliver warm, oligotrophic waters to the western coastlines. If terrestrial inputs of sediment and freshwater are low, coral reefs may thrive and vertically accrete at a rate keeping up with moderate sea-level rise. The latitudinal limits of coral reef growth are based on temperature (<16–18oC) and generally considered to be 30oN and 30oS (Spalding et al. 2001). Well know exceptions to the latitudinal boundary are Lord Howe Island, Australia (31oS), and Bermuda in the Atlantic (>32oN). These reefs owe their existence to the warm ocean currents, East Australian Current and Gulf Stream, respectively (Spalding et al. 2001).

While the SE Florida Reef Tract falls within the latitudinal boundaries of reef development, it is a marginal setting subjected to an urbanized coastline, North American continental weather systems, and terrigenous inputs to the narrow continental shelf. These provide unique opportunities for the study of human impacts on coral reef biological communities, the effects of variable environmental conditions on reef biota, and explore inventive ecosystem management strategies.

Causes of termination of accretion of the SE Florida reefs remain a puzzle. A number of hypothesizes, summarized by Banks et al. (2007), have been proposed, but none are strongly supported by data. In light of current discussions on environmental change in the future and the effect on ecosystems, the geohistory of the SE Florida Reef Tract could provide a relevant analogue to what may happen to extant reefs in the Western Atlantic in a world of changing temperatures, rapid sea-level rise, and anthropogenic stress.

17 Geobiological approach to reef studies Geobiology, also know as biogeology, is a research area that is based on the premise that the developments of the biosphere and geosphere cannot be studied independently. In the context of coral reef systems it weaves together such disciplines as organism-level biology; physiological, community, and population ecology; physical oceanography; chemistry; sedimentology; and geomorphology with a goal of understanding how biological communities are structured by the physical environment.

While many ocean habitats are subjected to seasonal or larger scale periodic variation, there is often an underlying stability. For example, temperate coastal marine habitats may experience large temperature fluctuations from summer to winter, but there is a range of temperature variation that is rarely violated. Coral reefs, on the other hand, are typically found in a relatively narrow range of environmental conditions, however, they are subjected to aperiodic physical phenomena, such as hurricanes, that can alter reef architecture (Blanchon and Jones 1997) and/or the structure of biological communities. How does a community that is adapted to relative environmental stability respond to disturbance that may often be catastrophic? Similarly, in a geological time frame, how does a reef community respond to ‘climatic’ disturbance, such as catastrophic sea level rise events (sensu Blanchon and Shaw 1995)? Such questions are best answered using a geobiological approach, incorporating multiple disciplines.

The advent of cost-effective, high resolution bathymetric mapping has allowed a detailed analysis of the geomorphology of the SE Florida coral reef complex (Banks et al. 2007). This knowledge provides a vital back-drop for the incorporation of information from other disciplines into the picture of the region’s reefs, i.e., a geobiological approach.

Thesis objectives

The objectives of this thesis are: i) to describe the geomorphology of a high latitude complex of relict shelf margin and mid-shelf coral reefs and adjacent nearshore limestone ridges; ii) analyze the modern coral reef-associated biological communities colonizing

18 this reef complex; and iii) summarize the state of knowledge of Southeast Florida’s Holocene and modern climate in order to understand the environment under which this reef system developed, transitioned from living to relict reef, and redeveloped as a non- accreting coral reef-associated biological community. The thesis is written in a paper format and the objectives of the individual chapters are outlined below:

Chapter 2 summarizes high-resolution methods for large-scale study of geomorphology and coral reef physical mapping. Chapter 3 describes the geomorphology of the Southeast Florida continental reef complex using high-resolution laser bathymetry, sub-bottom profiling, reef cores with subsequent age dating, and diver observation. A model for reef development and switch off in the Holocene is presented. Chapter 4 examines spatial trends in modern reef biological community structure and summarizes the knowledge of Holocene climate and the modern environmental setting in order to understand possible structuring mechanisms for the relict and modern reef system. Chapter 5 concludes the thesis with a discussion of the connection between reef geomorphology and spatial patterns in community structure.

References

Banks KW, Riegl BM, Shinn EA, Piller WE, Dodge RE (2007) Geomorphology of the Southeast Florida continental reef tract (Dade, Broward, and Palm Beach Counties, USA). Coral Reefs 26: Duane DB, Meisburger EP (1969a) Geomorphology and sediments of the inner continental shelf, Palm Beach to Cape Kennedy, Florida. USACE Coastal Eng Res Cent Tech Mem 34,82p Duane DB, Meisburger EP, (1969b) Geomorphology and sediments of the inner continental shelf, Miami to Palm Beach. USACE Coastal Eng Res Cent Tech Mem 29,47p Ginsburg RN, Shinn EA (1993) Preferential distribution of reefs in the Florida reef tract: the past is the key to the present. In: Ginsburg RN (ed) Global Aspects of Coral Reefs: Health, Hazards and History. University of Miami, Miami, pp21-26 Goldberg WM (1973) The ecology of the coral-octocoral communities off the southeast Florida Coast: geomorphology, species composition, and zonation. Bulletin of Marine Science, 23(3): 465-488

19 Lidz BH, Hallock P (2000) Sedimentary petrology of a declining reef ecosystem, Florida Reef Tract (USA). J Coast Res 16:675-697 Lidz BH, Reich CD, Shinn EA (2003) Regional Quaternary submarine geomorphology in the Florida Keys. Geol Soc Am Bull 115:845-866 Raymond WF (1972) A Geologic investigation of the offshore sands and reefs of Broward County, Florida. MS Thesis, Florida State University, Tallahassee, Florida, 95p Riegl B, Piller WE (2000) Reefs and coral carpets in the northern Red Sea as models for organism-environment feedback in coral communities and its reflection in growth fabrics, in Insalaco E, Skelton PW, Palmer TJ (eds) Carbonate Platform Systems: components and interactions. Geological Society, London, Special Publications, 178 Shinn EA, Hudson JH, Halley RB, Lidz BH (1977) Topographic control and accumulation rate of some Holocene coral reefs, south Florida and Dry Tortugas. Proc Int Coral Reef Sym 2:1-7 Shinn EA, Lidz BH, Kindinger JL, Hudson JH, Halley RB (1989) Reefs of Florida and the Dry Tortugas: A guide to the modern carbonate environments of the Florida Keys and Dry Tortugas. International Geological Congress Field Trip Guidebook T176, AGU, Washington DC, p55 Spalding MD, Ravilious C, Green EP (2001) World Atlas of Coral Reefs. Prepared at the UNEP World Conservation Monitoring Centre, University of California Press, Berkeley, California, USA, 424p Vaughan TW (1910) A contribution to the geologic history of the Floridian Plateau. Papers of the Tortugas Laboratory, 4(33): 99-185

2 Active Optical and Acoustic Remote Sensing Methods of Coral Reef Geomorphology

Introduction

Many coral reefs exhibit a common, distinctive pattern of geomorphologic zonation, which is generally a product of the interaction between reef developmental processes and the oceanic physical environment (Stoddart 1969). In fact, the foundation for understanding coral reef ecology and geology is the knowledge of reef surface form and internal structure.

The study of coral reef geomorphology has been hampered by a number of factors related to the nature of the reef itself. Coral reefs exist in shallow, high wave energy environments, often with large tidal ranges. Early studies were descriptive and based on ship-board or diver observations. Larger scale studies relied on standard land topographic survey techniques (see Stoddart 1978b for discussion of techniques). The limitations of these techniques in the marine environment are the inability to visualize reefs on a large scale due to inefficient mapping methods and determination of precise position. These methods were difficult to deploy on shallow portions of reefs because of waves and currents, however, they could only be used on shallow reef flats. Hydrographic survey techniques were necessary on the deeper portions of the reef.

Lead line depth sounding was the primary tool for determining water depth before acoustic techniques were deployed and large vessels, hampered by deep drafts, were unable to enter shallow reef zones. Accurate positioning and the difficulty of maneuvering vessels in proximity to shallow waters under high wave or current energy

21 conditions presented obvious risk for vessels and personnel. Some workers (Gardiner 1903, Verstelle 1932 and others) attempted to compare hydrographic surveys of reef areas over periods of years in order to determine reef growth or loss. Inaccurate positioning and depth sounding methods did not allow these studies to have any validity.

Since 1945, aerial photography has provided a useful tool for reconnaissance level studies in clear water environments (Hopley 1978). The development of aerial photography revealed the great diversity of reef features. This was first exploited by Maxwell (1968) who found that central topography of a reef to be as useful in classification as its gross morphology, but only a few papers dealt with the systematic interpretation of coral reef features from aerial photography (Steers 1946, Teichert and Fairbridge 1948, 1950).

The advent of satellite imagery and analysis techniques have greatly expanded the study of geomorphology and allowed researchers to gain a better understanding of approximations of reef morphology. Since light penetration is wavelength dependent (greater in blue wavelengths (400 nm) than, say, red wavelengths (600 nm)), some workers (Jupp 1988, Stumpf et al. 2003) have proposed methods for predicting patterns of bathymetry to a depth of approximately 25 m, although resulting bathymetric maps are not suitable for navigation (Mumby et al. 2004). Because geomorphic zones are associated with characteristic depth distributions and because they occur at spatial scales of tens to hundreds of meters they are amenable to remote detection by moderate- (e.g. Landsat Multispectral Scanner, TM, ETM+; SPOT-HRV; ASTER) and a fortiori high- resolution sensors (IKONOS, Quickbird).

Remote sensing and mapping of coral reefs and EFH has been a primary objective of resource managers since the Sustainable Fisheries Act outlined its importance in 1996. So mapping the extent and content of these and other coastal resources is now essential to all coastal marine management plans in the US (NOAA 1996)

22 The purpose of this chapter is to review efficient methods for large-scale study of reef geomorphology and physical reef boundary mapping (mesoscale). Special emphasis will be placed on applications appropriate for the continental reef tract of Southeast Florida where water clarity varies from clear (vertical visibility >20 m) to turbid (vertical visibility <6 m). This compromises the effectiveness of passive optical techniques, therefore, methods, such as satellite imagery and aerial photography, will not be discussed outside of a historical context.

Reef mapping

“Mapping”, as discussed herein, will be defined as the projection of reef boundaries onto a two dimensional, horizontal plane. Reef boundary maps can serve as base layers for geomorphic or habitat mapping. A great deal of reef mapping is based on georefernced aerial photography and optical remote sensing. In clear waters where optical sensors can penetrate to approximately 15-30 m water depth, this can be accomplished quickly and, for large areas, economically. Some reefs or hardground communities, however, exist in relatively high turbidity environments (Johnson and Carter 1987, Marshall and Orr 1931) so optical sensors are of limited value.

Some of the early oblique photography of southeast Florida reefs from the 1920s occasionally showed nearshore submarine features when turbidity was low (Finkl 1993). In the 1940s, coverage in vertical stereo-paired images along the shore was completed at a scale of (1:40,000), but practically no bottom information was provided. In the 1970s, Kodak experimented with a special water penetrating film that provided clear and detailed images of the seafloor. Experimental runs from Miami-Dade to northern Broward County provided some of the first areally continuous clear panchromatic pictures of the reefs, marking a real breakthrough in seafloor mapping from aerial photography (Finkl et al. 2005). The new experimental film was largely ignored until the Challenger space shuttle accident (28 January 1986), when it was used to search for shuttle debris on the seafloor. Realizing the strategic value of this film, the government placed security restrictions on water-penetrating films and suspended production of this

23 product for public use. The water-penetrating film was depth limited to about 15 meters, and although extremely useful for nearshore work, it was of little use farther offshore. Of all remote-sensing techniques, the Kodak water-penetrating film for a long time provided the best imagery for characterization of nearshore seafloor features.

For small scale mapping SCUBA divers can use dive scooters or swim along reef edges towing a small float. A vessel equipped with DGPS and position recording software, commonly used by hydrographic surveyors, tracts the float and records the position of the vessel at pre-determined distance or time intervals. The track line plot can be exported into a geographic information system (GIS) or mapping software for display or analysis. Diver limitations restrict this to small areas in shallow water. Towing a float can be difficult in deeper water or high currents. An additional constraint is vessel speed. Many boats can not maintain steering at slow speeds that divers are restricted to.

For regional scale mapping in the variable turbidity conditions of Southeast Florida, acoustic techniques have proven useful for two-dimensional mapping of reefs. In addition, some of these methods provide useful information on bottom type and biological community structure (Moyer et al 2005).

Sidescan sonar Seafloor substrate information can be collected as continuous coverage raster imagery from reflected acoustic intensity values. Because reflected intensities vary with substrate hardness, texture, slope and aspect, sidescan sonar has been used widely for over 30 years to create detailed mosaic images of seafloor features at resolutions as fine as 20 cm.

Sidescan sonar systems transmit two acoustic beams (broad in the vertical plane; narrow in the horizontal plane), one to each side of the survey track line. Using different frequencies (from 6.5 kHz to 675 kHz or higher), sidescan sonar achieves resolutions of 60 m down to 1 cm (Blondel and Murton 1997). Most sidescan systems use transducers mounted on a towfish pulled behind the survey boat (Fig. 2.1), but some are hull

24 mounted. Because towfish can be deployed well below the water’s surface, they can be used in deeper habitats than hull mounted systems.

25 Sidescan sonar beams interact with the seafloor and most of their energy is reflected away from the transducer, but a small portion is scattered back to the sonar where it is amplified and recorded. The intensity of the backscatter signal is affected by the following factors in decreasing order of importance: • Sonar frequency (higher frequencies give higher resolution but attenuate more quickly with range than lower frequencies) • The geometric relationship between the transducer and the target object (substrate slope) • Physical characteristics of the surface (micro-scale roughness) • Nature of the surface (composition, density)

For each sonar pulse or ping, the received signal is recorded over a relatively long-time window, such that the backscatter returned from a broad swath of seafloor is stored sequentially. This cross-track scanning is used to create individual profiles of backscatter intensity that can be plotted along track to create a continuous image of the seafloor along the swath.

Swath width is selectable, but maximum usable range varies with frequency. High frequencies such as 500kHz to 1MHz give excellent resolutions but the acoustic energy only travels a short distance (< 100 m). Lower frequencies such as 50kHz or 100kHz give lower resolution, but the distance that the energy travels is greatly improved (>300 m). Typical systems used for nearshore mapping have frequency ranges from 100 to 500 kHz with resolution as fine as 20 cm. Resolution also varies with swath width. Thus, while a 500 kHz system set at range of 75 m will cover a 150 m swath at 20 cm resolution, a 100 kHz system set at a range of 250 m will cover a 500 m swath but at a resolution closer to 1 m.

There is also a direct relationship between maximum allowable survey vessel speed and range. The shorter the range, the slower the speed and the more survey lines required to cover a given area. Typical sidescan sonar survey speeds are around 4-5 knots, but with newer systems have been increase to 10 knots.

26 Thus, the trade-off between swath width, resolution, survey speed, and financial resources must be considered when planning a survey. The choices will depend on: 1) the size of the area to be surveyed, 2) what resolution of substrate definition is required, and 3) how much time and money is available for the survey.

Most sidescan sonar systems cannot "see" the seafloor directly beneath the towfish. (Klein’s new multi-beam sidescan system is an exception.) As a result, if complete coverage of the seafloor is required, it will be necessary to have up to 100% overlap of the sidescan swaths, such that the port side of swath along one track line is completely covered by the starboard side of the swath from the adjacent track line. In this manner, the outer range of one swath can be used to "fill-in" the missing inner-range of the adjacent swath during post-processing. An additional advantage of designing overlap into the survey is to provide different views of the seafloor. This approach is especially important in areas of high relief, where features such as rock pinnacles may block the acoustic beam from striking and reflecting off that part of the seafloor hidden from towfish view. This interruption of the acoustic beam will create shadows or blind spots in the record, which can be filled with information from adjacent tracklines if there is sufficient overlap. Running track lines at different angles over the survey area can also be used to give a more complete picture of what the habitat looks like. Once the survey is completed, the swath images or sonographs can then be combined into a composite image or mosaic of the entire area surveyed. Traditionally, these sonographs were created as hardcopy originals by the sidescan recorder but are now more often recorded in digital form. As a result, all post-processing, including image enhancement, mosaicking and GIS product creation can be done electronically. Interfacing the sidescan with a differential GPS navigation system can produce georeferencing and imaging accuracy at submeter resolutions. To obtain this accuracy, however, requires that the off-set or "layback" between the sidescan sonar transducer and the GPS antenna is accurately determined and recorded throughout the survey.

Challenges specific to shallow water areas make sidescan sonar surveys in these areas more difficult, and costly than for deep water offshore surveys. Close to shore, waves are

27 often higher and small vessels must be used where larger ones will serve in deeper waters. These factors combined with the shorter cable lengths required for shallow water surveys mean that under a given set of conditions, there will be more wave induced vessel motion transferred to the towfish during a shallow water versus a deep water survey. Any towfish motion other than along track movement (e.g. pitch, yaw and heave) will create distortion in the sonograph. While motion sensors are available for single- beam and multi-beam bathymetry systems, they have not yet been developed to remove motion induced distortion from sidescan sonar data. For this reason, shallow water sidescan sonar surveys conducted when seas are > 2 m produce results of little value.

Geohazards are also more of a consideration in shallow waters because towfish altitude above the seafloor is often limited by water depth. Towfish altitude should be kept between 10% and 40% of the range if full coverage of the selected swath width is desired. Less than 10% will result in loss of signal from the outside part of the range, and greater than 40% will produce a large gap in coverage directly below the fish. In water depths of > 40 m a towfish could be kept up to 40m off the bottom while still maintaining a range of 100 m on a side. This margin of safety is not available, however, in water depths of 10 to 30 m, where the towfish must be kept at least 10m off the bottom but cannot be raised more that the water depth. Thus, a 20 m pinnacle in 30 m of water presents a very serious hazard to sidescan operations. For this reason, it is always advisable to conduct a bathymetric survey prior to the sidescan work in areas of uncertain seafloor morphology.

Acoustic echo analysis Acoustic echo analysis for ground discrimination has recently proved useful in mapping reefs in deeper water or high turbidity environments (Hamilton et al. 1999, Riegl and Purkis 2005). Active sonar sensors are usually towed behind a boat and measure the depth of the water and components of surface roughness and hardness (White et al. 2003). Compared to optical methods, these sensors have the following advantages: (i) greater depth of penetration, (ii) unconstrained by optical water properties, and (iii)

28 measurement of sea bed structure. However, disadvantages of the methods include: (i) they are difficult to deploy in shallow water (<0.5 m), (ii) they do not provide synoptic measurements over large areas and maps usually have to be generated by interpolating between acoustic tracks (Mumby et al. 2004). Two-dimensional planar mapping of reefs and reef surface characteristics can be accomplished and incorporated with other mapping methods, such as bathymetric mapping, to develop a better realization of reef geomorphology.

Acoustic ground discrimination devices such as QTC View, RoxAnn, and Echoplus have been extensively used over the past several years to remotely map benthic habitats and substrate surface characteristics (Hamilton et al. 1999, Lawrence and Bates 2001, Ellingsen et al. 2002, Freitas et al 2003, Moyer et al. 2005). Mapping with acoustic ground discrimination involves categorizing sonar return wave forms into classified points and plotting and interpolating those data into a continuous surface to be used in GIS. Accuracies of such tehniques are dependant on the distance between survey lines and can be lower than photogrammetric techniques (Riegl and Purkis 2005). The principles of acoustic ground-discrimination based on single-beam echosounders are reviewed in Chivers et al. (1990), Hamilton et al. (1999), Preston et al. (2000), Lawrence and Bates (2001), Bates and Whitehead (2001), Freitas et al. (2003), Riegl and Purkis (2005).

Point data on substrate type can also be acquired through co-processing or post- processing depth sounder data. For example, RoxAnn and QTC View make use of the multiple returns from echo sounders to classify seafloor substrates according to roughness and hardness parameters. This technology is similar to that applied in acoustic fishfinders, making use of the character and intensity as well as the timing of the return signal. With these add-on devices, it is possible to acquire information on the character of the substrate at each bathymetric sounding position. Similar approaches are now being developed for application to multi-beam sonar data. Rigorous ground-truthing to verify that the resulting classifications are accurate is essential, because the results from this

29 "automated" approach to seafloor substrate classification can vary widely between sites and with environmental conditions.

Although acoustic methods are not theoretically limited to a given depth range, several practical considerations generally preclude survey boat operations in the very nearshore (0-10 m). Wave height, reef and irregular coastlines all make boat based survey operations difficult to impossible within this depth zone along the open coast.

RoxAann RoxAnn is manufactured by Marine Micro Systems of Aberdeen Scotland. RoxAnn uses the first and second sonar echo returns to perform bottom composition classification. The first echo is reflected directly from the sea bed and the second is reflected twice off of the seabed and once off of the sea surface (Fig. 2.2). This method was first used by experienced fishers using regular echo sounders (Chivers et al. 1990). The fishers observed that the length of the first echo was a good measure of hardness in calm weather. The second echo, which mimicked the first echo, was much less affected by rough weather.

Fig 2.2: Diagrammatic representation of first and second sonar returns (from Chivers et al, 1990).

30 RoxAnn uses two values, E1 and E2, in order to estimate two key parameters of the sea floor, namely roughness and hardness. The first echo contains contributions from both sub-bottom reverberation and oblique surface backscatter from the seabed. It has been shown that oblique backscattering strength is dependent on the angle of incidence for different seabed materials. At 30 degrees there is almost a 10 dB difference in scattering level between mud, sand, gravel and rock (Chivers et al. 1990). The first part of the first echo contains ambiguous sub-bottom reverberations and is therefore removed (Fig. 2.3). Most or all, of the remaining portion of the first echo is then integrated to provide E1, the measure of roughness. The exact parameters within which E1 is integrated are difficult to estimate and is therefore based on empirical observations in a number of different oceans (Chivers et al. 1990). The entire second echo is integrated, which is the relative measure of hardness and is designated E2 (Schlagintweit 1995). A processor is used to interpret E1 and E2 such that bottom characteristics may be determined. Looking at E1, on a perfectly flat sea floor, non-incident rays would be expected to reflect away from the transducer. As the sea floor is not perfectly flat, the returning energy from non-incident rays coincides and interferes with the incident rays and indicates the roughness of the sea floor (Chivers et al. 1993). The specular reflection of the sea floor is a direct measurement of acoustic impedance relative to the sea water above it. Hardness can be estimated using E2 because the acoustic impedance is a product of the density and speed of longitudinal sound in the sea bed (Chivers et al. 1990).

Fig 2.3: First (E1) and second (E2) sonar return waveforms (from Schlagintweit 1995). RoxAnn integrates all of E2 and a portion of E1 (in blue).

31 Schlagintweit (1995) conducted a field evaluation of RoxAnn in Saanich Inlet offshore Vancouver Island using two frequencies, 40 kHz and 208 kHz. RoxAnn was deployed over a ground-truthed area that had been previously inspected by divers. A supervised classification method was used and a "modest" correlation was found at both frequencies. Classification differences between the two frequencies were due to the different sea bed penetration depths of these frequencies on various sea floor types. That is, the frequency dependent penetration factor into the sea floor depended on the local sea floor itself. Schlagintweit (1995) stated that the frequency should be chosen according to the application and that an unsupervised classification method would be the best alternative, i.e., let the system select the natural groupings and then look at ground truthing. Both the Chivers et al. (1990) support this method of an initial calibration. In separate tests, Kvitek et al. (1999) found quite good agreement between classes created from sidescan sonar interpretation and those created using unsupervised classification of RoxAnn E1 & E2 values at the Big Creek Ecological Reserve in Big Sur, California. Using sidescan imagery and video ground-truthing, Kvitek et al. (1999) found that RoxAnn successfully classified sand, rock, and coarse sand/gravel between 6-30m depth in a 2-3 sq km area. The application of RoxAnn to coral reefs has been used for mapping bottom type, as well as habitat (White et al. 2003, Sze et al. 2000), and Sze et al. (2000) stated that RoxAnn is a better alternative to in situ line transect methods and satellite images in terms of time, cost, and results gained for large-scale surveys.

The RoxAnn system is very compact. The entire unit consists of a head amplifier which is connected across an existing echosounder transducer in parallel with the existing echo sounder transmitter, and tuned to the transmitter frequency. The parallel receiver accepts the echo train from the head amplifier (Schlagintweit 1995). The installation requires no extra hull fittings; only space for the processing equipment. The required processing equipment includes an IBM compatible computer and an EGA monitor. Software which is specifically written to handle RoxAnn data must then be installed on the computer for processing analysis.

32 QTC View Acoustic data are collected during the typical hydrographic survey process., The transmitted signal and return echoes are digitized, subjected to Fourier analysis, wavelet analysis and analyzed for area under the curve, spectral moments and other variables In QTC Impact software (Legendre et al. 2002). Next, the effects of the water column and beam spreading are removed such that the remaining wave form represents the seabed and the immediate subsurface (Collins et al. 1996). Quester Tangent's echo shape analysis works on the principle that different sea beds result in unique wave forms. After being normalized to a range between 0 and 1, they are subjected to Principal Components Analysis (PCA) for data reduction. Each wave form is processed by a series of algorithms which subdivides it into166 shape parameters (Collins et al. 1996). A covariance matrix of dimension 166 x 166 is produced and the eigenvectors and eigenvalues are calculated. In general, three of the 166 eigenvectors account for more than 95% of the covariance found in all the wave forms. The 166 (full-feature) elements of the original eigenvector are reduced to three elements ("Q values"). These reduced feature elements will cluster around locations in reduced feature space corresponding to a sea bed type (Prager 1995). The user decides on the number of desirable clusters and also chooses which cluster is split and how often. Clustering decisions are guided by three statistics that are offered by the program called “CPI” (Cluster Performance Index), “Chi2” and “Total Score”. Total score decreases to an inflection point which is ‘a strong indication of best split level’ (Questar Tangent Corporation 2002). CPI increases with increased cluster split (Freitas et al. 2003b), while Chi2 decreases, reaching maximum/minimum values at optimal split level (Questar Tangent Corporation 2002). QTC View is manufactured and distributed by Quester Tangent Corporation of Sidney, British Columbia, Canada (Quester Tangent Corporation, 1997). Like RoxAnn, Quester Tangent's QTC View uses the existing echo sounder transducer; however, QTC View does not examine two different waveforms. Instead, analysis is performed on the first return only. Quester Tangent's other classification system ISAH-S (Integrated System for Automated Hydrography) is also available, and uses the same approach as QTC View in wave form analysis. However, ISAH-S offers multiple channels for multi-transducer platforms, integration with

33 positioning and motion sensors, and helmsman displays. QTC View is more of a standalone system accepting GPS input for georeferencing of echo sounder data.

Test Results QTC View was designed to operate in both the supervised and unsupervised classification modes. If no ground-truthing has taken place in an area of interest, QTC View will still cluster-like areas such that some type of calibration or ground truthing may be performed after the survey.

In a test conducted by the Esquimalt Defense Research Detachment, QTC View was found to have produced very good results. QTC View was used over the same area where the RoxAnn tests were conducted off of Vancouver Island in the unsupervised classification mode. QTC View was able to discriminate between eight different seabed types. After a calibration, QTC view was found to agree with each ground-truthed area and showed good transition from seabed type to seabed type (Prager 1995).

QTC View is comprised of a head amplifier and PC with a DX2/66 processor. The head amplifier is connected in parallel across the existing transducer and to the PC via a RS232 cable. The PC also accepts the GPS data in NMEA-0183 standard GGA or GGL format for georeferencing of data (Collins et al. 1996). The PC displays three windows: one for the reduced vector space, one for the track plot and classification and the third for seabed profile and classification. Fig. 2.4 illustrates the QTC View screen output. Moyer et al. (2005) noted that satellite and aerial photography methods have yielded unreliable results for Southeast Florida reefs and carried out an acoustic seabed classification survey with QTC View and compared it to in situ diver-based survey offshore Broward County. They found that the system discriminated bottom composition well and that reef classes reflected physical characteristics, such as composition, slope, rugosity, and porosity. It was further noted that as survey resolution becomes fine accuracy of the resultant maps decreases considerably.

Fig 2.4: QTC View Screen Display (from Quester Tangent, 1997).

Echoplus Echoplus, similar to RoxAnn, processes the tail of the first echo plus the entire second echo. Echoplus differs from RoxAnn as being suited to dual frequency sounder systems. Echoplus is entirely self-contained and internally compensates for frequency, depth, power level and pulse length, and can therefore be used with any depth sounder. Pulse amplitude and length are measured on every transmission, the outputs scaled accordingly, and absorption corrections factored in. The first echo is digitized and time-gated in a way that only its tail (backscatter component) is used for analysis along with the entire second echo. The measurements from first and second echo are collapsed into two indices, E1 and E2, for the first and second echo, respectively. The user has no influence on the formation of these indices and collects a georeferenced string of variables (latitude, longitude, E1, E2). All data above the 95th percentile and below the 5th percentile are rejected as outliers and all data are normalized to the 95th percentile, resulting in a range between 0 and 1.

35 Bathymetric mapping

Most optical remote-sensing investigations of coral reefs involve the use of passive techniques that rely upon reflected sunlight (Mazel 1999). This class of remote sensing can be used to survey coarse bathymetry (Lyzenga 1978, Sandidge and Holyer 1998), but cannot capture the fine-scale desirable for geomorphic studies.

A number of survey methods have been designed to acquire high-resolution bathymetric information, including multi-beam sonar and laser bathymetry (LIDAR, LADS) (Lillicrop 1996, Twichell 1996, Wells 1996, Galloway 2001, Anderson et al. 2002, Finkl et al. 2005). These sensors provide detailed seafloor topography that facilitates mapping geomorphology (Storlazzi et al. 2003, Finkl 2005, Finkl et al. 2005, Banks et al. 2007)

Depth or bathymetry data are usually recorded as x,y,z (easting, northing, depth) point data, and can be used to generate depth contours (line and area vector data); visualization images, such as surfaces, hillside shaded images (Fig. 2.5); as well as digital elevation models (DEMs). Depending on the horizontal spacing of the depth data, these products can be developed for determining the values for geomorphic parameters, such as exposure, rugosity, slope and aspect.

Bathymetry data can be collected using a wide variety of sensors including: lead lines, single-beam and multi-beam acoustic depth sounders, and airborne laser sensors. Each of these systems has its inherent advantages and limitations.

The utility of bathymetric data depends on the resolution at which it is collected. Until recently most bathymetric data were collected as discrete points along survey vessel track lines with single-beam acoustic depth sounders. The introduction of swathmapping and multi-beam bathymetry systems has dramatically improved the ability to acquire continuous high-resolution depth data. Bathymetric data with horizontal postings of less than 1 m are now routinely collected over wide areas using multi-beam techniques. Comparable data resolutions are also now possible with some of the new laser

36 topographic mapping systems, although water clarity generally limits their application to shallow, clear water nearshore environments (<20 m).

Fig 2.5: Geomorphological studies can be greatly facilitated by the use of high- resolution XYZ data which can be used to create (a) surface images, (b) shaded relief images, and (c) depth contour plots.

Single-beam echosounders The utility of bathymetric data is highly dependent on the resolution at which it is collected. Until recently most bathymetry data was collected as discrete point data along survey vessel track lines with single-beam acoustic depth sounders. These sounders work on the principle that the distance between a vertically positioned transducer and the seabed can be calculated by halving the return time of an acoustic pulse emitted by the transducer. All that is required is an accurate value for the speed of sound through the intervening water column. The speed value can be back calculated by adjusting the sounder to display the correct depth while maintaining a known distance between the transducer and an acoustically reflective object (e.g. seafloor measured with a lead line,

37 or calibration plate suspended at a known depth). The horizontal resolution, or posting, of single-beam acoustic data is defined by the sampling interval along the track lines and the spacing between track lines. Single-beam echosounders only provide information on the seabed immediately below the surveying vessel. Because it is generally impossible or too costly to space survey lines as close together as the interval between soundings along the track lines, most older bathymetry data sets tend to have much higher resolution along track than across track which is of particular problem in reefs with their inherent complex topography. This necessarily leads to considerable interpolation between track lines when constructing contours or surfaces. As a result, surfaces are generally either too course (postings at > 50m) or inaccurate for fine grain mapping at macro- or micro-feature scales. One advantage of single-beam depth sounders however, is the ability to interface them with acoustic substrate classifiers. These co-processors correlate the intensity values from the single-beam echo returns with seafloor substrate hardness and roughness.

Multi-beam echosounders Since the late 1980s, use of multi-beam bathymetry in hydrographic mapping has become increasingly common and accepted. Initially fraught with considerable accuracy and precision issues, multi-beam sonar technology has improved vastly and rigorous testing has established its reliability. The ability to acquire denser sounding data while surveying fewer tracklines (with greater spacing between lines) and simultaneously acquiring backscatter imagery using the same sensor, has made multi-beam a popular tool. Using this technology, however, requires attention to a number of considerations that are less crucial when using single-beam technology. Multi-beam depth sounders, as their name implies, acquire bathymetric soundings across a swath of seabed using a collection of acoustic beams (up to 120 for some instruments), as opposed to a single-beam, which ensonifies only the area directly below the transducer (Fig. 2.6). The number of beams and arc coverage of the transducer varies among makes and models, and determines the swath width across which a multi-beam sounder acquires depth measurements in a given depth of water. It is important to note that effective swath width is often somewhat less than potential swath width, as data from the outer most beams is often unusable due to

38 large deviations induced by ship roll and interference from bottom features such as pinnacles. The potential swath width may only be realized under calm conditions over a relatively flat bottom. Swath width is depth dependent, requiring closer line spacing in shallower water if full coverage is to be maintained. The mechanics and physics of how the beams are formed vary among makes and models and may be a consideration if extremely high resolution, precision, and accuracy are required.

Fig 2.6: Multi-beam depth sounders, as their name implies, acquire bathymetric soundings across a swath of seabed using a collection of acoustic beams. Backscatter values of multi-beam bathymetry data can be used to characterize bottom types.

In order for the multi-beam system to calculate accurate x, y, z positions for soundings from all off-nadir (non-vertical) beams (every beam other than the center beam), precise measurement of ship and transducer attitude is required. This includes measurement of pitch, roll, heading, and (preferably) vertical heave. Thus, a motion sensor must be interfaced to the unit, so that its output may be used to adjust and correct the multi-beam data in either real time or post-processing.

39 In addition, because of longer travel times for off-nadir beams, variations in the speed of sound in water (SOS) can induce relatively large errors in these beams, especially if temperature stratification exists in the water column. For this reason, sound velocity profiling should be conducted on site during a survey, and the SOS data used to adjust depth soundings. Controlling for variations in SOS is of increasing importance as depth increases. Multi-beam surveying also requires more rigorous system calibration to account for variations in, and improve the accuracy of, heading, roll, and pitch sensor values, as well as any adjustment to navigation time tags that will reduce timing errors between navigation and sonar data. This calibration, known as a "Patch Test", is typically conducted by running a series of survey lines over the same area with relative orientations that allow assessment of the variables listed above.

Multi-beam bathymetric surveying generates orders of magnitude more data than single- beam surveying, resulting in greater storage requirements, longer processing times, and the need in some cases for greater processing power. Gigabytes of data may be generated daily, (as opposed to megabytes in single-beam surveys), especially if backscatter imagery is being recorded as well. The removal of bad sounding data during the editing process is, accordingly, a much larger task in multi-beam than in single-beam surveys, although some processing packages allow some degree of automation of this process. The considerations and requirements listed above make multi-beam surveying a much more complex and expensive undertaking relative to single-beam, but the benefits in cost per unit effort and resolution can well outweigh the hardships, especially if extensive surveying is planned. Survey speeds of up to 30 knots are now possible with some systems.

In recent years, in an approach similar to sidescan sonar, analysis of backscatter values of multi-beam bathymetry data has been used to characterize bottom types. While multi- beam backscatter images generally lack the resolutions and detail found in conventional sidescan images, they can be corrected for distortion resulting from unintended sensor motion (e.g. role, pitch, and heave due to waves). This type of correction has not yet been developed for sidescan sonar systems. As a result, shallow water sidescan sonar

40 operations are generally restricted to days with relatively calm sea states. Multi-beam systems equipped with motion sensors can be used under a much wider range of sea conditions. One other advantage multi-beam systems have over sidescan sonar is continuous coverage directly below the sensor. Sidescan sonar systems have two side- facing transducers that do not ensonify the seafloor directly beneath the towfish. Survey tracklines with sufficient overlap are required to fill in this blank in coverage. Despite the high-resolution seafloor imagery obtainable using acoustic backscatter systems, their application can be limited by several factors including resolution, survey speed, swath width, and water depth.The relatively slow survey speeds (4-10 knots) required for acoustic surveys can make mapping large areas at high resolution a long and costly enterprise. This situation is especially true in shallow water habitats due to the limitations imposed on swath width by water depth. For sidescan and multi-beam systems, the closer the sensor is to the seafloor, the narrow the swath coverage. For most sidescan systems, swath width is limited to no more than 80% of the transducer altitude above the seafloor. Although multi-beam systems can have very wide beam angles, data from the outer beams are usually of questionable value, especially in high relief areas where much of the seafloor at the edges of the swath is blocked from "view" due to acoustic shadowing by the relief. Survey track line spacing for shallow water surveys must therefore be closer than for deeper water work, where wider swath ranges can be successfully used. Even where wider swaths can be used, however, there is a trade off with resolution, which is directly and inversely proportional to swath width. (A sidescan sonar resolution of 20 cm at the 50 m range, drops to 40 cm at the 100 m range.) Sidescan sonar is the only technology capable of producing continuous coverage imagery of the seafloor surface at all depths (Blondel and Murton 1997).

Sidescan sonar and multi-beam backscatter (see section, ‘Multi-beam sonar) are primarily useful for defining reef edges in the horizontal two-dimensional plane and relative rugosity by examining acoustic shadows in raster imagery. Reef edges that gradually slope into sand, however, are often indistinct on images so ground-truthing or other methods may be required to resolve these features.

41 Active optical methods (laser)

Laser hydrographic survey technology, such as LIDAR (Light Detection and Ranging) and LADS (Laser Airborne Depth Soundings) are based on the same principle as sonar, but they use light instead of sound to survey clear water to depths around 50 meters and have been used to map topography and bathymetry in marine and freshwater bodies of water. Laser techniques are deployed from an aircraft, either fixed-wing or helicopter. Systems for hydrographic mapping typically use a blue-green laser (532 nm) to optimize penetration depth. One such system, the SHOALS (Scanning Hydrographic Operational Airborne LIDAR Survey system) (Fig. 2.7), operated by the US Army Corps of Engineers (USACE), is capable of mapping both coastal topography and nearshore bathymetry simultaneously by the addition of a dual-frequency IR laser. One half of the altitude-dependent swath-width must be over water for this to function. At normal altitude (200 m), this allows a 50 m portion of the terrestrial coastline to be mapped. Other LIDAR systems optimized for terrestrial mapping might then be used if terrestrial elevation data beyond this 50 m swath are desired. Under normal operating conditions (an altitude of 200 meters and a speed of 60 or 120 knots) the system can survey up to 8-32 square kilometers in one hour, collecting depth soundings on a 4 meter horizontal grid.

Using DGPS, SHOALS references each depth measurement to a horizontal position accurate to 3 m and a vertical position accurate to 15 cm. RTK GPS can increase the horizontal accuracy to the sub-meter level. Water clarity affects the depth capabilities of LIDAR. Up to 60 m penetration (under ideal conditions) is possible depending on the optical behavior of what remote-sensing researchers call Case II (coastal) waters (Bukata et al. 1995; Finkl et al. 2004). Turbidity is due to a combination of factors that include colored dissolved organic matter (CDOM), phytoplanktons, and nonchlorophyllous particulate matter (including the suspended sediment concentration [SSC]) (Bukata et al. 1995). These materials limit depth penetration by optical sensors because of scattering and absorption, which greatly attenuate signals from passive systems (Mumby et al. 2004). The general rule thus follows the principal that the higher the turbidity (due to CDOM, SSC, and phytoplankton), the less penetration of water depth. Depth-sounding

42 surveys are thus well adapted to the clear Case II waters found along the southeast coast of Florida.

Fig 2.7: SHOALS LIDAR system uses a laser to obtain depth measurements. A blue- green laser (532 nm) is used to optimize penetration depth. SHOALS references each depth measurement to a horizontal position accurate to 3 m and a vertical position accurate to 15 cm.

The EAARL (Experimental Advanced Airborne Research Lidar) uses a temporal waveform-resolving, laser transmitter–receiver (Lefsky et al. 1999) and a green wavelength (532 nm) laser to enable water penetration and the surveying of shallow benthic substrates, similar to traditional bathymetric LIDAR (Guenther 2001). In other design aspects, the EAARL differs fundamentally from traditional high beam divergence (2 m ground spot diameter), low pulse repetition frequency (<1,000 Hz) bathymetric LIDARs that typically use a second near-infrared (1,064 nm) laser to sound the water surface for vertical spot positioning (Guenther 2001). In contrast, the EAARL employs a beam divergence (<20 cm ground spot diameter), high pulse repetition frequency (up to 10,000 Hz) laser mounted on an aircraft platform whose position is determined by carrier

43 phase kinematic differential GPS techniques. This hybrid design enables high spatial resolution observations of both subaerial and shallow submarine topography (Wright and Brock 2002).

The NASA EAARL is composed of four basic components: (1) a temporal waveform- resolving, pulsed laser altimeter, (2) GPS carrier phase tracking receivers, (3) a system for the determination of aircraft attitude, and (4) a raster scanner.

The EAARL platform is a twin-engine Cessna 310 aircraft. This light aircraft can operate from paved runways as short as 1,000 m in length, transit at 180 knots between operating areas, slow to about 100 knots (50 m/s) for survey operations, and has a maximum endurance of just over 9 h when operated at survey speed (50 m/s) and altitude (300 m). A single pilot and a LIDAR operator constitute the crew for most survey operations. The EAARL system incorporates an Axis 2120 downlooking digital network camera that continuously acquires digital aerial photographs at a 1 s time step. The digital camera is co-registered to the EAARL optical system, and its 45 wide across-track field of view slightly exceeds the EAARL scan width. During recent test flights over the relatively clear waters of the Florida Keys, under the most favorable conditions, the EAARL surveyed submarine topography to water depths in excess of 25 m (Wright and Brock 2002). Overall, the Florida Keys flights demonstrated that the EAARL can routinely map patch reef geomorphology, steepness of patch edges, holes as small as 1 m in diameter, and variable roughness across the top of the patch reefs ranging in depth from 0.3 to 15 m below the water surface. EAARL, a temporal waveform-resolving, airborne, green wavelength LIDAR (light detection and ranging), is designed to measure the sub-meter- scale topography of shallow reef substrates (Brock et al. 2004)

The Laser Airborne Depth Sounder (LADS; Tenix LADS Corporation, Mawson Lakes, South Australia, Australia) is a similar digital system that is used to sense water depth. LADS bathymetry has been used successfully to determine the geomorphology of parts of the Great Barrier Reef (Lewis 2001) and the reef tract of Southeast Florida (Banks et

44 al. 2007). LADS provides bathymetric data to a maximum depth of 70 m (Wellington 2001).

LADS uses a sounding rate of 900 Hz (3.2 million soundings per hour), has a position accuracy of 95% at 5 m circular error probable (CEP), has a horizontal sounding density of 4 m x 4 m, a wath width of 240 m, an area of coverage of 64 km2/hr, and a depth range of 70 m, depending on water clarity (Walker et al. in press).

Combined methods

All investigational methods have limitations whether they are level of accuracy, scale of resolution, or practicability for a given suite of environmental conditions. A logical follow-on is to use a combined approach. Moyer et al. (2005) used this in Southeast Florida, combining laser bathymetry and in situ ground-truthing with acoustic ground discrimination to develop reef habitat classification maps. Walker et al. (in press) expanded this approach for Southeast Florida to include sub-bottom profiling and aerial photography. They were able to differentiate areas of similar geomorphology by their acoustic diversity. Their approach yielded an overall accuracy of 89.6%, only slightly less than the photo interpreted NOAA Caribbean maps (91.1%). This demonstrates that large-scale areas with sub-optimum water clarity can be mapped accurately using non- optical techniques.

Conclusions

A number of methods are available for high resolution medium- and large-scale reef mapping and study of reef geomorphology. Southeast Florida’s highly variable water clarity limit the consistent use of passive optical techniques. The most useful technique for region-wide (100 km scale) geomorphological mapping has been the laser bathymetric techniques, such as LADS. This has allowed thorough study of the Southeast Florida reef tract (Banks et al. 2007). While multi-beam sonar can provide higher

45 resolution, extensive vessel survey time is required to map an entire region. This can be quite expensive, particularly when including potential weather delays.

Physical geomorphological mapping should be a first step when reef habitat mapping is considered. Topographic variability is a prime component of habitat complexity, an ecological factor that both expresses and controls the abundance and distribution of many reef organisms (Brock et al. 2004). Bathymetry data enable the analysis of topographic complexity using techniques developed from landscape ecology that allow the comparison of species distributions to areas of increased or decreased complexity. Variability in vertical relief, rugosity, both reflects and governs the spatial distribution and density of many reef organisms (Sale 1991, Sebens 1991, McCormick 1994). Rugosity surveys are useful in studies of reef ecological structure and function (Sebens 1991, McCormick 1994, Szmant 1997), catastrophic change due to hurricane impacts and ship groundings (Rogers et al. 1982, Rogers and Miller 2001), long-term cumulative disturbance or bioerosion (Sebens 1991, Aronson et al. 1994), fish assemblage structure (Sale 1991, Hixon and Beets 1993, Friedlander and Parrish 1998), and associated conservation value (Chapman and Kramer 1999, Edinger and Risk 2000). As a result, combined mapping approaches incorporating high resolution bathymetry; acoustic ground discrimination; in situ sampling; and passive optical techniques, if feasible, can be used to develop, both physical and biological habitat maps for large areas with high accuracy and resolution.

References

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3 Geomorphology of the Southeast Florida Continental Reef Tract (Miami-Dade, Broward, and Palm Beach Counties, USA)

Introduction

The continental shelf along the southeast Florida continental coast north of the Florida Keys is narrow (3-4 km) and bathed by relatively warm waters of the Florida Current, a branch of the Gulf Stream flowing at an average speed of 1.3 m s-1 between the Bahamas banks and SE continental Florida. Seismic surveys carried out by Duane and Meisburger (1969a, b) along the shelf margin of continental SE Florida revealed a series of shore- parallel, progressively deeper, reef-like ridges or terraces. These ridges are separated by sedimentary accretions of varying thicknesses (Duane and Meisburger 1969a, b; Raymond 1972; Shinn et al. 1977).

The reef-like ridges are a relict (no active accretion due to exceedingly low cover of reef builders; Moyer et al. 2003), Holocene shelf-edge and mid-shelf reef/ridge complex extending along the continental coast of SE Florida from Biscayne Bay (N25o35’) northward to offshore of Riviera Beach (N26o43’) in northern Palm Beach County, a distance of 128 km (Fig. 3.1; Moyer et al. 2003). The location of these reefs identifies them as a distinct and also presently non-accreting reef tract (Macintyre 1988) and although previous studies have stated that they are a continuation of the Florida Keys reef tract (Goldberg 1973; Toscano and Macintyre 2003), there has been no confirmation of this. The growth of corals on the Florida Keys reef tract is generally considered to terminate at Fowey Rocks (Vaughan 1914, Jaap 1984, Shinn et al. 1989). Lighty (1977), Lighty et al. (1982), and Lighty et al. (1978) suggest uncorrected 14C ages for the outer

52 reef of the northern, continental complex as between 8,000-11,000 cal BP (calibrated 14C age in years before present). The demise of the reefs has been variably attributed to cold counter-current water from the north, a major influx of sediment-rich water originating from the south during the Holocene transgression (Macintyre and Milliman 1970; Lighty et al. 1978; Macintyre 1988), low water temperatures during the early Holocene (Lighty et al. 1978), and/or catastrophic sea-level-rise events (Braithwaite 1979; Shinn et al. 1989, Blanchon and Shaw 1995; Blanchon et al. 2002).

Goldberg (1973) and Finkl et al. (2005) provided a descriptive geomorphology of some sections of this reef tract. Lighty (1977) and Lighty et al. (1978) described the reef lithofacies in a wastewater-pipe trench excavated through the outer reef, 40 km north of Miami, and confirmed that, like the Florida Keys reef tract, it is a Holocene Acropora framework that terminated growth approximately 8,000 cal BP (Toscano and Macintyre 2003). Most geomorphological descriptions, to date, are qualitative and/or based on observations of small areas. The recent availability of LIDAR high-resolution bathymetry now allows presentation of the geomorphology of the entire reef/ridge complex in finer detail.

The objectives of this paper are to 1) examine the geomorphic features of the continental portion of the SE Florida reef tract using high-resolution bathymetry, 2) describe its transitions to the extant Florida Keys reef tract, and 3) demonstrate the application of high-resolution bathymetric data to the study of reef geomorphology.

Fig. 3.1: Study area in SE Florida, USA. (a) The red band offshore indicates the position of the SE Florida reef tract. (b) The reef tract borders three counties. Place names used in the text are shown. The Florida Keys reef tract is located south of Biscayne Bay. A patch of LIDAR bathymetry shows the gross morphology of the reef lines of Broward County. White lines show locations of the sub-bottom profiles.

Materials and methods

Clarification of the terminology used in this paper is necessary to understand the unique structure of the reef/ridge complex of continental SE Florida. The three terraces deepest and farthest from shore will be defined as ‘reefs’ (outer, middle, inner, comparable to Moyer et al. 2003 as based on that of Lighty 1977). Inshore of the reef complex is a series of shallow, nearshore ridges. These will be referred to as the ‘ridge complex’ (Moyer et al. 2003) (Fig. 3.1). In addition, a regional distinction shall be made between the continental portion of SE Florida and the Florida Keys. Several authors (Toscano and Lundberg 1998; Lidz 2004) have used the term ‘south’ or ‘southeast’ Florida in reference to the Florida Keys, whereas others (Lighty 1977; Moyer et al. 2003) have used the term for the continental portion of SE Florida north of Biscayne Bay. Blanchon et al. (2002) referred to this region as north Florida. Toscano and Macintyre (2003), in their Table 2,

54 erroneously refer to Lighty’s (1977) samples from Broward County (Fig. 3.1) as being from the Upper Florida Keys, while in fact they were obtained from offshore the continental part of Florida. To avoid such confusion, we will use the term ‘SE Florida’ exclusively to represent the continental portion of Florida and will reserve the term ‘Florida Keys’ for the insular portion of SE Florida, south of Biscayne Bay (greater Miami area). This distinction is important because the Florida Keys reef tract is situated at the margin of a much wider shelf and is influenced by waters from Florida Bay as well as by the oceanic waters of the Florida Current (Ginsburg and Shinn 1993; Shinn et al. 1989; Lidz and Hallock 2000; Lidz et al. 2003). The continental reefs to the north are situated on a much narrower shelf and are under greater influence of hinterland drainage but are lacking the effects of Biscayne Bay (except at the southern extreme) and Florida Bay.

Bathymetric data collection and analysis The coastal waters off Broward, Miami-Dade, and Palm Beach Counties were surveyed using a Laser Airborne Depth Sounder (LADS) laser bathymetric survey. The 600-km2 survey area extended from the shoreline to an approximate depth of 40 m and was flown by Tenix Corporation of Mawson Lakes, South Australia, during 2001 (Broward County) and 2003 (Palm Beach and Miami-Dade Counties). LADS is an airborne hydrographic surveying system that measures water depth using pulsed lasers (1 kHz) from an aircraft (Brock et al. 2004). The swath width of survey lines was 240 m and survey speed was 175 knots. Survey resolution was 4 m horizontal and for water depths of <30 m, 0.3 m, for depths of >30 m, 1% of depth. Data were processed in North American Datum, 1983 (NAD83), Florida State Plane, East Zone, U.S. survey feet.

Non-uniform XYZ data were kriged to a uniform data grid (Middleton 2000; Davis 2002) and shaded relief and surface images were generated. To reduce data file size and zoom in on areas of interest, subsets of XYZ data for the selected features were extracted using a Fortran utility (LADS extractor; K. Kohler personal communication). Bathymetric transects were 5-m-wide data slices, perpendicular to examined features.

55 Subbottom profiling Subbottom profile data were collected using the Edgetech 512 X-Star Chirp full spectrum digital subbottom profiler with FM frequency pulse between 0.5 and 8 kHz, which provided best penetration and resolution of reflectors. This system uses matched filter correlation and waveform weighted techniques for increased penetration with high resolution. The profiler was towed with the GeoCat platform system, an inflatable catamaran that facilitates surveying in shallow water (H. Guarin personal communication). Raw data recorded in SEG-Y format were resampled, deconvoluted and bandpassed (300-2,500 Hz) during post-processing. Profiles were collected along nine east/west transects and two north/south transects (Fig. 3.1). For the identification of features, we cross-referenced presumed reflectors with known information from cores.

Coring Reef cores were obtained with a submersible hydraulic drill rig powered by a 14-hp Ruggerini diesel using a Micon Christensen HXB II wire-line system with 92.8-mm- diameter outer barrels with a Micon Christensen polycristalline diamond cutter drillbit and a 61.2-mm-diameter inner barrel that allowed removal of the core with the sleeve remaining in place. Thus, it was assured that no fragments fell into the drill hole during core removal, possibly creating artifacts in interpretation of rock structure and age dating. The cores, or fragments of core, were kept inside the barrel by a steel spring-type core catcher, assuring minimal loss. Core recovery was calculated by expressing recovered core length as a percentage of total barrel length that penetrated the substratum, which was measured and recorded on a slate by the drill operator. Five cores were obtained: one core on the inner reef that penetrated the reef framework entirely and recovered 50 cm of underlying coquina and mixed carbonate/quartz sand (3.6-m core length); one core in reef framework that was abandoned after 1-m depth; one core on the ridge complex (4.1-m core length); two cores on the middle reef, one abandoned after 1.62-m depth and one after 62-cm depth. Cores on the inner reef and the ridge complex coincided with, or were situated near subbottom profiling lines. For the identification of taphonomic processes in the cores, we used criteria of Perry (1998, 2000) and Blanchon and Perry (2004) as

56 guides. Mineralogy of coral samples from the middle reef was determined by x-ray diffraction at the University of Graz and samples were found to consist of aragonite. Although differences in peak height were found, the differences could be traced to textural effects of the different arrangements of aragonite crystallites within the skeletal components. Therefore, standard radiocarbon aging was performed and calibrated at Beta Analytical Inc. in Miami, FL. Absolute U/Th TIMS dates were obtained from the Lamont-Doherty Earth Observatory of Columbia University (R. Fairbanks personal communication). The TIMS provided absolute chronology, whereas the 14C ages were 14 12 corrected for the C/ C difference between atmospheric CO2 and the ΔCO2 of the surface-ocean mixed layer using CALIB 4.3 (Stuiver and Reimer 1993) or the calibrated data provided by Beta Analytical. Cal BP ages are based on the intercepts of the radiocarbon age with the calibration curve. Soft-sediment cores were obtained by vibracoring from three localities in northern Broward County

Analysis of geomorphology Features were identified using a combination of bathymetry, subbottom information, coring, and diver observations. Coral reefs were interpreted by a combination of texture on subbottom-profiler plots and bathymetric transects and showed a hard, highly rugose surface reflector, which set it apart from overlying or onlapping sandy sediments. Poor bottom reflectors, i.e., contact to lithified Pleistocene, were a result of poor penetration of chirp into unstratified rock substrate. Also, reefs always exhibited a steep, shoreward, backreef slope, which was absent in fossil shoreline features. Areas of changing slope in ridges tended to be more smoothly curved, whereas in reefs topography was steeper and more angular. Since cores were available precisely at or very near subsurface profiling lines, we were able to ascertain which structures made visible by the chirp lines should be interpreted as reef, sand, or erosional surfaces.

Results

57 Overall morphology As a rough generalization, between southern Miami-Dade County and Palm Beach County, three shore-parallel, increasingly deep ridges occur. The morphology is more complicated in the south (Fowey Rocks to Port Everglades) than north of Hillsboro Inlet. From there northward, first the inner reef, and then the middle reef eventually disappear, leaving only the outer reef. Seaward accretion of the modern shoreline has obscured the inshore structures at the latitude of Hillsboro Inlet. The outer reef terminates off Palm Beach County, where it abuts a series of beach ridges (Fig. 3.2).

Fig. 3.2: (a) The north end of known Holocene reef framework in Palm Beach County is located at 26º43’N. (b) Bathymetric block diagram shows final stretch of recurved north section of the outer reef terminating immediately adjacent to outermost set of beach ridges that make up a large complex in northern Palm Beach County. Depth in m below sea level, northings and eastings are in Florida State Plane, US survey feet, NAD83.

In the south, the SE Florida reef tract terminates off Biscayne Bay. In southern Miami- Dade County, the middle reef disappears and only the inner and outer reefs remain. Both disappear in an environment dominated by sand seaward of Biscayne Bay. The outer reef

58 terminates in a wide gap, to the south of which the outer reefs of the Florida Keys reef tract begin (Fig. 3.3). South of where the outer reef ends as a continuous feature, three small linear reefs occur off the south end of Key Biscayne. It is unclear whether these reefs are a continuation of the outer reef, an independent structure, or the beginning of the Florida Keys reef tract shelf-edge reefs (Fig. 3.3). The keys shelf-edge reefs seem to be situated on a deeper platform than the outer reef of the SE Florida reef tract, and have more pronounced framework buildup. They begin abruptly without a visible sign of

Fig. 3.3: (a) Location of the bathymetric block diagram (b), which shows clearly that neither the inner nor middle (which terminates further north) reefs correspond to the shelf-edge or outlier reefs of the Florida Keys. (c) Lower insert shows a terrace arching inward just north of the beginning of the Florida Keys reefs. It is not clearly resolved whether this inward-arching terrace on which the outer reef is located is the same terrace on which the shelf-edge reefs of the Florida Keys reef tract are located. The Fowey outlier reef is named after Shinn et al. (1991).

59 transition, and the platform on which the outer reef is situated seems to curve inward just north of the northernmost Florida Keys shelf-edge reefs (Fig. 3.3).

The outer reef The outer reef crests at approximately 16m below sea level and is a relict acroporid- framework reef (Macintyre and Milliman 1970; Lighty 1977; Lighty et al. 1978) (Fig. 3.4) extending from Biscayne Bay (Fig. 3.3c) northward to its distinct terminus at latitude N26o43.0’ (Fig. 3.5a). The northern terminus of the reef tract is recurved shoreward. Figures 3.3 and 3.5c show the transition into the Florida Keys tract via Biscayne Bay, where reef topography is reduced.

Fig. 3.4: (a) Inset shows the location of (b) subbottom profile and bathymetry of the outer reef.

Fig. 3.5: (a) North part of the reef tract showing direction of dominant sand transport due to longshore drift. Throughout most of Palm Beach County, no inner or middle reefs are found. (b) Middle part of the reef tract, where all three reef lines, as well as the ridge complex, are well-developed.(c) South part of the reef tract. The middle reef terminates before the inner and outer reef. (d) Maps show location of the bathymetric blocks.

Zonation of the SE Florida outer reef is similar to that of modern Florida Keys reefs (Shinn 1963; Enos 1977; Shinn et al. 1981; Lidz et al. 2006). Landward to seaward, a rubble apron (talus), back reef, reef crest, first terrace (17 m deep), and second terrace (23 m deep) are developed (Fig. 3.6). The forereef slope extends to 28 m below sea level. The first and second terraces show spur-and-groove zones. An additional terrace occurs at approximately 30 m below sea lavel. Table 1 compares structural zone depth and widths between reefs of the SE Florida reef tract and Grecian Rocks as a modern analogue. After adjustment of reef-crest depths to the same level (d=1 m), there is a direct depth correspondence among zones.

Fig.3.6: (a) Geomorphologic zonation of the outer reef. (b) Inset map shows location of bathymetric block diagram and depth transect.

A number of repetitive geomorphic features, reef gaps, collapse features and spurs and grooves occur along the outer reef. Collapse features, interpreted as products of

62 framework breakdown, are found throughout its length (Fig. 3.7). This interpretation is based on the observation that the edges of the features are characterized by vertical walls of A. palmata in growth position. In some locations, A. cervicornis framework in growth position can be observed. Acroporid rubble and sand comprise the bottom in the collapse features. Finkl et al. (2005) classified the shoreward, arcuate boundaries as debris aprons, but we found that these areas are often constructional and consist of A. palmata frameworks in growth position with a talus slope on the landward side. Figures 3.7a and 3.8b show that the shoreward boundary structure can indeed be higher than the associated reef crest and can therefore not purely consist of debris but must include some framework. This structure is very similar to the landward margin of the Sand Key outlier reef as described by Lidz et al. (1991) and to the landward sides of Alligator Reef and Davis Reef by Shinn et al. (1989).

Reef gaps are interpreted here as erosional relicts of paleo-inlets or river channels in underlying substrate. Figure 8b is a sub-bottom profile across a reef gap that shows the gap cutting through a significant portion of the reef. This suggests that the gap is a result of reef growth on either side of an erosionally produced topographic low and the depth of the gap supports Lighty’s (1977) statement that reef thickness is greater than 10 m.

Spurs and grooves similar to extant structures in the Florida Keys are only well developed on the outer reef, and are absent, or very weakly developed on the other reefs. Isolated spurs grow seaward of the main reef structure and attached grooves are an integral part of the main reef structure (Fig. 3.6, 3.7, 3.9). These spurs and grooves are similar to those described by Shinn (1963) and Shinn et al. (1981, 1989) from the Florida Keys.

From north to south (Palm Beach to Miami-Dade Counties), a latitudinal zonation can be observed in the overall plan-view appearance of the outer reef. In the north (Palm Beach), sections between reef gaps are relatively long with no apparent collapse features, whereas in the area of northern Broward County (approximately from N26º21’ to N26º11’) gaps and collapse features are more frequent. Southward (N26º11’ to N25º44’), the reef

63 becomes longer again and collapse features persist until south of N25º44’, where sediment intrusion from Biscayne Bay impacts the reef morphology, and parts of the reef are buried by sediments (Fig. 3.5a).

Fig. 3.7: Common geomorphic features on the outer reef. Bathymetry and subbottom profile show topographic low in outer reef framework. (a) Bathymetry and spur-and- groove structures are clearly visible. White line shows location of (b) subbottom profile. (c) Acropora cervicornis framework with collapsed rubble. Image was taken on the dropoff within the white square in (a). (d) Continuity in the northern part of the outer reef is lost and the reef breaks up into numerous individual reefs (a) or reef patches (d). (e) Map shows locations of (a), (b), (c), and (d).

Fig. 3.8: (a) Bathymetry and (b) subbottom profile of an outer reef gap, indicating that the gaps are due to antecedent topography.

The middle reef The middle reef is a linear and continuous feature inshore of the outer reef. The middle reef crests at approximately 15 m below sea level and extends from South Miami-Dade County (Fig. 3.9b), northward to Boca Raton Inlet (Fig. 3.9a). The middle reef does not display a detectable zonation. Subbottom profiles and bathymetry identify positive relief features intermittently along the extent of the structure that seem to indicate reef framework (Fig. 3.10) and patches, isolated by sand. Patches of acroporid framework were observed near the northern termination. The middle reef is almost certainly structurally controlled by a previously existing ridge, the age and composition of which are undetermined. Based on elevation, it is possible that this ridge was a shoreline at the time the outer reef was alive.

Fig. 3.9: (a) North and (b) south termini of the middle reef as detected by bathymetry. Spur-and-groove structures on the outer reef are clearly visible.

Fig. 3.10: (a) Map shows locations of (b) bathymetry and subbottom profile of middle reef. The data indicate that the reef may be a shoreline deposit overlain by patchy coral frameworks. Subbottom resolution did not allow clear differentiation of coral framework versus other types of limestones. Dashed line indicates presumed Pleistocene/Holocene contact.

Erosional channels, similar to those of the outer reef, are also found on the middle reef (Fig. 3.11). Some channels cross-cut the inner and outer reef, supporting the interpretation that they represent paleo-rivers. The rivers incised late Pleistocene substrate, and the resulting topography controlled reef growth to preserve the channels.

Additional structures, morphologically similar to the middle reef, are encountered in the generally sandy area between the inner and the middle and between the middle and outer reefs. These are low ridge-like structures that are mostly covered with sediment and are

67 not observed on all subbottom-profiles. It is unclear which of these structures are framework ridges or lithified sand ridges, since evidence for both exists (Fig. 3.12). A wastewater-pipe trench off Bal Harbor in Miami-Dade County traverses such a structure between the inner and

Fig. 3.11: (a) Map shows location of (b) paleo-erosional features cross-cutting the inner and middle reefs.

middle reefs and showed a thickness of 2.5 m of framework consisting of massive corals that grew on quartz sand. A Siderastrea sp. at the base, 16 m below sea level, had an age of 7,240 cal BP (Shinn et al. 1977; Fig. 3.12). A subbottom profile through the reef/ridge complex in central Broward County reveals a series of patch reefs between the outer and middle reefs. Some of the patch reefs have a high vertical relief, protruding above their sedimentary entombment. None, however, extend upward as far as the reef crest of the outer reef.

Two shallow cores (1.62 m and 0.62 m core length) taken on the middle reef (N26o08.9’ W80o04.9’) revealed a framework at this location of massive coral species, including Agaricia sp., Manicina aereolata, Montastraea cavernosa, M. annularis, and Siderastrea siderea. 14C-age ranges for the corals at the tops of these cores were 3,730 cal BP and 4,220 cal BP. A sample from a M. annularis colony 1.6 m downcore yielded an age of

68 5,815 cal BP. Table 2 provides a summary of radiocarbon ages for reef surfaces samples. Personal observations of physical damage at several locations on the middle reef in Broward and Miami-Dade Counties from pipeline installations also showed massive coral framework. No acroporid corals were observed in cores or in reef scars, except at a single location in Palm Beach County.

Fig. 3.12: Bathymetry shows intermediate ridge between (a) inner reef and middle reef and (b) outer reef (with collapse features) and middle reef. (c) The outcrop drawing is modified from Shinn et al. (1977). (d) Map shows location of features.

69 Table 3.2: Reef surface radiocarbon ages for the relict coral reef tracts offshore Broward County, Florida. Reference 1: Lighty et al. (1982), calibrations in Toscano and Macintyre (2003); 2: Precht et al., unpublished data, calibrations in Toscano and Macintyre (2003).

Reef Sample Reference Sample 14C age, Cal BP description depth convcentional (calendar (m MSL) (years and range) years) 1 outer Acropora palmata 1 -23.0 7696±70 8160 2 outer A. palmata 1 -16.5 8241±76 8770 3 middle Montastrea This study -16.8 3750±50 3730 cavernosa 4 middle M. cavernosa This study -16.9 4140±70 4220 5 inner Diploria strigosa This study -10.4 6010±80 6430 6 inner A. palmata 2 -7.8 5950 6800 7 inner A. palmata 2 -7.8 6200 7150 8 inner A. palmata 2 -7.9 6070 6970 9 inner A. palmata This study -8.3 TIMS U/Th 6003±17

The inner reef

The inner reef (Fig. 3.13) crests at 8 m below sea level and generally consists of an A. palmata framework, visible in cores and in an excavation of the framework made by the grounding of the submarine USS Memphis (Banks et al. 1998). Also, exposure of sections of the fore reef north of Port Everglades Inlet by ship groundings during 2004 revealed a thin (~1 m thick) massive coral lithofacies overlying a karst substrate. A calibrated 14C- age range of 6,430 cal BP was obtained from a surficial Diploria strigosa sample. Shinn et al. (1977) found only massive corals at an exposure created by dredging through the reef off Miami Beach. The coral had initiated growth on quartz sand with land snails and plant roots, which indicates control of reef location by underlying topography. It is not clear, however, from the precision of the location provided whether their sample was from the reef crest or fore reef. Acropora palmata samples exposed by the grounding of the USS Memphis had 14C ages of 6,800-7,420 cal BP (Toscano and Macintyre 2003) and a Siderastrea sp. collected by Shinn et al. (1977) from the base of the inner reef offshore Miami had an age of 7,240 cal BP.

The inner reef begins south of the middle reef off North Miami-Dade County at N 25º40’ and extends northward to Hillsboro Inlet at N 26º15’ in Broward County. The north end of the inner reef is co-linear with the shoreline on the north side of Hillsboro Inlet, which steps eastward from the south inlet shoreline. The inner reef may continue northward, but is buried under the modern shoreline sediment. The inner reef is not a continuous structure like the outer reef, but in most areas is a complicated amalgamation of patch reefs that can be fused to form longer structures, within which the individual patch reefs frequently remain identifiable. In central Broward County, topography of the inner reef is generally more dramatic than on the outer and middle reefs with vertical drop-offs along the edges of the patch reefs.

Fig. 3.13: (a) Bathymetry and (b) subbottom profile of middle and inner reef. Middle reef seems to be a shoreface with patchy reef development. The inner reef at this location seems to have a similar structure. (c) Map shows location of bathymetry and seismic line.

71 Shinn et al. (1977) found the inner reef to be 2.4 m thick at one location off Miami and to overlie a laminated soilstone crust that rests on lightly cemented cross-bedded quartz and carbonate sand. They interpreted the crust to be of eolian origin, based on the presence of the land snail Cerion and terrestrial roots. We obtained a core (Fig. 3.14a) through A. palmata framework that ended in a Diploria strigosa colony at the contact with a lithified coquina. A TIMS U-Th age of 6,003±17 yr. BP was determined for an A. palmata sample 1.5 m downcore.

Fig. 3.14: Two different cores through the inner reef off Broward County. (a) shows the entire core. Between “top” and “3 m”, all fragments are Acropora palmata. Above the hatched line, indicating contact between reef and underlying Anastasia Formation, is a Diploria strigosa. Note that both top and bottom of the Diploria specimen are eroded and covered with a gray cement crust, indicating specimen is likely not in growth position. (b) Reef core is arranged horizontally. All fragments are of Acropora palmata.

The core successfully penetrated the entire inner reef and provided 3.15 m of coral framework (Fig. 3.14a). Recovery was poor, <30%, because the framework consisted entirely of standing skeletons of A. palmata with conserved original primary porosity, except at the very bottom of the core. The height of the framework indicated a maximum of two generations of skeletal accretion. The top 15 cm of the core (contact with the

72 water) were heavily bioeroded and taphonomically altered. To a depth of 1.5 m, the recovered material consisted almost exclusively of A. palmata. Undersides of the fragments showed thin layers of gray, peloidal micrite cements. Many fragments had mollusk borings, mainly by Lithophaga sp. Below 1.5 m downcore, fragments were smaller and taphonomic alteration was stronger. Some fragments were almost entirely coated in gray, peloidal cement, and all fragments were heavily bored. We interpret the core content from 0 m to 1.5 m as being in situ A. palmata framework, and the section from 1.5 m to 3.0 m as being a dead understory consisting of bioeroded stumps and fragments. Between 3.0 m and 3.1 m, a D. strigosa colony marked the transition to a heavily eroded, altered, and encrusted surface of coquina. The D. strigosa was heavily bored with a gray cement crust on its equally eroded underside. Because the surface of the sediment also exhibited a gray cement crust, the D. strigosa was likely not in growth position.

Driving another core through the first reef was abandoned due to a fragment lodged in the drill-bit after penetrating 1.1 m. This core had excellent recovery (80%) and contained thick branches of A. palmata in a dense framework (Fig. 3.14b). A. palmata fragments were lined by dense, gray to reddish peloidal micritic cements and showed encrustations by bivalves, the foraminifer Homotrema rubrum, and the crustose coralline algae Porolithon sp. and Neogoniolithon sp. Coral fragments exhibited moderate evidence of boring, mainly by Lithophaga sp. and some Gastrochaena sp. The top of the core was clearly bioeroded and thus evidenced the time lag since the end of constructional activity. Taphonomic alteration was highest in the immediate top 10 cm of the core, after which the alteration decreased, then increased again toward the bottom. Many A. palmata fragments exhibited clear bioerosion bands consisting of small-chambered sponges (Entobia sp.), which were not always oriented in the vertical position. According to Blanchon and Perry (2004), the observed taphonomy indicates that this core was taken in a reef-crest facies. An outcrop in Miami-Dade County, at the Miami wastewater-pipe trench, showed the inner reef to consist of 3.4 m of coral framework with a 5,280 cal BP age of a Diploria strigosa growing directly on a Pleistocene surface (Shinn et al. 1977). The framework consisted of massive corals and initiated on a laminated crust. Such a

73 crust was absent in the Broward County core (Fig. 3.14). Thus, distinctly different framework growth fabrics (sensu Insalaco 1998) exist, i.e. Acropora framestone and massive coral domestone.

Ridge complex The nearshore ridge complex extends from N26º15’ (Hillsboro Inlet) southward to N25º51’ in Miami-Dade County and consists of shoreline deposits with visible karst features. One core, with recovery near 100%, on the ridge complex north of Port Everglades revealed 4.5 m of shelly, coarse sand throughout. The sediment varied in coarseness from shell hash to coarse sand and had variable siliclastic content. We interpret the sediment as cemented beach, or immediately nearshore deposits, consisting of a mixture of reworked Pleistocene Anastasia Formation and Holocene deposits.

The ridges likely extend farther north than observed in outcrop but are buried by the modern shoreline. North of Port Everglades Inlet, the majority of the substrate is coquina of the Anastasia Formation, a lithified foreshore deposit (Dubar and Johnson 1964; Osmond et al. 1970; Perkins 1977). South of Port Everglades Inlet, the substrate is a carbonate/quartz sandstone.

Raymond (1972) reported the presence of two features that he interpreted as wave-cut cliffs on the ridge complex. One is on the shallowest ridge at a water depth of approximately 5 m with a 1 m vertical relief. The other is on the outside of the ridge with a base water depth of 6 m and a relief of 3 m. We also observed (Fig. 3.15) a feature at 6 m below sea level with a relief of 1.5 m on the outer ridge that resembles a wave-cut cliff. Based on the sea-level curve of Toscano and Macintyre (2003) erosion of the cliff on the outer ridge would have occurred between 3,500 and 6,500 cal BP, although this curve shows no stillstand or slowed rise at that time. Based on elevation, this cliff is a possible shoreline for the period when the inner reef was alive and accreting. Lidz et al. (2003, 2006) also describe a nearshore rock ledge and scarp that could be an equivalent structure in the Florida Keys.

Fig. 3.15: (a) Bathymetric block diagram of ridge-complex showing purported wave-cut cliff. The cliff could have been a shoreline during the time when the inner reef was alive (until about 3.4 ka, see Table 1). (b) Map shows location of block diagram.

Discussion

Surficial geology Although the reefs and ridges off SE Florida are generally linear and shore-parallel, some features are more oblique or arcuate. The latter orientation likely reflects the effect of dominant wave-energy flux at the time of formation of the underlying late Pleistocene topography, which probably determines reef form in plan view. Dubar and Johnson (1964), Cooke (1945), and Osmond et al. (1970) stated that these antecedent structures represent isotope substage-5e interglacial subtidal sand bars. Though a substage-5e age is possible for some of the structures, as in the case of the Anastasia Formation, some other structures may be much younger, possibly even early Holocene, because plant roots in the exposure off Bal Harbor reported by Shinn et al. (1977) were still wood and the snails were not leached and/or converted to molds (Shinn personal observation). During substage-5e time, when sea-level was approximately 6 m higher than present (and the

75 Florida Keys were accumulating as live coral reefs and/or ooid shoals), the northern Bahama Banks were deeper and their islands smaller, creating a less efficient wave break to high-energy swells from the open Atlantic Ocean. This presumed exposure to higher energy may have resulted in a more dynamic wave field in SE Florida than at present. Modern maximum wave-energy flux is predominately from the north and northeast (Fig. 3.16, black arrows showing infinite fetch from the N and NNE) generated by continental cold-front passage in the winter. Wave-energy flux decreases in the southern portion of the region because of the shadowing effect of the Little and Great Bahama Banks. The likelihood that reef footprint is primarily determined by underlying topography is evidenced by the observation that reef fronts are not oriented parallel to the primary wave-energy-flux direction but are, instead, oriented in a shore-parallel direction. Shinn et al. (1977), Lidz (2004), and Lidz et al. (2003, 2006) also suggested that linearity and distribution of parallel reefs in SE Florida were controlled by underlying dune topography.

Fig. 3.16: Windroses throughout the study region show increasing northerly component of fetch and wind, which would result in higher-energy wave conditions in the northern counties. WIS=wave information system. Axes are relative contribution of wind magnitude to the illustrated sectors. Dominant sector is colored gray. Black lines represent relative fetch (distance over which wind generates waves). Arrows show infinite fetch in the N and NNE due to exposure to open ocean.

Furthermore, the recurving nature of the northern terminus of the outer reef may have been caused by the relatively high wave-energy flux from the northern quadrant. Wind-

76 driven waves from the north to northeast would refract around the basement substrate of the reef. Framework growth on the terminus would orient parallel to the wave fronts, causing a curvature shoreward. Alternatively, a hook-shaped feature may have already been developed in the antecedent topography. Such features are commonly observed on barrier islands in Florida and can control morphology of subsequent reef growth, such as on the northern end of Pulley Ridge in SW Florida (Jarrett et al. 2005). These hook- shaped features generally occur at the down-drift end of barrier islands or spits. In modern SE Florida, we would expect them at the southern end, so it remains problematic why we observe this feature at the northern end. Coring would be required to determine if this reef feature is constructional or is indeed inherited from antecedent topography. North of the reef terminus is a complex of arcuate structures that most likely represent lithified shoreline deposits.

The geomorphology at the southern end of the SE Florida continental reef tract is influenced by water and sediment emanating from Biscayne Bay (Fig. 3.5c). As Biscayne Bay flooded during the last transgression, sediment release over the reef may have affected growth and position of framework-building corals. There are gaps in reef development off Biscayne Bay, which make it difficult to ascertain with bathymetric data alone whether the shelf-edge reefs of the Florida Keys reef tract are a continuation of the outer reef of the SE Florida continental reef tract. A problem remains whether the outer reef or even the middle or inner reefs are continuous or analogous with the outlier reefs of the Florida Keys, as suggested by Toscano and Macintyre (2003, Fig. 3.3). Our Figure 3 shows clearly that the location and growth control by antecedent morphology of the outer reef can at best be equivalent to that of the Florida Keys shelf-edge reefs. There are many structural similarities between the outlier reefs of the Florida Keys reef tract (Lidz et al. 1997) and the SE Florida outer reef, but the outliers are situated on late Pleistocene reefs and are capped by Holocene corals. It is possible that the reefs initiated and grew in a similar environment that would have caused similar morphological structures. However, the outliers are discontinuous structures in isolated position in front of the shelf edge, whereas the SE Florida outer reef is a largely continuous structure (at least in its southern extent in Miami-Dade and Broward Counties) situated at the shelf edge itself. We believe

77 that certainly the outlier reefs and maybe the shelf-edge reefs of the Florida Keys originated on deeper terraces than the SE Florida outer reef (Fig. 3.3). More drilling and detailed seismic profiling are necessary to resolve this question. All these reefs are most likely based on coastal dunes, either Pleistocene or early Holocene, dependent on water depth.

At the northern terminus, the middle and inner reefs probably disappeared due to burial by an increase in sediment supply. The northern end (Fig. 3.5a), off West Palm Beach, is subjected to a large volume of littoral, siliciclastic sediment transported from the north. The USACE (1996) estimated that 98,000 m3yr-1 of sediment reaches Lake Worth Inlet (Palm Beach County), in contrast to 4,590 m3yr-1 reaching Government Cut just north of Biscayne Bay (Miami-Dade County). In the south, the appearance and orientation of sand waves (Fig. 3.5c) indicates significant transport of carbonate sediments from Biscayne Bay. Increasing sediment transport into the SE Florida continental reef tract during the Holocene transgression may have significantly impacted framework accretion on all reefs.

Depositional framework In the subsurface chirp sonar investigation, at least one marked reflector was observed that could be linked by drilling to the Pleistocene unconformity on which Holocene carbonate deposition took place. Thus, observed reflectors support our statements concerning topographic control by representing erosion and cementation during lowstands corresponding to glacial periods. We observed in outcrop on the inner reef and intermediate ridge between the inner and middle reefs that contact with the Pleistocene showed clear signs of subaerial exposure (crusts, roots, land snails). The uppermost depositional sequences investigated in our study area consist primarily of reefal sediments, i.e., framestones in the inner and outer reefs and a mixture of reef-derived and transported non-reefal sediments between the reef lines. The framestones are generally juxtaposed on the shoreward side by dense surficial rubble beds that grade into mixed carbonate-siliciclastic sediments (Fig. 3.17). The siliciclastics stem from reworked older

78 nearshore sediments that were subsequently transported off bank. Sediment cores reveal rubble facies in deeper layers that accrued during the Holocene transgression.

Fig. 3.17: (a-c) Interpreted sediment cores from sand deposits between SE Florida middle and outer reefs. The sand is a mixture of quartz and carbonate. (d) Map shows location of (e) bathymetry on which core locations are noted (white dots).

Reconstructed growth history The known (Lighty 1977; Lighty et al. 1978) and newly determined ages of the reef lines coupled with their geomorphology allow us to develop a conceptual model of stepwise aggradation and backstepping in response to sea-level history (Fig. 3.18). During the oxygen isotope substage-5e highstand approximately 125 ka, the SE Florida shelf experienced a higher wave-energy flux than today, because submergence of the Bahama Banks reduced value of the banks as wave-barriers. We propose that the increased energy flux onto the shelf modified the morphology of offshore sand bars that later became indurated during the next lowstand. During renewed sea-level rise in the early Holocene, reef growth initiated on the topography controlled by antecedent indurated sand bars near

Fig. 3.18: Proposed sequence of development of the SE Florida reef system. BP = before present. (a) In the late Pleistocene/early Holocene, sand ridges were indurated during lowstands. (b) During early Holocene sea-level rise, the outer reef initiated growth and accreted. The ridge underlying the middle reef may have been a shoreline. (c) With increasing sea-level rise, outer-reef accretion ceased, and massive corals settled on the previous shoreline to form the middle reef. The inner reef initiated as a backstepped Acropora palmata reef. The sea cliff on the ridge complex (arrow) may have been the locus of a temporary shoreline during the growth phase of the inner reef. (d) Sea-level reached its present level, and middle and inner reefs ceased growth at about 3.6 and 3.4 ka.

80 the shelf edge to become the outer reef. Judging from internal structure of the reef, Lighty et al (1978) noted that it initiated as a fringing reef and transitioned to an extensive shelf- edge barrier reef as rising sea level submerged the back reef shelf margin. Lighty (1977) puts this outer reef initiation at >10,200 cal BP and its demise at 8000 cal BP. A series of patch reefs grew between the present day outer and middle reefs which are now mostly buried by sediment (Fig. 3.12). It is unclear whether the locus of the present middle reef is an antecedent, indurated subtidal sand bar or a shoreface that might have been coeval with formation of the outer reef. A further rise in sea level led to the initiation of the inner reef. The ages of our inner reef cores (6,003 yr. BP U/Th age at a 1.5-m-framework depth, 6,430 cal BP at the reef surface; Table 3.2) are almost 2,000 years younger than the age given for the uppermost layers of the outer reef in Lighty (1977), which indicates that a true reef backstepping had occurred. The ages obtained from the middle reef (~4,200 cal BP and ~3,700 cal BP for the uppermost layers) are younger than the timing of inner reef termination. Thus our present, still fragmentary, knowledge suggests the following formation and backstepping sequence: growth of the outer reef from ~>10,200- 8,000 cal BP at which time a beach and beach-ridge system existed at the later locus of the middle reef. Transgression caused the reef to backstep to the locations of the present middle and inner reefs. It is not known whether the middle and inner reefs initiated at the same time or not. The inner reef grew actively until ~6,000 cal BP while the middle reef continued growth until ~3,700 cal BP. A clear ecological differentiation seems to have existed: Acropora palmata framework on the shallower inner reef, and massive, less environmentally sensitive corals (Montastrea spp. Diploria spp., Siderastrea spp.) on the middle reef and on the ridges between the middle and inner reefs. Termination of inner reef accretion cannot be attributed to the rate of sea level rise since the rate at the time of demise was 2-3 mm yr-1 (Toscano and Macintyre 2003), far less than the maximum reef- accretion rate of 14 mm yr-1 (Buddemeier and Smith 1988).

It is unclear what caused the end of reef accretion. However, demise of Acropora is not unique to South Florida. Hubbard et al. (2005) found a Caribbean-wide gap in A. palmata reef building from ~6,000-5,200 cal BP, within which period falls inner reef termination.

81 Thus, a Caribbean-wide event seems to have significantly reduced coral cover on many reefs in the recent past and permanently terminated dominance of A. palmata in SE Florida, north of the Florida Keys. Parallels to the observed crisis in the modern Caribbean, with Acropora being gravely disadvantaged throughout much of its range, become strikingly obvious. In each case, the cause or causes remain elusive.

Acknowledgments I thank Miami-Dade, Broward and Palm Beach Counties for making the LADS datasets available. H. Guarin of Bert Instruments, Inc., collected and processed subbottom profiling information with his Geocat II. K. Kohler wrote LADS extractor. R. Fairbanks kindly provided us with a TIMS age. I thank three reviewers for useful criticism and B.H. Lidz for a careful review, thorough editing, and many helpful remarks. Support by NOAA-CSCOR grants NA16OA1443 and NA03NOS4260046 to NCRI.

References

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83 Lighty RG, Macintyre IG, Stuckenrath R (1982) Acropora palmata reef framework: a reliable indicator of sea-level in the western Atlantic for the past 10,000 years. Coral Reefs 1:125-130 Macintyre IG (1988) Modern coral reefs of western Atlantic: new geologic perspectives. AAPG Bull 72:1360-1369 Macintyre IG, Milliman JD (1970) Physiographic features on the outer shelf and upper slope, Atlantic continental margin, southeastern United States. Geol Soc Am Bull 81:2577-2598 Middleton GV (2000) Data analysis in the earth sciences using Matlab. Prentice Hall, Upper Saddle River, NJ Moyer RP, Riegl B, Banks K, Dodge RE (2003) Spatial patterns and ecology of benthic communities on a high-latitude South Florida (Broward County, USA) reef system. Coral Reefs 22:447-464 Osmond JK, May JP, Tanner WF (1970) Age of the Cape Kennedy barrier-and-lagoon complex. J Geophys Res 75:469-491 Perkins RD (1977) Depositional framework of Pleistocene rocks in south Florida. In: Enos P, Perkins RD (eds) Quaternary Sedimentation in South Florida. Geol Soc Am Mem 147:131-198 Perry CT (1998) Macroborers within coral framework at Discovery Bay, north Jamaica: Species distribution and abundance, and effects on coral preservation. Coral Reefs 17:277-287 Perry CT (2000) Macroboring of Pleistocene coral communities, Falmouth Formation, Jamaica. Palaios 15:483-491 Raymond WF (1972) A geologic investigation of the offshore sands and reefs of Broward County, Florida. M.S. thesis, Florida State University, p95 Shinn, EA (1963) Spur and groove formation on the Florida reef tract. J Sediment Petrol 33:291-303 Shinn EA, Hudson JH, Halley RB, Lidz BH (1977) Topographic control and accumulation rate of some Holocene coral reefs, south Florida and Dry Tortugas. Proc 3rd Int Coral Reef Sym 2:1-7 Shinn EA, Hudson JH, Robbin DM, Lidz B (1981) Spurs and grooves revisited – construction versus erosion, Looey Key Reef, Florida. Proc 4th Int Coral Reef Sym 1:475-483 Shinn EA, Lidz BH, Kindinger JL, Hudson JH, Halley RB (1989) Reefs of Florida and the Dry Tortugas: A guide to the modern carbonate environments of the Florida Keys and Dry Tortugas. International Geological Congress Field Trip Guidebook T176, AGU, Washington DC, p55 Shinn EA, Lidz BH, Hine AC (1991) Coastal evolution and sea-level history: Florida Keys, Proceedings: Coastal Depositional Systems in the Gulf of Mexico, Quaternary Framework and Environmental Issues. Twelfth Annual Research Conference Gulf Coast Section Society of Economic Paleontologists and Mineralogists Foundation, Adams's Mark Hotel, Houston, Texas, pp237-239. Stuiver M, Reimer PJ (1993) Extended 14C database and revised CALIB radiocarbon age calibration 24,000-0 cal BP. Radiocarbon 35:215-230

84 Toscano MA, Lundberg J (1998) Early Holocene sea-level record from submerged fossil reefs on the southeast Florida margin. Geology 26:255-258 Toscano MA, Macintyre IG (2003) Corrected western Atlantic sea-level curve for the last 11,000 years based on calibrated 14C dates from Acropora palmata framework and intertidal mangrove peat. Coral Reefs 22:257-270 USACE (1996) Coast of Florida Erosion and Storm Effects Study-Region III, Appendix D-Engineering Design and Cost Estimates (draft). US Army Corps of Engineers, Jacksonville, Florida, District, pp233 Vaughn TW (1914) Investigations of the geology and geologic processes of the reef tracts and adjacent areas in the Bahamas and Florida. Carnegie Inst Wash Yb 12:pp183

4 Environmental Geology of the Continental Southeast Florida Reef Tract (Miami-Dade, Broward and Palm Beach Counties, USA)

Introduction

Although South Florida coral reefs are frequently considered to be confined to the Florida Keys, a complex of relict early Holocene shelf-edge and mid-shelf reefs as well as limestone ridges extends along the continental coast of Southeast Florida (Fig. 4.1) from offshore south Miami (N25º34’) northward to offshore West Palm Beach (N26º43’). This extends the distance spanned overall by reefs in SE Florida by 125 km (Fig. 4.2). The nomenclature proposed by Moyer et al. (2003) and Banks et al. (2007) identifying these structures as ridge complex and inner, middle, and outer reef will be used herein. The reefs are arranged linearly and parallel to the trend of the shoreline. They are separated by sandy sedimentary deposits of varying thicknesses that overly erosional hardground surfaces (Duane and Meisburger 1969a, b; Raymond 1972; Shinn et al. 1977, Banks et al. 2007). The reefs themselves are presently not framebuilding but are colonized by a rich tropical fauna otherwise characteristic of the West Atlantic/Caribbean reef systems.

The continental shelf along the SE Florida coast is narrow and bathed by the relatively warm waters of the Florida Current, a branch of the Gulf Stream flowing northward between SE Florida and the Bahamas banks. Although SE Florida is located at the convergence of the subtropical and temperate climate zones (Chen and Gerber 1990), the influence of the Florida Current and the absence of any major rivers have provided in the early and mid Holocene conditions suitable for reef building and, after the demise of framebuilding, the maintenance of extensive coral reef associated communities.

Fig. 4.1: Location map of Southeast Florida with key geographic features.

Fig. 4.2: The continental Southeast Florida reef tract extends from Biscayne Bay in Miami-Dade County (N25o35’) northward to West Palm Beach in northern Palm Beach County (N26o43’). It is composed of a complex of limestone ridges and shelf-edge and mid-shelf reefs.Rohmann et al. (2005) estimated that 30,801 km2 of inshore areas situated in less than 18.3 m depth around South Florida could potentially support shallow-water coral reef ecosystems. An area of 19,653 km2 remains outside the Florida Keys and Dry Tortugas and is discussed here with regard to SE Florida and in chapter 4 by Hine et al. with regard to the West Florida shelf. In comparison, estimates for other areas capable of providing habitat for reefs and reef-associated fauna in the United States are 108 km2 in Guam, 1,231 km2 in the Main Hawaiian Islands and 2,302 km2 in Puerto Rico.

88 Goldberg (1973) provided the first description of the reef communities north of the Florida Keys based on studies of the reef community offshore Boca Raton, Florida (N26º20.8’). This work was limited to a small area in the northern part of the reef complex. Infrequent and regionally isolated reef community monitoring carried out in association with dredging for beach nourishment projects followed (Courtney et al. 1972, 1975, 1980; Continental Shelf Associates 1980, 1984; Goldberg 1981; Blair and Flynn 1989; Dodge et al. 1995). These projects, however, did not provide a continuous record of biotic dynamics nor were the study sites chosen to describe regional patterns of reef community structure.

Beginning in 1997, the Broward County Environmental Protection Department instituted a long term status and trends monitoring program at 18 fixed sites distributed across the shelf and from N26º00.26’ to N26º20.80’ latitudes (Gilliam et al. 2007). Coral cover, as well as octocoral and sponge density, have been measured annually using a single, fixed, 30 m2 belt-transect (1.5 m x 20 m) at each site. In 2004 the program was expanded to 25 sites.

In 2003, the Florida Fish and Wildlife Conservation Commission extended the Florida Keys Coral Reef Evaluation and Monitoring Program (CREMP) into the SE Florida region (Southeast Florida Coral Reef Evaluation and Monitoring Program [SECREMP]) by installing 10 permanent stations. Relative bottom cover is determined annually from video transects at each station (total transect area at each station=528 m2). In addition, stony coral species inventory, clionid sponge cover (at 66 m2 transect), Diadema antillarum abundance, and stony coral condition are measured. This activity covers the area from Palm Beach County (N26º42.63’) to Miami-Dade County (N25º50.53’) with 3 sites in each county and one additional site in Broward County at a site of unusually high Acropora cervicornis cover (Gilliam 2007).

An extensive investigation of spatial patterns in community structure among reef tracts was carried out in Broward County by Moyer et al. (2003) who measured relative bottom cover using 6 replicate, 50m point intercept transects at 31 sites within 3 cross-shelf

89 corridors (Broward County north, central and south), each containing all three reef tracts. While limited to the central part of SE Florida, the study was extensive enough to identify some latitudinal and cross-shelf patterns. Foster et al. (2006) expanded this study to include community patterns within reef tracts at the 3 corridors, the effects of sampling scale on the analysis of community structure, and the influence of certain environmental factors on community structure. Their measurements were based on 32 photoquadrats (0.75 m x 0.50 m each), replicated 6 times (72 m2) at each of 99 sites (33 in each corridor; north, central, south).

A SE Florida regional reef habitat mapping project was begun in 2004 by the National Coral Reef Institute (NCRI) for the Florida Fish and Wildlife Research Institute (FWCC). Data from laser airborne depth sounder (LADS) bathymetry, multi- and single-beam bathymetry, acoustic seafloor discrimination, ecological assessments, and groundtruthing were integrated into maps created with Geographic Information System (GIS) (Walker et al. 2007). Habitat categories were based on the NOAA biogeography program. Field verification of habitat types was used for quality assurance. Maps were completed for Broward County and Palm Beach and Miami-Dade counties are planned or underway (NCRI 2004).

Regional setting The reef tracts are believed to be founded on shore-parallel lithified Late Pleistocene beach ridges (Shinn et al 1977, Banks et al. 2007). These ridges are likely an offshore extension of the shore-parallel ridge complex (Fig. 4.2).

The continental shelf of SE Florida is narrow, approximately 3 km wide offshore Palm Beach County and 4 km wide offshore Miami-Dade County. Bottom slope steepens at approximately 80 m depth where the East Florida Escarpment begins (Fig. 4.3). The East Florida Escarpment terminates at a depth of 200-375 m at the Miami Terrace, a drowned early to middle Tertiary carbonate platform (Mullins and Neumann 1979). The Terrace extends from N25º20’ northward to N26º30’ and resembles a long, low obtuse triangle. It

90 covers approximately 740 m2 with a maximum width of 22 km and two levels separated by a discontinuous ridge. The upper terrace is a drowned limestone formation which was subaerially exposed in the middle to late Miocene and is presently marked by karst features. The ridge is probably a drowned Miocene or post-Miocene bank margin complex. The lower terrace (600-700 m depth) is erosional and discontinuous. Its formation is believed to be related to increased flow of the Florida Current and subsequent bioerosion at the time of tectonic uplift and closure of the Isthmus of Panama in mid-Miocene time. Seaward of the lower terrace a large linear depression parallel to the Florida-Hatteras slope separates the Miami Terrace from a broad, unconsolidated sedimentary ridge near the center of the Straits of Florida (Mullins and Neumann 1979).

Climatology The climate of SE Florida and the Florida Keys is defined as Tropical Savanna (Aw) in the Köppen Climate Classification System (Trewartha 1968). This class is characterized by a pronounced dry season with the driest month having less than 60 mm precipitation and the total annual precipitation less than 100 mm. Average temperature for all months is 18ºC or greater. Table 5.1 presents a summary of climatological data for SE Florida.

91 Table 4.1: Climate data for West Palm Beach and Miami, Florida (Palm Beach County, upper number ; Miami-Dade County, lower number). Temperatures (Co) are based on means from 1971-2000. West Palm Beach and Miami wind data are based on means from 1942-2005 and 1949-2005, respectively (Tave=average monthly temperature, Tmax=maximum monthly temperature, Tmin=minimum monthly temperature, Wave=average monthly wind speed (m/s), Wdir=average monthly wind direction) (NOAA 2005).

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Ave

19.0 19.6 21.4 23.2 25.7 27.3 28.1 28.2 27.6 25.6 22.8 20.2 24.1 ave T 20.1 20.6 22.4 24.3 26.4 28.0 28.7 28.7 28.0 26.0 23.6 21.1 24.8

23.9 24.6 26.2 27.8 29.9 31.4 32.3 32.3 31.5 29.4 26.9 24.7 28.3 max T 24.7 25.4 27.1 28.8 30.7 31.9 32.7 32.6 31.7 29.7 27.3 25.3 29.0

14.1 14.6 16.6 18.6 21.4 23.2 23.9 24.1 23.7 21.8 18.8 15.6 19.7 min T 15.3 15.8 17.8 19.8 22.2 24.0 24.7 24.7 24.3 22.3 19.7 16.8 20.6 4.5 4.7 4.9 4.9 4.4 3.7 3.4 3.4 3.9 4.5 4.6 4.5 4.3

ave W 4.2 4.5 4.6 4.7 4.2 3.7 3.5 3.5 3.7 4.1 4.3 4.1 4.1 SE SE SE SE

NW NW NW NW ESE ESE ESE ESE ESE dir W E E NN NN NN ESE ESE ESE ESE ESE ESE ESE ENE

92 During the dry fall/winter/spring months (November-March), Florida experiences the passage of mid-latitude synoptic-scale cold fronts (Hodanish et al. 1997) which bring strong winds from the northeast. These “northeasters” usually last for 2-3 days. From late spring to early fall (the wet season, June-September), differential heating generates mesoscale fronts, creating sea breezes. Convergence of these moisture-laden sea breezes, developing from the different water bodies (Atlantic Ocean, Gulf of Mexico, and Lake Okeechobee), coupled with high humidity in the Everglades, result in a low pressure trough developing across the Florida peninsula. This leads to intense thunderstorm activity, which moves from inland to the coasts, delivering large amounts of freshwater to the coastal shelf. South Florida receives 70% of its annual rainfall during these months. Trewartha (1968) refers to the daily sea breeze circulation as a "diurnal monsoon". The mean wind direction during most of the SE Florida wet season is from southeast (tropical)

Hurricanes From June through November, Florida is a prime landfall target for tropical cyclones, although storms have been documented as early as March and as late as December. The numbers of direct hits of hurricanes (strength based on the Saffir-Simpson scale) affecting SE Florida in the 100 years from 1899-1998 (Neumann et al. 1999) are: 5, Category 1 (winds of 119-153 km/hr); 10, Category 2 (winds of 154-177 km/hr); 7, Category 3 (winds of 178-209 km/hr); 4, Category 4 (winds of 210-249 km/hr); and 1, Category 5 (winds >249 km/hr). Table 5.2 presents the number of hurricanes and tropical storms affecting Palm Beach, Broward, and Miami-Dade counties from 1871- 2006.

Hurricanes Floyd, 1987; Andrew, 1992; Irene, 1999; Frances, 2004; Katrina and Wilma, 2005 affected SE Florida in the last decade. Hurricane Andrew was the most severe with winds at landfall in SE Florida (Elliot Key in Biscayne Bay) of 269 km/hr (Landsea et al. 2004). Tropical storm winds extended 225km from the center. Wave hindcast predicted significant wave heights of 7 m at water depths of 8-9 m. This prediction accounted for the attenuation of the Bahamas Banks (Neumann et al. 1999, Grymes and

93 Stone 1995) which, coupled with the high forward speed of the storm, substantially weakened Hurricane Andrew (Boss and Neumann 1995).

Table 4.2: Storm frequencies for Southeast Florida (USACE 1996). Number of tropical storms or hurricanes passing within a 50-mi radius of Palm Beach, Broward, and Miami- Dade Counties (a single storm may affect more than one county).

Palm Beach County Broward County Miami-Dade County Time Period Hurricanes Tropical Hurricanes Tropical Hurricanes Tropical Storms Storms Storms 1871-1880 3 0 1 0 0 0 1881-1890 2 2 1 2 2 2 1891-1900 0 2 0 1 1 1 1901-1910 2 4 2 3 3 2 1911-1920 0 0 0 0 0 1 1921-1930 3 1 4 0 3 0 1931-1940 3 0 2 1 1 2 1941-1950 5 1 4 1 5 1 1951-1960 0 2 0 2 0 2 1961-1970 2 0 2 0 2 0 1971-1980 1 1 1 1 0 1 1981-1990 0 2 0 2 1 1 1991-2000 0 2 1 0 1 1 2001-2006 3 0 1 0 0 1

Hurricanes that form in June and July are spawned entirely in lower latitudes on the western side of the Atlantic and in the Western Caribbean. Storms at this time of year are usually weak. Hurricanes occurring in August and September usually form in the Atlantic Ocean and often become mature, severe storms. Hurricanes late in September through October and into November form mainly in the western Caribbean and Gulf of Mexico (USACE 1996).

Hurricanes can have significant influence on the reefal biota of Florida (Tilmant et al 1994), which can range from wholesale destruction of biota with subsequent regeneration (Shinn 1976) to facilitation of asexual recruitment in some coral species (Fong and Lirman 1995, Lirman 2003) and by cleaning macroalgal and bacterial overgrowth from corals (Banks, pers. comm.).

94 Regional Physical Oceanographic Processes

Water Temperature Thermograph data from between July 2001 and December 2003 are presented in Fig. 4.4 (monthly mean, minimum and maximum temperatures for the 3-year period). Highest monthly temperature observed was 30.5ºC in August, 2000, on the ridge complex (Fig. 4.4) and lowest minimum of 18.3ºC, also on the ridge complex, was recorded in January 2001. Temperatures on the inner, middle and outer reefs were generally similar to one another but the ridge complex was warmer in the summer and cooler in the winter than the other tracts. This reflects the more rapid heat gain or loss of the shallower water over the ridge complex due to air temperature and/or solar insolation. For the three-year period the minimum air temperature also occurred in 2001 (11.9ºC, Miami WSCMO Airport).

Long term temperature records will be available in the future from the FWRI (Fish and Wildlife Research Institute) Southeast Coral Reef Ecological Monitoring Program (Gilliam 2007). Temperature loggers have recently been installed at each of the monitoring sites and continuous temperature data are being collected every two hours. These data will be publicly available from 2007 onward from FWRI.

Circulation The Florida Current flows north (with intermittent reversals) and is the dominant ocean current affecting the SE Florida shelf. It is a portion of the Gulf Stream that intrudes into the Gulf of Mexico as the Loop Current and reverses flow to return to the Straits of Florida before moving in a northeasterly direction towards Europe (Jaap and Hallock 1990). The average monthly low velocity is 1.0 m/s in November and the average monthly high is 2.3 m/s in July. Approximately 2 km offshore, the current speed is 2.5 m/s (USACE 1996). The western edge of the current meanders from far offshore on to mid-shelf.

Fig. 4.4: Monthly average, minimum, and maximum water temperatures from data collected hourly on the seafloor of the: a ridge complex; b inner reef; c middle reef; d outer reef offshore central and south Broward County from July, 2000, to December, 2003. Cross-shelf variations in water temperature are illustrated by comparing ridge complex and outer reef water temperatures: e minimum water temperature on ridge complex are lower that the outer reef; f maximum temperatures are higher on the ridge complex.

96 The coastal circulation along the SE Florida shelf is strongly related to the dynamics of the Florida Current. The Florida Current follows the steep bottom terrain along the shelf break separating the deep ocean (Florida Straits) from the coastal zone. Mixing between the shelf and deeper ocean waters is affected by transient features created at the western edge of the current. Sub-mesoscale spin-off eddies (Lee and Mayer 1977; Shay et al. 2002) are important to local coastal circulation because they affect the continental shelf and largely determine the water properties on the shelf (Soloviev et al. 2003).

Tides in the region are semi-diurnal with amplitudes of approximately 0.8m and tidal plumes influence coastal circulation near navigation inlets. Seven navigational inlets, approximately 16 km apart, are maintained in SE Florida. At the southern extent of the region, tidal passes allow exchange of water from Biscayne Bay onto the coastal shelf. The relative contribution of the inlets to coastal circulation can be estimated by comparing inlet tidal prisms (volume of water exchanged in the estuary between high and low tide) (Table 5.3). Other factors also affect coastal circulation, such as inlet dimensions, shelf width at the inlets, offshore distance of the Florida Current, tidal plume constituents and salinity. Soloviev (personal communication) believes that salinity stratification in the plumes substantially influences local circulation. The salinity of the plumes from the inlets is significantly different in the wet season (June-September) than the dry season (October-May).

Table 4.3: Southeast Florida tidal inlet characteristics (Stauble 1993, Powell et al. 2006).

Flow area Tidal prism Tidal range Tidal inlet/pass Latitude (m2) (m3) (m) Lake Worth Inlet N26o46.35’ 1400 24,000,000 1.0 South Lake Worth N26o32.72’ 100 3,000,000 0.9 Inlet Boca Raton Inlet N26o20.16’ 180 4,900,000 0.9 Hillsboro Inlet N26o15.44’ 300 8,100,000 0.9 Port Everglades nlet N26o05.63’ 2900 18,000,000 0.9 Bakers Haulover Inlet N25o54.00’ 520 10,194,666 0.8 Government Cut N25o45.63’ 1400 2,700,000 0.8

97 Ocean Waves

In winter, low pressure systems form on the Atlantic coast of the USA. Short period, wind-driven waves develop near the center of these lows. As these seas move away from the center of low pressure they can develop into long period swells, locally known as “ground swells”, and affect SE Florida. The wave climate of SE Florida is influenced by the shadowing effect of the Bahamas and, to a lesser extent, Cuba. In the northern part of the SE Florida region, swells from the north are of relatively high energy since they are not influenced by the shallow Bahamas Banks. Broward and Miami-Dade Counties are less affected by this wave energy because of the shadowing effect of the Bahamas Banks.

Long period swells result in increased sediment suspension and turbidity, particularly in shallow water. If northeasters occur when the moon is in perigee, abnormally high tides can result in greater ebb flows at the inlets, increasing the delivery of inlet waters to the reef system. This combination of events can cause more sediment suspension and turbidity than an average hurricane due to relatively short time duration of hurricanes (USACE 1996). Hanes and Dompe (1995) measured turbidity concurrently with waves and currents in situ at depths of 5 m and 10 m offshore Hollywood, Florida (Broward County) from January, 1990 to April, 1992. They found a significant correlation between wave height and turbidity. In addition, there was a threshold wave height (0.6 to 0.6 m) below which waves do not influence turbidity.

The primary sources of regional wave data are the US Army Corps of Engineers Wave Information Study (WIS, frf.usace.army.mil/cgi-bin/wis/atl_main.html) hindcast and the Summary of Synoptic Meteorological Observations (SSMO, NOAA National Data Center). SSMO is a large dataset of observations and was used to calibrate WIS which is hindcast at 3-hour time steps for 1956-1975. Fig. 4.5 presents wave roses for the SE Florida region from WIS. It is important to note that wave energy flux decreases in a southerly direction due to the increasing wave shadow cast by the Bahamas.

Fig. 4.5: Wave conditions throughout the Southeast Florida region show increasing northerly component of wave energy flux in the northern part of the region. Information based on US Army Corps of Engineers Wave Information System (WIS) hindcast data (http: frf.usace.army.mil/cgi-bin/wis/atl_main.html). WIS data is hindcast at 3-hour time steps for 1956-1975: a mean and maximum wave height (Ho) and period (Tp) increase with latitude (large maximum wave heights and periods at N25.5o are due to the passage of Hurricane Andrew in 1992); b vector plot of average wave direction and relative magnitude shows that average wave direction trends more northerly with increasing latitude and wave magnitude increases with latitude.

99 Holocene Climate The maximum extent of glaciation (LGM) during the last glacial period occurred during the Pleistocene Epoch approx 18k BP. Warming had started prior to this in Greenland and Antarctica at about 23 k BP in phase with the increase in northern insolation (Blunier et al 1997, Alley and Clark 1999, Alley 2000, Blunier and Brook 2001). Also prior to the LGM, the rise in sea level, due to the melting of northern ice sheet, started at 19 k BP (Yokohama et al. 2000) from an elevation approximately 120 m lower than today (Matthews 1986, Fairbanks 1989).

Flower et al. (2004) compared SST for Gulf of Mexico, based on Mg/Ca ratios in planktonic foraminifera from sediment cores, to polar ice-core records and found a gradual warming of >3oC from 17.2 – 15.5 cal k BP. There is disagreement on Caribbean sea surface temperatures (SST) at this time. CLIMAP (1976) stated that they were less than 2oC cooler than present which generally agrees with estimates of recent data and global climate models of approximately 2.5oC cooler (Crowley 2000). Some (Guilderson et al. 1994, Beck et al. 1997) contend that SST may have been as much as 4-5oC cooler than present. Trend-Staid and Prell (2002) concluded that SST in the western tropics and subtropics during LGM was not significantly different from present.

The Florida Current was reduced during the LGM possibly because of the reduction of North Atlantic deepwater (NADW) formation and of the compensatory transport of water and heat from the subtropics (Lynch-Stieglitz et al. 1999, Grimm et al. 2006). This may have reduced the thermal buffering of the warm current to the Southeast Florida region. In the Caribbean this degree of cooling would not, in itself terminate reef development through the last major glacial-interglacial cycle. However, at higher latitudes, such as Southeast Florida, slight cooling such as this might have made conditions unfavorable for reef development. Pandolfi (1999) speculated that there was a major loss of habitat as sea level dropped in the LGM so there was rapid extinction of some widespread species. Kleypas (1997), on the other hand, calculated that coral reef growth during LGM was more extensive than previously thought.

100 Generally, the climate during the LGM was colder and more arid than present day. Currently available evidence suggests that intertropical areas probably cooled 1 to 3oC in the surface ocean (Labeyrie et al. 1999). Most cooling during LGM was at high latitudes with only small changes over the tropical oceans (Labeyrie et al. 1999). Grimm et al (2006), studying pollen and plant macrofossils in a 60,000-year sediment core record from Lake Tulane in central Florida, found a strong antiphase relationship in temperature between Florida and the North Atlantic, i.e., cold periods in the North Atlantic were warm periods in Florida. 54 million km3 of continental ice (Yokohama et al 2000) melted in 10,000 yrs at the termination of the glacial period. During this deglacial interval, meltwater flow may have switched rapidly between the Mississippi River drainage and the eastern drainage systems, triggering episodic cooling and warming in the North Atlantic region (Clark et al. 2001). The timing and magnitude of Laurentide meltwater input to the Gulf of Mexico and/or meltwater diversion to the North Atlantic via the St. Lawrence River and other eastern outlets may have influenced North Atlantic Deep Water (NADW) formation and hence regional to global climate.

At least two sudden sea-level rise (SLR) events occurred due to the collapse of the Laurentide ice-sheets and the release of subsequent massive volume of polar meltwater during deglaciation. These events are referred to as either Meltwater Pulses (MWP) 1A and 1B (Fairbanks, 1989) or catastrophic rise events (CRE) 1 and 2 (Blanchon and Shaw 1995) (Fig. 4.6). Dates of these events were derived from calibrated 14C and U-Th dating of A. palmata reef cores in the Western Atlantic (Fairbanks 1989, Bard et al. 1990).

The oldest and most severe sea-level rise event was MWP-1A, which initiated approximately 14.2 (± 0.1) cal k BP with a magnitude of 13.5 (± 2.5) m (Blanchon and Shaw 1995 from Bard et al. 1990). Liu et al. (2004) refined this to 14.3 to 14.0 cal k BP, with a rise of 23 m (rise rate = 75 mm a-1). This meltwater pulse, which raised sea level by about 20 m between 14.2 and 13.8 cal k BP, corresponds to a short cooling phase in Greenland (called Older Dryas in Europe, Mangerud et al. 1974). Byrd ice δ18O (Blunier et al. 1997) do not show significant temperature changes during MWP 1A, but

101 temperatures did decrease later (the Antarctic Cold Reversal). The cold reversal terminated during the Younger Dryas at about 12 k BP. Blanchon and Shaw (1995) also suggest a third episode of rapid sea level rise (SLR) at approx. 7.6 cal k BP.

The Younger Dryas (YD) stadial corresponds to the period at about 12 ka BP when Northern Atlantic temperatures returned to glacial levels for more than 1 ka, despite the fact that Northern summer insolation was at its maximum. One possibility put forth by Broecker and Denton (1989) was that the YD event was a result of the re-routing of the Laurentide meltwater from the Mississippi Delta, through which it was flowing until about 13 cal k BP (Kennett and Shackleton 1975) to the St Lawrence estuary. This added low density meltwater near the sources of deep water formation may have inhibited deep convection in the North Atlantic and reduced northward heat transport leading to regional cooling (Flower et al. 2004, Broecker and Denton 1989, Keigwin et al. 1991). Alternatively, De Vernal et al. (1996) found evidence that during the Younger Dryas, the St Lawrence estuary was sea-ice covered most of the time, with very limited output of freshwater and no evidence of a meltwater spike. Broecker’s idea is therefore not clearly supported. Available data indicates that continental ice melting decreased significantly during the YD (Fairbanks 1989). O18/O16 ratios in ostracod shells in sediment cores from Lake Miragoane, Haiti, indicated that climate in the Caribbean was dry during the latter part of Younger Dryas chronozone (10.5-7.0 cal k BP) (Hodell et al. 1999). The YD interval (ca 12.9-11.6 cal k BP based on Greenland ice cores, Grootes et al. 1993) appears to be divided into a warm early phase and a phase that was ≈1.5oC cooler ca. 12.2-11.5 cal k BP, followed by SSTs reaching early Holocene values of 27.8±0.4oC by 11.3 k BP (Flower et al. 2004). The YD is well established in North America but evidence is not clear worldwide. Ruter et al. (2003) compared general circulation models with proxy records and found support for global extent, although signals varied in strength.

The second less pronounced SLR event, MWP 1B, initiated approximately 11.5 (± 0.1) cal k BP with a magnitude of 7.5 (± 2.5) m (Blanchon and Shaw 1995). Liu et al. (2004) refined this to 11.5 cal k BP to 11.2 cal k BP with a sea level rise of 13 m (rise rate = 40

102

Fig 4.6: Data and coral-peat Holocene sea-level curve. MWP 1A and 1B refer to periods of very rapid deglacial sea-level rise dring which A. palmata reefs could not keep up with rise. Overlap between two solid lines indicates a progressively larger depth offset over that time frame (modified from Toscano and Macintyre 2003).

mm a-1) and stated that, for the combined MWP 1A and 1B, as much as 30% of glacial ice may have melted in no more than 600 years.

The Holocene has not been a period of uniformly warm climate conditions (Keigwin 1996, Bond et al. 1997, deMenocal et al. 2000, Thompson et al. 2002, Friddell et al.

103 2003). The entire 10,000 year period has been punctuated by millennial-scale cooling events (Alley et al. 1997, Bond et al. 1999). In the Caribbean the early Holocene was wetter (Hodell et al. 1991a) and this persisted for nearly 4000 years. The wet conditions of the Caribbean persisted into the mid-Holocene (Hodell et al. 1999, Higuera-Gundy et al. 1999) and were replaced by drier conditions during late Holocene (Haug et al. 2001). The southeast US was dryer and warmer at this time (Ruter et al. 2003, Grimm et al. 2006).

The early Holocene climate was probably more similar to the glacial period than with more recent historical times. In the glacial aftermath (9000-8000 cal yr BP) large ice sheets remain in the northern hemisphere (Mayewski et al. 2004). In Florida only deep sinkholes held water during the arid late glacial interval and earliest Holocene (Watts and Hansen 1994). There is evidence that the low-latitude climate system may have been an important driver of deglacial climate change, through its influence on poleward heat and vapor transport (Flower et al. 2004, Cane and Clement 1999).

Sea surface temperature (SST) increased from LGM values of 23.6±0.5oC to early Holocene values of 27.8±0.4oC beginning between 17.2 and 15.2 cal k BP. SST warmed between 14 and 10 k BP; reached a maximum between 10 and 6 k BP; and cooled during late Holocene to modern values (Balsam 1981, Ruddiman and Mix 1991, Bradley 2000).

Broecker (1994) stated that the mid-Holocene has been known as a brief period of relative climatic stability compared with the bulk of the last glacial-interglacial cycle. Recent studies, however, indicate that the mid-Holocene was a period of profound climatic change (Steig 1999, Bond et al 1997). A mid-Holocene warm period, the Holocene Climate Optimum, occurred from 9 to 5 k BP (Pielou 1991, Maul 1992, Thompson et al. 1998, Kerwin et al. 1999, Haug et al. 2001, Curtis and Hodell 1993, deMenocal et al. 2000). Data from terrestrial records indicate that climate in North America was 2 to 4oC warmer than today (Folland et al. 1990). However, during the 9.0 to 8.0 cal k BP period widespread aridity occurred at low latitudes that was midway through a prolonged humid period that began in the early Holocene (de Menocal et al.

104 2000). Taggart (2006), based on δ18O values from bivalves collected in a subaerially exposed coral reef complex in the Enriquillo Valley (18°30’N, 71º40’W), Dominican Republic, suggested that higher temperatures and/or higher precipitation peaked at the thermal max (≈5595 BP). This was attributed to increased insolation or seaway restriction, precipitation from increased seasonality at the thermal maximum, or northward migration of the ITCZ, which is associated with especially heavy rainfall. His δ18O values positively corresponded to those from Lago Enriquillo. Curtis and Hodell (1993) attributed overall δ18O trends to increasing warm, wet conditions from 10 - 7 BP that persisted from 7 - 4 BP. The persistent moist period corresponds to increased seasonality resulting from insolation changes associated with the precession cycle of Earth’s orbital parameters and northward migration of the ITCZ during mid-Holocene (Greer and Swart 2006). Numerous studies indicate that the ITCZ may have extended significantly farther north during the mid-Holocene (Haug et al. 2001) although the northerly extent has not determined it may have extended into northern Antilles (Greer and Swart 2006). Wetter conditions occurred in Florida and the Caribbean, although other areas in the world, such as tropical Africa became more arid (Mayewski et al. 2004). Climate simulations indicate that SST may have been at least 4oC warmer than today at 6 k BP (Kerwin et al. 1999). Faunal based SST estimates indicate that winter SST’s were slightly warmer than modern during mid-Holocene. Poore et al (2003) provide evidence for a mid-Holocene interglacial max or hypsithermal in the GOM that is consistent with records of a mid-Holocene hypsithermal in the region (e.g. Haug et al. 2001). Increased transport of Caribbean surface waters and moisture into the GOM region associated with a northward migration of the average position of the ITCZ occurred in the mid-Holocene between 6.5 and 4.5 k BP.

In the North Atlantic there was a short-lived cool period called the “8.2 k” event (Alley et al. 1997) and it may have been generally cooler over much of the Northern Hemisphere. Trade wind strength and/or rainfall fluctuated dramatically over the Caribbean and widespread, persistent drought occurred in Haiti and the Amazon basin. This appeared to be a partial return toward glacial conditions following an orbitally driven delay in the Northern Hemisphere deglaciation. The 8.2 k event appears to be one of several periods

105 during the Holocene when low-salinity polar water and the iceberg melting zone penetrated southward (Duplessy et al. 1988, Labeyrie et al. 1999). The demise of the outer reef occurred in this general time frame and it is possible that this cooling contributed to this event.

There is abundant evidence for rising tropical mid- to late Holocene temperature. Regional changes in precipitation have been documented for this time also, most often as a transition from cool and dry to warm and wet conditions (Peterson et al. 1991, Hodell et al. 1995). Tedesco and Thunell (2003) used high-resolution planktonic foraminiferal δ18O records from a Cariaco Basin sediment core to reconstruct climate history of the Caribbean region for the past 6,000 years and found that periods of increased salinity and decreased SST occurred at least six times in tropical Atlantic in last 6,000 years: ≈6.0 - 5.0, 4.5 - 4.2, 3.8 - 3.2, 3.0 - 2.8, 2.2 - 2.0, and 1.2 - 0.8 cal k BP. At 3.2 k BP climate became drier which prevailed through the late Holocene. The long term changes in Caribbean climate can be largely explained by orbitally induced (Milankovitch) variations in seasonal insolation

Environmental records in coral skeletons

Massive reef building corals, Montastraea sp., Siderastrea sp., and Diploria sp. which possess annual density bands, are present in SE Florida. The size and concomitant age within SE Florida is generally limited to small colonies (< 1 m) on the order of a few decades in age. Recently, large Montastraea faveolata corals with ages of 200 to 300 years have been discovered and cored (Fig. 4.7). The longest of these records has been dated by the annual density band chronology back to 1694 (K. P. Helmle, pers. comm.). These multi-century coral records are long enough to identify a range of conditions from natural growth rates to anthropogenically influenced growth and include climatic conditions from the Little Ice Age up to the recent period of rapid climate change.

Measurements of extension, bulk-density, and calcification from coral slab X-radiographs provide a metric for assessing the influences of an ever-changing environment on coral

106 growth rates. For example, a three decade period of stress ca. 1940 to 1970 (Fig. 4.8, K.P. Helmle, pers. com.), defined by significantly decreased extension rates and increased bulk-densities, coincides with dramatically increased freshwater discharge rates from construction of major canal systems linking Lake Okeechobee to the SE Florida coast. These consecutive stress bands primarily reflect local-scale anthropogenic influences. Conversely, stress bands in 1988 and 1998-99 are present and correspond with two of the strongest El Niños of the past 50 years in 1987 and 1997-98 which illustrates connections between coral growth and global-scale climate patterns.

Linear extension rates for M. faveolata in Broward County Florida exhibit strong correlation within and between mid (9 m) and deep water (18 m) from Hollywood, Fort Lauderdale, Pompano Beach, and Deerfield Beach (Table 5.4). The strong correlation within and between depths demonstrates that linear extension rates in M. faveolata of SE Florida generally respond commonly to environmental influences and thus provide robust records of historical growth response to anthropogenic impacts and climate change over hundreds of years.

107

Fig. 4.7: a) Montastraea faveolata coral head 2.5 m in height with core X-radiograph on right dating this coral back to 1694. b) M. faveolata coral head 2 m in height and dating back to the early 1800’s.

108

Fig. 4.8: Canal discharge data from North New River Canal illustrating high levels of discharge from 1940 to 1970. Arrows indicate 1940, 1970, and 2000 on coral core X- radiograph below. Note high density skeleton (dark) and low extension rate from 1940 to 1970 compared with 1970 to 2000.

109 Table 4.4: Growth Correlations for Montastraea faveolata (M.f.) for mid (9m) and deep (18 m) depths. correlation coefficients between master chronologies over 1985-1970

n=16, d.f.=14 for p<0.01, r-crit>0.624

MID DEEP ALL M.f. M.f. M.f. MID M.f. -- 0.82 0.97 DEEP M.f. 0.82 -- 0.93 ALL M.f. 0.97 0.93 --

Average internal correlation Mean n MID M.f. 0.84 6 DEEP M.f. 0.73 3 ALL M.f. 0.75 21

Characterization of Southeast Florida Reefs

Geomorphology Reef growth in Florida is frequently said to be unique to the modern Florida Keys reef tract and considered to terminate at Fowey Rocks (Vaughan 1914; Jaap and Adams 1984; Shinn et al. 1989) but nonetheless reefs and reef-like ridges persist further north (Fig. 4.2). The reef-like ridges are a relict (no active accretion due to exceedingly low cover of reef builders; Moyer et al. 2003). The location of these reefs identifies them as a distinct and also presently non-accreting reef tract (Macintyre 1988). The geomorphology of these reefs has recently been described in detail by Finkl et al (2005) and Banks et al. (2007) and will only be briefly reiterated here.

110 Between southern Miami-Dade County and Palm Beach County, beginning at the northern end of Biscayne Bay and terminating off the city of Palm Beach at N26º43.1’, up to three shore-parallel, ridge-systems occur in increasing depth. These were in the early to mid Holocene the locus of reef framework development and are called, in increasing distance from shore, the inner reef, middle reef and outer reef (Fig. 4.9). Their morphology is more complicated in the south (Fowey Rocks to Port Everglades) than north of Hillsboro Inlet, where the inner and the middle reefs eventually disappear. The northern termination of the outer reef is off Palm Beach County, where it is replaced by a series of beach ridges that probably represent a drowned headland (Fig. 4.2). The southern termination of the SE Florida reef tract is off Biscayne Bay. In southern Dade County, the middle reef disappears and only the inner and outer reefs remain which then both disappear in a sandy environment seaward of Biscayne Bay. Banks et al. (2007) demonstrated that the SE Florida outer reef is located on a ridge that bends landward near Fowey rocks, and continues behind the Fowey rocks outlier reef. Therefore, the SE Florida outer reef would be most likely equivalent with the Florida Keys shelf-edge-reefs, while the outlier reefs would constitute a separate, more seaward trend initiated on a deeper terrace.

Fig. 4.9: Bathymetric block diagrams showing representative samples of morphology of a) the ridge complex, inner and middle reef, b) the outer reef. Inset map shows location of bathymetry blocks (modified from Banks et al. 2007 by permission of Springer).

111 The outer reef (Fig. 4.9.b) is a relic acroporid-framework reef (Macintyre and Milliman 1970; Lighty 1977; Lighty et al. 1978) that crests at ~16m below sea level. It extends more or less uninterrupted (with the exception of reef gaps) from Biscayne Bay northward to its distinct terminus at latitude N26o43’. At a lower sea level stand this distance of about 125 km would have made it one of the best-developed fringing reefs in the western Atlantic, especially when combined with the Florida Keys reefs. Geomorphologic zonation as well as that of major constructors within the framework of the SE Florida outer reef is similar to that of modern Florida Keys reefs (Shinn 1963; Enos and Perkins 1977; Shinn et al. 1981; Lidz et al. 2006). Rubble aprons (talus), back reef, reef crest, spur-and-groove zones and two seaward terraces (17 m and 23 m deep), and second terrace (23 m deep) are developed (Fig. 4.9). Reef gaps and collapse features are striking and repetitive features (Banks et al. 2007). The reef gaps are erosional structures with bases deeper than the reef framework and correspond to similar erosional features in the middle and inner reefs. They, thus likely, represent the courses of paleo- river channels. The outer reef initiated before 10.2 cal BP (calibrated 14C-dated years before present) and grew until 8 cal BP (Lighty 1977).

The middle reef is also a mostly continuous feature where it exists and crests at ~ 15 m below sea level. It extends from South Dade County northward to Boca Raton Inlet. Unlike the outer reef, it does not display a detectable zonation and reef framework is apparently not continuous throughout or at least variable in development. Any frameworks that do exist are developed on, or drape, a well-defined antecedent slope that is interpreted as the shoreline of the time when the outer reef initiated and began to accrete. Frameworks are mostly dominated by massive corals (Montastraea spp., Diploria spp.) and only few isolated A. palmata frameworks have been found to date. Also the middle reef is dissected by erosional features that connect to reef gaps in outer and inner reefs. The growth history of the middle reef is incompletely understood, but surficial ages obtained so far range from 4.2 – 3.7 cal BP.

The inner reef is the most variable and discontinuous of the three reef tracts and is, in most areas, a complicated amalgamation of patch reefs that can be fused to form longer

112 structures, with individual patch reefs frequently remaining identifiable. It crests at ~ 8 m below sea level and generally consists of A. palmata framework. The inner reef begins south of the middle reef off North Dade County at N25º40’ and extends northward to Hillsboro Inlet at N26º15’ in Broward County where it disappears under the shoreline that in this region changes trend. It is between 2 and 3 m thick and rests either on coquina (Broward County) or laminated soilstone crusts (South Broward and Miami-Dade Counties). Ages obtained from the inner reef range from 5.9 – 6.2 cal BP.

The nearshore ridge complex extends from N25º51’ in Miami-Dade County to N26º15’ (Hillsboro Inlet) and consists of shoreline deposits with visible karst features. Sediment in cores varied in coarseness from shell hash to coarse sand and had variable siliclastic content. The sediment was interpreted as cemented beach, or immediately nearshore deposits, consisting of a mixture of reworked Pleistocene Anastasia Formation and Holocene deposits. A possibly wave-cut feature exists at 6 m below sea level with a relief of 1.5 m on the outer ridge. The sea-level curve of Toscano and Macintyre (2003) would put erosion of that cliff at 3.5 to 6.5 cal BP, which would make it a possible shoreline for the period when the inner reef was alive and accreting. Lidz et al. (2003, 2006) also describe a nearshore rock ledge and scarp that could be an equivalent structure in the Florida Keys. In Palm Beach County, the substrate of the nearshore ridges is covered by colonies of tube-building polychaete (Phragmatopoma) worms (commonly known as “worm rock”), which considerably expand the complexity of this habitat and supports a diversity of macroalga, small stony corals, boring sponges, worm rock, and tunicates.

Banks et al. (2007) proposed a conceptual model of development of this reef system that included stepwise aggradation and backstepping in response to sea-level history. The basis of any reefal accretion is believed to be submarine sand dunes that originally formed during the oxygen isotope substage-5e highstand (approximately 125 BP). At that time, the SE Florida shelf experienced higher wave-energy due to the submergence of the Bahamas Banks with consequently less buffering of waves. These sand shoals fell dry during subsequent lowstands and became indurated. In the early Holocene, as sea level rose, the sand shoals near the shelf became the locus of accretion of the outer reef. Lighty

113 et al (1978) noted that it initiated as a fringing reef and transitioned to an extensive shelf- edge barrier reef as rising sea level submerged the back reef shelf margin during its growth from >10.2 cal BP and its demise at 8 cal BP (Lighty 1977). The middle reef is situated possibly on the shoreline that might have been coeval with formation of the outer reef. A further rise in sea level led to the initiation of the inner reef. The available inner reef ages (~6 cal BP) are almost 2 ky younger than the uppermost outer reef (Lighty 1977). At least from the outer to the inner reef, true reef backstepping had occurred. The middle reef is at 4.3-3.7 cal BP another 2 ky younger than the inner reef, at least on its surface and may thus have initiated sooner and persisted longer. Banks et al. (2007) propose the following backstepping sequence: growth of the outer reef from ~12-8 cal BP at which time a beach and beach-ridge system existed at the later locus of the middle reef; backstepping to the locations of the present middle and inner reefs during transgression. The initiation sequence of middle and inner reefs is still unresolved, but one would assume that the deeper middle reef initiated first. An ecological differentiation seems to have existed: Acropora palmata framework on the shallower inner reef, and massive, less environmentally sensitive corals (Montastraea spp. Diploria spp., Siderastrea spp.) on the middle reef. Causes for termination of inner reef accretion are unclear but cannot be linked to the rate of sea level rise since at the time of demise it was 2-3 mm yr-1 (Toscano and Macintyre 2003), far less than the maximum reef-accretion rate of 14 mm yr-1 (Buddemeier and Smith 1988).

Despite being largely unexplained, the demise of SE Florida Acropora is interesting insofar as it was apparently not unique to South Florida. Hubbard et al. (2005) found a Caribbean-wide gap in A. palmata reef building at around the same time (~6-5.2 cal BP). Parallels to the modern Acropora crisis in the Florida Keys and Caribbean become obvious. In each case, the cause or causes remain elusive.

114

Fig. 4.10: Cross-sections of the ridge complex and reef tracts offshore of Southeast Florida. Bathymetry is extracted from a Lidar dataset of Broward County (Banks et al. 2007).

Benthic Habitat Mapping Walker et al. (2007) created maps of the nearshore benthic habitats from 0 to 35m depth by employing a combined-technique approach which incorporated high resolution laser bathymetry, aerial photography, acoustic ground discrimination (AGD), video groundtruthing, and limited subbottom profiling (Figure 5.10 a, b, & c). Features were

115 classified based on their geomorphology and benthic fauna using similar criteria to NOAA Caribbean biogeography mapping including a similar classification scheme. In situ data, video camera groundtruthing, and AGD were used to help substantiate the classification of the habitat polygons.

Acoustic ground differentiation, which evaluates the shape of sound waves bounced off the seafloor from which different categories of wave shapes are classified that correspond to different habitats, was also used to further discriminate the sea floor based on the density of organisms (Moyer et al. 2005; Riegl et al. 2005). These data supplemented the geomorphology-based layer to include not only mapping between features (inner, middle, & outer reefs), but also the variability of habitat within these features (Walker et al. 2007).

This combined technique approach ensured high accuracy by utilizing the data with highest resolution (LADS bathymetry) as the base and supplementing it with lower resolution data of different information content. The maps yielded user and producer accuracies comparable to the photo-interpreted NOAA Caribbean maps (near 90%).

116

Fig. 4.11a: Habitat maps for the Continental SE Florida reef tract (Palm Beach County) based on a combined method approach using laser bathymetry, acoustic ground discrimination, visual groundtruthing (Walker et al. 2007). (modified from Walker et al. 2008 by permission of Journal of Coastal Research).

117

Fig. 4.11b: Habitat maps for the Continental SE Florida reef tract (Broward County) based on a combined method approach using laser bathymetry, acoustic ground discrimination, visual groundtruthing (Walker et al. 2007). (modified from Walker et al. 2008 by permission of Journal of Coastal Research).

118

Fig. 4.11c: Habitat maps for the Continental SE Florida reef tract (Miami-Dade County) based on a combined method approach using laser bathymetry, acoustic ground discrimination, visual groundtruthing (Walker et al. 2007). (modified from Walker et al. 2008 by permission of Journal of Coastal Research).

119 Biogeography of Southeast Florida Reefs

The biogeographic setting of the SE Florida reef system is a complex of potentially interconnected habitats and the confluence of oceanic (clear, oligotrophic water; stable temperature) and continental (higher temperature variability, land run-off, human impacts, submarine groundwater discharge) influences. The Florida current delivers planktonic larvae from the upstream sources (Yeung and Lee 2002) in the Florida Keys and Tortugas (tropical, insular) and the estuaries and lagoons of Biscayne Bay and Florida Bay (subtropical, continental). Estuaries within the southeast continental region with tidal inlet connectivity to the reef system include northern Biscayne Bay with seagrass and mangroves, mangrove habitat in Broward County, and mangrove and sea grass habitats in the Lake Worth Lagoon of Palm Beach County. The western Bahamas Banks lie only approximately 80 km eastward of SE Florida but are separated by the deep water and rapid currents of the Florida Straits.

Studies on the extent and direction of gene flow or connectivity among reefs in the SE Florida biogeographic region are limited to work on amphipods and ophiuroids by Richards et al. (2007). Genetic connectivity was studied along 355 km of the Florida Keys and SE Florida reef tract (Fig. 4.12) from assessment of gene flow in three commensal invertebrate species displaying contrasting reproductive strategies. The three species, two amphipods (Leucothoe kensleyi and Leucothoe ashleyae) and a brittle star (Ophiothrix lineata), are all commensal within the branching vase sponge Callyspongia vaginalis (Fig. 4.13). The brittle star is a broadcast spawner, whereas the amphipods brood their young and lack planktonic larvae. Although O. lineata is a broadcast spawner, it possesses an apparently rare form of development in ophiuroids where embryos develop inside a fertilization membrane for six to eight days before emerging as miniature crawl-away juveniles (V.P. Richards, unpublished data). This mode of development suggests that its embryos are passive propagules and exposure to currents for up to eight days should give O. lineata enhanced dispersal abilities. These contrasting reproductive strategies led to expectations of strong gene flow (high connectivity) among reefs for the broadcasting brittle star, but low connectivity for the brooding amphipods.

120

Fig. 4.12: Map showing individual collection sites for the study of genetic connectivity along the SE Florida coastline (color scheme corresponds to Fig. 4.14.). Blue arrows depict a counter current flowing through Hawk Channel (after Yeung & Lee 2002). Inset shows the four major collection locations relative to the collection site in Belize: PB, Palm Beach; FT, Ft Lauderdale; LK, Long Key; KW, Key West; GVS, Glover’s Reef. Depth contour data from http://www.ngdc.noaa.gov/mgg/ibcca.

121

Fig. 4.13: Richards et al. (2007) used the amphipods: a Leucothoe kensleyi; b L. ashleyae; c brittle star, Ophiothrix lineata, which are all commensals with: d the sponge, Callyspongia vaginalis, to study gene flow among reefs in the Southeast Florida biogeographic region. (photos by: a, b Vince Richards; c scanned with permission from Hendler et al. (1995)).

Findings suggest that reproductive life history is not always a reliable predictor of genetic connectivity. Commonplace within reefs are positive species interactions such as commensalism and mutualism (i.e., facilitation), which have substantial influence on the structure and function of these communities (Bruno et al. 2003). The dynamics of connectivity among reef populations is complex, and factors such as shallow coastlines, deep expanses of open water, and interaction among species involved in facilitation also need to be considered.

Measures of genetic differentiation among populations showed high levels of connectivity overall along the Florida reef tract for all three species (i.e., there was no significant difference in the distribution of haplotypes among populations; Fig. 4.14). The Ft Lauderdale population of L. ashleyae did not follow this general pattern and represented the only instance of restricted gene flow along the SE Florida coastline (see Richards et al. 2007 for further discussion on possible reasons for this exception). Paradoxically, only the brittle star showed a statistically significant pattern of genetic

122 isolation by geographic distance along the Florida reef tract (i.e. individuals from neighboring populations were more closely related to each other than individuals from more distant populations).

The high levels of connectivity detected for both amphipod species along the Florida reef tract were unexpected given their lack of planktonic larvae, and raises the question of how they are able to disperse so effectively along the SE Florida coastline. If the amphipods (which usually only attain an adult size of < 5.0 mm) were dispersing via crawling or occasional short-range swimming bursts, a pattern of genetic isolation by distance would exist. The lack of this signal suggests that another dispersal mechanism is operating. One where the amphipods are likely being dispersed along the reef tract inside sponge fragments generated during strong storms and hurricanes. Asexual fragmentation is an important dispersal mechanism for many branching sponge species (Wulff 1991), and the type of severe storms and hurricanes often experienced along the SE Florida coastline are capable of detaching and transporting numerous sponge species considerable distances (Wulff 1985; 1995a, b). Thus, at least a portion of SE Florida’s benthos may have recruited by simply “rolling north” along the linear drowned reef systems.

An estimate of migration indicated that the amphipods were migrating up and down the SE Florida coastline with approximately equal frequency, a result consistent with random, bi-directional transport mediated by storms. In notable contrast, the brittle star showed a strong southerly migration bias in the Florida Keys. Although the strong northerly flow of the Florida Current is assumed to be an important dispersal agent along the Florida coastline; instead, the well characterized counter current that runs southwest through Hawks Channel in the Florida Keys (Lee and Williams 1999; Yeung and Lee 2002) may be the dominant dispersal agent for O. lineata embryonic propagules in this region. The southerly bias to O. lineata migration was not evident along the Broward and Palm Beach county coastlines, where migration occurred with high frequency in both directions. This complex pattern may result from the dynamic counter currents and eddies

123 created as the Florida current intrudes over the shelf break (Lee and Mayer 1977; Shay et al. 2002; Soloviev et al. 2003).

Richards et al. (2007) also tested the hypothesis that deep water acts as a barrier between populations by examining the connectivity between Florida and Belize. Because O. lineata embryo propagules are non-swimming, their dispersal can be assumed to be passive and, therefore more likely to be influenced by physical oceanographic factors. Consequently, the deep water between Florida and Belize and entrapment in eddy currents over the Meso-American Barrier Reef System (Sheng and Tang 2004) are factors that could affect dispersal. Furthermore, the strong genetic isolation-by-distance signal detected across all locations. Consequently, connection of these suggests that geographic distance is also an important factor influencing connectivity patterns in this species. The results for L. ashleyae represent a dramatic contrast in dispersal ability dependant on the physical environment: high gene flow along a shallow coastline despite a brooding reproductive strategy, with absence of gene flow between populations separated by deep water resulting in potential cryptic speciation..

Richards also sampled the amphipods, Leucothoe kensleyi and L. ashleyae in Bimini, Bahamas which is 95km from the Florida coast, yet separated by deep, high current velocity water. Although the geographic distance from Fort Lauderdale to Bimini is less than a third the distance from Palm Beach to Key West, the genetic distance was much higher, so these amphipods are strongly connected along shallow coastlines, yet show no connectivity across very short distances of deep water.

The finding of high levels of genetic connectivity for three species within the Florida reef tract (Figs. 5.10, 5.12) has important implications for the management and conservation of Florida reefs. Northern reefs receive considerably less management attention than reefs in the south (Causey et al. 2002), and are likely being adversely impacted by extensive urban development in this region (Lapointe 1997; Finkl and Charlier 2003). The continued decline of the northern reefs could impact southern reefs, as a reduction in

124

Fig. 4.14: Statistical Parsimony networks depicting the relationship among different mitochondrial COI haplotypes for (A) Leucothoe kensleyi, (B) Leucothoe ashleyae, and (C) Ophiothrix lineata. Colored circles = individual haplotypes; small black circles = haplotypes that hypothetically should exist in the population, but were not sampled; connecting lines = one base pair mutation. Circle size for each haplotype is proportional to its frequency of occurrence and all three networks have the same scale. Different colors correspond to the five major geographic sampling regions (see Fig. 4.12). Due to the large genetic distance between the Florida and Belize L. ashleyae haplotypes (79 base pair mutations), there is no statistical support for any connection point between them. Consequently, connection of these haplotypes in the same network is precluded. Networks were created using the software package TCS version 1.13 (Clement et al. 2000).

125 gene flow from the north could reduce genetic diversity in the southern reefs rendering them less adaptable to environmental perturbation.

Planktonic larval supply transported northward by the Florida Current from the Florida Keys and Caribbean provinces may contribute to diversity gradients in the region. Studies of planktonic larvae distributions in the SE Florida are lacking and could provide insight into regional variations in community structure.

Patterns in Reef Community Structure Although the continental SE Florida reefs have a fauna similar to the Florida Keys, Bahamas and Caribbean, the community structure is different (Moyer et al. 2003). The only major reef building coral missing from SE Florida is Acropora palmata, although isolated colonies do exist (Banks, personal observation). Recent claims that Acropora occurrences in Broward County are indicative of ocean warming (Precht and Aronson 2004) require further verification, since widespread rubble of the species in question indicates that these corals have already previously had a repeated, but ephemereal presence in the area over the last centuries. Aside from a dominance of bare substratum, relative cover is dominated by macroalgae or octocorals, while scleractinian cover is low. Isolated patches of higher coral cover can be found on the ridge complex offshore central Broward County where one site, dominated by massive corals, has approximately 16% cover and another area is covered by large colonies of Acropora cervicornis with 34% cover.

Region-wide benthic community structure A summary of relative bottom cover data for SE Florida is given in Table 5.5. Methodological and sample size differences likely contribute to variations in cover among studies. Based on the averages of data collected by Blair and Flynn (1989), Thanner et al. (2006), and Gilliam et al. (2007) overall faunal density is dominated by porifera (15.7/m2), followed by octocorals (7.7/m2) and scleractinia (2.5/m2). A list of all

126 reported species of macroalgae, sponges, octocorals and stony corals reported is provided in Appendix 5.1.

Macroalgal cover is generally lower in SE Florida than in the Florida Keys and Tortugas (Beaver et al. 2005, FWCC 2005). Foster et al. (2006) found that Dictyota spp. and Halimeda spp. were the dominant algal species. Abundance of macroalgae can be seasonal or vary over different time scales.

Paul et al. (2005) reported that the cyanobacteria Lyngbya confervoides and L. polychroa (Fig. 4.15) covered extensive areas of reef offshore Broward County in recent years,

Table 4.5: Average relative bottom cover for ridge complex and reef tracts of Southeast Florida. FWCC (2006) data averaged over 2003-2004 and based on 3 sites per county (4th site in Broward is large stand of Acropora cervicornis). Two Broward sites have unusually high stony coral cover (one, 40% cover A. cervicornis and one, 12% cover of massive corals on ridge complex sites). Values in parentheses do not include these high cover sites. Data from other studies are averaged over all sites for each county. Palm Beach Broward County Miami-Dade County County (3) (1) (3) (2) (3) Bare 70% 10% 73% (80%) 54% 73% substrate Macroalgae 1% 66% 4% (4%) 15% 9% Octocoral 20% 12% 8% (12%) 16% 12% Porifera 7% 8% 2% (4%) 8% 3% Scleractinia 1% 2% 13% (0%) 5% 1% other 1% 2% 1% (0%) 3% 2% (1) Foster et al. (2006) (2) Moyer et al. (2003) (3) FWCC (2006)

particularly in 2003. Extensive blooms subsided in 2005 and 2006, although shorter time scale boom/bust cycles are apparent. Tichenor (2005) reported a persistent bloom on the outer reef offshore of Palm Beach County. Causes of these blooms are unknown although he attributed them to treated wastewater discharge from an outfall pipe up-current of his study site. Foster et al. (2006) included presence/absence data of Lyngbya sp during their

127 studies and found significant occurrences on all reef tracts but not on the ridge complex. The fine filamentous morphology of this genus probably contributes to an underestimated cover based on point count of images, therefore not contributing significantly to macroalgal cover estimates.

In spring, 2007, a macroalgae bloom comprised of Cladophora liniformis, Enteromorpha prolifera, Centroceras clavulatum (Fig. 4.15c) (identification by Brad Bedford, Harbor Branch Oceanographic Institute) occurred. Other species may have been present but were not identified. These macroalgae formed a thick mat on sand bottom and reef in northern Broward and southern Palm Beach Counties. The cause has not been identified.

All datasets (Goldberg 1973, Moyer et al. 2003, Gilliam et al. 2007, Foster et al. 2006 ) consistently showed that octocorals dominate faunal cover on SE Florida reefs (Table 5.6), although porifera dominated in abundance. Forty eight species were reported by Foster et al. (2006) and the dominant groups were Eunicea/Muricea spp. and Briareum asbestinum. Thanner et al. (2006) reported similar dominant taxa in Miami-Dade County. Octocoral cover on SE Florida reefs is similar to that in the Florida Keys (Beaver et al. 2005, Gilliam et al. 2007).

The dominant sponges are the basket sponge, Xestospongia muta, Anthosigmella varians and Spheciospongia vespariuum. 41 species of scleractinian have been reported for SE Florida (Moyer et al. 2003, Foster et al. 2006, FWCC 2006, Goldberg 1973), including the Indo-Pacific azooxanthellate coral, Tubastrea coccinea (Fenner and Banks 2004). Cover is low and most colonies are of small size, typically less than 50 cm. SE Florida has lower species richness and cover than Florida Keys and Tortugas (1.5% versus >5% coverage; Beaver et al. 2005, FWCC 2006). Montastraea cavernosa is dominant in terms of cover, although Siderastrea siderea is numerically the most abundant. This species recruits frequently but does not reach large sizes. Similar dominance of M. cavernosa has been reported for other high latitude reefs (Bermuda and Brazil; Laborel 1966, Castro and Pires 2001) and reefs in turbid settings like windward Barbados (Lewis 1960). Loya (1976) found a correlation between the abundance of M. cavernosa and heavy turbidity and sedimentation, and the SE Florida reefs can certainly be called a usually turbid

128 environment. Species of the Montastraea annularis complex are all present in SE Florida but, in contrast to the Caribbean, are not dominant (Knowlton 2001, Moyer et al. 2003).

Fig. 4.15: a, b) The cyanobacteria, Lyngbya confervoides and L. polychroa formed persistent blooms on the reefs in 2003 and smothered many reef organisms, particularly branching octocorals, such as Pseudopterogorgia spp. c Extensive blooms of Cladophora liniformis, Enteromorpha prolifera, Centroceras clavulatum, and others bloomed on inter-reef sand plains and reef tracts of northern Broward County and southern Palm Beach County in the spring of 2007. (photos by: a, b Karen Lane; c )

129 Table 4.6: Average relative faunal cover for ridge complex and reef tracts of Southeast Florida. FWCC (2006) data averaged over 2003-2004 and based on 3 sites per county (4th site in Broward is large stand of Acropora cervicornis). Two Broward sites have unusually high stony coral cover (one, 40% cover A. cervicornis and one, 12% cover of massive corals on ridge complex sites). Values in parentheses do not include these high cover sites. Data from other studies are averaged over all sites for each county. Palm Beach Broward County Miami-Dade County County (3) (1) (3) (2) (3) Octocoral 68% 48% 34% (75%) 50% 65% Porifera 23% 34% 10% (22%) 25% 16% Scleractinia 4% 8% 53% (2%) 16% 6% other 5% 10% 3% (1%) 9% 13% (1) Foster et al. (2006) (2) Moyer et al. (2003) (3) FWCC (2006)

Moyer et al. (2003) reported significant north/south variation in benthic community structure on the ridge complex and outer reefs. In general, diversity increased from north to south in Broward County. A number of factors could account for this, including temperature variations, planktonic larval supply, substrate characteristics, and wave energy. Planktonic larval supply is transported northward by the Florida Current from the Florida Keys and Caribbean provinces, thus the observed S-N gradient may indicate attenuation of larval supply towards the north. Studies that could verify such a hypothesis are lacking. Substrate differences may also affect community structure. Vertical relief of the ridge complex declines towards the north, eventually reaching <1 m. This seems to be accompanied by decreasing live benthic cover and increased sponge dominance. In the south, where relief is greater than 1 m, the benthic fauna is dominated by octocorals and the zoanthid, Palythoa caribbaeorum. Combined with lower relief, the northern areas also receive higher wave energy, since the protection of the Bahamas banks is felt less towards the north. Wind waves from the north and northeast are generally higher in the northern portions of SE Florida which may results in more sediment suspension and turbidity in the northern nearshore.

130 The cover by scleractinians and octocorals showed no significant temporal changes in the 1997-2005 monitoring dataset obtained by Gilliam et al. (2007), but sponges declined significantly in 2000/2001 and stabilized after that. Concomitant sedimentation monitoring showed high rates at all sites in the winter of 2001 which may have contributed to sponge mortality.

Cross-shelf patterns in benthic community structure The reef cross sections shown in Fig. 4.10 illustrate the depths of the reef tracts and ridge complex. In addition to depth, variation in substrate composition and morphology among reef tracts can impact benthic composition. Among other factors, the porosity of the limestone on the narrow shelf may allow groundwater to seep up onto the reef (Finkl and Charlier 2003) potentially exposing the community to groundwater-borne pollutants. In general, environmental conditions on the ridge complex and possibly the inner reef are more variable than on the middle and outer reefs due to less depth and proximity to shore. Moyer et al. (2003) found that benthic communities on the middle and outer reefs were similar but both differed from the inner reef communities (Fig. 4.16 and 4.17).

Foster et al. (2006) investigated the effect of depth, bottom slope, rugosity and sediment thickness on the structure of benthic communities. Similar to Moyer et al. (2003), they found the community on the ridges and inner reefs to differ from the middle and outer reefs (Table 5.7 and 5.8). Living benthic substrate cover increased from onshore to offshore. Table 5.9 shows lowest scleractinian density on the inner reef when sites with high Acropora cervicornis and anomalously high coral cover were removed (Gilliam et al. 2007). Overall, octocoral and sponge densities are lowest on the ridge complex and inner reef, which might be a direct response to increased wave energy. Kinzie (1973) and Yoshioka and Yoshioka (1991) suggested that wave energy may influence octocoral populations by detachment of colonies. While living cover clearly differed, species richness of hard and soft corals and sponges among reef tracts was relatively constant.

131 Vargas-Angel et al. (2003) reported extensive patches of flourishing Acropora cervicornis approximately 400-800 m offshore on the ridge complex offshore Broward County in 3-7 m depth. The area of the patches ranged from ~0.1 to 0.8 ha. Coral cover was 5-28% within reef patches with 87-97% of the cover by A. cervicornis. In 2002 they reported Type I White Band Disease (WBD) in all thickets but no bleaching. The WBD was more common at the center of the patches than the periphery where cover was lower. These populations were found to be fertile and to spawn each summer (Vargas-Angel et al. 2003; Vargas-Angel et al. 2006).

132

Fig. 4.16: Photos of ridge complex communities illustrate: a) and b) typical flat pavement-like substrate and abundance of octocorals; c) the encrusting zoanthid, Palythoa caribaeorum, is common on the ridge complex and inner reef; d) patches of relatively high stony coral cover are occasionally found on back- and foreslopes; e) and f) relatively large, monotypic patches of Acropora cervicornis are found offshore central Broward County (photos by: a,e,f, Kenneth Banks; b, c, d, David Gilliam, Susan Devictor).

133

Fig. 4.17: Photos of the outer reef illustrate: a) typical diversity of sponges, octocorals and scleractinians; b) the massive sponge, Xestospongia muta, is common on all reef tracts in Southeast Florida; c) the alcyonacean, Icilligorgia schrammi is common on the outer reef and areas of high rugosity on the middle reef; d) reef-perpendicular sand channels commonly incise the outer reef (photos by David Gilliam, Susan Devictor).

134 Table 4.6: Average relative faunal cover for ridge complex and reef tracts of Southeast Florida. FWCC (2006) data averaged over 2003-2004 and based on 3 sites per county (4th site in Broward is large stand of Acropora cervicornis). Two Broward sites have unusually high stony coral cover (one, 40% cover A. cervicornis and one, 12% cover of massive corals on ridge complex sites). Values in parentheses do not include these high cover sites. Data from other studies are averaged over all sites for each county. Palm Beach Broward County Miami-Dade County County (3) (1) (3) (2) (3) Octocoral 68% 48% 34% (75%) 50% 65% Porifera 23% 34% 10% (22%) 25% 16% Scleractinia 4% 8% 53% (2%) 16% 6% other 5% 10% 3% (1%) 9% 13% (4) Foster et al. (2006) (5) Moyer et al. (2003) (6) FWCC (2006)

Table 4.7: Average relative bottom cover for ridge complex and reef tracts of Broward County. FWCC (2006) data averaged over 2003-2004 and based on 3 sites per county (4th site in Broward is large stand of Acropora cervicornis). Two Broward sites have unusually high stony coral cover (one, 40% cover A. cervicornis and one, 12% cover of massive corals on ridge complex sites) and are not included in the average values. Ridge Complex Inner Reef Middle Reef Outer Reef d<6m d=6-10m d=10-20m d=15-30m (1) (2) (3) (1) (2) (3) (1) (2) (3) (1) (2) (3) Bare 15% 72% - 12% 53% - 8% 46% - 4% 43% - substrate Macroalgae 68% 4% - 73% 17% - 70% 22% - 60% 18% - Octocoral 7% 11% - 6% 12% - 10% 17% - 23% 25% - Porifera 3% 3% - 4% 7% - 10% 10% - 12% 10% - Scleractinia 3% 8% 4% 2% 3% 1% 1% 4% 2% 1% 4% 2% Other 4% 2% - 3% 8% - 1% 1% - 0 1% -

135 Table 4.8. Average faunal density for ridge complex and reef tracts of Broward County. Gilliam et al. (2007) data averaged over 2003-2004 and based on 3 sites per county (4th site in Broward is large stand of Acropora cervicornis). Two Broward sites have unusually high stony coral cover (one, 40% cover A. cervicornis and one, 12% cover of massive corals on ridge complex sites) and are not included in the average values.

Ridge Inner Reef Middle Reef Outer Reef Complex d=6-10m d=10-20m d=15-30m d<6m

(1) (1) (2) ave (1) (2) (3) ave (1) (2) (3) ave

Octocoral 5.9 9.8 3.0 6.5 4.9 4.0 9.5 8.5 8.9 11.5 12.9 11.1

Porifera 7.7 7.5 4.9 6.2 12.6 3.3 50.8 22.2 8.6 3.3 43.3 14.0

Scleractinia 2.4 1.0 4.0 2.5 2.6 3.5 2.2 2.8 2.7 1.4 2.8 2.3 (1) Gilliam et al. (2007) (2) Blair and Flynn (1989) (3) Thanner et al. (2006)

136 Fish community structure Miami-Dade and Broward Counties In total, over 350 fish species have been recorded from Broward and Miami-Dade Counties. However, this total is certainly an underestimate and could substantially increase if piscicide (e.g. rotenone) collections of cryptic fishes were conducted (Ackerman and Bellwood 2000, Willis 2001, Collette et al. 2003).

Generally, the fish assemblages associated with hardbottom reef communities in SE Florida resemble those found throughout the Florida Keys, Greater Caribbean, and Gulf of Mexico. All the common families are represented (Labridae, Pomacentridae, Haemulidae, Gobiidae, etc.; Fig. 4.18). Nonetheless, given the northern latitude at which these reef communities exist, temperate fish (Orthopristis chrysoptera [Haemulidae]) can be commonly observed in winter months. The Broward County reef fish community exhibits cross-shelf variation in fish assemblage structure correlated with changes in depth. The deeper, outer reef sites harbor higher fish densities and more species than the shallower inner reef sites (Ferro et al. 2005).

Nearshore hardbottom (<300 m from the shoreline; colonized pavement) fish assemblages show considerable differences in assemblage structure when compared to the more offshore sites on the inner, middle, and outer reefs. Typically, the inner reef is dominated by juvenile grunts (Haemulidae) (Jordan et al. 2004), whereas wrasses (Labridae) and damselfishes (Pomacentridae) dominate the middle and outer reefs. Due to its close proximity to shore and shallow depths (<7 m), the nearshore hardbottom habitat is ephemeral with movements of large amounts of sediments during major storm events (Walker 2007). Nevertheless, when compared to other natural reef habitats in the area, this low-relief hardbottom contains disproportionately high densities of juvenile fishes (Lindeman and Snyder 1999, Baron et al. 2004, Jordan and Spieler 2006). The ephemeral nature of the nearshore hardbottom and its high proportion of juveniles (with their intrinsic recruitment variability) are likely responsible for the large annual population fluctuations recorded for this dynamic habitat (Jordan and Spieler 2006).

137 Additionally, anthropogenic impact appears to be intense in this habitat. For example, recent (2005-2006) beach renourishment activities (deposition of sand to widen beaches) buried approximately 30,000 m2 of nearshore hardbottom along a 9-km segment of coastline. Although the habitat loss was mitigated by deploying large boulder artificial reefs (total area ~8.9 acres), preliminary results show that, while these mitigation boulders harbor juveniles at densities similar to the nearshore hardbottom, the percent contribution of juveniles to the total fish assemblage was substantially lower. That is, more adult-stage fishes and a higher piscivore density were found on the boulders, possibly affecting the natural predation rate on neighboring natural substrate (Freeman, personal communication).

Reef fish community studies in Miami-Dade County are limited to work by Thanner et al. (2006) who compared benthic and fish communities on artificial and natural reefs offshore northern Miami-Dade County. They found that the middle reef was strongly dominated by Gobiidae, while the outer reef was dominated by Pomacentridae with Scaridae and Labridae closely following. They reported 44 and 48 fish species on the middle and outer reefs, respectively.

As previously mentioned, Broward County has sites with unusually high densities of Acropora cervicornis for SE Florida (section 5.1). The corresponding fish assemblages are also unique to the area. High densities of both juveniles (mainly Haemulon flavolineatum [Haemulidae]) and piscivores have been recorded at the A. cervicornis thickets (Gilliam et al. 2007). Given the size of the juveniles present, it is likely that this habitat acts as refuge for early juvenile and subadult haemulids. Despite the attraction of juvenile fishes, the natural meshwork created by the branching coral appears to limit larger piscivores from entering.

Also characteristic of Broward County reef fish assemblages are its conspicuously low densities of legal-size groupers and snappers (variable for different species). Ferro et al. (2005) analyzed data from 667 point-counts in Broward County and found only two grouper (Serranidae) of legal size. When compared to reefs in the Upper Florida Keys

138 (Dixie Shoals), Broward County fish assemblages have a substantially lower density of groupers. Point-counts from Dixie Shoals exhibited an abundance of groupers that was four times greater than surveys from Broward County. At Dixie Shoals, on average, two commercially and recreationally important groupers were seen per point-count survey; while in Broward County even single grouper was infrequently seen (Table 5.10). Although legal-sized grouper were recorded during only two of 667 surveys, large grouper exist in Broward County waters albeit at a lower frequency than in the Florida Keys, as evidenced by low commercial landings (Johnson et al. 2007).

Table 4.10: Grouper (Serranidae) abundances from point-count surveys in Broward County, Florida and Dixie Shoals (Florida Keys). Broward County Dixie Shoals Species Abundance Abundance Cephalopholis cruentata (Graysby) 127 40

Cephalopholis fulva (Coney) 2 20

Epinephelus adscensionis (Rock hind) 4 2

Epinephelus guttatus (Red hind) 8 2

Epinephelus morio (Red grouper) 232 5 Mycteroperca bonaci (Black grouper) 0 16 Mycteroperca interstitialis (Yellowmouth 1 1 grouper)

Mycteroperca phenax (Scamp) 8 1

Mycteroperca venenosa (Yellowfin 1 8 grouper) Number of Point-count Surveys 667 47 Grouper per Point-count Survey 0.57 2.02

Remotely operated vehicle (ROV) surveys along deep habitat at 50-120 m depth (Bryan 2006) revealed little hardbottom. What existed had low vertical relief (<1 m). Of the 27 species recorded from ROV surveys on the 50-120 m depth natural substrate, nine were absent from the more extensive, shallow reef survey.

139 In addition to its natural hardbottom, Broward County has an abundant and diverse range of artificial reefs deployed with the intention of enhancing fishing and scuba diving activities. Vessel-reefs consisting of ship hulls intentionally scuttled for recreational fishing and diving use at ~21 m depth (Arena et al. 2007) have significantly higher fish abundance and species richness than natural hardbottom, as well as different species composition and trophic structure. Planktivores dominated the vessel-reef fish assemblages (53% versus 27% of total abundance on the nearby natural hardbottom). The higher planktivore densities recorded on vessel-reefs may have been due to entrainment of planktonic food resources as a result of laminar flow disruptions from the tall vertical profiles of the structures (Arena et al. 2007). Vessel-reefs also harbored several species not seen during natural hardbottom surveys (Lutjanus buccanella [Lutjanidae] and Epinephelus niveatus [Serranidae]) (Arena et al. 2004). Bryan (2006) conducted ROV surveys on three vessel-reefs located between depths of 50-120 m. Anthiinae (mostly Pronotogrammus martinicensis [Serranidae]) numerically dominated vessel-reefs and were likely the forage base of the numerous, large, piscivorous fishes inhabiting these same vessel-reefs. Unlike at shallow vessel-reefs, herbivorous fishes were absent from the deep vessel-reefs (Bryan 2006).

Besides the many vessel-reefs in SE Florida, several hundred artificial reef modules (~1 m3 in size) have been deployed for use as: replicate units for scientific studies examining reef fish colonization and predation, habitat mitigation, and restoration tools. Gilliam (1999) compared fish recruitment on caged and uncaged artificial reef modules at 8 m depth and showed that seasonal density-dependent predation is one of several factors affecting the structure of the associated fish assemblages. Nearshore (8 m) sites had a lower disparity in newly settled Haemulidae abundance between caged and uncaged modules suggesting predation pressure to be lower in the nearshore environment. This supports the notion that nearshore hardbottom habitats are nurseries for juvenile fishes (L. Jordan, pers. comm.).

140

Fig. 4.18: a) Gag grouper (Mycteroperca microlepis) at staghorn coral thicket. b) Juvenile lane snapper (Lutjanus synagris) on nearshore harbottom. c) Longspine squirrelfish (Holocentrus rufus) on outer reef. d) Red grouper (Epinephelus morio) at staghorn coral thicket. e) Foureye butterflyfish (Chaetodon capistratus) on outer reef. f) Goldspot goby (Gnatholepis thompsoni). (a-e by L. Jordan, f by K. Kilfoyle).

141 Table 4.11: Top 20 nearshore species listed for both N and S Palm Beach County with sighting frequencies. “N FREQ” is the sighting frequency for north Palm Beach County. “S FREQ” is the sighting frequency for south Palm Beach County. N S Family Family Common name Scientific name FREQ FREQ Surgeonfish Acanthuridae Ocean Surgeon Acanthurus bahianus 33.2% 70.8% Surgeonfish Acanthuridae Doctorfish Acanthurus chirurgus 87.5% 59.2% Surgeonfish Acanthuridae Blue Tang Acanthurus coeruleus 47.3% 86.7% Foureye Butterflyfish Chaetodontidae butterflyfish Chaetodon capistratus 19.5% 69.7% Spotfin Butterflyfish Chaetodontidae Butterflyfish Chaetodon ocellatus 24.5% 70.2% Butterflyfish Chaetodontidae Reef Butterflyfish Chaetodon sedentarius 32.5% 70.6% Grunt Haemulidae Black Margate Anisotremus surinamensis 61.7% 62.5% Grunt Haemulidae Porkfish Anisotremus virginicus 91.6% 89.0% Grunt Haemulidae Tomtate Haemulon aurollneatum 54.2% 66.1% Grunt Haemulidae French Grunt Haemulon flavolineatum 78.3% 77.8% Grunt Haemulidae Sailor's Choice Haemulon parra 66.8% 48.9% Grunt Haemulidae Bluestriped Grunt Hemulon sciurus 66.4% 77.6% Spadefish Ephippidae Atlantic Spadefish Chaetodipterus faber 73.3% 36.5% Bermuda/Yellow Chub Kyphosidae chub Kyphosus sp. 69.5% 36.5% Wrasse Labridae Spanish Hogfish Bodianus rufus 38.0% 75.0% Wrasse Labridae Slippery Dick Halichoeres bivittatus 67.5% 33.3% Yellowhead Wrasse Labridae Wrasse Halichoeres garnoti 30.0% 67.3% Wrasse Labridae Bluehead Wrasse Thalassoma bifasciatum 79.6% 58.0% Snapper Lutjanidae Schoolmaster Lutjanus apodus 68.5% 31.6% Snapper Lutjanidae Gray Snapper Lutjanus griseus 66.8% 50.7% Snapper Lutjanidae Lane Snapper Lutjanus synagris 63.3% 23.6% Goatfish Mullidae Spotted goatfish Pseudupeneus maculatus 33.6% 78.9% Angelfish Pomacanthidae Queen Angelfish Holacanthus ciliaris 64.6% 48.7% Angelfish Pomacanthidae Rock Beauty Holacanthus tricolor 25.8% 74.5% Angelfish Pomacanthidae French Angelfish Pomacanthus paru 85.0% 88.1% Damselfish Pomacentridae Sergeant Major Abudefduf saxatilis 85.9% 86.2% Damselfish Pomacentridae Beaugregory Pomacentrus leucostictus 73.9% 32.4% Bicolor Damselfish Pomacentridae Damselfish Pomacentrus partitus 52.4% 82.3% Redband Parrotfish Scaridae Parrotfish Sparisoma aurofrenatum 29.5% 67.7% Yellowtail Parrotfish Scaridae Parrotfish Sparisoma rubripinne 64.2% 21.7% Stoplight Parrotfish Scaridae Parrotfish Sparisoma viride 28.5% 79.3% Drum Sciaenidae High-Hat Equetus acuminatus 71.0% 63.4% Barracuda Sphyraenidae Great Barracuda Sphyraena barracuda 73.8% 26.0%

142 Palm Beach County

A total of 2,440 fish surveys conducted at 109 sites in Palm Beach County between 1993 and 2007 documented 400 species of fish. Of these, 7 were sightings of exotic species found only on offshore reefs. Comparison of species reported for north versus south Palm Beach County found 300 species in common. 43 species were recorded in the north and not in the south compared to 56 additional species recorded in the south but not the north. The most frequently sighted species differed markedly. Table 5.11 lists the top 20 species documented for both north and south Palm Beach County. Markedly different assemblages reflect the differing reef habitats between north and south Palm Beach County. Only 5 of the most common species are shared between the north and the south (porkfish, sergeant major, bluehead, French grunt, and bluestriped grunt).

Comparison of species reported from nearshore reefs for north versus south Palm Beach County found 163 species in common. 92 species were recorded in the north and not in the south compared to only 26 additional species recorded in the south but not the north. The most frequently sighted species recorded for nearshore reefs shared 11 species in common in the top 20 species recorded. In Table 4.12, the top 20 species documented for both north and south PBC nearshore reefs are listed with sighting frequencies.

In north Palm Beach County, 343 species of fish were recorded. Of these, 255 were recorded at nearshore sites and 285 were recorded offshore. In south Palm Beach County, 356 species were recorded, and of these, 189 species were recorded in the nearshore, 171 recorded at the second reef, and 351 recorded offshore. As would be expected, there is an increase in species richness on the more rugose offshore tracts compared to the inshore tracts (Ettinger et al., 2001).

143 Table 4.12: Top 20 nearshore species listed for both N and S Palm Beach County with sighting frequencies. “N FREQ” is the sighting frequency for north Palm Beach County. “S FREQ” is the sighting frequency for south Palm Beach County.

Family Family Common name Scientific name N FREQ S FREQ

Surgeonfish Acanthuridae Ocean Surgeon Acanthurus bahianus 10.9% 47.3% Surgeonfish Acanthuridae Doctorfish Acanthurus chirurgus 96.7% 73.6% Surgeonfish Acanthuridae Blue Tang Acanthurus coeruleus 28.0% 47.3% Jack Carangidae Bar Jack Caranx ruber 50.2% 73.6% Snook Centropomidae Snook Centropomus undecimalis 95.0% 5.2% Anchovies Engraulidae 89.0% 26.3% Spadefish Ephippidae Atlantic Spadefish Chaetodipterus faber 94.9% 10.5% Mojarra Gerreidae Yellowfin mojarra Gerres cinereus 76.7% 57.8% Grunt Haemulidae Black Margate Anisotremus surinamensis 62.6% 71.0% Grunt Haemulidae Porkfish Anisotremus virginicus 94.3% 60.5% Grunt Haemulidae French Grunt Haemulon flavolineatum 86.0% 50.0% Grunt Haemulidae Sailor's Choice Haemulon parra 80.3% 52.6% Bermuda/Yellow Chub Kyphosidae chub Kyphosus sp. 88.4% 39.4% Wrasse Labridae Slippery Dick Halichoeres bivittatus 81.1% 73.6% Wrasse Labridae Bluehead Wrasse Thalassoma bifasciatum 83.0% 60.5% Snapper Lutjanidae Schoolmaster Lutjanus apodus 91.9% 5.2% Snapper Lutjanidae Gray Snapper Lutjanus griseus 76.7% 50.0% Snapper Lutjanidae Lane Snapper Lutjanus synagris 86.6% 52.6% Orangespotted Filefish Monacanthidae Filefish Cantherhines pullus 10.0% 55.2% Angelfish Pomacanthidae French Angelfish Pomacanthus paru 96.1% 42.1% Damselfish Pomacentridae Sergeant Major Abudefduf saxatilis 97.6% 94.7% Damselfish Pomacentridae Beaugregory Pomacentrus leucostictus 92.5% 52.6% Damselfish Pomacentridae Cocoa Damselfish Pomacentrus variabilis 50.9% 68.4% Yellowtail Parrotfish Scaridae Parrotfish Sparisoma rubripinne 97.7% 60.5% Drum Sciaenidae High-Hat Equetus acuminatus 87.8% 50.0% Porgy Sparidae Silver Porgy Diplodus argenteus 95.3% 65.7% Barracuda Sphyraenidae Great Barracuda Sphyraena barracuda 92.9% 42.1%

144 Environmental Factors Influencing Reef Biology In addition to water depth and topographic variations, cooling of surface waters during severe winter cold fronts can be a major environmental control on the distribution of corals with depth. Offshore southern Miami-Dade County, shallow reefs nearest to tidal passes (points of cool water discharge) have the least developed reef communities (Burns 1985). The relatively high latitude of the SE Florida reef system (N25º34’ northward to N26º43’, a distance of 125 km) exposes the SE Florida reefal biota to low air temperatures during the passage of winter cold fronts. At the northern and southern end of the reef system air temperatures of 14 and 15ºC, respectively, were reported. The durations of temperature minima are usually short (hours) and water temperatures are moderated by the large mass of warm water of the Florida Current. In a regional sense, the influences of cold air are confounded by the proximity of the Florida Current to the shelf, i.e., closer in the north and farther in the south. Such air temperature minima are near the lower tolerance limit for many reef-associated biota with scleractinia in Florida having a reported lethal limit at 14ºC (Porter et al. 1982). Persistence of cold air can have deleterious consequences for many reef associated organisms. In the Florida reef tract, even further south, Roberts et al. (1982) documented water temperatures of 12.6-16.0oC at a depth of 4.3 m for 8 days in January 1977 (24 o56’N) and Lee (in Burns (1985)) reported surface temperatures of 13.3oC (25 o13’N) and 15.2oC (25 o01’N) in January 1981. During summer 2003 water temperatures were 5-7oC lower than air temperatures at the northern end of the region (Aretxabaleta et al. 2006) due to upwelling caused by a complex interaction between local and remote atmospheric forcing and open ocean effects which apparently caused mortality of fish and sea-turtles (local media reports).

Lowest average monthly temperatures were in January 2001 with values of 18.3ºC (Fig 5.4e). Average maximum monthly water temperatures in this time period exceeded 29ºC in the summers of 2001 and 2002 (Fig 5.4f). Elevated water temperatures can induce coral bleaching and while bleaching of some stony corals and Palythoa caribbeorum colonies has been observed, mass bleaching events have not occurred since the El Nino of 1997-98. Roberts et al. (1982) reported cold-water disturbances in Florida Bay in January 1977 with temperatures below 16oC sustained for 8 days (minimum recorded

145 water temperature was 12.6oC). Burns (1985) attributed the lack of acroporids on the shallow fore-reef, the increase in total coral cover with depth and the greater abundance of Montastraea annularis in the deepest zones in the upper Florida Keys as a result of cooling of surface waters during severe winter cold fronts. Water temperatures in SE Florida were likely similar or lower than the low temperatures recorded in the Florida Keys in 1977 (Roberts et al. 1982). Thus, aperiodic chilling processes have a limiting influence on reef community development throughout the Florida Keys Reef Tract but probably even more so at the higher latitude reefs of SE Florida.

Sedimentation and turbidity can affect reef organisms by shading, burial of epibiota, and burial of substrate necessary for recruitment and survival of epibiota. The responses of organisms to shading and temporary burial are complicated by adaptation. Telesnicki and Goldberg (1995) documented depressed photosynthesis:respiration ratios and mucous production in the corals Dichocoenia stokesii and Meandrina meandrites due to elevated turbidity.

Gilliam et al. (2007) have used sediment traps to measure sedimentation on all reef tracts in Broward County since 1997. Their data indicate that the inner reef typically has the highest rate of sedimentation, as well as largest grain size, followed by the middle reef and then the outer reef. This trend is a result of increasing depth and therefore decreasing wave energy. This was illustrated in 2005 when severe sea conditions during hurricane Katrina (25 August 2005) resulted in the highest sedimentation rates measured in that year. FWCC (2006) reported burial of fixed monitoring sites on the ridge complex offshore Palm Beach County in 2005. The cause was unknown, although hurricanes Jeanne and Frances in 2004 may have contributed to substantial sand movement in the shallow ridge complex area.

In 2004, after the Gulf of Mexico and Atlantic coasts of Florida were impacted by 4 hurricanes (Charlie, Frances, Ivan, and Jeanne), widespread accumulation of silt/clay size sediment was observed on nearshore hardbottom from Cape Canaveral to Fort Lauderdale (Kosmynin and Miller 2007). This material filled sand depressions on the

146 inter-reef sand plains and buried patches of nearshore hardbottom and persisted through at least the winter of 2007 (Fig. 4.19). The origin is unknown but Kosmynin and Miller (2007) hypothesized that hurricane generated waves and currents transported silt/clays shoreward from deeper parts of the continental shelf.

Fig. 4.19: Persistent deposits of silt/clay size sediments were found in sediment depressions and topographic lows on the a reef tract and b inter-reef sand plains following the passages of hurricanes, Charley, Frances, Ivan, and Jeanne, in 2004 (photos by: a Vladimir Kosmynin; b,c Kenneth Banks).

Human Impacts and Conservation Issues

The proximity of the SE Florida reef tract to a highly urbanized coastal zone contributes a number of human-related stressors to the reef communities. Water pollution, over- fishing, coastal construction activities, vessel anchoring and grounding, as well as ballast water discharge impact the region’s reefs. While balancing economic growth with

147 environmental protection is challenging, the economic value of the coral reefs is considerable. Johns et al. (2003) determined the economic contribution by recreational users of artificial and natural reefs (fishers, divers, snorkelers, visitors viewing reefs from glass-bottomed boats) over the period June 2000 to May 2001 to have been US$2.3 billion in sales and US$1.1 billion in income. 36,500 full and part-time jobs were related to the recreational use of the reefs.

Water Quality Water quality monitoring in SE Florida is limited to inland waters (Trnka and Logan 2006, Caccia et al. 2005, Torres et al. 2003, Carter 2001). Long term data does not exist for ocean waters, however the Broward County Environmental Protection Department began a coastal water quality monitoring program in 2005 (Craig 2004). Three study sites were established around Port Everglades Inlet where nutrients, chlorophyll, salinity, dissolved oxygen, and pH are measured monthly.

Lapointe (1997) provided evidence that macroalgal blooms on the reefs offshore Palm Beach County were caused by nitrogen from land-based sewage. Finkl and Charlier (2003) and Finkl and Krupa (2003) estimated that nutrient loading of nitrogen and phosphorus from inland agriculture to the coastal waters offshore of Palm Beach County via surface water discharge are 2473 and 197 metric tons/year, respectively, and via submarine groundwater discharge (SGD) 5727 and 414 metric tons/year, respectively. They projected that even if nutrient loading to groundwater was to be stopped immediately, effects would still persist 5-8 decades into the future due to slow groundwater flow. Fauth et al (2006) used cellular diagnostics to detect signs of nutrient- related stress in Porites astreoides offshore Broward County when compared to samples from the Bahamas. Stress responses of corals adjacent to treated (secondary treatment) human wastewater discharges as well as corals from the Florida Keys National Marine Sanctuary were consistent with sewage exposure while responses of offshore colonies were consistent with xenobiotic detoxification.

148 Coastal Construction Before 2000, coastal construction activities in SE Florida were primarily related to installation of cross-shelf wastewater outfall pipes and dredging projects for inlet channel maintenance and beach restoration. The proximity of the reef tracts and hard bottom communities to the coast increases the potential for impacts from any dredging or other coastal construction activities.

Six wastewater pipes cut through the reef tracts in SE Florida (Fig. 4.20), which were constructed at a time when there was little awareness of reef resources or concern for the environment in general. The pipes were placed in deep trenches cutting through the reef. An overburden of boulders or articulated concrete block mats was used for protection where pipes traversed sand. The discharge points for the pipes are on the lower foreslope of the outer reef.

Seven navigational inlets exist in SE Florida (Fig. 4.1). North Lake Worth Inlet (locally called Palm Beach Inlet), Port Everglades Inlet and Government Cut service seaports and are maintained for large vessel traffic. South Lake Worth Inlet (also called Boynton Inlet), Boca Raton Inlet, Hillsboro Inlet, and Haulover Inlet are limited to use by smaller vessels due to depth constraints or bridge clearances. Although all of the inlets are jettied, littoral transport of sand from the north results in in-filling of the inlet channels with ebb or flood shoals. Maintenance dredging usually involves removing this sand to down-drift beaches or to deepwater Offshore Dredge Material Disposal Sites (ODMDS) (EPA 2004). A number of harbor deepening projects have been proposed in recent years as a result of a trend toward larger, deeper draft commercial ships. Since the inlet channels cross the reef tracts, large areas of reef will be removed. Physical damage to reef and hardbottom in the vicinity of dredging activity can occur from slack tow cables scraping the bottom, sedimentation resulting from tug boat propeller thrust in shallow water, and vessel anchors. Potential impacts to reefs from these dredging projects are primarily related to suspended sediments and turbidity. While the larger grain size sediments settle out rather quickly, the finer grain material may remain suspended for long periods of

149 time. Advection by ebb tidal flows can lead to exposure of the surrounding reefs to turbidity and sediment deposition.

Fig. 4.20: General location of treated human wastewater outfall pipes in Southeast Florida that discharge effluent on lower foreslope of the outer reef.

Another common type of dredging project in SE Florida is for the restoration of eroded beaches. Beach erosion is a problem because inlet jetties interrupt the transport of quartzose sands from the north causing sand starvation downdrift. In addition, coastal development has narrowed the beach zone, preventing the beach from absorbing wave energy. Regular nourishing of the beaches began in the early 1970’s and continues to the present day. Eroded beaches are filled with sand dredged from between reef tracts and are

150 generally re-nourished on 10-15-year intervals. Cutter-head and hopper dredges used for beach nourishment are large vessels and must maneuver in small areas when dredging around reefs. The result is an increased risk of physical impacts from cutter-heads and drag arms hitting the reef and tow cables of support vessels dragging over the reef. As in the case for inlet dredging, sedimentation and turbidity are also problematic. Nearshore hardbottom is often directly buried during beach filling or during the adjustment of the beach profile after filling.

Rapid population growth in the SE Florida region has resulted in an increased demand for energy and communications infrastructure. A number of linear, cross-shelf natural gas pipelines and communications cables are planned or have been constructed.

Three natural gas pipelines have been proposed for SE Florida. Initial plans were to use horizontal directional drilling (HDD) to create pilot holes under the reef tracts which would subsequently be enlarged to the necessary diameters for pipeline installation. Because of the risk of frac-outs (leakage of drilling muds through the porous substrate underlying the reefs) and other potential impacts from the release of drilling muds, HDD was abandoned in favor of tunneling under the coastal shelf. This technology is well developed and minimizes risks to the reefs.

Communications cables are laid directly on the sea floor and although their diameters are small (24 cm), their lengths and numbers can result in significant primary physical reef impacts. Since cable-laying vessels have to come into shallow waters for the installation there is a high risk of impact from propeller wash and tow cable scrapes. ATT’s installation of 2 fiberoptic telecommunications cables resulted in dislocated scleractinian and octocoral colonies, as well as physical damage to many remaining colonies. Re- cementing of stony coral colonies and mitigation were required (PBS&J 1999).

Environmental protection measures used during coastal construction projects has progressed greatly in recent years because of a greater conservation ethic by the public and increased awareness of the resources present. In a recent beach restoration project

151 completed by Broward County, environmental protection and monitoring costs for the project were approximately 20% of the total construction costs. The average for similar projects is approximately 10% (Chris Creed, pers. comm.). The availability of high resolution bathymetry and advances in positioning technology and remote, real-time monitoring of vessels’ position allow the establishment of transit corridors for vessels to minimize vessel-related impacts.

The increased extent and duration of reef impact monitoring associated with coastal construction projects has resulted in an increased knowledge of the reef-associated communities, however, understanding of long term impacts of these projects remains unclear. Highly urbanized SE Florida presents a number of stressors to reef communities so it is difficult to find suitable experimental control for monitoring. The recent use of molecular and organismal level techniques to determine stress before impacts occur at the community level may be a portent of the future monitoring of project impacts. Vargas- Angel et al. (2006) used histological techniques to determine sedimentation induced stress on corals and attempt to calibrate a visual method of determining organismal stress. Fauth et al (2006) used enzymatic biomarkers in the stony coral, Porites astreoides, coupled with analysis of community structure and healing of lesions to look for possible impacts of wastewater outfall pipes and inlet discharges. These techniques using multiple levels of monitoring could be expanded to examine impacts from coastal construction.

Ship Groundings and Anchor Damage on Reefs Commercial shipping into the ports at Palm Beach, Port Everglades, and Miami is an important part of the economy of SE Florida and increased 150% between 1964 and 2002 (Andrews et al. 2005). The proximity of reefs to the navigational inlets and commercial ship anchorages leads to a high risk for ship groundings and anchor damage with subsequent reef damage. This reaches an extreme around Port Everglades Inlet where a relatively shallow (d=20m) anchorage lies in sand offshore of the middle reef tract. Between 1993 and 2007, eleven ships have grounded on reefs inshore of this anchorage, impacting over 40,000 m2 (Fig. 4.21) and fortunately vessel owners have been relatively

152 responsive in carrying out reef restoration. Efforts among federal, state and local government agencies to eliminate the shallow anchorage are underway in order to reduce impacts and a study of alternative anchorages has been completed (Moffatt and Nichol 2006).

Fig. 4.21: Position of shipgroundings near Port Everglades, Broward County. Most groundings are due to ships breaking anchor and drifting from the anchorage during onshore winds.

Anchoring of ships outside the designated anchorage and even small boat anchors pose other problems. The number of recreational boats in SE Florida increased by 500% from 1964 to 2002 (Andrews et al. 2005). There is no documentation of the extent of resulting reef damage. To lessen anchor damage by small boat, over 100 moorings were installed in Broward County. Reef impacts due to concentration of reef users around moorings are currently being investigated by Klink et al. (2006).

153 Climate Change Increases in sea temperature, sea level rise and, possibly, increasing levels of ultraviolet radiation due to global climatic change may affect coral reefs in SE Florida. Locally or regionally, changes in tropical cyclone patterns may directly impact the coral communities, and changes in rainfall patterns may affect sedimentation, salinity, nutrient and pollutant inputs (Edwards 1995). Rainfall data for 1890-2000 show that there has been a decline in rainfall since the 1960’s for unknown reasons, and global climate models predict a reduction of precipitation for South Florida ultimately resulting in decreased runoff (SFWMD 1996). This may, in itself, be beneficial to reef biota. For example, Dodge and Helmle (2003) found that lower salinities (relative to normal seawater) slowed coral growth rates (see also section 5.2.4). However, a region’s landscape (urbanization) can influence rainfall (Pielke et al. 1999) so the prediction of future rainfall levels is complicated by other factors, including water use patterns by an ever increasing local population.

While many local climatic changes occur on relatively smaller time scales, global events such as eustatic sea level rise and atmospheric warming occur on much larger time scales. Sea level rise is of great concern for low elevation coastal regions, such as SE Florida. The Intergovernmental Panel on Climate Change (IPCC 2007) reported that global sea level rise for the period 1961-2003 averaged 1.8 mm/yr (1.3-2.3) and increased to 3.1 (2.4-3.8) mm/yr over 1993-2003. Wanless (1989) reported that since 1932 tide gauge records from Key West and Miami show relative sea level rise in South Florida has accelerated and more recent rates are 3-4 mm/yr. Titus (1995) estimated that by the year 2050 eustatic sea level will likely rise at least 15 cm (2.7 mm/yr) and there is a 10% probability that it will rise 30 cm (5.4 mm/yr). Others (Buddemeier and Smith 1988) estimate future rates of 15±3 mm/yr as probable over the next century. Such high rates could impact corals directly by shifting them to a deeper, lower light position in the water column. Acroporid reefs would drown under these conditions since their sustained reef accretion rates are only about 10 mm/yr. Since SE Florida’s reefs are already non- framebuilding relicts in which reef-building biota are small and the reef-associated biota dominate space, one would assume them not to be as sensitive to climatic changes in the

154 shorter term. However, secondary impacts, such as increased sedimentation and turbidity from coastal flooding and erosion, would degrade water quality and could affect reef growth.

Present Status of Reef Health

It is difficult to compare the health of the reefs of SE Florida with extant Acroporid coral dominated reefs in other areas of the western Atlantic and Caribbean. The Acroporids ceased dominating cover in SE Florida 5-7 cal BP (Lighty 1978, Banks et al. 2007). Most of the declines reported in other areas have been a result of loss of Acropora spp. to white band disease (Gardner et al. 2003). White band disease has been reported in 1.8% of the cover of the Acropora cervicornis thickets offshore of Broward County described by Vargas-Angel et al. (2003).

The Caribbean-wide decrease of Diadema antillarum was also experienced in SE Florida where Goldberg (1973) reported this sea-urchin to have been abundant offshore Boca Raton. In contrast, FWCC (2006) reported none at 10 SECREMP sites from Palm Beach to Miami-Dade Counties. Six were seen at 4 sites in 2004 and 15 at 6 sites in 2005. Recovery therefore seems to be lagging.

Ward-Paige et al. (2005) surveyed clionid sponges on the Florida Keys reef tract and found a relationship with sewage contamination. In SE Florida FWCC (2006) reported Cliona delitrix at all sites, except at the A. cervicornis thickets. Montastraea cavernosa, the regionally most abundant scleractinian, was most affected by this sponge. Diver observations by one of us (KB) indicate that C. delitrix is abundant throughout Broward County, particularly on the ridge complex and inner and middle reefs (Fig. 4.22).

155 on the reefs offshore of Broward County. These blooms have had a significant impact on reef-associated organisms by smothering and out-competing recruits of sessile benthos (Lapointe 1997). For example, at a study site of Gilliam et al. (2007) on the inner reef, significant coverage of Lyngbya spp. in 2003 had affected most erect octocorals and their densities declined steadily from 2003-2005. Also sponge density dropped from ≈13/m2 in 2002 to ~6/m2 in 2003. Some subsequent recovery increased numbers in 2004 to ~8/m2. Scleractinian cover did not appear to be impacted by Lyngbya spp.

Fig. 4.22: a) The boring sponge, Cliona delitrix, occurs extensively offshore Southeast Florida and may indicate human sewage contamination of the coastal waters (Ward-Paige et al. 2005). b) Aerial photo of the hardbottom adjacent to the north jetty at Hillsboro Inlet shows high coverage of C. delitrix that may correlate with tidal plume contamination. (photos by: a K. Banks; b D. Behringer).

156 The incidence of coral bleaching and disease has been relatively low in SE Florida since 2004, when data were first collected. In 2004, 19 diseased coral colonies were identified in the 10 study sites. In 2005, 21 diseased colonies were identified, 10 of which had apparently been infected in 2004. Nine of those were Siderastrea siderea with dark spot syndrome and had recovered by 2005. White complex disease was more prevalent in 2005 (FWCC 2006). No totally bleached coral colonies were observed although partial bleaching was more common than disease.

Conclusions

The SE Florida reef system consist of relict, early Holocene Acropora palmata framework reefs and indurated sand ridges that still maintain a rich, typically Caribbean, but non-framebuilding fauna today. The dominant hard corals are Montastrea spp. but living space cover by hard corals is overall low (<6 %). Rich alcyonacean communities of typically Caribbean composition cover the majority of benthic space, allowing high benthic space cover. Three shore-parallel reefs (inner, middle, outer) are separated by sandy plains. The middle and outer reefs generally harbor denser benthic cover, dominated by sponges and alcyonacean soft corals. The inner reef is generally more sparsely settled, but has some large patches of dense Acropora cervicornis growth, which represents the northern latitudinal distribution limit for these corals. The fish communities are typically Caribbean and similar in composition to the Florida Keys, but changes in community composition are observed in Palm Beach County. Heavy recreational fishing pressure has reduced size classes and population densities of groupers and snappers. Threats to the area’s reefs are pollution, coastal construction and dredging projects. Recently, benthic cyanobacteria and algae blooms have caused heavy mortality among algyonacean and hard corals. Despite being relatively little known, the local economic value of these reefs is in the range of US$ 2.3 billion in sales and $ 1.1 billion in income per year. 36.500 jobs rely on the use of the reefs.

157 Acknowledgements

Special thanks to Alexander Soloviev of NSU, for information on SE Florida coastal circulation; Chris Creed, coastal engineer at Olsen Associates, Inc., for comments on relative costs of beach nourishment projects; and Brettany Cook (NSU) and Guynette Alexandre (Broward County Environmental Monitoring Division) for organizing ocean temperature data.

References

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167 the Dry Tortugas: A guide to the modern carbonate environments of the Florida Keys and Dry Tortugas. International Geological Congress Field Trip Guidebook T176, AGU, Washington DC, p55 Soloviev AV, Luther ME, Weisberg RH (2003) Energetic baroclinic super-tidal oscillations on the southeast Florida shelf, Geophys Res Lett 30(9):1463 Stauble DK (1993) An overview of Southeast Florida inlet morphodynamics. J Coastal Res SI18: 1-28 Steig EJ (1999) Paleoclimate-Mid-Holocene climate change. Science, 28: 1485-1487 Taggart JR (2006) Mid-Holocene climate change in the southwestern Dominican Republic: proxy evidence from stable isotope values and molluscan indices. 19th Annual Keck Symposium; http://keck.wooster.edu/publications Tedesco K and Thunell R 2003. High resolution tropical climate record for the last 6,000 years. Geophysical Research Letters, 30(17): 2-1 – 2-4. Telesnicki GJ, Goldberg WM (1995) Effects of turbidity on the photosynthesis and respiration of two South Florida reef coral species. Bull Mar Sci 57: 527-539 Thanner SE, McIntosh TL, Blair SM (2006) Development of benthic and fish assemblages on artificial reef materials compared to adjacent natural reef assemblages in Miami-Dade County, Florida. Bull Mar Sci 78:57-70 Thompson LG, Mosley-Thompson E, Davis ME, Henderson KA, Brecher HH, Zagorodnov VS, Mashiotta TA, Lin P-N, Mikhalenko VN, Hardy DR, Beer J (2002) Kilimanjaro ice core records: evidence of Holocene climate change in tropical Africa. Science, 298: 589-593 Tichenor E (2005) Environmental Conditions Status Report Cyanobacteria Proliferation Gulf Stream Reef, Boynton Beach, Florida, May 2005. Palm Beach County Reef Rescue, Boynton Beach, Florida, USA, 83p Tilmant JT, Curry RW, Jones R, Szmant A, Zieman JC, Flora M, Robblee MB, Smith D, Snow RW, Wanless H (1994) Hurricane Andrew's Effects on Marine Resources BioScience 44: 230-237 Titus JG (1995) The probability of sea level rise. Environmental Protection Agency, Rockville, Maryland, USA Torres AE, Higer AL, Henkel HS, Mixon PR, Eggleston JR, Embry TL, Clement G (2003) US Geological Survey Greater Everglades Science Program: 2002 Biennial Report. USGS Open File Report 03-54, Tallahassee, Florida, USA Toscano MA, Macintyre IG (2003) Corrected western Atlantic sea-level curve for the last 11,000 years based on calibrated 14C dates from Acropora palmata framework and intertidal mangrove peat. Coral Reefs 22: 257-270 Trewartha GT (1968) An Introduction to Climate. McGraw-Hill, 408 pp Trnka M, Logan K (2006) Land-based Sources of Pollution Local Action Strategy, Combined Projects 1 and 2. Florida Department of Environmental Protection, Southeast Florida Coral Reef Initiative, 196p USACE (1996) Coast of Florida Erosion and Storm Effects Study-Region III, appendix D-Engineering Design and Cost Estimates (draft). US Army Corps of Engineers, Jacksonville, Florida, District, 233 p Vargas-Angel B, Thomas JD, Hoke SM (2003) High-latitude Acropora cervicornis thickets off South Lauderdale, Florida, USA. Coral Reefs 22: 465-473 Vargas-Angel B, Riegl B, Gilliam D, Dodge R (2006) An experimental histopathological

168 rating scale of sedimentation stress in the Caribbean coral Montastraea cavernosa. Proc 10th Int Coral Reef Sym: 1168-1173 Vargas-Angel B, Colley SB, Hoke SM, Thomas JD (2006) The reproductive seasonality and gametogenic cycle of Acropora cervicornis off Broward County, Florida, USA. Coral Reefs 25: 110-122 Vaughan TW (1914) Investigations of the geology and geologic processes of the reef tracts and adjacent areas in the Bahamas and Florida. Carnegie Inst Wash Yb 12: 183 Walker BK, Riegl B, Dodge RE (in press) Mapping coral reef habitats in SE Florida using a combined-technique approach. Journal of Coastal Research Ward-Paige CA, Risk MJ, Sherwood OA (2005) Clionid sponge surveys on the Florida Reef Tract suggest land-based nutrient inputs. Marine Pollution Bulletin, 51: 570- 579 Wanless HR (1989) The inundation of our coastlines: past, present, and future with a focus on South Florida. Sea Frontiers, 35(5): 264-271 Watts WA, Hansen BCS (1994) Pre-Holocene and Holcene pollen records of vegetation history from the Florida peninsula and their climatic implications. Palaeogeography, Palaeoclimatology, Palaeoecology, 109: 163-176 Willis TJ (2001) Visual census methods underestimate density and diversity of cryptic reef fishes. J Fish Biol 59: 1408-1411 Wulff JL (1985) Dispersal and survival of fragments of coral reef sponges. Proc 5th Int Coral Reef Congr. 5: 119-124 Wulff JL (1991) Asexual fragmentation, genotype success, and population dynamics of erect branching sponges. J Exp Mar Biol Ecol 149: 227-247 Wulff JL (1995a) Effects of a hurricane on survival and orientation of large erect coral reef sponges. Coral Reefs 14: 55-61 Wulff JL (1995b) Sponge-feeding by the Caribbean starfish Oreaster reticulates. Mar Biol 123: 313-325 Yeung C, Lee TN (2002) Larval transport and retention of the spiny lobster, Panulirus argus, in the coastal zone of the Florida Keys, USA. Fisheries Oceanography 11: 286-309 Yokohama Y, Lambeck K, Dekker PD, Johnston P, Fifleds KL (2000) Timing of the Last Glacial Maximum from observed sea-level minima. Nature, 406: 713-716 Yoshioka PM, Yoshioka BB (1991) A comparison of the survivorship and growth of shallow-water gorgonian species of Puerto Rico. Mar Ecol Progr Ser 69: 253-260

169 Appendix 4.1: List of species reported for Southeast Florida ridge complex and reefs Macroalgae Scleractinia/Zoanthidia Octocorallia Porifera Cyanobacteria Dictyota bartayressi Acropora cervicornis Briareum asbestinum Agelas clathrodes Dictyota spp. Diodogorgia A. palmata nodulifera A. conifera Galaxaura obtusata Agaricia agaricites Ellisella barbadensis A. wiedermyeri Erythropodium Halimeda discoidea A. fragilis caribaeorum Amphimedon compressa H. opuntia A. humilis Eunicea calyculata Anthosigmella varians Jania adherens A. lamarcki E. clavigera Aplysina cauliformis Lyngbya confervoides Astrangia solitaria E. fusca A. fistularis L. polychroa Cladocora arbuscula E. laciniata A. fulva Padina spp. Colpophyllia natans E. laxispica A. lacunosa Dendrogyra cylindrus E. palmeri Callyspongia plicifera . Dichocoenia stokesii E. pinta C. vaginalis Diploria clivosa E. succinea Chondrilla nucula D. labyrinthiformis E. tourneforti Cinachyra spp. D. strigosa Gorgonia ventalina Cliona celata Eusmilia fastigiata Iciligorgia schrammi C. delitrix Lophogorgia Isophyllia sinuosa cardinalis Diplastrella megastellata Leptoseris cucullata Muricea laxa Dysidea spp. Madracis decactis M. muricata Ectyoplasia ferox M. mirabilis M. pendula Haliclona spp. M. pharensis Muriceopsis petila Holopsamma helwigi Manicia areolata Nicella schmitti Iotrochota birotulata Meandrina meandrites Plexaura flexuosa Ircinia campana Plexaurella Millepora alcicornis dichotoma I. felix Montastraea annularis f. annularis P. fusifera I. strobilina M. annularis f faveolata P. grisea I. variablis M. annularis f franksii P. pumila Microciona juniperina Pseudoplexaura M. cavernosa crucis Monachora barbadensis Pseudopterogorgia Mussa angulosa acerosa M. unguifera Mycetophyllia danaana P. americana Mycale laevis M. lamarckiana P. elisabethae Myrmekioderma styx M. aliciae P. navia Niphates digitalis Oculina diffusa P. rigida N. erecta Palythoa caribaeorum Pterogorgia citrina Ophiactis spp. Phyllangia americana P. guadalupensis Pellina carbonaria

170

Appendix 4.1 (continued): List of species reported for Southeast Florida ridge complex and reefs

Macroalgae Cyanobacteria Scleractinia/Zoanthidia Octocorallia Porifera

Pseudaxinella Porites astreoides P. citrina lunaecharta P. porites P. guadalupensis Pseudoceratina crassa Scolymia cubensis Swiftia exserta Ptilocaulis spp. Spheciospongia S. lacera vesparium Siderastrea radians Strongylacidon spp. S. siderea Tedania ignis Solenastrea bournoni Ulosa ruetzleri S. hyades Verongula rigida Stephanocoenia intersepta Xestospongia muta Stylaster rosea Tubastrea coccinea Based on data from Blair and Flynn (1989), Foster et al. (2006), Gilliam et al. (2007), Gilliam (personal communication), Goldberg (1973), Kosmynin (personal communication), Riegl et al. (2002)

171

5 A Synopsis of the Geobiology of the Southeast Florida Continental Reef Tract

Introduction

Recent applications of high resolution hydrographic survey technology have allowed the examination of meso- and micro-scale (regional and local) geomorphology of the SE Florida Reef Tract and limestone ridge complex. Expansion of reef community structure studies via fixed study sites, landscape analysis, and acoustic ground discrimination methods are, for the first time, allowing the integration of regional reef geomorphology and ecology in the region.

The key to furthering this integration of the physical and biological will be the development of monitoring programs that, not only measure status and trends of biological communities, but measure environmental and geological status and trends. Correlations among these will provide a much deeper understanding of both historical and modern structuring processes, allowing prediction of the impacts of environmental stressors.

Biological Aspects of the Southeast Florida Reef tract

The first description of the reef benthic communities north of the Florida Keys was provided by Golberg (1973). This work was limited to a small area in the northern part of the reef complex, but did discuss ecology and geomorphology, although not in an inter- related context. Subsequent, infrequent, and regionally isolated reef community monitoring was carried out in association with dredging for beach nourishment projects (Dodge et al. 1995; Blair and Flynn 1989; Continental Shelf Associates 1980, 1984;

172 Courtney et al. 1972; Courtney et al. 1975; Courtney et al. 1980; Goldberg 1981). While these projects were intended to address the impacts of physical disturbance, i.e., sedimentation and turbidity, on reef communities, they did not incorporate measurements of physical parameters, nor was geomorphology considered. The effects of rugosity would have provided insight into how sedimentation impacts reef biota. Some recent status and trends monitoring have added sedimentation measurements (Gilliam et al. 2007) and temperature (FWCC 2006), but this information has not been related to the biological information.

While these previous studies clarified some of the broad-scale ecology and community structure in the SE Florida Reef Tract (Fig. 5.1), many more questions remain, and much remains to be learned about the spatial patterns and community structure within each individual reef system. Moyer et al. (2003) observed patchy distribution and apparently distinct spatial patterning of the benthic communities. Geomorphic variability within and among the reef tracts was shown by Banks et al. (2007) and correlations with benthic patchiness should be further explored in order to build upon our current understanding of the functioning of the coral reef ecosystem in SE Florida. To be able to understand the processes that influence the apparently patchy distribution of organisms within reefs, a geological landscape ecology approach that explicitly examines patterns of patch- distinctness and connectivity (besides other parameters) appears promising. Kareiva (1994) postulated that the study of landscapes and space in ecology should be considered the “final frontier” of ecological theory and Farina (1998) identified the classification of landscapes as a central tool in natural resource planning and management. It is anticipated that a study of SE Florida benthic assemblages using a geological landscape ecology approach will not only lead to an improved classification schemes of reefal assemblages, but also one that is more relevant to resource management. It will allow assessment of the scale of patterns that occur; whether “stacked patterns”, i.e. several communities exhibiting patterns at different scales exist; and whether patterns are more or less arbitrary (i.e. driven by chance events) or strongly determined by environmental variables and community history. These considerations are of key importance when assessing the value of any given component of the ecosystem, for example in habitat

173 equivalency analyses, which is used to determine compensatory mitigation for anthropogenic damage to habitats (Dodge and Kohler 2006).

Although there are many publications on the principles, methods, and applications of landscape ecology in terrestrial systems (see Farina 1998 for a review), only recently have these techniques been successfully applied to the marine environment (see Robbins and Bell 1994, Aronson and Precht 1995, Edmunds and Bruno 1996, Bythell et al 2000, Wargo et al. 2002, among others). While many more coral reef researchers are considering issues of landscapes, pattern and scale in their studies (Green et al 1987, Robbins and Bell 1994, Aronson and Precht 1995, Edmunds and Bruno 1996), there remains a paucity of knowledge about ecological structure on coral reefs in terms of the spatial distribution of organisms within a community (i.e. their ecological patchiness) and the nature of their spatial distribution (homogeneous, heterogeneous, random) and how geomorphic variability is a structuring mechanism.

Foster et al. (2006) expanded upon the work by Moyer et al. (2003) to look at benthic community patterns within reef tracts and the influence of certain environmental factors on community structure. They measured reef slope, rugosity and sediment bedload and found no correlation with reef faunal cover. They suggested that depth was the only environmental factor that they measured which influences community structure.

Faunal cover, however, may not be the preferred method of describing reef community structure. Parameters, such as relative species abundance within major groups, i.e., scleractinian, octocorallia, porifera, etc.; variation in growth forms and size distributions of colonial benthos; species diversity; species interactions; and species recruitment patterns may provide more insight into relationships of community structure and environmental conditions. For example, field observations in SE Florida by the author indicate that the relatively deep-water Alcyonacean, Iciligorgia schrammi, is commonly found on steep reef slope areas in shallow water. This would not necessarily be reflected in relative faunal cover estimates. On Australia’s Great Barrier Reef van Woesik and Done (1997) found significant correlations between a site’s taxonomic composition and

174

Fig. 5.1a: Habitat maps for the Continental SE Florida Reef Tract based on a combined method approach using laser bathymetry, acoustic ground discrimination, visual groundtruthing; Palm Beach County (modified from Walker et al. in press).

175

Fig. 5.1b: Habitat maps for the Continental SE Florida Reef Tract based on a combined method approach using laser bathymetry, acoustic ground discrimination, visual groundtruthing; Broward County (modified from Walker et al. in press).

176

Fig. 5.1c: Habitat maps for the Continental SE Florida Reef Tract based on a combined method approach using laser bathymetry, acoustic ground discrimination, visual groundtruthing; Miami-Dade County (modified from Walker et al. in press).

177 depth, distance to mainland, and exposure. These correlations were only significant, however, when taxa were defined to the level of genus or better. Significant correlations were also found when scleractinian coral size class was used as the descriptor. This exemplifies the complex interrelationship among environmental conditions and community structure.

It is reasonable to assume that reef geomorphic features would have similar complex influences on benthic community structure. Rogers et al. (1983), working on reefs in the U.S. Virgin Islands, found that scleractinian corals recruited more frequently to vertical surfaces than to horizontal. Therefore, large slopes or highly rugose substrates would be expected to have higher recruitment of corals, thus affecting coral community structure.

Ferro et al. (2005) examined the effect of coarse geomorphology (reef edge vs. reef crest) on fish populations and found correlations with fish species richness and total abundance. For reefs of Broward County, south of Port Everglades, the western reef edge had greater abundance and richness values than the eastern edge or the crest. In contrast, north of Port Everglades, the eastern edge predominated in, both, abundance and richness. They attributed these differences to topographic variables and noted that the eastern edges of the northern count sites had higher vertical relief, and attendant refuge, than the southern count sites. They also found correlations with rugosity and depth to some extent.

Techniques for measuring rugosity using high resolution laser bathymetric techniques have been developed by Brock et al. (2004) and have applicability to geobiological studies of reefs. Recent reef mapping in SE Florida (Walker et al. in press, Foster et al. 2006) has used this approach on a regional scale to some extent, however, community level ecology and temporal dynamics have yet to be incorporated.

Two anomalies in the modern reef community, discussed in Chapter 4, are the existence of extensive, dense thickets of Acropora cervicornis and areas of high massive coral coverage (≈17%). Both of these occur in close proximity on the ridge complex. Precht (2004) proposed that the northward expansion of Acropora in high latitude areas of the

178 Western Atlantic is a result of recent increases in water temperature or “climate flickers”. It was pointed out in Chapter 4 that ridge complex temperature variation is more sensitive to air temperature changes than the outer reef so it is reasonable to use changes in minimum average air temperature as a proxy for minimum water temperature variation. Long-term water temperature records do not exist for offshore SE Florida, but an examination of average minimum air temperatures during the period of 1948 to 2004 show a general increase after 1981 (Fig. 5.2). It is indeed likely that this local increase in air temperature minima favored an increase in cover of Acropora cervicornis. It is, however, premature to label this as a “climate flicker”, which was implied by Precht and Aronson (2004) to be a millennial-scale event. There appears to be an incipient decrease in average minimum air temperature after 1991, but it remains to be seen whether this decrease will continue.

Fig. 5.2: Average minimum air temperatures during the period of 1948 to 2004 for Miami, Florida (NOAA 2005).

Thickets of fossil A. cervicornis have been observed on the inner reef. Average branch diameters appear similar to the extant thickets on the ridge complex. Ages of these fossil corals are unknown, but that information in relation to the age of the inner reef

179 framework, coupled with isotope studies to determine contemporaneous temperatures would aid in understanding the extant thickets of A. cervicornis.

Geological Aspects of the Southeast Florida Reef Tract

Few geological studies of SE Florida’s reefs have been undertaken. Duane and Meisburger (1969a, b) used course bathymetry, coring, and sub-bottom investigations to describe the sediments and geomorphology of the inner continental shelf. The focus of the investigation was to locate and describe possible sources of sand for beach restoration. Lighty (1977) and Lighty et al. (1978) described the reef lithofacies in a wastewater-pipe trench excavated through the outer reef, 40 km north of Miami, and confirmed that, like the Florida Keys Reef Tract, it is a Holocene Acropora framework that terminated growth approximately 8 k BP cal BP (calibrated ages from Toscano and Macintyre 2003). Enos and Perkins (1977) summarized the knowledge of Quaternary sedimentation in South Florida, but their emphasis was on the Florida Keys and cores taken from the coast of SE Florida.

A number of basic questions regarding the geohistory of SE Florida’s remain. The times and foci of initiation of the outer, middle and inner reef tracts have not been determined. It has been proposed that the reefs initiated on topographic highs created during the Late Pleistocene and sea level rise rates allowed reef to initiate and keep-up for a period of time (Precht et al. 2000, Banks et al. 2007). Ages of termination have been determined for the reef tracts at isolated locations, but latitudinal variation in these ages may exist in the region that would aid in determining the causes of termination.

A number a causative factors for reef termination have been proposed: i) extensive flooding of flat areas of the continental shelf resulting in high turbidity and increased temperature extremes, ii) transport of turbid waters from the south as the lagoonal areas of Florida and Biscayne Bays were flooded, iii) regional climatic cooling after the mid- Holocene warm period (Lighty 1978), and iv) ‘catastrophic sea-level rise events’, i.e., CRE-3 at ≈7.6 k BP, caused give-up of the outer reef (Blanchon and Shaw 1995). Other

180 possibilities, not observable in the fossil or sedimentological record, exist, such as coral disease epidemics; macroalgal overgrowth from increases in upwelled, nutrient-rich water; and changes in the thermal characteristics of the Florida Current.

Extensive reef coring with stable isotope analyses would provide information on regional Holocene temperature changes, terrestrial inputs to the water mass, and changes in upwelling patterns. Reef facies analyses would provide insight into temporal changes in wave energy. Blanchon and Jones (1997), Gamble and Greenstein (2000), Bishop and Greenstein (2001), Hubbard et al. (2001), and Riegl (2001) found that the internal fabric of reefs in the hurricane-prone Eastern Caribbean was dominated by coral rubble and that reefs in less hurricane-prone areas, such as Curaçao, had a greater portion of in situ coral framework (Meyer et al. 2003). The SE Florida Reef Tract s are separated by deep inter-reef sand plains (Chapter 3). The stratigraphy of these sand plains may hold a story of temporal changes in storm frequency that may have implications to reef architecture.

The middle reef presents a unique feature in the reef geological landscape of SE Florida. Based on a limited number of cores and the geomorphology of the reef, the framework is composed primarily of massive coral species (Chapter 3). This is a paradox since the reef is located between the outer and inner reef which have an Acroporid framework. Cores of the middle reef are restricted to a penetration of 1.6 m so the entire reef fabric has not been examined (Banks et al. 2007). A coral reef community dominated by massive corals indicates an environment unsuitable for growth of Acropora palmata, the primary reef- building coral in the Western Atlantic and Caribbean. Environmental characteristics unsuitable for growth of A. palmata include, low wave energy, low temperature, high turbidity, water deeper than 5 m (Schlager 1981). Knowledge of timing of initiation of the middle reef and its growth fabric is critical to understanding the cause of termination of the outer reef. The inner reef initiated in the same time frame as the demise of the outer reef, indicating that water quality, wave energy and water temperature were conducive to growth of A. palmata. If the framework of the middle reef is composed of domestones throughout its fabric and initiation is coeval with termination of the outer reef, the Blanchon and Shaw (1995) hypothesis for a meter-scale catastrophic sea level

181 rise ≈7.6 k BP is supported. The story of the middle reef provides an example of application of geobiology, integrating paleo-ecology and climate with coral reef geology.

Oceanographic Influences on the Southeast Florida Reef Tract

The Florida Current is a portion of the Gulf Stream that intrudes into the Gulf of Mexico as the Loop Current and reverses flow to return to the Straits of Florida before moving in a northeasterly direction towards Europe (Fig. 5.3). It is the dominant ocean current affecting the SE Florida shelf (Jaap and Hallock 1990). The flow of the Florida Current is a result of both wind-driven processes in the subtropical gyre and the surface compensating flow for North Atlantic Deep Water formation. The average annual flow of the current is 31 million m3s-1 (Schmitz and Richardson 1991), and the heat transport into the North Atlantic Ocean is 1.3 PW (1 PW = 1015 Watts) (Lund et al. 2006). The Gulf Stream is an important agent of poleward heat transport and is associated with large ocean-atmosphere heat flux. Continental air masses moving from the north are moderated by the relatively stable temperature and large water mass of the current, any change in its path may have significant regional climatic impacts (Matsumoto and Lynch-Stieglitz 2003).

The Florida Current follows the steep bottom terrain along the shelf-break separating the deep ocean (Florida Straits) from the coastal zone. Mixing between the shelf and deeper ocean waters is affected by transient features created at the western edge of the current. Sub-mesoscale spin-off eddies (Lee et al. 1995; Shay et al. 2002) are important to local coastal circulation because they affect the continental shelf and largely determine the water properties on the shelf (Soloviev et al. 2003). Lee et al. (1995) found that sea surface temperatures (SST) of the Florida Current in the Florida Keys decreases due to the episodic formation of Tortugas eddies, which occur when the Loop Current penetrates into the eastern Gulf of Mexico. When the Loop Current retreats, water flows directly from the Yucatan Channel to the Straits of Florida, and Tortugas eddies fail to materialize. As a result, the axis of the Florida Current shifts northward and Florida Keys’ SST increases. Maul and Vukovich (1993) found no seasonal signal of northward

182

Fig 5.3: Advanced very high resolution radiometer (AVHRR)-based sea surface temperature estimates for the (a) Gulf of Mexico and (b) Western Atlantic, 13-14 March 1996, illustrating the location and spatial relationship of the Loop Current, Florida Current and Gulf Stream (modified from Ocean Remote Sensing Group, John Hopkins University Applied Physics Laboratory).

183 penetration of the Loop Current (required for Tortugas eddy formation) and the shedding of anticyclonic rings from the Loop Current, which occurs when the Loop Current is well developed, also seems to be aperiodic (Vukovich 1988, Sturges and Leben 2000). Lund and Curry (2004) concluded that, due to their stochastic nature, Tortugas eddy formation has little effect on mean Florida Current flow on centennial and longer timescales.

In the context of the SE Florida Reef Tract, how have centennial and millennial-scale changes in offshore (Florida Current) and coastal circulation (spin-off eddies, up-welling) affected the development of the inner, middle, and outer reef tracts? Hypotheses (discussed above) have been proposed to explain demise and back-stepping, but none have suggested affects of changes in the Florida Current as a factor of impacting reefs. Not only would an alteration in flow of the Florida Current affect regional climate, it could also affect larval dispersal and water quality, e.g., up-welling of nutrient-rich water and advection of lagoonal water from Biscayne and Florida Bays.

The Florida Current/Gulf Stream system has been extensively studied, but almost nothing is known about its behavior on centennial to millennial timescales (Lund and Curry 2004). Matsumoto and Lynch-Steiglitz (2003) used δ18O measurements on deep-dwelling planktonic foraminifera from the western margin of the North Atlantic and found that the Gulf Stream separated from the western boundary of the Atlantic Ocean near Cape Hatteras, North Carolina at the Last Glacial Maximum (LGM) at almost the same latitude as it does today. This implies a similar flow regime in the LGM to the present. However, Lund and Curry (2004, 2006) and Lund et al. (2006), based on isotopic studies of planktonic foraminifera in the Florida Keys, demonstrated long-term variability in the surface density, i.e., salinity and/or temperature, and flow rate of the Florida Current over that past 5200 years. Considering the large flow rate of the Florida Current/Gulf Stream, small variations in flow may not be sufficient to cause variations in large scale features, such as latitude of separation. Data for Florida Current conditions is not presently available for early to late Holocene so it is not possible to determine if Florida Current variability affected the SE Florida Reef Tract, but it is reasonable that small sea surface

184 temperature or salinity changes could have large impact on coral reefs located at high latitude.

Status of the Southeast Florida Reef Tract and Prediction of Near-Future Trends

The SE Florida Reef Tract is subjected to a number of natural and anthropogenic stressors. Its proximity of the SE Florida Reef Tract to a highly urbanized coastal zone contributes a number of human-related stressors to the reef communities. Water pollution, over-fishing, coastal construction activities, vessel anchoring and grounding, as well as ballast water discharge impact the region’s reefs. Natural stressors include upwelling of nutrient-rich water, high temperature variability, submerged groundwater discharge, and run-off.

It is difficult to compare the health of the reefs of SE Florida with extant Acroporid coral dominated reefs in other areas of the Western Atlantic and Caribbean. The Acroporids ceased dominating cover in SE Florida 5-7 cal k BP (Lighty 1978, Banks et al. 2007). Most of the declines reported in other areas have been a result of loss of Acropora spp. to white band disease (Gardner et al. 2003). White band disease has been reported in only 1.8% of the cover of the Acropora cervicornis thickets, described by Vargas-Angel et al. (2003), offshore of Broward County.

The long spined sea urchin, Diadema antillarum, controls macroalgal overgrowth on reefs, allowing space for colonization by reef epifauna. The Caribbean-wide decrease of D. antillarum was also experienced in SE Florida. Goldberg (1973) reported this sea- urchin to have been abundant offshore Boca Raton. In contrast, FWCC (2006) reported none at 10 Southeast Coral Reef Environmental Monitoring Program (SECREMP) in 2003 at 10 fixed monitoring sites stretching from Palm Beach to Miami-Dade Counties.

185 Six were seen at 4 sites in 2004 and 15 at 6 sites in 2005. Recovery may occur but seems to be lagging.

Ward-Paige et al. (2005) surveyed clionid sponges on the Florida Keys Reef Tract and found a correlation of cover with sewage contamination. In SE Florida FWCC (2006) reported Cliona delitrix at all 10 sites, except at the A. cervicornis thickets. Montastraea cavernosa, the regionally most abundant scleractinian, was most affected by this sponge. Diver observations by the author indicate that C. delitrix is abundant throughout Broward County, particularly on the ridge complex and inner and middle reefs.

In SE Florida harmful algal blooms of Caulerpa brachypus have occurred extensively offshore Palm Beach County during the past decade (Lapointe et al. 2006). In February 2007, Caulerpa brachypus spread into northern Broward County. Paul et al. (2005) reported extensive blooms of the cyanobacteria, Lyngbya confervoides and L. polychroa, on the reefs offshore of Broward County. These blooms have had a significant impact on reef-associated organisms by smothering and out-competing recruits of sessile benthos (Lapointe 1997). For example, at a study site of Gilliam et al. (2007) on the inner reef, significant coverage of Lyngbya spp. in 2003 had affected most erect octocorals and their densities declined steadily from 2003-2005. Also sponge density dropped from ≈13/m2 in 2002 to ≈6/m2 in 2003. Some subsequent recovery increased numbers in 2004 to ≈8/m2. Scleractinian cover did not appear to be impacted by Lyngbya spp.

The incidence of coral bleaching and disease has been relatively low in SE Florida since 2004, when data were first collected. In 2004, 19 diseased coral colonies were identified in the 10 SECREMP study sites. In 2005, 21 diseased colonies were identified, 10 of which were diseased in 2004. Nine of those affected in 2004 were Siderastrea siderea with dark spot syndrome but had recovered by 2005. White complex disease was more prevalent in 2005 (FWCC 2006). No totally bleached coral colonies were observed although partial bleaching was more common than disease.

186 In order to predict future changes in reef community and framework structure, it is necessary to develop a thorough understanding of current reef status and trends, as well as understand the response of reefs to past environmental change. An adequate monitoring program, incorporating a geobiological approach and with clear objectives, must be undertaken. Many papers, describing and critiquing reef monitoring, have been published (Bohnsack 1979, Rogers et al. 1983, Ohlhorst et al. 1988, French et al. 1990, Porter 1990, and others). Most of these protocols emphasize biological aspects of the reef, but, in order to understand the structuring processes of the reef community, it is important to add environmental and geological components. These would include, sediment characteristics, sedimentation rates, bioerosion measurements, zonation patterns, substrate rugosity and slope, light intensity, water temperature and chemistry, and wave and current measurements.

Increases in sea temperature, sea level rise and, possibly, increasing levels of ultraviolet radiation due to global climatic change may affect coral reefs in SE Florida. Locally or regionally, changes in storm patterns may directly impact the coral communities, and changes in rainfall patterns may affect sedimentation, salinity and nutrient and pollutant inputs (Edwards 1995). Rainfall data for 1890-2000 show that there has been a decline in rainfall since the 1960’s for unknown reasons, and global climate models predict a reduction of precipitation for South Florida ultimately resulting in decreased runoff (SFWMD 1996). This may, in itself, be beneficial to reef biota. For example, Dodge and Helmle (2003) found that lower salinities (relative to normal seawater) slowed coral growth rates. However, a region’s landscape (urbanization) can influence rainfall (Pielke et al. 1999) so the prediction of future rainfall levels is complicated by other factors, including water use patterns by an increasing local population which could have negative impacts on reefs.

Riegl (2003) and Riegl and Piller (2003) identified particular reef settings as possible refugia in times of environmental stress. Corals at high-latitude reefs in upwelling areas and coral areas at medium depth were found to recover more quickly from bleaching than offshore bank and island reefs in a scenario of increased SST and solar UV radiation.

187 Water temperatures at these sites were moderated by upwelling of cool subsurface waters. Reefs in the Arabian Gulf and South Africa have rich coral faunas with little to no recent reef-framework production. In some regards, these reef settings are similar to the SE Florida Reef Tract, i.e., high latitude, corals at medium depth and no recent framework production, although the SE Florida Reef Tract has a depauperate coral fauna. The anomalously high coral cover areas offshore Broward County might serve as possible local, micro-scale refugia for Acropora cervicornis at one site and the massive coral species (Montastraea cavernosa, Diploria spp., Meandrina meandrites, Colpophylia natans) present at the other. The predominantly northward currents at a regional scale in SE Florida, however, would inhibit gene flow in a southward direction. Sub-mesoscale spin-off eddies could result in entrainment of coral larvae on the coastal shelf, but these eddies appear to migrate northward (Shay et al. 2002) which would not allow larval delivery to the Florida Keys.

While many local climatic changes occur on relatively smaller time scales, global events, such as eustatic sea level rise and atmospheric warming, occur on much larger time scales. Sea level rise is of great concern for low elevation coastal regions, such as SE Florida. The Intergovernmental Panel on Climate Change (IPCC 2007) reported that global sea level rise for the period 1961-2003 averaged 1.8 (1.3-2.3) mm/yr and increased to 3.1 (2.4-3.8) mm/yr over the period, 1993-2003. Wanless (1989) reported that since 1932 tide gauge records from Key West and Miami show relative sea level rise in South Florida has accelerated and more recent rates are 3-4 mm/yr. Titus (1995) estimated that by the year 2050 eustatic sea level will likely rise at least 15 cm (2.7 mm/yr) and there is a 10% probability that it will rise 30 cm (5.4 mm/yr). Others (Buddemeier and Smith 1988) estimate future rates of 15±3 mm/yr as probable over the next century. High rates such as this could impact corals directly by shifting them to a deeper, lower-light position in the water column. Acroporid reefs would drown under these conditions since their sustained reef accretion rates are only about 10 mm/yr. Since SE Florida’s reefs are already non-framebuilding relicts in which reef building biota are small and reef associated biota dominate, one would assume that they would not be as sensitive to climatic changes in the shorter term. However, secondary impacts, such as increased

188 sedimentation and turbidity from coastal flooding and erosion, would degrade water quality and could affect reef growth.

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