The REEFS of BROWARD COUNTY

written and photographed by Bill Raymond

Bill Raymond, local resident and Fort Lauderdale native, Teceived his Master's Degree in marine geology from State Uni versity. His thesis topic was "A Geolog.ic Investi­ gation of the Offshore Sands and Reefs of Broward County, Florida." Mr. Raymond is interested in natural history,par­ ticulary offshore studies, and has done extensive research studies on reefs and for more than a dozen years.

INTRODUCTION toration projects in which offshore sedi­ Prior to 1967, the coral reefs of Broward ments were utilized to renourish eroding County might well have been called "mys­ beaches. As a result of the engineering tery reefs. II All that was known about studies of these sediments and surveys of them was thei r su rface topog raphy . In the reefs, one can on ly be di smayed to 1967 a set of charts was prepared by discover their current state of crisis. Ocean Science and Engineering, Inc., in which the bathymetry and subsurface to­ pography were mapped from the shoreline AN HISTORICAL OVERVIEW area to a di stance of one nautical mi Ie off­ OF THE REEFS shore. Two years later, the United States During the ice ages, large volumes of wa­ Army Coastal Engineering Research Center ter were siphoned out of the sea to form (1969) conducted a study from Palm Beach thick glaciers over the high latitude con­ to Miami of the sediments and reefs in tinents, leaving the level of the sea con­ which the latter were described as mar­ siderably lower than it is today. Sub-ma­ ginal edge reefs capping three step-like rine sea level features indicate that the marine terraces. sea level has been as low as -400 feet There have been several publ ications (Curray,1965).Apparently,conditions were which describe the geology of the reefs not favorable for growth during and provide an analysis of their forma­ this time because no remains of reefs tion. This author published the first in have been detected at those depths. 1972. Later that year, Courtenay et al. The original beaches were stranded described the biology of the reefs in Pom­ high above the water during the ice ages, pano,Dania and Hallandale. In 1977,Lighty forming a series of inland beach ridges on described in detai I the outer reef at a the exposed sea floor. Terrestial vegeta­ trench cut for a sewer outfall in Pompano tion 9 revv over the beach ridges and es­ Beach. Lighty's study represented the tablished r-oots in the sandy soil. Eventu­ first confirmation of Raymond's specula­ ally, the sand ridges became cemented tion that the th i rd reef had been created by acidic rain water and formed fossil by el khorn coral ( palmata) at a beaches by preserving their seaward lower sea level, although no trace of live sloping strata, root casts, ridge profiles exists today on the third and inlet gaps. reef. The most prominent ridge has been The information presented in the follow­ named the Hillsboro Ridge because it is a ing article was obtained during monitoring submerged extension of the coastal ridge and reef damage surveys for beach res- under Hillsboro Beach. Because the sea -2 - level has risen since the last ice age, a the West Indies were ki lied by some un­ water-cut cl iff has formed at the seaward known catastrophe between 4,000 and edge of the Hillsboro Ridge, a half mile 7,000 years ago (Braithwaite,1979). offshore from Fort Lauderdale and Pom­ Some geologists have cited a drop in pano Beach. Finally, these ice age beach­ sea temperature as the reason (Vaughan, rock ridges have evolved into submerged, 19'16, 1918; Goldberg, 1979). Others have reef-like ridges on which a coral cap has suggested sedimentation and turbidity re­ grown. su Iti ng from the erosion of land sediments The most prominent coral cap is the as the sea level rose and flooded the marginal reef at the seaward edge of the coastal areas (Adey, et al., 1977). Another series of beach rock ridges, two-th irds of a possible cause is the world wide flood, mile offshore, where a high profile spur­ recorded in historic literature (Genesis and-groove coral reef was built by elk­ 6-8) . horn coral 2,500 years ago. Whatever the cause of death, the thi rd

Seaward of the beachrock ridges and reef was bui It by el khorn coral between I the coral cap at the outer edge are true 4,000 and 9,000 years ago. Minor reef, coral reefs. These grew on shallow hard building star, starlet and brain corals con­ grounds during low sea level positions be­ tinue to populate the reef to this day but ~ tween 7,000 and 9,000 years ago (Lighty, have not added significantly to its struc­ 1977). Geologically speaking, they are not ture. al ive now, but neither are they old enough The second reef is actuaily composed of , to be classified as fossil reefs because three reefs, if one includes the most land­ they are less than 10,000 years old. ward coral reef cap that Iies on the outer At that time sea level was 80 feet lower edge of the beach ridge complex. Geologi­ than at present and was rising (Blackwel­ cally, this reef cap may be considered a der,et al.,1979). During this time, a mas­ part of the first reef. Very little is known sive barrier reef grew along the east about the midd Ie and outer second reefs,

coast of Florida and extended as far primarily because they are mostly buried I north as Cape Hatteras, North Carolina in sand. Two exploratory cores in the out- : (Macintyre and Milliman,1970). er second reef have penetrated only star This reef continued to grow rapidly un­ and brain corals to an 11~ foot depth. til 4,500 years ago (Raymond,1978).Then, Radiocarbon dates of these corals indicate it suddenly died and the sea level rose 45 that this reef grew between 3,000 and feet to its present elevation.lt is not fully 7, 000 years ago. Thus, it is contempora­ understood why the growth of the reefs neous to the third reef. The only informa­ did not keep pace wi th rising sea level. tion available about the middle second Perhaps, at fi rst, the ri se was sudden, reef is its subsurface profile defined in submerging the reefs to depths below the geophysical exploration surveys of borrow el khorn zone. Slower 9 r owi ng su rvivi ng areas for beach renourishment materials. corals would not have been able to match As the sea level continued to rise, flood­ the subsequent ri se of the ocean to its ing the nearshore continental shelf, a reef present level during the last 4,000 years q r ew and flourished landward of the se­ (Scholl and Stuiver, 1967). cond and third reefs, just seaward of a Coral geologists do not agree on what prominent sub-marine cliff. This reef, killed the reefs (Goldberg, 1979; Lighty, which may be considered part of the first and Macintyre, 1979; Braithvvaite, '1979). or second reefs, as noted before, grew Moreover, they do not even agree on the from about four to six feet high during date. Although some have reported a date the last 4,000 years. There, a few survi­ of 7,000 or 8,000 years ago (Lighty,1977; ving stands of elkhorn coral and pillar Adey,et al.,1977), r ecerrt information sug­ coral exist even today. gests that the event may have occu rred as recently as 4,500 years ago (Raymond, ELKHORN CORAL 1978). Evidence of the more recent reef The third (outer) reef in Broward County qr'owth in other study areas may have was bu iIt of el khorn coral (Acropora ~­ been erased by subsequent erosion of the mata), a rapidly growing reef building reef after its death. In any case, there is coral which is common today in the Flori­ mounting evidence that all the reefs in da Keys and among the West Indies reefs.

-3- TOP: (fig.A) A s mall t r ump e t fish hangs sus­ p e n de d at the edge of a cave in the c or al cap reef at - 22 ' o f f Ft.Ld. Eroded clam-and-sponge­ encrusted remains of elk ­ h orn c or al are cle a r l y v i sible on the walls of the cave. A f r a gme n t of this coral was carbon-14 dated at 2500 B.C. BOTTOM (fig.B) Ten inch pillars on a large pillar coral 3/4'5 of a mile off Ft.Ld. The long furry polyps have retracted and show the skeletal structure of the live coral. Pillars grow to be several feet in height on reefs in the Florida Keys. Stubby, short pillars in Broward County may be the re­ sult of turbid water.

-4- In shallow depths and exposed to high individual stands of el khorn coral exist on wave energy, this coral forms massive la­ the reefs of Broward County. On the near­ byrinthine barriers of sharp spi red shore beachrock ridges, live corals cover stems. These are oriented obliquely shore­ less than 5% of the surface area, the re­ ward and sometimes resemble a stack of mainder is covered by fleshy algae, spon­ rifles pointed at a 45° angle on the sea­ ges and other simple life forms. ward face of a reef. In depths of -15 to Soft corals occur in approximately equal -20 feet and in shallow protected areas, its numbers to the hard corals (D. E. Britt growth form is more of a broad-blade Assoc., Inc., 1981). Low profile,encrusting moosehorn shape, sometimes resembling a forms dominate the coral species living on giant orange four leaf clover. EI khorn the reefs. Coral species that form tall, I coral does not grow well below -20 feet columnar hemispherical or domed shapes I and is ' rarely 'fou nd below -30 feet, ap­ in the Keys tend to develop encrusting or , parently because of insufficient light at massive ' shapes in Broward County until " those depths. they grow to a height above bottom which ': Elkhorn coral is probably the most im­ frees them from storm sedimentation. ,: portant coral in coral reefs. Wherever it The Hillsboro Ridge forms a silt or sub- '.: grows, reefs are considered "alive." Its merged barrier, trapping nearshore sed- '~ prolific growth rate and regenerative ca­ iments that had been agitated by the . pability are factors which enable reefs to storm waves. Cold water, which can be € grow in high energy environments. Slower lethal to branching corals, also tends to '.: growing corals cannot keep pace with the get trapped behind this barrier. The : destructive forces at the reef front where branching (Acropora cer- '.: waves expend their force. Thus, the elk­ vicornis) grows most prolifically on the '\ horn coral serves as an energy absorbing seaward face of this ridge at a depth of ~, buttress and provides shelter for the star -20 feet. ~ and ' heads. EI khorn coral grows Stony corals are best formulated on the :'1 diagonally upward to the level of mean fi rst coral reef, east of the ridge, two- '1 sea level, exposing its branches out of thirds of a mile offshore in -20 to -25 ,,' the water during low tide. During a ris­ foot depths. This is because of the reef's.' ing sea level, ' an elkhorn reef can grow shallow depth and high profile and the i upward as fast as one inch per year. protection provided it by the Hilisboro i Ridge between it and the shore. BROWARD REEF ECOLOGY The diversity of the coral species also ! Today, only a minimal number of isolated reaches its peak on this reef. Of the 41 t: I - - ..I CONTINENTAL SHELF EAST OF BAHIA MAR, Ft.LAUDERDALE

-WIlt SEA LEVEL .... - HOLOCENE ;1

i ' Acropora palmata'

9000-~500years' ago I, ANASTASIA FORMATION <, :1 • Blachrock· .

ECOHO ..' MEr

CO"Al "ElF.

(R ep roduced by permission of D.E. Britt Associates, Inc .)

-5- iment damage to the reefs in the vicinity and did not destroy them, it was there­ of Port Everglades in Fort Lauderdale and fore assumed tolerable. That is, the reefs Dania, apparently related to previous har­ would replenish themselves after dredging bor dredging projects. The beach restor­ projects had been terminated. ation pr-ojects of the 1970s have acceler­ These two facts are known. Heavy en­ ated this decline. vironmental stress is applied to our coral Orie million cubic yards of sand have reefs during dredging projects and the been dredged in Pompano; 400,000 in Hal­ reefs off Fort Lauderdale have continued landale; 1.1 million in Fort Lauderdale; to decline since formal monitoring studies and, just recently, three million cubic began. Now, five years after dredging, yards in Hollywood and Hallandale. Each for reasons yet to be determined, those of the beaches built in these projects is reefs continue to decline rather than re­ expected to last only 10 years. Thus, one cover. Is this a result of the 1976 dredg­ can expect to witness a repeat of this le­ ing project? Could the 1979 Hollywood-Hal­ vel of dredging in the 1980s and in every landale project have affected Fort Lauder­ subsequent decade. dale's reefs so adversely? Can the reefs tolerate this continual Perhaps the cause is not even the bombardment of unusual sedimentation? beach restoration project. Regardless, be­ Until recently, it appeared that they fore another dredging project is launched could. In 1976 sediment damage from a caution should prevail until these matters closely monitored dredging project was have been resolved. Hopefully, this trend minimal, despite the heavy amount of sed­ wi II be reversed before the reefs undergo imentation that fell on the reef. The ten­ a total eco-collapse as the Hens & Chicken tative official posture was that, because Reef did in 1970 in Key Largo (Thomas, dredging only slightly injured the reefs 1979) .

FOOTNOTES

Adey, Macintyre, Stuckenrath & Dill, Goldberg, liThe Ecology of the Coral­ Raymond, B., "Marine Geology of Brow­ IIRelict Barrier Reef System off st. Octocoral Communities off the SE Flor­ ard County," (final report to Broward Croix, Western Atlantic," Proc. 3rd ida Coast," BULLETIN OF MARINE County Erosion Prevention District, Intll Coral Reef Symp., (1977)15. SCIENCE, (1973) 23,465-488. 1972) FSU master's thesis, 92p. Barnes,D., "Growth in Colonial Scler­ Goldberg, W. ,"Shelf Temperatures and Raymond, B., "Reef Damage Survey: actJnians,"BULLETIN OF MARINE SCI­ Reef Growth on the SE Coast" (a dis­ An I nterim Report," Broward County ENCE,(1973) 23, 2, 280-298. cussion),NATURE,(1979) 278,669-670. Erosion Prevention District,(1978) 51p.

Blackwelder,B., Pilkey,O. & Howard, Hoffmeister,J. & Multer, H., "Growth J., II Late Wisconsin Sea Levels on the Rate Estimates of a Pleistocene Coral scnon.r». & Stuiver,M., "Recent Sub­ SE US Atlantic Shelf Based on Inplace Reef of Florida,lI BULLETIN GEOL. mergence of Southern Florida: A Com­ Shoreline Indicators," SCIENCE,(1979) SOC. AMER.,(1964) 75,353-358. 204, 618-620. parison with Adjacent Coasts & Other Eustatic Oata ;" GSA BULLETIN, (1967) Lighty, R., "Relict Shelf-Edge Holo­ 78, 437-454. Braithwaite,"Holocene Reef Growth on cene Coral Reef: SE Coast of Florida," the Edge of the Florida Shelf, II NA ­ PROC.3rd INT'L.CORAL REEF SYMP., Shinn, E., IISpur-and-Groove Formation TURE, (1979) 278, 281-282. (1977) 2, 215. on the Florida Reef Tract, II JOUR.

SED. PET. I (1963) 33, 291-303. COU rtenay , W. , Herrema, D., Thompson, Lighty, R. , Macintyre, I. & Stuckenrath, M., Azzinaro, W., and van Montfrans, "Replv" (a discussion),NATURE,(1979) J. , IIEcological Monitoring of Two Thomas, L., "Who's Killing the Cor­ 278, 670. ats ? ;" SPORT DIVER, (1979) 69-76. Beach Nourishment Projects in Broward County, Florida,lI SHORE & BEACH, Macintyre,l. & Milliman,J.,llphysiogra­ (1972) 40, 2, 8-13. Vaughan, T., PROC. NAT'L. ACAD. phic Features on the Outer Shelf and SCI. USA, (1916) 2, 95-100. Upper Slope, Atlantic Continental Mar­ Curray, liThe Quaternary of the US; gin, SE US,II GSA BULLETIN, (1970) Vaughan, T., "The Temperature of the In NW Gulf of Mexico,/l PRINCETON 81, 2577-2598. UN I V. PRESS, (1965) 723. Florida Coral Reef Tract,lI CARNEGIE INSTITUTE OF WASHINGTON, (1918) Marshall,S. & Orr, A., "Sedimentation 213, 321-339. Duane,D. & Meisburger, E., "Gecrnor> of Low I sles Reef and its Relation to phology & Sediments of the Nearshore Coral Growth, Ex­ Wells, J., IINew and Old Scleractinian Continental Shelf, Palm Beach to Mi­ peditiori ;" SCI. REP. BRIT.MUS. (NH) Coral s from Jamaica, II MA R IN E SC I­ ami, II CERC TM, (1969) 29. (1931) I, 5, 94-133. ENe E I (1973) 23 I 1, 16-58.

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