Unique Deep-Water Ecosystems Unique Deep-Water Ecosystems
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or collective redistirbution of any portion of this article by photocopy machine, reposting, or other means is permitted only with the approval of The Oceanography Society. Send all correspondence to: [email protected] ofor Th e The to: [email protected] Oceanography approval Oceanography correspondence all portionthe Send Society. ofwith any permitted articleonly photocopy by Society, is of machine, reposting, this means or collective or other redistirbution This article has This been published in S P E C I A L Iss U E O N O C E A N E XPL O RATI on Oceanography Unique journal of The 20, NumberOceanography 4, a quarterly Society. , Volume Deep-Water Ecosystems OFF THE SOUTHEASTERN UNITED STATES B Y S T E V E W. Ross C opyright 2007 by The 2007 by opyright Oceanography Society. If nothing else, research in deep-sea envi- has increased significantly, resulting in exploration, mining). ronments teaches us how little we know three international symposia (a fourth Our research team began studies on about such important and productive is planned for 2008), a variety of review continental slope habitats in the early habitats. The relatively recent discov- papers (Gass, 2003; Hain and Corcoran, 1990s, concentrating on an unusual can- ery of hydrothermal-vent and cold-seep 2004; Morgan et al., 2006; Roberts et al., yon system on the Hatteras middle slope ecosystems illustrates this paucity of 2006; Lumsden et al., 2007), and numer- (locally known as “The Point;” Figure 1). knowledge, and the subsequent explo- ous other publications. Likewise, during Driven by interest in oil exploration, A sion of research on these systems is a the last seven years, deep-reef research this relatively small, biologically and ll rights reserved. good example of the impact such con- has also steadily expanded on the south- physically unique area became one of the centrated efforts can have on marine sci- eastern US (SEUS) slope, where deep-sea most studied portions of the US conti- ences (see the March 2007 special issue of corals are common (see review in Ross nental slope (Diaz et al., 1994; Ross et al., P ermission is granted to copy this article for use in teaching and research. article use for research. and this copy in teaching to granted is ermission Oceanography on InterRidge, and Levin and Nizinski, 2007). Some revelations 2001; Bauer et al., 2002). Continuing our et al., 2007). The recent surge of interest from these efforts are that: (1) deep-sea research at The Point (Sulak and Ross, in deep-sea corals is another example corals are widespread on continental 1996), in 1999 we began a whole-water- of how focused research on a particular margins and seamounts at all latitudes column trophodynamics study and even- subject can result in new perspectives and in all oceans, (2) they and other tually added deep-coral Lophelia pertusa on continental slope biotopes. Although structures support significant, impor- banks and shelf-edge hardground reefs deep-sea corals have been known for over tant, but poorly documented deep-sea off central North Carolina for commu- 200 years, they were viewed as somewhat centers of biodiversity, (3) the overall nity structure comparisons (Figure 1). of a novelty, and research on them was area of deep-sea corals probably exceeds Ultimately, we added other deep-coral P sporadic, typically geologic, and usually that of all known shallow-water, tropical study sites (Figure 1) to better represent O Box 1931, only documented their occurrences coral reefs, and (4) these ecosystems are the Blake Plateau (Cape Lookout to Cape (e.g., Stetson et al., 1962; Neumann et al., at risk from a variety of anthropogenic Canaveral). Because biological data were R ockville, MD 20849-1931, R epublication, systemmatic reproduction, reproduction, systemmatic epublication, 1977; Paull et al., 2000). activities that range from ocean acidifi- lacking from the deep-coral systems, our Over the last 10 years, worldwide cation (Guinotte et al., 2006) to the gen- initial objectives were to characterize research on deep-sea corals, sea- eral spread of exploitation activities into their fish communities. Study objectives mounts, and other deep-sea structures deeper waters (e.g., fishing, hydrocarbon were expanded to include examining U S A . 130 Oceanography Vol. 20, No. 4 Figure 1. Map: continental slope and shelf-edge reef (white boxes), deep- coral (red stars), and canyon (yellow dot) study sites of Ross et al. (1991– present) off the southeastern United States. Photos: example benthic habitats at these sites. The Point represents a muddy canyon environment with very rugged topography as illustrated in the SeaBeam image of the bottom (far left). The three animals are typical of that area, from top left to right: Phycis chesteri, Lycodes atlanticus, Ilex sp. The other study areas are all dominated by different types of hard substrata ranging from various types of rocks to hard and soft corals and sponges. Oceanography December 2007 131 fish distributions over the whole water the Gulf Stream facilitates the main- 1996; SEAMAP-SA, 2001). The Blake column, discovery and mapping of deep- tenance of a productive subtropical Plateau, a platform scoured and shaped coral and reef habitats, distributions and reef community on the outer shelf by the Gulf Stream (400–1250-m depths; ecology of benthic macroinvertebrates, (about 50–100-m depth) as far north Popenoe and Manheim, 2001), domi- population structure and taxonomy of as Cape Hatteras. nates the continental slope through corals and other dominant taxa using Although few sweeping generaliza- much of the SEUS (Schlee et al., 1979). Deep corals are common along the edges of the scarps and ridges and on the mounds in this region (Stetson et al., 1962; Pratt and Heezen, 1964). The During my first multibeam mapping cruise Charleston Bump, a dominant topo- off the SEUS, I learned more concerning the graphic structure of the Blake Plateau, deflects the Gulf Stream seaward and is distribution and topography of deep-coral heavily scoured by this current, exposing areas in about 30 hours of mapping than in the hard substrata (Popenoe and Manheim, previous six years using more standard methods. 2001). The western side of the Blake Plateau, particularly, has been heavily eroded by the Gulf Stream, exposing numerous depressions, Cretaceous to Miocene hard substrata, and mounds genetic techniques, and paleoecology tions apply, the continental shelf and (Uchupi, 1967). On the northeastern using black and bamboo corals as prox- slope of the SEUS do share some large- end of the Blake Plateau, the Blake Ridge ies for environmental data. scale physical characteristics. Both are contains extensive gas hydrate depos- This paper summarizes parts of our unusually broad, tapering at the north its and the only known methane seep deep-reef research on the slope of the and south ends, and both have high community in this area (Borowski et al., SEUS, emphasizing data from a vari- percentages of emergent hard substrata. 1997; van Dover et al., 2003). In contrast, ety of interdisciplinary projects. Other Overall, the SEUS shelf and slope repre- the study site on the Hatteras middle slope and continental shelf-edge habi- sent a carbonate sedimentary province, slope (The Point) is geologically more tats we have studied facilitate wide-area where inshore shelf sediments (with like other Middle Atlantic Bight habitats, comparisons across different habitats. higher quartz and shell-fragment con- and is composed of fine sediments and This review points to a need for further tent) have more terrigenous origins, and bisected by rugged canyons (canyons are research, especially into the mechanisms the amount of biogenic carbonate sedi- absent in the SEUS region). that regulate deep-sea slope communi- ment increases with increasing distance The Gulf Stream (or Florida Current) ties in this region. offshore (Gorsline, 1963; Pratt, 1968). is the dominant oceanographic feature The shelf and especially the shelf edge that shapes much of the geology and SETTING FOR DEEP-REEF (about 80–100-m depth) throughout HABITATS OFF THE SOUTH- this region are marked by numerous STEVE W. Ross ([email protected]) is EASTERN UNITED STATES topographic prominences (Macintyre Associate Research Professor, Center The marine waters of the SEUS have and Milliman, 1970; Avent et al., 1977; for Marine Science, University of North long been of scientific interest and are Thompson and Gilliland, 1980), and Carolina Wilmington (UNCW), North well known for economically valuable these hardground habitats of varying Carolina, USA, and is currently assigned marine resources. The shelf and slope profiles provide substrata for attachment (through the Intergovernmental Personnel waters of this region have a diversity of a well-developed, largely subtropical Act) to the US Geological Survey, of benthic habitats, and warming by reef fauna (including corals) (Riggs et al., Saint Petersburg, FL, USA. 132 Oceanography Vol. 20, No. 4 biology of the outer shelf and slope more complex around coral-mound or shape deep-coral mounds off North off the SEUS. This well-known system rocky features and accelerate through Carolina (Figure 2), but that conditions influences bottom conditions even at valleys and over the tops of mounds/ are different at the deeper Stetson area. continental slope depths by prevent- ridges. Recent multibeam sonar map- Bottom temperatures around SEUS ing shelf sediment delivery to offshore ping that I have conducted indicates deep-coral habitats (370–780 m) range areas, transporting sediments and biota that long-term current scouring helped from 5.4° to 12.3°C, and bottom salini- northward, and facilitating high cur- rent speeds (> 2.5 knots, 125 cm/s) on the bottom (Pratt, 1968; Popenoe and Manheim, 2001). The Gulf Stream mod- erates temperature (generally > 27°C) and salinity (generally > 36) over the outer shelf and slope. This complex current meanders (influenced in part by bottom topography) and produces eddies that spin away from the main cur- rent (Atkinson et al., 1985; Bane et al., 2001).