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Reef Morphology and Invertebrate Distribution at Continental Shelf Edge Reefs in the South Atlantic Bight
Sarah B. Fraser and George R. Sedberry

Southeastern Naturalist, Volume 7, Number 2 (2008): 191–206

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2008 SOUTHEASTERN NATURALIST 7(2):191–206 Reef Morphology and Invertebrate Distribution at Continental Shelf Edge Reefs in the South Atlantic Bight Sarah B. Fraser1,2,* and George R. Sedberry3 Abstract - Video footage recorded from 14 submersible dives on the continental shelf edge was used to describe and categorize reef morphology and quantify density and number of morphotypes of large sponges and corals. Significant variation in number of morphotypes and density of three dominant species among temperature classes, depth classes, and reef morphology categories was tested using a multiple response permutation procedure. The greatest densities of Ircinia campana, Stichopathes sp., and Muricea pendula, and the largest numbers of morphotypes were found between 18.1 and 21.0 °C and at depths between 51.0 and 60.9 m. Among reef morphology types, those that contained unconsolidated sediments such as “sand” and “large boulders with sand” exhibited the lowest densities and richness of morphotypes, while “block-shaped boulders,” “buried block-shaped boulders,” and “low-relief bioeroded” reefs had the greatest densities and largest numbers of coral and sponge morphotypes. Rocky reefs along the shelf edge with rough texture, complexity, and relief provide favorable conditions for epibenthic invertebrates. The warming and stabilizing effect of the Gulf Stream along the continental shelf edge allows some sessile macrofauna to inhabit deeper waters and more northern latitudes. Introduction Rocky bottom formations are found throughout the South Atlantic Bight (SAB) between Cape Canaveral, FL and Cape Hatteras, NC among large expanses of sand (Miller and Richards 1980, Struhsaker 1969). Rocky outcrops and hard bottom reefs at the continental shelf edge are important habitats for sessile marine invertebrates and they are often densely encrusted with sponges, corals, tunicates, algae, hydroids, and bryozoans because they provide stable attachment surfaces (Barans and Henry 1984, Miller and Richards 1980, Struhsaker 1969, Van Dolah et al. 1994, Wenner et al. 1983). Variations in rock morphology and amount of relief (Barans and Henry 1984), as well as differences in density and diversity of epibenthic fauna (Wendt et al. 1985; Wenner et al. 1983, 1984), have been observed among hard bottom habitats of the shelf edge. However, the relationship between reef morphology and density and richness of sessile invertebrates has not been examined. The shelf edge is composed primarily of limestone, sandstone with calcareous cement, or carbonate sediments at depths of 45–110 m (MacIntyre and Milliman 1970, Parker 1986, Struhsaker 1969). Shelf-edge reefs vary from low-relief (<0.5 m) outcrops with rounded or gentle slopes to highrelief (2.0–15.0 m) scarps and ridges with steep walls (Barans and Henry 1Environmental Studies Program, College of Charleston, 66 George Street, Charleston, SC 29424. 2Current address - 11 Jett Court, Asheville, NC 28806. 3Gray’s Reef National Marine Sanctuary, 10 Ocean Science Circle, Savannah, GA 31411. *Corresponding author - sarahbfraser@gmail.com. 192 Southeastern Naturalist Vol.7, No. 2 1984). Temperature and salinity on the shelf edge remain relatively stable throughout the year due to infl uence from the Gulf Stream (Matthews and Pashuk 1986, Miller and Richards 1980, Struhsaker 1969). However, lateral meanders in the path of the Gulf Steam at specific locations allow cold upwellings and intrusions towards the coast (Atkinson and Targett 1983, Bane and Brooks 1979, Blanton et al. 1981, Mathews and Pashuk 1986, Menzel et al.1993). Hydrographic stability, warmth provided by the Gulf Stream, and hard substrate produce favorable conditions for tropical and subtropical species to permanently inhabit the continental shelf as far north as North Carolina (Cerame-Vivas and Gray 1966, MacIntyre and Pilkey 1969, Miller and Richards 1980, Struhsaker 1969, Wenner et al. 1983). Previous studies investigating hard bottom reefs within the SAB concentrated on general descriptions of habitats (Barans and Henry 1984), fish assemblages (Sedberry and Van Dolah 1984), fish spawning habitats and behavior (Sedberry et al. 2006), occurrence of invasive species (Meister et al. 2005), and ichthyoplankton assemblages (Powles and Stender 1976). Early studies of epibenthic invertebrates primarily focused on cataloging the number and type of species found (Cain 1972, Cerame-Vivas and Gray 1966, MacIntyre and Pilkey 1969, Pearse and Williams 1951). More recent work has described assemblages of SAB invertebrates in terms of depth, latitude, and seasonality (Wenner et al. 1983, 1984). Association with artificial reefs (Wendt et al. 1989) and evaluation of damage to sessile biota from trawling (Van Dolah et al. 1987) have also been investigated. This research project describes reef habitat and assesses density and richness of sessile megafauna in relation to reef morphology. Large sessile invertebrates include sponges and corals, which anchor to the sea fl oor substrate as larvae. As they grow, these organisms contribute to reef complexity and support a variety of other invertebrate and fish species. Methods Field site description Hard bottom reef sites were selected for sampling based on known areas of shelf-edge reef (Barans and Henry 1984, Wenner et. al. 1984, Van Dolah et al. 1994), the occurrence of reef fish species (Miller and Richards 1980, Sedberry and Van Dolah 1984, Sedberry et al. 2006), and historical data on snappers (Family Lutjanidae) and groupers (Family Serranidae) obtained by the Marine Resources Monitoring, Assessment, and Prediction (MARMAP) program, a fishery-independent monitoring survey conducted in the SAB by the South Carolina Department of Natural Resources (SCDNR) since 1973. Sites were located along the shelf edge between north Florida and northern South Carolina (Fig. 1). Dive locations were accessed by the R/V Seward Johnson II and the Clelia submersible during 2001, and the R/V Seward Johnson and Johnson Sea Link II (JSL II) submersible during 2002 and 2003. In 2001, three dives were conducted on the Savannah Scarp, a shelf-edge reef east of Savannah, GA (Fig. 1). In 2002, eight dives were made at five shelf-edge locations: St. Augustine Scarp, Jacksonville Scarp, Julians Ridge, Scamp Ridge, and Georgetown Hole (Fig. 1). In 2003, two dives were made, one each at Tattler Town and Razorback (Fig. 1). 2008 S.B. Fraser and G.R. Sedberry 193 Field methods The Clelia and JSL II submersibles were equipped with a SeaBird Electronics (SBE) 25 Sealogger CTD to record environmental variables, and a video camera with two fixed distance lasers for measurements of fish length. Depth, temperature, salinity, and the laser points were visible on the videotape. The submersible conducted four-minute transects along the length of the main reef at a distance of 1–2 m off the bottom. Transect width was Figure 1. Location of submersible dive sites 2001–2003 on the continental shelf between north Florida and northern South Carolina. Dives were conducted by Johnson Sea Link II and Clelia submersibles. 194 Southeastern Naturalist Vol.7, No. 2 approximately 7 m, and average transect length was 76.7 m. Location fixes of the submersible’s position were taken using the ship’s ORE Trackpoint II system. Currents and bottom topography caused variations in submersible speed and altitude. During each transect, the video camera mounted on the sub was zoomed out to the furthest extent and pointed down towards the seafl oor at approximately a 45-degree angle. The video camera recorded visual observations and audio notes onto mini digital video (DV) tapes. Analysis of videotapes Some transects were excluded from analysis because of poor video quality or changes in camera zoom during the transect. Examination of invertebrate fauna was limited to large, erect sponges and corals because it was not possible to accurately distinguish other organisms and quantify them from the videotape. Encrusting sponges were not included. Large sponges and corals were identified to the lowest possible taxon based on known species distributions, assistance from marine invertebrate experts, and published identification guides (Hooper and van Soest 2002, Smith 1971, Veron 2000). Some organisms seen on videotape could be compared to reference material collected by the submersible during the dives. Without specimens for microscopic examination, it was impossible to make accurate identification to the species level of many sponges and corals. Therefore, morphotypes were counted, and each assigned a unique identification code (sequential number) with a description of the external morphological characteristics used to differentiate it from others. This unique identification code, along with descriptions and potential classifications, were useful for making richness estimates. Species richness is a measure of diversity, and richness of morphotypes in this study is presumably a refl ection of species richness (Kikkawa 1986). Using a Sony DV Recorder, each transect was viewed three times on a 14-inch fl at-screen color monitor. A count was made of large sponge and coral morphotypes. Each transect was again reviewed and assigned a reef morphology category based on size and shape of rocks, amount of bioerosion, presence of sand or crevices, and occurrence of holes in the reef. When transects crossed multiple morphology categories, each category type was noted; however, these transects were not used for statistical analyses. Eleven reef morphology categories describe transect morphology and habitat in this study (Table 1). Transects were also grouped into the following relief and sediment categories: high relief (>2 m) = “block-shaped boulders” and “high-relief bioerosion;” moderate relief (1–2 m) = “buried block-shaped boulders,” “bioeroded rocky fl at,” “large boulders with sand,” and “moderate-relief bioerosion;” low-relief (<1 m) = “slab pavement,” “buried rocky fl at,” “sand with scattered rocks,” “low-relief bioerosion,” and “sand;” high sediment = “sand,” “sand with scattered rocks,” “buried rocky fl at,” and “large boulders with sand;” moderate sediment = “buried block-shaped boulders,” “bioeroded rocky fl at,” “moderate relief bioerosion,” and “low-relief bioerosion;” and low sediment = “block-shaped boulders,” “slab pavement,” and “high-relief bioerosion.” Total numbers of organisms were compiled and graphed for each relief and sediment grouping. 2008 S.B. Fraser and G.R. Sedberry 195 Table 1. Reef morphology categories describing transect habitat. Relief categories: High relief = >2 m, moderate relief = 1–2 m, and low relief = <1 m. Reef morphology Dive location Description Relief Sediment Block-shaped boulders (BSB) St. Augustine Scarp Large square boulders with fl at edges along a continuous reef ridge High Low Buried-block shaped boulders (BBB) Jacksonville Scarp Continuous reef ridge, fl at on top with partially buried square shaped Moderate Moderate boulders Slab pavement (SP) Jacksonville Scarp Large slabs of fl at rock with narrow fractures filled with sand Low Low Large boulders with sand (LBS) Razorback Large boulders mixed with patches of sand, some boulders partially Moderate High buried Bioeroded rocky fl at (BiRF) Savannah Scarp Hard bottom, low relief rubble, and rocky pavement. Rocks appear Moderate Moderate pitted and eroded Buried rocky fl at (BuRF) Savannah Scarp Similar to Bioeroded rocky fl at, but with sand partially covering the Low High hard bottom High relief bioeroded (HRB) Julians Ridge and Complex reef heavily pitted with crevices, holes, overhangs, and High Low Scamp Ridge rock ledges (>2m) Moderate relief bioeroded (MRB) Julians Ridge and Rough texture with depressions and small crevices (1–2m) Moderate Moderate Scamp Ridge Low relief bioeroded (LRB) Georgetown Hole Low mounds of exposed bioeroded hard bottom with moderate sand Low Moderate and Julians Ridge and sediment (<1m) Sand with scattered rocks (SSR) Tattler Town Flat expanses of coarse sand with widely scattered rocks Low High Sand (S) Tattler Town, Savannah Coarse unconsolidated sediment with no visible rock Low High Scarp, Razorback 196 Southeastern Naturalist Vol.7, No. 2 Submersible tracks and fixes were plotted in ArcView v 3.2 (ESRI, Redlands, CA), and transect lengths were estimated by measuring the distance between each transect start and end point. Width of the visible transect field was estimated at a random point within each transect using the 25-cm distance between lasers for measurement. Temperature, depth, and salinity were recorded from the on-screen data logger display, and mean values for these variables were calculated for each transect. Statistical analysis Ircinia campana Nardo (stinking vase sponge), Stichopathes sp. (whip coral), and Muricea pendula Verrill (pinnate spiny sea fan) were chosen to determine whether significant differences in species densities existed among temperatures, depths, or reef morphology categories. These organisms were selected because they were identified with confidence, were found throughout many of the dive locations, and typically had high abundances within most transects at each dive location. Density data were tested for normality in JMP v 5.0 (SAS Institute Inc., Cary, NC) by applying a Shapiro-Wilks goodness-of-fit test (p ≥ 0.05). This test revealed that the data were not normally distributed. Both log and square root transformations were attempted, but failed to normalize the data, so a non-parametric multiple response permutation procedure (MRPP) was used to evaluate significance. The MRPP reports an overall p value to evaluate significant difference, and an agreement statistic, A, that describes within-group homogeneity compared to random expectation. In addition, the test provides pairwise comparisons that allow assessments between groups. All MRPP significance tests were conducted at the 0.05 significance level using PC-Ord v. 5.0 (MJM Software, Glen Eden Beach, OR). Sorensen (Bray-Curtis) distances were employed as the distance metric. Water temperatures ranged from 13.7–22.6 °C and were divided into four classes: 12.1–15.0 °C, 15.1–18.0 °C, 18.1–21.0 °C, and 21.1–24.0 °C. Similarly, depth ranged from 44.5–78.3 m and was divided into four classes: 41.0–50.9 m, 51.0–60.9 m, 61.0–70.9 m, and 71.0–80.9 m. Median densities for I. campana, Stichopathes sp., and. M. pendula were calculated for each temperature class, depth class, and reef morphology category. The median was selected over the mean as the best measure of the center of the data because of the large number of zero values in the data set. Significant differences in median densities for I. campana, Stichopathes sp., and M. pendula were tested using a MRPP. Richness of sponge and coral morphotypes and mean numbers of morphotypes were evaluated within each transect by each temperature class, depth class, and reef morphology category in terms of number of morphotypes observed. Significant variation among morphotypes was tested in Minitab v. 13.0 (Minitab Inc., State College, PA) using a non-parametric Kruskal-Wallis analysis of variance on ranks. Results A total of 143 transects from 14 submersible dives at eight different locations were analyzed. Approximately 29,500 m2 were surveyed with a 2008 S.B. Fraser and G.R. Sedberry 197 mean transect area of 225 m2. Transects conducted at Scamp Ridge covered the largest area, 6790 m2, while only 1308 m2 were surveyed at Georgetown Hole (Fig 1.). A total of 8241 organisms from 32 different morphotypes were counted in this study. The largest numbers of organisms (4590) were recorded at St. Augustine Scarp, the most southerly site, while the lowest numbers of organisms (17) were observed at Tattler Town. While only 10 of the morphotypes represented were corals, they accounted for 6224 individuals, while the remaining 22 morphotypes were identified as sponges and totaled 1989 individuals. I. campana, Stichopathes sp., M. pendula, and “sponge morph 4” accounted for 91.2% of all individuals counted. Reef morphology Most transects (104) covered only one of the 11 reef morphology categories. Video clips of examples of each reef morphology can be viewed at http://www.csc.noaa.gov/seageofish/. Total area observed on those transects was approximately 21,000 m2. The remaining 39 transects crossed multiple habitat types and were therefore eliminated from statistical analysis comparing biota among reef morphology categories. The largest number of transects were categorized as “low-relief bioeroded” habitat, and the fewest were classified as “large boulders with sand.” St. Augustine Scarp and Jacksonville Scarp had a well-defined ridge with a noticeable drop-off, while the reefs at the more northern dive sites appeared less distinct. When reef morphology categories were grouped by amount of relief and sediment, those transects characterized by large vertical relief (>2 m) and low amounts of sediment had the greatest numbers of sessile invertebrates (Fig. 2). Density Ircinia campana and Stichopathes sp. were not found at temperatures colder than 15.0 °C or at depths greater than 70.0 m, while M. pendula was found in all temperature and depth classes. The greatest densities of I. campana and Stichopathes sp. were found at temperatures within the 18.1–21.0 °C class, while M. pendula densities were greatest within 21.1–24.0 °C (Figs. 3, 4, 5). All three organisms had the greatest densities within the 51.0–60.9 m depth class (Figs. 3, 4, 5). Significant differences in densities of I. campana, M. pendula, and Stichopathes sp. were found among all temperature classes (A = 0.246, p = 0 .000), and among all depth classes (A = 0.449, p = 0.000). The greatest densities of I. campana and Stichopathes sp. were found within reef morphology categories with moderate to high relief, and moderate to low sediment (“buried block-shaped boulders” and “block-shaped boulders”) at St. Augustine Scarp (Fig. 6). The largest densities of M. pendula were found on transects that crossed reef morphologies of low relief and moderate sediment (“low-relief bioerosion”) at Julians Ridge (Fig. 6). All three organisms were found in low densities or were absent from transects that crossed low-relief and high-sediment reef morphology categories such as “sand,” “sand with scattered rocks,” and “buried 198 Southeastern Naturalist Vol.7, No. 2 Figure 3. Mean density of I. campana, by temperature and depth. The four bar shades represent the four temperature categories. Figure 2. Number of organisms by relief and sediment classes. High relief (>2 m): block-shaped boulders and high-relief bioerosion; moderate relief (1–2 m): buried block-shaped boulders, bioeroded rocky fl at, large boulders with sand, and moderate- relief bioerosion; and low-relief (<1 m): slab pavement, buried rocky fl at, sand with scattered rocks, low relief bioerosion, and sand. High Sediment: sand, sand with scattered rocks, buried rocky fl at, and large boulders with sand; moderate sediment: buried block-shaped boulders, bioeroded rocky fl at, moderate relief bioerosion, and low relief bioerosion; and low sediment: block-shaped boulders, slab pavement, and high relief bioerosion. See Table 1 for summary of reef morphology categories. 2008 S.B. Fraser and G.R. Sedberry 199 rocky flat” (Fig. 6). No I. campana or Stichopathes sp. and few M. pendula were found at the Tattler Town dive site. MRPP tests indicated significant differences in species densities among reef morphology categories (A = 0.999, p = 0.000). However, pairwise comparisons revealed that densities between the “sand with scattered rocks” and “large boulders with sand” and between the “moderate” and “high-relief bioeroded” reef morphology categories were not significantly different. Figure 4. Mean density of Stichopathes sp. by temperature and depth. The four bar shades represent the four temperature categories. Figure 5. Mean density of M. pendula by temperature and depth. The four bar shades represent the four temperature categories. 200 Southeastern Naturalist Vol.7, No. 2 Richness Among temperature classes, the number of morphotypes was lowest within 15.1–18.0 °C and highest within 18.1–21.0 °C (Fig. 7). The number of morphotypes was also highest within the 51.0–60.9 m depth classes and lowest within the 71.0–80.9 m depth class (Fig. 7). The greatest number of morphotypes was found on “low-relief bioeroded” reef morphology and the fewest on “sand” (Fig. 8). Significant differences in mean numbers of morphotypes were Figure 6. Mean density of I. campana, Stichopathes sp., and M. pendula by reef morphology category. See Table 1 for summary of reef morphology categories and abbreviations. Figure 7. Number of morphotypes by temperature and depth. 2008 S.B. Fraser and G.R. Sedberry 201 found among temperature classes (σ = 1.794, p = 0.000), depth classes (σ = 1.756, p = 0.001), and reef morphology categories (σ = 1.925, p = 0.000). Discussion Each dive location site was nearly distinct from all others in its reef morphology. “Block-shaped boulders” were found only at St. Augustine Scarp, “buried block-shaped boulders” and “slab pavement” only at Jacksonville Scarp, and “bioeroded rocky fl at” and “buried rocky fl at” only at Savannah Scarp. “Large boulders with sand” were found only at Razorback, and “sand with scattered rocks” occurred only at Tattler Town. “High-relief” and “moderate- relief bioerosion” were both found at Julians Ridge and Scamp Ridge, and “low-relief bioerosion” was found at Julians Ridge and Georgetown Hole. Generally, the southern dive sites had the most well-defined ledge or ridge features, while reefs north of Florida exhibited less distinct forms. Bioerosion refers to the mechanical and chemical activity of algae, sponges, polychaetes, mollusks, barnacles, fish, and other marine organisms that penetrate and break down the substrate (Wilkinson 1983). This process appears to be a significant force controlling reef morphology among continental shelf edge reefs within the SAB, with the more northern reefs off the coast of South Carolina exhibiting greater amounts of bioerosion than reefs off Florida and Georgia. The organisms responsible for the erosion could not be identified or quantified among sites, and the observed erosion may have been caused by communities that are no longer present on the reefs. High A values reported by the MRPP test refl ect strong within-group homgeneity and suggest that reef morphology categories are distinct from Figure 8. Number of morphotypes observed within each reef morphology category. See Table 1 for summary of reef morphology categories and abbreviations. 202 Southeastern Naturalist Vol.7, No. 2 one another. The p values for the pairwise comparisons clarify the exceptions. “Large boulders with sand” and “sand with scattered rock” could be lumped together, as could “moderate” and “high-relief bioeroded” reef morphology categories. “Low,” “moderate,” and “high-relief bioeroded” sites as well as “bioeroded rocky fl ats” and “block-shaped boulders” generally exhibited the greatest densities and diversity of large sessile invertebrates in this study, and had far greater densities than sandy habitats. Hard substrates such as these provide an environment more suitable for attachment than sandy sites (Barans and Henry 1984, Miller and Richards 1980, Powles and Barans 1980, Wenner et al. 1983). Near-bottom currents create migrating sand waves, scouring, and re-suspension of sediments that can bury fl at hard bottom or the organisms associated with that habitat. Relief of 2–3 m (such as found at some of these sites) offers protection from these types of disturbances. Other research has shown greatest densities and diversities of sessile invertebrates to be associated with hard surfaces, rough texture, and relief. Wenner et al. (1983) and Bright et al. (1984) noted greater diversity of epifaunal macro-invertebrate communities on rocky bottom than on soft, sandy seafl oors. Bell and Smith (2004) observed that diversity of sponges on an Indonesian reef was higher on vertical and inclined surfaces than horizontal planes. Goldberg (1973) described three terrace-like reefs off the coast of southeast Florida and noted that the terrace with the most vertical relief and rugged texture exhibited the greatest diversity and density of gorgonian and scleractinian corals. Erwin (1976) discovered at Strangford Lough in Northern Ireland that distribution of epifaunal and infaunal organisms was closely related to bottom type and water movement. Densities of I. campana, Stichopathes sp., and M. pendula were greatest within the 51.0–60.9 m depth class and at temperatures between 18.1 and 21.0 °C. The deepest (71.0–80.9 m) and coldest (12.1–15.0 °C) transects had relatively low abundances and diversities of sessile invertebrates. This finding may be explained by the fact that these transects were conducted over fl at sand and sand with scattered low-relief rock morphologies, providing relatively little suitable habitat for attachment and growth of sessile organisms. Previous sampling in the SAB (Cerame-Vivas and Gray 1966, Pearse and Williams 1951, Wenner et al. 1983) indicates I. campana and Stichopathes sp. are typically found at shallower and more southern sites. It is likely that the warming and stabilizing infl uence of the Gulf Stream along the continental shelf edge allows these organisms to exist in deeper waters and at more northern latitudes. Studies conducted at depths of 0–30 m have shown that richness, evenness, and density of sponges and coral in reef habitats often increase with depth up to 30 m as disturbance and temperature fl uctuations decrease and available space increases with light attenuation (Andres and Witman 1995, Bell and Barnes 2000, Dinesen 1983, Huston 1985, Liddell and Ohlhorst 1987, Schmal 1990). In the present study, the number of sponge and coral morphotypes increased with depth until 60.9 m. At greater depths, transects sampled mostly “sand” and “large boulders with sand,” habitats not suitable for attachment. 2008 S.B. Fraser and G.R. Sedberry 203 In recent years, recorded video footage has been used to investigate marine fauna and habitat. Observations made from video recordings provide the unique and complementary opportunity to note variation in bottom topography, texture, and behavior of fish and invertebrates in relation to bottom features. Video recordings made from submersibles offer several advantages over remotely operated underwater televisions and diver-held cameras. Submersibles can operate in deeper waters and for longer periods of time than divers, and are often equipped to accommodate sample collection. Finally, video footage recorded on these dives provides permanent documentation without destroying fauna and habitat (Parker 1986). One of the primary goals of recent submersible operations off the southeastern US coast has been to explore spawning locations of commercially or recreationally important reef fishes, such as our sampling sites (Sedberry et al. 2006). Declining catch per unit effort (CPUE) of several of these species indicates overfishing and collapsing populations, despite efforts to manage these fisheries (McGovern et al. 1998, Miller and Richards 1980, Sedberry 1988, Sedberry and Van Dolah 1984). Spawning locations on shelf edge reefs represent important habitat essential for fish life cycles. Large sponges and corals may be important components of these habitats because they enhance structural complexity of the environment and therefore contribute shelter and hiding places attractive to fishes (Van Dolah et al. 1987). Additionally, these large sessile organisms provide microhabitats for various smaller invertebrate species that may provide food for a variety of reef and pelagic fishes (McGovern et al. 1998, Miller and Richards 1980, Sedberry 1988, Sedberry and Van Dolah 1984, Weaver and Sedberry 2001). Results of this study suggest differences in relief, sediment, and density and diversity of invertebrate macrofauna on shelf edge reefs in the SAB. These factors may be important considerations in natural resource management Fishery management has recently shifted from single species management to an ecosystem approach. In response to this change, studies utilizing submersible video have included analyses of fish composition, density, and behavior (Schobernd 2005). The present study and others focused on lower food-web components and abiotic elements help provide a more ecosystemwide understanding. Implementation of ecosystem-based fishery management relies on evaluation of biodiversity, genetic variability, and ecological functionality (Lubchenco et al. 2003, Roberts et al. 2003). Management actions include development of marine protected areas (MPAs) to protect bottom habitat. Reefs along the continental shelf edge off the southeastern US are potential candidates for MPA designation (SAFMC 2004, Sedberry et al. 2006). Effective positioning of reserves will maximize protection of important species and habitat and, hopefully, serve as biotic sources for neighboring waters. Fish biomass and production are thought to be related to the presence of sessile invertebrates and reef morphology, but that remains to be demonstrated. Quantitative measurements of reef morphology, angle of the reef slope, position of the organisms on the reef, and fl ow regime could help explain distribution of sessile megafauna and fish because these variables infl uence current velocity, sedimentation rates, extent of benthic structure, and available 204 Southeastern Naturalist Vol.7, No. 2 light for benthic photosynthesis. For example, bioerosion rates may affect habitat relief and structure available for fish and benthic invertebrates. Verification of substratum age could explain differences in reef morphology and shed light on why the northern dive sites exhibited greater amounts of bioerosion and less relief. Acknowledgments This research was funded by NOAA Ocean Exploration grants NA16RP2697, NA03OAR4600097, and NA0ROAR4600055, G.R. Sedberry, Principal Investigator. We thank Leslie Sautter, Rick DeVoe, Cass Runyon, Christina Schobernd, Matt Fraser, and Dana Griffin for constructive criticism and advice; Jessica Stephens for database assistance; Susan Thornton-DeVictor, David Knott, Stacie Crowe, and Cara Fiore for invertebrate identification; Josh Loefer, Tim Snoots, and Karen Swanson for technical help; and Martin Jones and Jodi Slapcinsky for statistical advice. Literature Cited Andres, N.G., and J.D. Witman. 1995. Trends in community structure on a Jamaican reef. Marine Ecology Progress Series 118:305–310. Atkinson, L.P., and T.E. Targett. 1983. Upwelling along the 60-m isobath from Cape Canaveral to Cape Hatteras and its relationship to fish distribution. Deep-Sea Research 30:221–226. Bane, J.M., and D.A. Brooks. 1979. Gulf Stream meanders along the continental margin from the Florida Straits to Cape Hatteras. Geophysical Research Letters 6: 280–282. Barans, C.A., and V.J. Henry, Jr. 1984. 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