ICES CM 2004/AA:05

Not to be cited without prior reference to the author

Macrofaunal structure and habitat utilization within deep coral bank communities on the southeastern United States slope

Martha S. Nizinski, Steve W. Ross, and Kenneth J. Sulak

Martha S. Nizinski: NOAA/NMFS National Systematics Laboratory, National Museum of Natural History, Washington, DC 20560-0153, USA [tel: +1 202 633 0671; fax +1 202 357 2986; email: [email protected]]. Steve W. Ross: Center for Marine Science, Univ. North Carolina-Wilmington, 5600 Marvin Moss Lane, Wilmington, NC 28409, USA [tel: +1 910 395 3905, email: [email protected]]. Kenneth J. Sulak: U.S. Geological Survey, Center for Aquatic Resource Studies, 7920 NW 71st Street, Gainesville, FL 32653, USA [tel: +1 352 264 3500, fax: +1 352 378 4956, email: [email protected]].

ABSTRACT

Deep coral banks, composed mostly of pertusa, occur in scattered patches off the southeastern US (350-700 m). Fish and invertebrate communities of these banks are poorly known. Also, the affinity of organisms for reef habitat in the deep sea is not well understood. From 2000-2004 we surveyed the macrofauna of deep coral banks off the Carolinas using a research submersible and bottom trawls. We documented community structure (composition, abundance, sizes, habitat utilization) of macrofauna on and near the coral habitat, and investigated to what extent the fauna is obligate to the reef. In particular how are organisms distributed within the reef structure (prime high reef, secondary low colonies, coral rubble zones)? Continental slope Lophelia coral banks off the southeastern US support a distinctive fish assemblage compared to non-coral habitats of similar depths. We have identified over 41 fish and approximately 20 invertebrate species on coral banks. Numerically dominant fish species observed on this habitat include Beryx decadactylus, Helicolenus dactylopterus, Laemonema melanurum, Hoplostethus occidentalis, Conger oceanicus, and L. barbatulum. Numerically dominate invertebrates include two ( picta, Rochinia crassa) and four echinoderms (Ophiacantha bidentata, Echinus gracilis, E. tylodes, ). Several fishes (Squalus asper, L. melanurum, H. occidentalis, S. meadi, and B. decadactylus) may be restricted to the coral habitat and should be considered primary reef fishes. The invertebrates, however, are common locally and may use the habitat more opportunistically. Further investigation will add species to this deep reef assemblage and help refine our hypothesis of primary reef associates versus opportunistic reef utilization.

Deep corals occur widely along the continental slope of the southeastern United States. They may be attached to hard substrates or they may form large banks or mounds. Comprised mostly of the ahermatypic coral, Lophelia pertusa, these reef-like formations are widespread in the western Atlantic, occurring not only on the Blake Plateau and in the Straits of Florida, but also in the Gulf of Mexico and off Nova Scotia. Although published data are lacking, this deep water coral habitat may be more important to western North Atlantic slope species than previously known. For example, some commercially important deep water fishes, such as the wreckfish (Polyprion americanus) and blackbelly rosefish (Helicolenus dactylopterus) congregate around Lophelia habitat. Additionally, various crabs and echinoderms are also abundant on these deep reefs. Thus, Lophelia reefs appear to be oases offering both shelter and food on the relatively barren plain of the Blake Plateau and other regions on the continental slope.

Deep coral reef systems are receiving increasing attention worldwide, yet data are lacking on basic biology and ecology of the fishes and megainvertebrates associated with these reefs. Although the identification of the associated species is of primary importance, our understanding these habitats requires information on the structure of the community as a whole. Only then we can begin to assess whether these deep reef communities are merely fortuitous assemblages of organisms in a specific location or tightly linked and structured groups of interacting species with obligate associations to the habitat. Several factors which we are investigating, including relative abundance, spatial distribution, species diversity, size structure within populations, and trophic complexity, provide the foundation for this type of analysis.

Our objectives, covered in this presentation, were to: (1) describe and characterize fish and invertebrate assemblages on and near coral banks, and (2) classify habitat for associated fish and invertebrate assemblages. Two general reef associated habitats, primary reef and transition-rubble zone, are compared and discussed.

During the last five years (2000-2004), our team has completed six summer cruises off the coast of the southeastern United States. Two basic sampling techniques were utilized for benthic organisms. The primary sampling method was a manned submersible with priority to make in situ observations, collect video footage, and collect specimens while maintaining the integrity of the habitat. Over this time period we completed 46 dives covering a depth range of 366 to 783 m between Cape Lookout, NC and Cape Canaveral, FL. The more detailed analysis presented here uses data collected during 23 submersible dives from 2000-2003. Otter trawls (15 tows) were used in locations away from (but close to) primary reef habitat to sample the fauna associated with rubble or transition zones near some of the North Carolina sites (374-488 m).

Comparisons between primary reef and transition-rubble zone fauna differed between fishes and invertebrates. For fishes, 30 species were observed or collected by submersible from primary reef, whereas 25 species were recorded from the transition- rubble zone. Of these species, 21 were found in both zones; however, the relative abundance of species varied between the zones. Four commonly occurring fish species were found exclusively in primary reef habitats. Five other species, previously thought to be rare, were closely associated with Lophelia reef habitat, also. Thus, these nine species of fishes appear to have an affinity for these coral habitats and could be indicative of a primary reef fauna much like that reported for shallow-water tropical reefs. No species of fishes were found exclusively in transition-rubble zone. This zone shared species between the primary reef and the adjacent sandy bottom habitats, and thus was transitional in both habitat complexity as well as faunal diversity. Conversely, fewer species of megainvertebrates (approximately 20 species identified to date) were conspicuously associated with primary reef habitat. The species that were represented, however, were relatively abundant. Additionally, there was significant overlap between the species associated with the primary reef and those associated with the transition- rubble zone. Two species of crustaceans, however, were collected exclusively in the transition-rubble zone and were not observed on the primary reef. Thus, the associated invertebrate fauna may use the reef habitat more opportunistically than some of the fishes. The trawl data produced 44 species of fishes and approximately 24 species of invertebrates, with the dominant species being largely the same as those observed by submersible over transitional habitat. This further reinforces the nature of the transition reef fauna, suggesting that submersible artifacts (e.g., lights and noise) did not strongly bias the data.

Our 2004 cruise provided the opportunity to explore Lophelia reefs over a larger geographic area (North Carolina to central Florida). Preliminary data indicate a faunal and habitat transition with latitude. In addition to changes in reef structure and morphology, relative abundance decreased, overall species diversity increased, and numerical dominance between species decreased with decreasing latitude (moving north to south).

In conclusion, the fauna associated with Lophelia reefs occurring off the coast of the southeastern United States is abundant and diverse. Deep reef fishes in this area appear to be behaving and using the habitat in a manner similar to that observed for shallow water reef fishes. Therefore, the habitat specific fish fauna should be regarded as primary reef fauna. Conversely, the associated invertebrate assemblage appears to be using the reef in a more opportunistic manner. Preliminary data indicate that the composition of the associated fauna varies with latitude, but other factors (e.g., currents, sediment loadings, depth) still need to be investigated. Although these other factors can be confounding, there does seem to be a faunal transition with latitude, suggesting multiple deep reef faunas. Caution, therefore, should be exercised when making broad generalizations regarding deep reef faunal characterizations. We intend to continue to explore deep reef habitats in this area with regard to potential structuring mechanisms.