Thiago B.S. Correa

Habitat Characterization, Distribution, and Areal Extent of Deep-sea Coral Ecosystems off Florida, Southeastern U.S.A.

Abstract. The deep-sea (200–1000 m) seafloor off the southeastern U.S. has a variety of extensive deep-sea coral ecosystem (DSCE) habitats including: deep-water coral mounds; various hard-bottom habitats off Florida including the Miami Terrace, Pourtalès Terrace, and deep-water canyons (Agassiz and Tortugas Valleys); and deep island slopes off western Bahamas and northern Cuba. The dominant structure-forming scleractinian corals are Lophelia pertusa and Enallopsammia profunda; other structure-forming taxa include stylasterid corals, gorgonians, black corals, and sponges. This biota is associated with hard-bottom seafloor of variable high-relief topography which can be remotely identified from bathymetric data. NOAA bathymetric contour maps and digital elevation models were used to identify and delineate the areal extent of potential DSCE habitat in the region from northeastern Florida through the Straits of Florida. These were ground-truthed with 241 dives with submersibles and remotely operated vehicles which confirmed deep-sea coral habitat. We estimate a total of 39,910 km2 of DSCE habitat in this region. By comparison, the estimated areal extent of shallow-water coral habitat for all U.S. waters is 36,813 km2. Bottom trawling remains the greatest threat to DSCEs worldwide, and as a result NOAA has established five deep-water Coral Habitat Areas of Particular Concern (CHAPCs), encompassing 62,714 km2 from North Carolina to south Florida, which will protect much of the known deep-sea coral habitat in this region. High-resolution surveys are not only critical to define DSCE habitats but also to define areas devoid of coral and sponge habitats that may allow for potential bottom fisheries and energy development.

Deep Acoustic Applications

Because cold-water coral ecosystems exist at relatively inaccessible depths of 500–1,000 m, only a limited number of accurate maps have been produced for this resource. This chapter describes a combined acoustic survey approach used to acquire high-spatial resolution (up to 0.5 m) maps from two cold-water coral sites in the Straits of Florida. The approach consists of reconnaissance surveys using hull-mounted multi-beam systems, followed by deployment of multi-beam and side-scan sonar systems on an autonomous underwater vehicle (AUV). The wide swath of the reconnaissance survey tools permitted coverage of large areas, producing coarse (20 and 50 m) resolution maps that identified coral-building mounds larger than 2,600 m2. Areas of interest identified using the reconnaissance tools were then surveyed with the AUV platform, which resolved cold-water coral fields at 0.5–3 m resolution. The AUV maps detected mounds as small as 81 m2 and revealed fine-scale coral ridges up to 20 m high that were not resolved by the reconnaissance maps. The AUV maps, and other remotely acquired data, were ground-truthed with submersible dives to produce an integrated, geo-referenced dataset. Spatial and quantitative analyses were applied to this dataset in order to characterize the morphology and distribution of coral-building features in each surveyed site. In the Miami Terrace site, where corals build low-relief ridges, a habitat classification map and spatial analyses show that coral patches preferentially grow on and along the northern sides of the ridges. A southward flowing bottom current, measured by the AUV, dictates the observed asymmetrical coral distribution. In the site on the lower slope of Great Bahama Bank, where corals form individual mounds, morphometric analyses show a lack of correlation between bottom current regime and mound morphology. Results from these analyses indicate that the two cold-water coral sites in the Straits of Florida are highly variable in terms of coral distribution, spatial parameters, and current regime. Given its high-resolution, the approach presented here is ideal for determining the biophysical processes that underlie these and other remote, fragile ecosystems. Assessment and monitoring of coral distribution and mound abundance based on geophysical data is crucial for managing cold-water coral habitats and is an important research priority.