Determination Of Different Benthic Reef Communities In Broward County, Florida (Usa) Using Acoustic Remote -Sensing and in Situ Techniques

Determination Of Different Benthic Reef Communities In Broward County, Florida (Usa) Using Acoustic Remote -Sensing and in Situ Techniques

Alvin Sherman Library 2053

Typical Caribbean reef communities of variable composition and density exist on four parallel ridges, at varying depths along the Broward County (FL, USA) coast. Two of these ridges, at 7-13m and 15-30m depth, are drowned early Holocene coral reefs of 5 ky and 7 ky uncorrected radiocarbon age, respectively. Previous work has shown that the reef communities overlying these reef-ridges can be detected and mapped using acoustic remote sensing and has suggested that different benthic assemblages may exist between each of the reef ridges. In this study, in situ community data was taken for each reef- ridge using traditional 50m line-intercept transects. These data were analyzed and clustered using multi-dimensional scaling (MDS) and compared with similarly clustered data obtained from an acoustic survey of the same area. The in situ community data show four distinct benthic communities, each corresponding to a single reef-ridge. This clustering agrees well with the acoustic data which, when using principle components analysis(PCA),similarlyshowauniquehabitattypeoneachofthefourreef-ridges. The reef-ridge community closest to shore (5-7m depth) showed 38% live cover, and was dominated by Alcyonaceans (15% total cover). The second reef-ridge (7-13m depth) was dominated equally by Macroalgae and ecrusting zooanthids, with each group representing 15% of the total cover. Total live cover on the second reef-ridge community was about 49%. The third reef-ridge community from shore (13-16m depth) had about 60% living cover and was dominated by Macroalgae, which accounted for 30% of total cover. On the fourth and deepest (15-30m) reef-ridge community, Alcyonaceans were the dominant fauna (20% total cover), however, sponges were nearly as abundant (14% total cover). Total living cover on the deepest reef-ridge community was 42%. Total Scleractinian cover was generally low on all reef ridges (4% mean cover for all reef-ridge communities), with the first reef-ridge having the highest total scleractinian cover (6%) and the second reef-ridge having the lowest (3% total cover). This total data set suggests a depth-dependant zonation pattern that does not occur across a single-reef ridge, but rather on a larger spatial scale across the entire reef-ridge system of Broward County.