Theses and Dissertations

Defense Date

7-2015

Document Type

Thesis

Degree Name

M.S. Marine Biology

Second Degree Name

M.S. Coastal Zone Management

Department

Oceanographic Center

First Advisor

Brian Walker

Second Advisor

David Gilliam

Third Advisor

Charles Messing

Abstract

The Florida Reef Tract (FRT) extends from the tropical Caribbean northward along the Florida coast into a warm temperate environment where tropical reef communities diminish with increasing latitude. This study was designed to map the nearshore benthic habitats including coral reefs and evaluate how the benthic communities differ between habitats and along the coast.

Benthic communities across the northern FRT from Key Biscayne to Hillsboro Inlet (25.5°-26.3° N) were digitized from aerial photography taken in 2013 at a 1:1,000 scale. Three main hard-bottom habitat types were identified that ran parallel to shore and consecutively further away from shore: Colonized Pavement, Ridge, and Inner Reef. Five 1-km wide cross-shelf corridors (numbered 1-5, south to north) were designated and spaced as evenly as possible throughout the region. Five sites per habitat per corridor (70 total) were randomly selected and quantitative data collected within 4,200 m2.

Significant differences in percent benthic cover among habitats were found in all corridors and within habitat types between corridors, indicating cross-shelf and latitudinal variation. Mean stony coral density increased with depth, with the Inner Reef habitat being significantly higher than both the Colonized Pavement and Ridge. Mean stony coral species richness also increased with depth, with all habitats significantly different from one another. A total of 22 stony coral species were identified within the mapped region, the three most abundant being Porites astreoides, Siderastrea siderea, and Acropora cervicornis.

Results from this study support the ecosystem regions denoted in the Walker (2012) study. Corridor 1, located in the Biscayne Region, was the only corridor to contain any seagrass. In addition, Corridor 1 Inner Reef had significantly higher values for mean stony coral density, mean stony coral species richness, mean gorgonian density of the plume morphotype, and mean density of stony corals infected with Cliona spp. Corridors 2-4, located in the Broward-Miami Region, had some variability associated with them, but were generally similar in benthic composition. Corridor 5, likewise located in the Broward-Miami Region but in close proximity to the Deerfield Region, also had differences associated with it. Both the Colonized Pavement and Ridge habitats in Corridor 5 had the lowest mean coral species richness, as well as total absence of both sponge species noted in this study. Corridor 5 Inner Reef also had significantly lower mean stony coral densities compared to Corridors 1, 2, and 4. As such, these results support the idea of different biogeographic regions occurring off the southeastern Florida coast.

This study produced two key findings. It discovered over 110 large (>2 m) resilient coral colonies, of which 50 were alive in various conditions. This study also found 38 acres of dense Acropora cervicornis patches, tripling the previously known area within the study region. These are the largest dense patches in the continental United States.

Comments

This study was funded under the SEFL Nearshore Mapping Report, provided in part by a Coastal Services Center grant from the U.S. Department of Commerce, National Oceanic and Atmospheric Administration (NOAA) National Ocean Service Award No. NA11N0S4820003, and by the Department, through its Office of Coastal and Aquatic Managed Areas.

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