ANTECEDENT TOPOGRAPHY AND LOCAL GEOLOGIC AND PHYSICAL PROCESSES CONTRIBUTE TO A UNIQUE ESTUARINE HARDBOTTOM COMMUNITY: TAMPA BAY, FL

Tampa Bay is a shallow, well-mixed, subtropical estuary located on the west-central Florida coast, and is the site of a unique hardbottom benthic community. Diver transects and a grid of 13 trackline km of CHIRP subbottom profiler data have been used to map this ~ 3 km square feature. The morphology of the substrate varies from low relief (< 0.5 m ) ledges to loose gravel-size rubble to fused pavement. The hard substrate is dominated by several subtropical species of algae, hard and soft corals, and sponges. Several geologic factors contribute to the location and diversity of the associated biological community. Previous seismic studies have identified near surface reflectors representing limestones underlying this area that dip northwestward beneath the bay. This limestone represent the only antecedent topographic high found in the bay. The shallow subsurface stratigraphy, as imaged with CHIRP, intersects and/or lies just below (< 0.5m) the seafloor as strong undulating, discontinuous reflections which correlate with hardbottom locations and ledges. Sediment input processes are ineffective, making this area sediment-starved. Biogenic sediments and bioerosion contribute to the patch sediment cover. The benthic community is much closer in composition to those found offshore under open marine conditions than elsewhere in the bay, suggesting potential recruitment from offshore populations. Regional geology (antecedent topography), local geologic processes (sediment starvation), and physical processes (recruitment via tidal currents) thus combine to create conditions conducive to this unique estuarine feature.