LARGER FORAMINIFERS OF THE FLORIDA REEF TRACT, USA: DISTRIBUTION PATTERNS ON REEF-RUBBLE HABITATS

Multi-year data sets for benthic populations of any taxa are particularly valuable in present conditions of rapid environmental change. This study examines distribution patterns and population densities of larger benthic foraminifers (LBF) from the Florida reef tract, specifically abundance data collected from reef rubble at offshore (1995-2000, 2006-07) and patch reefs (1996, 2000-02, 2006-07). Six years (1995-2000) of data collected quarterly from two offshore reefs, Conch (at 10, 18, and 30 m) and Tennessee (at 8 and 20 m), reveal that assemblages of LBF primarily vary with habitat depth, reflecting available light, and water motion. Assemblages are dominated by Amphistegina gibbosa and Laevipeneroplis proteus, which tend to occur together, typically making up at least 40-50% of the assemblages. Both overall abundance and evenness of the assemblages exhibit the greatest variability at shallower depths, where environmental conditions tend to be more variable. Interannual variability reveals the resilience of populations of LBF following mortality events caused by bleaching and hurricanes. Across the Keys, location along the reef tract, reef type (offshore-shallow [<10 m], offshore-deep ([10-30 m], or patch reefs [<10 m]), and symbiont type strongly influence assemblages of LBF. At upper Keys sites, assemblages share the highest degree of inter-reef similarity (73%), while Biscayne National Park (BNP) and lower Keys sites have the lowest inter-reef similarity (similar to 60%). This difference likely reflects greater variability of habitats found in the latter areas, especially BNP patch reefs. Foraminiferal taxa hosting chlorophytes are typically more abundant in shallow waters than at offshore-deep sites. Taxa hosting diatoms, primarily A. gibbosa, are always dominant at depths of 10-30 m.