Graduation Year

2008

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Marine Science

Major Professor

Pamela Hallock Muller, Ph.D.

Committee Member

Benjamin Flower, Ph.D.

Committee Member

Elizabeth Fisher Moses, Ph.D.

Keywords

Florida Keys, bioindicators, Amphistegina, distribution, assemblage

Abstract

Studies of larger symbiont-bearing foraminifers on reefs have revealed their potential as indicators of environmental stress because of their physiological analogies to corals (dependence on algal symbionts for growth and calcification) and relatively short life cycle (a few months to 2 years or more). The purpose of this study is to report distribution patterns and population densities of larger benthic foraminifers (LBF) of the Florida reef tract, specifically reporting abundance data collected from offshore (1995-2000, 2006, 2007) and patch reefs (1996, 2006, 2007).

Six years of quarterly data collected from two offshore reefs, Conch (10, 18 and 30m) and Tennessee (8 and 20m), revealed that LBF assemblages primarily varied with habitat depth, in turn reflecting available light and water motion.These assemblages were dominated by Amphistegina gibbosa d'Orbigny and Laevipeneroplis proteus d'Orbigny, which tended to occur together, making up ~40-50% of the assemblages and up to 80% at the Tennessee 20m site. Both overall abundance and evenness of the LBF assemblage structure exhibited the greatest variability at shallower depths. Evenness was inversely related to densities of A. gibbosa, which were typically higher at depth keeping evenness below 0.5.

Across the Keys, region (location along the reef tract), reef type (offshore shallow, deep or patch reefs) and symbiont type strongly influenced LBF assemblage dynamics. Upper Keys sites shared the highest degree of inter-region similarity among assemblages (73%), while Biscayne National Park (BNP) and lower Keys sites had the lowest similarity (~60%). This likely reflects the greater variability of habitats found in the latter areas, mainly patch reefs.Chlorophyte-bearers were typically more abundant in shallower turbid waters, with diatom-bearers more abundant at depth. Additionally, I observed a significant two-fold decrease in the proportion of chlorophyte-bearers in the middle Keys likely due to light-limitation by turbid Florida Bay outflow.

Finally, data comparisons revealed an inverse relationship between LBF abundances and percent coral cover. Coral cover (2005) was staggeringly low on offshore reefs (5%), but was significantly higher on nearshore patch reefs (12%). Contrastingly, LBF species showed either no difference in abundance between reef types or a greater abundance on offshore reefs.

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