DEPTH TRENDS IN MICROENDOLITH COMMUNITIES OVER TIME IN BIVALVE SHELLS DEPLOYED OFF THE COAST OF LEE STOCKING ISLAND, BAHAMAS

In marine carbonates it has been found that community structures of endolithic microbial organisms vary predictably with environmental conditions, such as light availability. Therefore, ichnofacies produced by microendoliths may provide a signature of environmental conditions during the life and fossilization of marine host species. The goal of this project was to quantify endolithic populations in bivalve shells that have been placed at different depths off the coast of Lee Stocking Island, Bahamas, and retrieved after two and six years. Shells were imbedded in epoxy under vacuum to ensure microboring traces were filled. In order to view boring traces under a scanning electron microscope, shells were dissolved to reveal boring reliefs. Shells were then examined in map view to identify morphospecies and calculate percent cover by endoliths.

Results show that shallower waters are dominated by autotrophs such as cyanobacteria and chlorophytes and deeper waters are dominated by heterotrophs such as fungi. In samples placed below 73m, heterotroph surface cover appears to increase between two and six years. On an organism level, two and six year samples show distinct community populations at all depths. However, more data are needed to confirm signatures for these communities. Based on preliminary data for percent endolith cover, no trends stand out between two and six years, however, trends were observed within each retrieval year. In samples recovered after two years, endolith density appears to decrease with water depth until 215m. Surprisingly, at 265m endoliths cover a much greater surface area in some samples. In samples recovered after six years, endolith density follows a shows a more predictable decrease with depth through 265m.

These findings indicate that microendolithic community structure in bivalve shells can vary with depth and time, depending on the shell’s environment. It should be noted that the sample size is small and each shell may experience a different microenvironment on the sea floor. More work is necessary to understand these variations and delineate a signature for different depth and time exposures.