EFFECTS OF METAZOAN GRAZING ON MODERN HYPERSALINE LAKE MICROBIALITE MORPHOLOGY USING BULK SAMPLING AND PHOTOGRAMMETRY, STORR’S LAKE, SAN SALVADOR ISLAND, THE BAHAMAS

Identifying the effects of active grazing on microbialite morphology is paramount to understanding microbialite development for both modern and fossil examples. Storr’s Lake on San Salvador Island, the Bahamas, a shallow (0-1.5m), low energy, hypersaline lake environment, is a premier locality with abundant metazoan grazers as well as sub-fossil and actively growing microbialite buildups of varying morphology. The grazer community is limited to three gastropod taxa: C. costata, B. minima and Truncatella spp. Microbialite morphology varies with depth and location within the lake, as does gastropod abundance and diversity. Sampling was carried out along five transects within three distinct lake regions accommodating varied microbialite and gastropod assemblages. A total of 54 samples were collected, including both active and subfossil microbialite of varied morphology, as well as associated soft sediment which was bulk sampled for gastropod assemblage. The highly abundant and dominant species, C. costata, included over four thousand specimens from 14L of processed microbialite and sediment. Microbialite morphological difference analysis included utilizing qualitative descriptors of surface morphology and quantitative photogrammetric methods of three-dimensional point cloud analysis. In-situ data from nearby Salt Pond of recent abiotic precipitate is included as a control. Quantifying the relationships between microbialite morphologic diversity and grazing intensity highlights the importance of a systems-level approach to understanding microbialite development.