IDENTIFYING SPATIAL VARIANCE IN THE GEOCHEMISTRY OF SHALLOW MARINE SEDIMENTS: A STUDY OF GRAND CAYMAN

Geochemical conditions have the potential to impact organisms that have a close interaction with the substrate. Developing a more comprehensive understanding of the geochemistry of marine sediments heightens our perspective on an organism’s relationship with the environment it inhabits, and thus its overall function within the ecosystem. This research provides an analysis of the geochemical composition of shallow marine sediments collected around the Caribbean island of Grand Cayman with the goal of identifying variation in the geochemical composition of sediments based on locality and the ecology of the environments from which samples were collected. Three primary offshore locations to the north, south, and east of Grand Cayman Island were sampled during June 2018. Distances between each site ranged from approximately 10 to 20 km. At each locality, bulk carbonate sediments were collected via SCUBA from two environments: 1) Thalassia testudinum-dominated seagrass beds and 2) bare sand substrates containing little to no vegetation or other significant epifauna (e.g. corals). In addition, seagrass and algae censuses were conducted within each seagrass bed to account for variation in species composition and density. Following collection, sediment samples were milled, dried, and pressed into pellets that were then analyzed individually using an X-ray fluorescence (XRF) spectrometer. A series of four XRF scans were applied to analyze the geochemical composition of each sample. Both common and trace elements that have environmental significance were considered in the analytic process. These elements were then subjected to a series of quantitative analyses. Preliminary results suggest broad geochemical similarities among the sampling localities, but additional multivariate analyses may be able to detect more subtle differences. If present, we plan to compare geochemical variation to other environmental variables, including: type of substrate (seagrass or sand) and composition of the molluscan community present. We hope this approach will aid in our understanding of the relationship between ecological variables and potential drivers of geochemical variation.