MOLLUSCS AS PROXIES FOR ENVIRONMENTAL CHANGES AND COMMUNITY SHIFTS IN HOLOCENE CARIBBEAN REEFS

Molluscs are diverse, well-studied, and easily preserved in sediments, making them ideal proxies for environmental change in both the fossil and near-fossil records. They are, therefore, powerful tools for creating baselines, assessing habitat degradation, and setting targets for restoration in the late Holocene when used to reconstruct environments and benthic marine communities before human impact. Here, we present two case studies from Panama and Belize that leverage the power of molluscan proxies to reconstruct changes in coral reef communities over the past several millennia. We collected reef matrix cores, using SCUBA and a vibracoring technique, from sandy areas adjacent to coral reefs. We then identified and quantified bivalve and gastropod shells from the matrix to track changes in taxonomic and functional group composition of the molluscan reef community through time. We used molluscs as proxies for changes in substrate type, sediment oxygen levels, and overall community diversity. Molluscs, used in combination with other proxies including reef accretion rates, fish teeth, foraminifera, and urchin spines, indicate reef degradation beginning ~250 years ago in the Panamanian core. Additionally, a decrease in the abundance of the bivalve Dendostrea indicates an apparent loss of soft corals from these reefs. In contrast, molluscs in the cores from Belize indicate later (19^th century) changes in reef ecosystem health, primarily changes in hard substrate availability, despite historic overfishing. Ecosystem degradation, interpreted from the skeletal record of these cores, occurs concurrently with changes in terrestrial land use, particularly the establishment of plantations, in both Panama and Belize, emphasizing the interconnectedness of terrestrial and marine communities in coastal environments.