HISTORICAL RECONSTRUCTION OF SEDIMENTATION ON CORAL REEFS IN ST. JOHN, USVI

Coral reefs are highly diverse and fragile marine ecosystems susceptible to many anthropogenic threats. In coastal coral reefs, land-based runoff from impermeable surfaces and soil erosion carries pollutants, nutrients, and sediments that have sublethal and lethal effects on the marine life, including the living coral themselves. Sedimentation can be reconstructed using the chemistry of coral skeletons due to the uptake of metals associated with sediment runoff during skeletal growth. As corals grow, distinct growth bands form that can be used to date the coral records with the same methods as tree rings. Sediment runoff in Virgin Islands National Park, US Virgin Islands has been assessed at approximately monthly resolution for several years using sediment traps, but coral records have the potential to extend these records back decades or centuries. An initial study was undertaken to assess reproducibility of metal/Ca signals between coral colonies of Siderastrea siderea in St. John, USVI. This coral species has not typically been used to reconstruct sediment runoff, but is more common in the USVI and less threatened than the Orbicella species that have been used in the past. Core samples were collected from multiple small living Siderastrea siderea coral colonies in Great Lameshur Bay, and metal/Ca ratios were analyzed using laser ablation-inductively coupled plasma-mass spectrometry at UMass Boston. Preliminary observations indicate that metal/Ca LA-ICP-MS line scan ratios follow similar trends over time with regard to individual metal uptake in the coral skeleton. Results from quantitative between-colony reproducibility assessment and comparisons to rainfall and runoff datasets will be presented.