Knowledge Bank

The island of St. John in the U.S. Virgin Islands has experienced a general decline in the health of coral reefs that fringe the eastern part of the island in and around Coral Bay. While, the exact cause(s) for the observed decline are still unclear, the past several decades have also seen increased development of roads and buildings, which in turn has enhanced the amount of land-based sediment that has entered the marine environment. Therefore, coral reef health may be in decline in response to the increase of land-based sediment. In particular, I hypothesize that clay minerals, the smallest of particles, could play an important role. To address this, I analyzed a series of sediment samples along a transect from high elevation on land to samples on the bay floor collected previously from my colleague Trevor Browning in 2015. I then sieved the samples to determine grain size analysis. Grain size results show an increase in the overall component of fine grained sediments as we approach the shoreline, thus confirming large amounts of fine grains are entering the marine environment. The study has shown that fine grained sediment is entering Coral Bay on St. John.