A RECORD OF PAST LAND USE ACTIVITY IN A CORAL FROM GUÁNICA BAY, PUERTO RICO

Coral reefs face a multitude of stressors, including land based sources of pollution, yet they support a diverse marine ecosystem. Corals deposit a calcium carbonate skeleton in annual bands that can serve as a record of past environmental change. In Guánica Bay, Puerto Rico, the nearshore coral reefs are exposed to sediment and nutrient plumes from the Rio Loco Watershed that has undergone extensive anthropogenic modification associated with agricultural and urban activities. To determine a record of past land use, a coral core was collected from Siderastrea siderea and sampled in 1 mm-increments for stable isotopes (δ¹⁸O and δ¹³C) and a suite of trace metals (Ba, Cu, Fe, Mn, V, and Mg), representing coral growth between 1920 and 2017. We expect that increased levels of trace metals will be associated with local slash-and-burn agricultural practices used during sugarcane harvesting that was at its peak in the late 1960s. While shorter coral cores from this location did not correlate with sea surface temperature, precipitation or river discharge, the δ¹⁸O of this longer record may more accurately reflect past environmental change. This longer coral chronology may also help identify when land based activities in the Rio Loco Watershed first began to negatively influence nearshore reefs, distinguishing long-term chronic stressors on reefs from those that are more acute.