Ecological Change in Guam: Historic Insights from the Foraminiferan, Baculogypsina sphaerulata

Because of their abundance and preservation in sediment, foraminifera are useful tools in environmental monitoring. Species that harbor algal symbionts thrive in oligotrophic environments and are sensitive to various stressors associated with human development, making them excellent proxies for changes in water quality. Due to uncertainties surrounding the impacts of Guam’s expanding population on local reef ecosystems, it is critical to document historic stressors to inform future conservation efforts. This study uses sediment cores taken from back-reef habitat in Agaña Bay, a site heavily affected by development, and Shark’s Hole, a less impacted site, to analyze changes in the relative abundance of Baculogypsina sphaerulata, the most prevalent symbiont-bearing foraminiferan. B. sphaerulata abundance declined over the past 570 years in Agaña Bay, but increased during the past 560 years in Shark’s Hole. These data suggest historic anthropogenic deterioration of water quality in Agaña Bay. Because of its important role in reef carbonate production, test thickness (mg/mm shell) measurements are also made to document geophysical changes of B. sphaerulata’s calcite over time. Unexpectedly, we find an increase in test thickness over time in Agaña Bay.