SHIFTING DOMINANT BENTHIC FORAMINIFERA IN GRAND BAY, MISSISSIPPI OVER THE LAST 100 YEARS INDICATES ENVIRONMENTAL CHANGE

Grand Bay, Mississippi has undergone multiple geomorphic changes over the last few centuries including, and as a result of, the diversion of the Escatwpa River, the creation of new inlets along Dauphin Island, and the degradation of Grand Batture Island which separated Grand Bay estuary from Mississippi Sound. To investigate how landscape changes may have altered Grand Bay estuary proper, sediment push cores were collected for foraminiferal and radiochemical analyses. The cores were processed for lead-210 downcore by alpha spectroscopy and geochronologies were determined with the constant rate of supply model. Based on down-core age-depth relationships, select intervals were analyzed for foraminifera in order to assess alterations in the microfossil assemblage in Grand Bay over the last century. Benthic foraminifera can provide quantitative evidence of altered environmental conditions in marshes and estuaries, both in response to natural processes and anthropogenic pressures. All estuarine samples were low diversity; two species, Ammotium salsum and Paratrochammina simplissima, dominated all downcore assemblages. Paratrochammina simplissima increased in abundance up-core from a minor subsidiary species to co-dominant with A. salsum, and exhibited a 21.1% to 52.6% shift in abundance over the last 100 years in six cores. This shift may indicate an environmental change preferable to P. simplissima though prior to 10 years ago, P. simplissima was not referenced in taxonomic data from the northern Gulf of Mexico. Was this a taxonomic oversight due to lumping with Trochammina inflata, or has this species found a new region or environment in which it can thrive?