AFTER-THE-FACT ESTIMATIONS OF THE COMPOSITION AND QUANTITY OF CALCAREOUS NANNOPLANKTON ASSEMBLAGES PRESENT DURING THE 2010 MACONDO OIL SPILL IN THE GULF OF MEXICO: PRELIMINARY RESULTS

Calcareous nannoplankton are important photosynthetic protist constituents of the base of the food chain in the Gulf of Mexico (GOM), however, no quantitative studies have been published on their abundance and seasonal variability in this region. Thus, the effects of the BP Macondo Oil Spill from April 20 to July 15, 2010, on these skeletal-bearing phytoplankton can only be determined by after-the-fact measurements and comparisons with unpublished data. We report here the preliminary results of a study in progress, the first step in the reconstruction of nannoplankton populations at the time of the spill. We began monthly sampling in January, 2011, along three transects across the shelf of the Florida Panhandle. Unfortunately, samples taken a year after the spill cannot represent floras at the time of the spill because the 100-year Mississippi flood event that placed a thick lens of fresh water over our study area, thus our more recent samplings from May to July, 2012, should provide the most reliable results to date.

We have taken some 900 samples through the photic zone via Niskin-bottle rosettes which also provide water-chemistry and chlorophyll data. Quantitative nannoplankton census data are taken via scanning electron microscopy. Our results to date indicate that De Soto Canyon funnels open GOM waters high up onto the shelves in the Florida Panhandle region so that near-shore nannoplankton assemblages there can at times mimic those of the open ocean. In addition, quantitative nannofossil counts are being take from De Soto Canyon sediments that accumulated before, during and after the Macondo Oil Spill. Our goal is to use all of these data to predict the effects of any future oil spills in the GOM on calcareous nannoplankton.