Investigation and interpretation of variations in NE Gulf of Mexico nannoplankton assemblages following the Macando well blowout: Months of August-November

The biodiversity and biomass of coccolithophore species observed in the NE Gulf of Mexico during the months of August through November from 2011 to 2013 are quite dynamic. Following the Macondo well blow out in 2010, analyses have been carried out on samples taken during the subsequent three years in the photic zone at 28 sites along four transects across the continental shelf and slope to observe ecological patterns in the calcareous nannoplankton assemblages. By extracting living cells from water samples collected via a CTD rosette and analyzing individual cell counts to identify specific species types and abundances, I have traced the vertical and horizontal distribution of these taxa over the 3-year interval.;The number of observed species increases from station to station as one moves from shallow waters across the continental shelf into deeper waters. This is due to a two water-layer configuration observed during August to November. As one moves into deeper waters the salinity, temperature and amount of light penetration begin to change, which is useful in tracing the thermocline and distinguishing the two layers. Once the depth exceeds 75 meters a new assemblage of deeper photic-zone dwellers consisting of oligotrophic species can be observed. Therefore, two separate nannoplankton assemblages can be observed, the top in the mixed layer from the surface to 75 meters depth, and the lower oligotrophic assemblages below the thermocline from 75 meters to the lower limits of the photic zone, which for the Gulf of Mexico is 200 meters.;A comparison of site biodiversity and biomass across stations during the study period also shows an increase in both cell density and number of species observed for each successive year sampled. The lowest cell-per-liter and species diversity is observed in 2011 with increasing numbers in 2012 and the highest recorded in 2013. Shifts in temperature and salinity recorded via the CTD are provided along with florescence profiles help us understand species distributions. I also noted a species, Navilithus altivelum, previously unknown in the Gulf of Mexico and the western hemisphere. This observation shows how rare and diverse these oligotrophic species can be as well as how important it is to conduct long-term census work.