Abundance and distribution of planktonic decapods in the northern Gulf of Mexico before and after the Deepwater Horizon oil spill

Abundances of target decapod taxa were analyzed from bongo samples collected in the northern Gulf of Mexico to assess any possible ecological effect of the 2010 Deepwater Horizon (DWH) oil spill. Plankton samples were collected during Southeast Area Monitoring and Assessment Program (SEAMAP) and Natural Resource Damage Assessment (NRDA) plankton surveys. Data were analyzed in two main periods, prespill (2003, 2007, and 2009) and postspill (2010-2011), each period covering one spring and two summer-fall cruises. Target taxa were holoplanktonic shrimps, important components of trophic plankton dynamics, and planktonic stages of crabs, shrimps, and lobsters that support valuable fisheries. Portunid zoeae and megalopae, penaeid larvae, and sicyoniid larvae were more abundant during the prespill period. In contrast, holoplanktonic shrimps (Lucifer spp.) and sergestids, penaeid postlarvae, and lobster phyllosomata were more abundant postspill. Generalized linear models were conducted for each taxon/stage with seven predictor variables including the period (pre- and post-DWH oil spill) as a categorical factor. Output models indicated that salinity, Mississippi River outflow, winds, and fluorescence were the best predictor variables affecting decapod abundances. The period factor indicated a significant effect only for the holoplanktonic Lucifer spp. and sergestid shrimps. A direct effect of the DWH oil spill on planktonic decapods could not be determined in the present study. However, the reduction in portunid and penaeid larvae and the increase in holoplanktonic shrimps during the postspill period raise concerns about a possible shift in the plankton food web community associated with long-term effects of the accumulation of oil on organisms and sediments.