Distribution of Pfiesteria piscicida cyst populations in sediments of the Delaware Inland Bays, USA

The toxic dinoflagellate, Pfiesteria piscicida, is a common constituent of the phytoplankton community in the Delaware Inland Bays, USA. In this study, molecular methods were used to investigate the distributions of benthic stages (cysts) of P. piscicida in sediment cores from the Delaware Inland Bays. Cores from 35 sites were partitioned into nephloid and anoxic layers and analyzed for P. piscicida by nested amplification of the 18S rDNA gene using P. piscicida-specific primers. The presence of inhibitory substances in the PCR reaction was evaluated by inclusion of an exogenous control DNA in the extraction buffer, thus eliminating samples that may yield false-negative results. Our results indicate a patchy distribution of P. piscicida in sediments of the Delaware Inland Bays, with distinct differences between each of the three bays. Overall, P. piscicida was found more frequently in sediments from Rehoboth Bay compared to Indian River and Little Assawoman Bays. These differences suggest (i) that populations of P. piscicida may be more widely distributed in Rehoboth Bay, (ii) that populations of P. piscicida may have been introduced to Rehoboth Bay at an earlier time, (iii) that past blooms of P. piscicida in Rehoboth Bay estuaries may have seeded the sediments with higher numbers of cysts, and/or (iv) that Rehoboth Bay sediments may be more resistant to clearing due to storm turbulence.