Low abundance distribution of Pfiesteria piscicida in Pacific and Western Atlantic as detected by mtDNA-18S rDNA real-time polymerase chain reaction

Information on the abundance of Pfiesteria piscicida in thenatural environment is needed for understanding the ecologicalroles of this dinoflagellate. In this study, a real-time polymerasechain reaction (PCR) assay was developed using mitochondrialcytochrome b upstream region and 18S rDNA (PpmtDNA and Pp18S),and the geographic and temporal distribution of P. piscicidawas investigated in several locations. Both PpmtDNA and Pp18Sgenerally gave similar results, indicating that P. piscicidawas present at all studied regions along the American coast(from Maine to North Carolina along the US Atlantic coast andLos Lagos along the Chilean Pacific coast). Despite its widespreaddistribution, P. piscicida was only detected in 36% of the 431water samples analyzed, and its abundance was generally low(<1.0–1.5 cells mL^–1). Populations detected atthe five stations in the Neuse River (North Carolina) and twostations in Chesapeake Bay (Maryland) were genetically homogeneous,whereas those from other locations appeared to be geneticallydiverse. It can be concluded that (i) the PpmtDNA–Pp18Sreal-time PCR assay is sensitive and specific for detectingand quantifying P. piscicida in the natural environment and(ii) P. piscicida is widespread along the American coasts, butnormally only as a minor component of plankton even in the high-riskestuaries (Neuse River, Chesapeake Bay).