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 the natural environment is needed for understanding the ecological roles of this dinoflagellate. In this study, a real-time polymerase chain reaction (PCR) assay was developed using mitochondrial cytochrome b upstream region and 18S rDNA (PpmtDNA and Pp18S), and the geographic and temporal distribution of P. piscicida was investigated in several locations., Both PpmtDXA and Pp18S generally gave similar results, indicating that P. piscicida was present at all studied regions along the American coast (from Maine to North Carolina along the US Atlantic coast and Los Lagos along the Chilean Pacific coast). Despite its widespread distribution, P. piscicida was only detected in 36% of the 431 water samples analyzed, and its abundance was generally low (< 1.0-1.5 cells mL(-1)). Populations detected at the five stations in the Neuse River (North Carolina) and two stations in Chesapeake Bay (Maryland) were genetically homogeneous, whereas those from other locations appeared to be genetically diverse. It can be concluded that (i) the, PpmtDXA-Pp18S real-time PCR assay is sensitive and specific for detecting and quantifying P. piscicida in the natural environment and (ii) P. piscicida is widespread along the American coasts, but normally only as a minor component of plankton even in the high-risk estuaries (Neuse River, Chesapeake Bay).