Molecular quantification of toxic Alexandrium fundyense in the Gulf of Maine using real-time PCR

The toxic dinoflagellate Alexandrium fundyense is widespread in the northeastern part of North America, including the Gulf of Maine, and is responsible for seasonal harmful algal blooms in these regions. Even at low cell densities, A. fundyense toxins can accumulate in shellfish and result in paralytic shellfish poisoning (PSP). PSP can be debilitating or lethal to humans and other shellfish consumers and is a public health concern. As a result, accurate measurements of A. fundyense distributions, particularly at low cell density, are critical to continued PSP monitoring and mitigation efforts. Towards this end we have developed a real-time quantitative PCR (qPCR) method to monitor A. fundyense. Laboratory validation indicates that the qPCR assay is sensitive enough to detect 10 cells per sample, and that it does not detect co-occurring dinoflagellates such as Alexandrium ostenfeldii. The qPCR methodology was used to quantify A. fundyense cell densities in samples collected during a spring 2003 transect in the Gulf of Maine, and the data were compared to those obtained in parallel from light microscope and DNA hybridization-based methods. Results show that A. fundyense cell density was low during this period relative to typical cell densities required for PSP contamination of local shellfish, and that qPCR values were comparable to numbers determined by independent methods.