Paralytic shellfish poisoning (PSP) toxins in Miramichi Bay (New Brunswick, southern Gulf of St. Lawrence) : seeking the source / by Claude E. Léger and Stephen S. Bates.: Fs97-4/3002E-PDF

"A study was carried out to investigate the origins of irregular occurrences of Paralytic Shellfish Poisoning (PSP) toxins in molluscs in the Miramichi Bay (New Brunswick, Canada) area, where they were first recorded in 1988. PSP toxins are produced by the dinoflagellate Alexandrium tamarense, and may become concentrated in the flesh of filter-feeding molluscs. When toxin concentrations in molluscs exceed the regulatory limit, mollusc harvesting areas are closed to safeguard human health. Such closures, from 2001 to 2008, are documented in this report. Data from regulatory analyses were used to infer patterns of toxic bloom dynamics and timing. Alexandrium tamarense cells also produce cysts that settle to the bottom, where they lay dormant until conditions again become favourable for growth and a bloom is initiated. To evaluate A. tamarense cyst presence in sediments, sediment was sampled in Miramichi Bay and points north, during 2007 and 2009. However, in this study only a limited number of A. tamarense cysts were found in sediments from the 17 sites sampled. Phytoplankton was sampled near mollusc sampling sites, but no relation was found between numbers of A. tamarense cells in the water column and occurrences of toxins in molluscs, with one notable exception. Although the origins of the toxic blooms remain elusive, indirect evidence suggests that offshore A. tamarense blooms from the southern Gulf of St. Lawrence are swept into Miramichi Bay by tidal or other currents. A direct link between toxic blooms in Miramichi Bay and those in the St. Lawrence Estuary is not supported by the available evidence. We conclude that hydrodynamics complicates the relationships among cysts in bottom sediments, vegetative cells in the water and toxic bivalves. Hence, cyst mapping is unlikely to be of great use in Miramichi Bay and surrounding embayments"--Abstract, page iv.

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