Seasonal dynamics of Alexandrium tamarense and occurrence of paralytic shellfish poisoning toxins in bivalves in Nanji Islands, East China Sea

A monitoring program for seasonal dynamics of A. tamarense and paralytic shellfish poisoning toxins (PSTs) in bivalves was carried out from April 2006 to March 2007 in Nanji Islands, East China Sea. Low abundances of A. tamarense (fewer than 4.0 × 102 cells L–1) were first observed on 15 April 2006. During middle May, blooms of A. tamarense were documented, with the mean density of 3.8 × 103 cells L–1 and 0.75 × 103 cells L–1, corresponding to surface and bottom water columns, respectively. Environmental conditions of temperature range 18–20°C and salinity range 29.5–31 coincided with a high abundance of A. tamarense in the region, and the bloom collapse was likely to be a response to P limitation. Toxin concentrations in cultured Patinopecten yessoensis, Mytilus galloprovincialis and wild Mytilus coruscus during A. tamarense blooms ranged from 68.9 to 96.3 μg STXeq per 100 g flesh. Toxin profiles were similar among bivalve shellfish samples, dominated by C1 and C2 in 51.4–64.6 mol% of toxins, with an average of 60.6 mol%, followed by GTX5, GTX1–GTX4, dcGTX2 and dcGTX3. However, from January to March 2007, lower toxin concentrations, 18.9–40.8 μg STXeq per 100 g were found only in the wild Oyster sp., comprising GTX4, GTX5 and GTX1.