| Summary: | Levels of okadaic acid, a DSP toxin, were determined in the soft tissues of the blue mussel Mytilus edulis. The mussels were collected by divers at Långskär, an island a few kilometres off Tvärminne in the western Gulf of Finland. The dived mussels were placed in plastic baskets at two stations, at Storgadden (59°47´N, 23°19´E) in the western Gulf of Finland, and at Huovari (60°24´N, 27°40´E) in the eastern Gulf of Finland. Due to economical difficulties the mussels couldn´t be systematically sampled by divers. At both stations, between April and September, the mussels were kept for 3–4-week periods in baskets at depths of 5 m and 30 m. After 3–4 weeks, the sampled mussels in the baskets were replaced with the new ones. During each sampling, in Storgadden and Huovari, the mussels from both depths were combined for toxin analysis. Plankton samples were taken from the surface water layer (0–10 m) during mussel sampling. At Storgadden, the mussels sampled in May and at Huovari in July contained small amounts of okadaic acid: 21.7 ± 3.6 (mean ± method error) ng g–1 d.w. and 82.5 ± 16.5 (mean ± method error) ng g–1 d.w. in May and July, respectively. No toxins were detected in samples from August–September. This preliminary study shows that okadaic acid can be detected in Mytilus edulis in the Gulf of Finland, although toxic levels were not found, nor was there found any correlation between the density of dinoflagellates and the okadaic acid levels.
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