Alexandrium is detected throughout Scottish coastal waters on a near annual basis, and corresponding paralytic shellfish poisoning (PSP) toxins are found in Scottish shellfish. Previous studies at selected Scottish sites have shown diversity within the genus Alexandrium. In order to examine the distribution, diversity and toxicity of Alexandrium populations around the Scottish coast, historic cyst and cell data were compiled and cultures established from sediment and water samples. Historic data showed high cell densities of Alexandrium in Shetland, Orkney, the Western Isles and mainland east coast. Low abundances of Alexandrium cysts were observed along the west coast. Four species of Alexandrium (A. tamarense, A. ostenfeldii, A. minutum and A. tamutum) were established in laboratory culture and identified using morphological criteria. Sequencing of LSU rDNA from isolates of A. ostenfeldii, A. minutum and A. tamutum confirmed their identification and showed them to be similar to other European strains. Alexandrium tamarense, identified by morphological criteria, was observed to have a widespread distribution around the coast. Both toxin-and non toxin-producing strains of this species were isolated, suggesting the presence of A. tamarense Groups I and III. Alexandrium ostenfeldii was isolated from the east coast and Shetland Isles and was observed to produce both spirolide and PSP toxins. Alexandrium tamutum was identified from cultures isolated from Shetland and Orkney, the most northerly observation of this species to date. PSP toxins were not detected in isolates of A. minutum from the east coast and Orkney or of A. tamutum under the culture conditions used. This study has highlighted the diversity of Alexandrium in Scottish waters and reveals the requirement for temporal and regional studies on a species level in order to understand the variation in cell densities and PSP toxicity that is observed on an annual and decadal scale.

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Contamination of shellfish with paralytic shellfish poisoning (PSP) toxins produced by Alexandrium species poses a potential threat to the sustainability of the Scottish aquaculture industry. Routine LM analysis of water samples from around the Scottish coast has previously identified Alexandrium (Dinophyceae) as a regular part of the spring and summer phytoplankton communities in Scottish coastal waters. In this study, Alexandrium tamarense (M. Lebour) Balech isolated from sediment and water samples was established in laboratory culture. Species identification of these isolates was confirmed using thecal plate dissections and by molecular characterization based on their LSU and, in some cases, ITS rDNA sequence. Molecular characterization and phylogenetic analysis showed the presence of two ribotypes of A. tamarense: Group I (North American ribotype) and Group III (Western European ribotype). Assessment of PSP toxin production using hydrophilic interaction liquid chromatography-tandem mass spectrometry (HILIC-MS/MS) showed that A. tamarense Group I produced a complex array of toxins (∼2,000 fg STX equivalents · cell(-1) ) with the major toxins being C2, neosaxitoxin (NEO), saxitoxin (STX), gonyautoxin-4 (GTX-4), and GTX-3, while A. tamarense Group III did not produce toxins. Historically, it was considered that all Alexandrium species occurring in Scottish waters produce potent PSP toxins. This study has highlighted the presence of both PSP toxin-producing and benign species of A. tamarense and questions the ecological significance of this finding.

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