Distribution, diversity and toxin composition of the genus<i>Alexandrium</i>(Dinophyceae) in Scottish waters

Abstract

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.