Monitoring Programme for the Presence of Toxin Producing Plankton in Shellfish Production Areas in Scotland. Reporting period 01 April 2008 - 31 March 2009

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This report presents the results from the monitoring carried out to detect the presence of toxin-producing phytoplankton in shellfish production areas in Scotland over the period 01- Apr-08 to 31-Mar-09. A total of 991 seawater samples collected from 52 coastal locations were analyzed, by light microscopy, for the presence of eight potentially toxic genera or species of phytoplankton. For the samples analyzed over the reporting period, counts above threshold levels were observed for Pseudo-nitzschia spp. in 13% of all samples. Almost 30% of those collected during July 2008 had Pseudo-nitzschia present above concentrations of 50,000 cells per litre (threshold), although only 10% of these blooms had any associated ASP toxicity. By contrast, although Pseudo-nitzschia was recorded above threshold in only 15% of the samples analyzed in September 2008, more than half of these blooms were associated with ASP toxic events. Alexandrium spp. was present in almost one quarter of all the samples during the reporting period. It was most frequently observed in the spring and summer, and was present in about 38% of all May samples. Dinophysis spp. was recorded at concentrations likely to be harmful in approximately 6% of samples during 2008, and was most prevalent during August when almost 19% of the samples analyzed had Dinophysis cell densities above threshold. During 2008, blooms of Pseudo-nitzschia were first recorded on the Scottish west coast (Isle of Skye and Sutherland) and around Shetland in early April. Similar to 2007, dense Pseudonitzschia concentrations were mostly absent in southwest Scotland and southern Argyll during 2008, although relatively less dense blooms appearing in Loch Striven in August and West Loch Tarbert in October did have some associated toxicity. The largest recorded Pseudo-nitzschia bloom was observed in NE Shetland in early June, with a cell density of > 2.8 million cells per litre. Bloom duration was generally between three to five weeks over the summer months, although at two sites in Shetland (Ronas Voe and Clift Sound), Pseudonitzschia was observed at potentially harmful cell concentrations for a continuous period of over 12 weeks from mid June to mid September. Toxic Pseudo-nitzschia species were present in north Argyll in July and September, and around Shetland in August. A Pseudonitzschia concentration of approx. 70,000 cells per litre recorded in the Western Isles in early September resulted in ASP toxicity above permitted levels in shellfish. Similar to 2007, toxic Pseudo-nitzschia species were present in the Dornoch Firth during October. Overall, Alexandrium was observed less frequently in 2008 compared with 2007, and at lower concentrations. The largest blooms recorded during 2008 were all observed in Clift Sound (southwest Shetland) over a period of approximately four months, with peaks in May, June and August, the maximum being 1,440 cells per litre in mid June. Low levels of PSP toxicity were frequently reported throughout the period from March through to October at many sites, although Alexandrium cell counts were below detection levels in the water samples. A relatively low density bloom of 160 cells per litre occurring in the Dornoch Firth in May 2008 was associated with elevated levels of PSP toxicity in shellfish (detected by bioassay). Similar to Alexandrium, Dinophysis was also generally at lower concentrations compared with both 2006 and 2007. Dinophysis was first observed in concentrations likely to be harmful in Loch Roag (Western Isles) and Loch Eishort (Isle of Skye) in early May 2008, where densities of 460 and 180 cells per litre were recorded, respectively. Dinophysis was not recorded above threshold level (100 cells per litre) after mid September 2008, with the latest blooms being observed in north Argyll (Lochs Creran and Melfort). The largest bloom occurred in Loch Roag (Western Isles) in early June, with a density of 2,220 cells per litre. Other blooms were recorded from the north west: 1,080 cells per litre in Loch Laxford in late July; 840 cells per litre in Loch Ewe in mid August; and from Argyll: 600 cells per litre in Loch Striven in early July. Both the Loch Laxford and Loch Striven blooms had associated DSP 2 toxicity. However, DSP positive results in shellfish did not always coincide with an elevated Dinophysis cell count. Prorocentrum minimum was frequently observed at Scottish monitoring sites during 2008, with blooms above background level first noted in Shetland, Orkney and the Isle of Skye in April. The largest recorded bloom occurred in Loch Roag in early June, with a density of >4 million cells per litre. Maximum cell density of Prorocentrum lima reached 340 cells per litre in Colonsay in mid June. Protoceratium reticulatum was recorded on 13 occasions during 2008. Cell concentrations of 40 cells per litre were observed in samples from Orkney and Shetland during April. Lingulodinium polyedrum was observed at only one monitoring site in 2008, as in 2007 (West Loch Tarbert, Argyll). Maximum cell density reached 180 cells per litre in early September. Protoperidinium crassipes was observed infrequently at sites in Argyll and Shetland, with a maximum cell density reaching 100 cells per litre in Loch Fyne (Argyll) in mid September.
Original languageEnglish
PublisherScottish Association for Marine Science
Number of pages47
Publication statusPublished - May 2009

Publication series

NameSAMS Internal reports


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