Monitoring Programme for the Presence of Toxin Producing Plankton in Shellfish Production Areas in Scotland. Reporting period: 01 April 2007 - 31 March 2008.

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-07 to 31-Mar-08. A total of 930 seawater samples collected from 48 coastal locations were analyzed, by light microscopy, for the presence of eight potentially toxic genera or species of phytoplankton. Of all the samples analyzed over the reporting period, counts above threshold levels were observed for Pseudo-nitzschia (11% of samples), Alexandrium (34%) and Dinophysis (13%). Blooms of Pseudo-nitzschia were observed in early April 2007, and were more geographically widespread than in April 2006, particularly on the west coast of Scotland and around Shetland. Dense Pseudo-nitzschia concentrations were mostly absent in southwest Scotland and south Argyll & Bute during 2007. Pseudo-nitzschia blooms were widespread during July and the largest bloom recorded in 2007 was from southwest Shetland in early July at a concentration of 2.5 million cells per litre. Pseudo-nitzschia was present above threshold levels in north Argyll & Bute between June and August, and around Shetland in July and September 2007, and was associated with ASP toxic events. A large bloom of Pseudo-nitzschia (365,000 cells per litre) in the Western Isles in late August also resulted in ASP toxicity above permitted levels in shellfish. By October most Pseudo-nitzschia blooms had disappeared, persisting only around Orkney and on the east coast. Toxic Pseudonitzschia species were present in Dornoch Firth throughout October and continued into mid November. Alexandrium was observed much more frequently during April 2007 compared with the same time the previous year, with a large bloom present around Orkney from mid April to mid May (up to 6,060 cells per litre). It was generally less widespread at all phytoplankton monitoring sites during September 2007, compared with September 2006. The largest bloom recorded in 2007 was from southwest Shetland in late July (9,180 cells per litre). Although PSP toxicity was detected below permitted levels at most monitoring sites during 2007, there was some toxicity associated with the presence of Alexandrium on the west coast during April, May and June. Alexandrium occurring around Shetland in April, July, August and September was also associated with toxic events. Dinophysis was present above threshold levels from late April 2007 onwards, initially appearing most frequently in Argyll & Bute, northwest Scotland and Orkney. Blooms appeared in the Shetland Islands and on the east coast in June, with the largest blooms (up to 5,300 cells per litre) occurring around Shetland in July. These were associated with extended periods of DSP toxicity in Shetland shellfish recorded between June and August. Most other 2007 DSP toxic events occurred in Argyll & Bute in May and June. The largest Dinophysis bloom recorded in 2007 was from Elie, Fife in July (58,000 cells per litre). Prorocentrum minimum was frequently observed at Scottish monitoring sites during 2007, with blooms occurring from mid April to early September. Similar to 2006, the largest blooms occurred around Shetland, with a maximum recorded level of >2.4 million cells per litre observed in late May. Blooms were also noted around Orkney and Sutherland (north and east coast) at this time, but it was only recorded in small numbers at other monitoring sites. Prorocentrum lima was observed in relatively low numbers during 2007, and frequently occurred at the same sites. Maximum cell density reached 560 cells per litre in Shetland in mid June. Protoceratium reticulatum was recorded infrequently from sites in Shetland, Orkney and Argyll & Bute. The largest bloom recorded was from Orkney in late April (140 cells per litre). Lingulodinium polyedrum was observed at only one monitoring site in 2007 (West Loch Tarbert, Argyll & Bute) and recorded from June through to September. Maximum cell density reached 60 cells per litre in early September. Protoperidinium crassipes was observed at three monitoring sites in 2007, all in Argyll & Bute. Maximum cell density reached 100 cells per litre in mid July.