Monitoring Programme for the Presence of Toxin Producing Plankton in Shellfish Production Areas in Scotland: April 2006 - March 2007

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-06 to 31-Mar-07. A total of 918 seawater samples collected from 41 coastal locations were analyzed, by light microscopy, for the presence of eight potentially toxic genera or species of phytoplankton. The diatom Pseudo-nitzschia was not a major problem during 2006 in inshore coastal areas. Spring and autumnal Pseudo-nitzschia blooms occurred in most areas, and at some sites there were three distinct bloom periods. Subsequently, between mid October 2006 and the end of March 2007, Pseudo-nitzschia counts were below threshold for all the samples analyzed. Pseudo-nitzschia counts above trigger level (at which toxicity may become a problem) were mostly absent in southwest Scotland and the south of Argyll & Bute throughout the whole reporting period. During June and July, increasing concentrations of Dinophysis were detected and in July, over 50% of the samples examined had Dinophysis present above threshold concentration. Dinophysis continued to be recorded in samples throughout August and September. A change from a period of good weather followed by bad weather in early August appeared to coincide with a decrease in the number of Dinophysis cells and a bloom of Alexandrium. During August, Alexandrium was found in almost half the samples analyzed. The densest Alexandrium blooms occurred in Shetland between mid August and early September and Alexandrium continued to be present into mid October at some sites.