Interannual variability of PSP outbreaks on the north east UK coast

Paralytic shellfish poisoning (PSP) occurs sporadically on the NE UK coast. The degree of toxicity shows considerable interannual variability, but particularly severe events occurred in 1968 and 1990. The time sequence of PSP toxin production in 1990 is described and compared with 1989 when no significant PSP toxin occurred. In 1990, PSP toxin was widespread in shellfish samples taken on 300 km of coastline, from Betwick to Whitby, and toxin was present at high concentrations for >1 month. The distribution of Alexandrium tamarense cysts in the sediments is described. High concentrations were found in the Firth of Forth and also in a number of regions offshore of the Scottish and English coasts. A water transport model has been used to estimate back trajectories, with the aim of determining the source of the A. tamarense bloom. The Firth of Forth has previously been suggested as the seed bed for A. tamarense outbreaks in the area, but the transport model clearly shows that A. tamarense moved inshore over a wide area in 1990; there was no single source of the bloom. Sea surface temperatures, estimated from satellite imagery, show that water temperatures were much higher at the end of April 1990, when the bloom occurred, than in 1989 when PSP toxin incidence was very low. These conditions would have resulted in early seasonal stratification and would have favoured phytoplankton growth in the water column.