Paralytic shellfish poisoning on the east coast of the UK in relation to seasonal density-driven circulation

Paralytic shellfish poisoning (PSP) toxin associated with the dinoflagellate Alexandrium tamarense is found on the north-east coast of the UK in late spring/early summer. Severe outbreak an sporadic, and knowledge of the cause and origin of the phytoplankton blooms and whether they develop from a diffuse source or from a seed population is uncertain. Recent observations of the circulation of the region demonstrate a persistent southward near-coastal flow associated with strong bottom fronts bounding a pool of cold dense bottom water isolated below the seasonal (spring/summer) thermocline. Flows extend continuously for similar to 500 km from the Firth of Forth to Flamborough Head before passing offshore to the Dogger Bank. These observations suggest that dinoflagellates originating from the high concentrations of A. tamarense cysts in the sediment of the Firth of Forth act to maintain a dinoflagellate population in the coastal region south to Flamborough Head, thereby maintaining the risk of PSP outbreaks.