Control of lipophilic shellfish poisoning outbreaks by seasonal upwelling and continental runoff

Closures of mussel rafts in the Ría de Ares–Betanzos (NW Spain) because of the occurrence of lipophilic shellfish poisoning outbreaks over the period 1999–2007 have been studied in relation to the coastal wind and precipitation regimes of the area. More than 85% of the episodes concentrate on the summer and autumn that coincide with the upwelling-favourable/dry season and the transition to the downwelling-favourable/wet season, respectively. We obtain that the percentage of days closed in summer can be predicted by the average continental runoff (Qr) during the preceding spring (86% of the variance explained by the average Qr of May) and the percentage of days closed in autumn by the average offshore Ekman transport (EkL) during the preceding summer (91% of the variance explained by the average EkL of August). A rainy spring will produce extensive closures in summer and a windy summer extensive closures in autumn. We speculate that this seasonal lag between atmospheric forcing and lipophilic shellfish poisoning outbreaks, which provides a chance to forecast mussel toxicity, is compatible with the obligate mixotrophic nutritional mode of the Dynophysis acuminata complex, the dominant lipophilic shellfish poisoning species in the Ría de Ares–Betanzos.