To design a method for predicting outbreaks of paralytic shellfish poisoning (PSP) in scallop fishing grounds, the relationship between the distribution of the toxic dinoflagellate, Alexandrium tamarense and the dynamics of the Soya Warm
Abstract:To investigate the mechanisms influencing the spatial distribution of the toxic dinoflagellate Alexandrium tamarense in the Okhotsk Sea off Hokkaido, Japan, intensive field surveys were conducted at 34-37 stations in late July every year from in [2002][2003][2004][2005][2006][2007]. Alexandrium tamarense occurred every year. However, the abundance of A. tamarense fluctuated year by year, with extremely low cell densities of A. tamarense in 2005. High abundances of A. tamarense were found frequently in the oceanic area of the surface low-salinity water (LSW, salinityՅ32.5) and the mixed water (MW). Low abundances were found along the coastal area of the Soya Warm Current (SWC, salinityՆ33.6) and in the dichothermal water (DTW, temperatureՅ2°C) in the layer of oceanic areas deeper than 30 m. The PO 4 -P concentration in each water mass was in the order DTWϾMWϾLSWϾSWC and the lowest PO 4 -P concentration that occurred in the SWC is considered to be a potential limiting factor for the growth of A. tamarense. The reason for the low A. tamarense abundance in the DTW is considered to be the low water temperature and low light intensity. It is concluded that the water mass of LSW has favorable conditions for the growth of A. tamarense. The relative frequency of each water mass fluctuated every year and the results suggest that the frequency of occurrence of the LSW and MW is one of the most significant factors controlling the abundance of A. tamarense in the area.
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