In 2018 an unusually intense red tide of the common dinoflagellate Alexandrium minutum, cyst-forming producer of paralyzing toxins, provoked social alarm and closure of bivalve production in the Rias of Vigo and Pontevedra because saxitoxin exceeded the legal limit. INTECMAR monitors marine environmental quality and enforces sanitary standards of marine products in Galicia (NW Spain). Since 1992, weekly analysis of bivalve and infaunal molluscs are carried out. When the concentrations of PSP toxins in the molluscs exceed 800 μg equiv. STX/kg, mollusk extraction in the affected zone is prohibited. INTECMAR also monitors weekly salinity and temperature data and phytoplankton at 42 marine and 16 coastal sites. The seawater is analyzed directly and fixed with formaldehyde for species identification. Quantification is done by the Utermöhl method on 25 mL samples fixed with lugol. The taxonomy of Alexandrium minutum were confirmed by plate staining with calcofluor, scanning electron microscope and microarrays. The cells, with the posterior sulcal plate wider than long and its pore characteristic of 1’, and temporal cysts were observed. In the 2018 outbreak, maximum cellular concentrations reached 1.5 and 0.8 .106 cells L-1 in July at two sites near urban wastewater treatment plants. The maximum coincided with surface temperatures >20ºC, low tide, and upwelling relaxation (upwelling Index < 500). Oceanographic analysis, including satellite observation, revealed the red tides originated in the bay of Baiona and later extended throughout the Ria de Vigo and into the Ria de Pontevedra. Maximum saxitoxin levels found were 5000 μgSTXKg-1 in mussels from Baiona

12th International Phycological Congress, 22-26 March 2021

Consellería do Mar. Xunta de Galicia

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