Long-term monitoring of potentially toxic phytoplankton, marine biotoxins and hydrographic variables in open waters off the Basque coast (SE Bay of Biscay)

Description

This dataset shows hydrographic variables, phytoplankton abundance (potentially toxic taxa), and levels of marine biotoxins in bivalves from an offshore shellfish production area on the Basque coast (southeastern Bay of Biscay). Two zones were monitored: one at an aquaculture experimental site (from December 2013 to December 2023), and another at a mussel farm (from June 2019 to December 2023). Not all variables were measured throughout the entire monitoring period. Sampling frequency also varied, although generally, monthly or fortnightly surveys were conducted (except from September 2015 to March 2016). Hydrographic variables (temperature, salinity, density (sigma theta), light transmission, photosynthetically active radiation, chlorophyll "a", dissolved oxygen concentration, and oxygen saturation) were measured in situ at different depths using continuous vertical profilers, Sea-Bird SBE 25 and 25plus CTD instruments. Due to the multi-year duration of the monitoring, phytoplankton and biotoxin analyses were conducted by different laboratories. The Utermöhl method was employed for the identification and counting of phytoplankton, from May 2014 to May 2017 by the University of the Basque Country, and onwards by Oceansnell. Mussels and oysters were analysed to determine the concentration of toxins related to the Amnesic Shellfish Poisoning (ASP) and the Paralytic Shellfish Poisoning (PSP), together with several lipophilic phytotoxins (i.e., Okadaic Acid (OA), Dinophysistoxins (DTXs), Pectenotoxins (PTXs), Yessotoxins (YTXs) and Azaspiracids (AZAs)). These biotoxins were analysed by the laboratories of Intecmar (from December 2013 to December 2019) and Cecopesca-Anfaco (from January 2020 to June 2023) following the standardized methodology specified in the corresponding EU Regulations. This work was supported by the Fisheries and Aquaculture Directorate, Department of Economic Development, Sustainability and Environment of the Basque Government through the ACULAB Project.

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