The composition and dynamics of microalgae play an important role in shellfish aquaculture, since phytoplankton is the main source of energy for filter-feeding bivalves as well as the main potential toxicity risk. Together with the increase in world aquaculture production in the last decades, there is recent interest in the implementation of shellfish aquaculture on the Basque coast (southeastern Bay of Biscay). In this context, the study of the potentially toxic phytoplankton abundance and dynamics has become essential, since the viability of shellfish aquaculture in the area could be compromised by biotoxins. In the present study, two euhaline sites of the Basque shelf, one inshore (Mutriku) and the other offshore (Mendexa), were compared during a one-year period. The main aim was to determine which site was more suitable for the development of shellfish aquaculture, from the perspective of exposure to toxic phytoplankton, by comparing the composition and abundance of the potentially toxic phytoplankton community and the concentrations of toxins in mussel flesh. The mussels that grew offshore presented a higher amount of okadaic acid (OA), in accordance with the fact that this site (Mendexa) also presented a higher cell abundance of Dinophysis acuminata, a potential producer of OA. In addition, although Dinophysis spp., Pseudo-nitzschia spp. and Alexandrium spp. exceeded their cell alert thresholds several times at both studied sites, the dinoflagellates presented a higher frequency of exceedance at Mendexa. Moreover, the percentage of samples with toxin concentrations that exceeded quantification limits was higher at Mendexa as well. Therefore, from the perspective of the currently regulated biotoxins, in the Basque Country, inshore euhaline waters seem to be more suitable for mussel aquaculture than offshore waters.

微藻的组成和动力学在贝类水产养殖中起着重要作用，因为浮游植物是滤食性双壳类动物的主要能源，也是主要的潜在毒性风险。在过去的几十年中，随着世界水产养殖产量的增加，最近人们对在巴斯克海岸（比斯开东南湾）实施贝类水产养殖感兴趣。在这种情况下，对潜在毒性浮游植物的丰度和动力学的研究已变得至关重要，因为该地区贝类水产养殖的生存能力可能会受到生物毒素的损害。在本研究中，在一年期间比较了巴斯克大陆架的两个真盐站点，一个位于近海（Mutriku），另一个位于近海（Mendexa）。主要目的是从暴露于有毒浮游植物的角度，通过比较潜在有毒浮游植物群落的组成和丰度以及贻贝肉中毒素的浓度，确定哪个地点更适合发展贝类水产养殖。在此附近生长的贻贝呈现出更高的冈田酸（OA）含量，这是因为该地点（Mendexa）也呈现出更高的细胞丰度。Dinophysis acuminata，潜在的OA生产商。另外，虽然Dinophysis属，Pseudo-nitzschia属。和亚历山大号。在两个研究站点中，鞭毛鞭毛虫都多次超过其细胞警戒阈值，因此在门德萨，鞭毛鞭毛虫的出现频率更高。此外，在Mendexa，毒素浓度超过定量限的样品百分比也更高。因此，从目前受管制的生物毒素的角度来看，在巴斯克地区，近海真盐类海水似乎比近海更适合贻贝养殖。