This study describes the phytoplankton community in sheltered euhaline waters of the Basque coast (southeastern Bay of Biscay). Phytoplankton composition, cell size, abundance, biomass and the presence of potentially toxic taxa, together with chlorophyll a, nutrients and hydrographic and optical conditions were measured, from August 2016 to August 2017, in the Mutriku port, with the main aim of assessing the suitability of the phytoplankton community as a food resource for bivalves. The water column in Mutriku showed the typical environmental conditions of Basque marine waters, with no significant nutrient enrichment caused by anthropogenic pressures. Haptophytes represented the greatest contribution to cell abundance (31–47%), and diatoms were the dominant group in terms of biomass (52–79%), which could favour mussel growth due to their high fatty acid content. In addition, the size structure of the phytoplankton community was suitable for mussel ingestion, since the predominant cell size was 2–20 µm. Regarding toxic phytoplankton, the genera that pose a risk for human health and those that affect negatively mussel physiology and survival were considered. Altogether, ten toxic phytoplankton taxa were identified, contributing in less than 5% to the total cell abundance of Mutriku. However, median chlorophyll a concentration was low (0.5 µg L⁻¹), reflecting the oligotrophic conditions of the area. Therefore, even if the composition of the phytoplankton community could be favourable for bivalve aquaculture, biomass values are low compared to other zones of bivalve production.

这项研究描述了巴斯克海岸（比斯开东南湾）的避风塘淡水域中的浮游植物群落。浮游植物的组成，细胞大小，丰度，生物量以及存在潜在毒性的类群以及叶绿素a在2016年8月至2017年8月期间，对Mutriku港口的营养，水文和光学条件进行了测量，其主要目的是评估浮游植物群落作为双壳类食物资源的适宜性。Mutriku的水柱显示了巴斯克海水的典型环境条件，没有人为压力引起的明显养分富集。足部植物对细胞丰度的贡献最大（31-47％），而硅藻则是生物量的主要组成部分（52-79％），由于它们的高脂肪酸含量，它们可能有利于贻贝的生长。另外，浮游植物群落的大小结构适合贻贝的摄食，因为主要的细胞大小是2–20 µm。关于有毒的浮游植物，考虑了对人类健康构成威胁的属以及对贻贝的生理和生存产生负面影响的属。总共确定了十种有毒的浮游植物类群，对Mutriku的总细胞丰度贡献不到5％。但是，叶绿素的中位数一个浓度较低（0.5微克大号^-1），反映该区域的贫营养条件。因此，即使浮游植物群落的组成可能对双壳类水产养殖有利，但与其他双壳类生产区相比，生物量值仍较低。