Distribution, frequency and intensity of harmful phytoplanktonic species are impacted by changes in environmental conditions. In the Bay of Brest, Alexandrium minutum has been responsible for several harmful algal blooms (HABs) associated with toxin production causing paralytic shellfish poisoning (PSP). Additionally, Lepidodinium chlorophorum causes green water and hypoxia locally in the Bay of Biscay. Previous studies revealed that L. chlorophorum’s success was related to possible competitive exclusion. Therefore, the phytoplankton composition and the environmental conditions should be taken into account. This study aims to assess the combined effect of changes in habitat conditions and community structure with the occurrence of HAB species, on a spatial-temporal scale. For the investigation we first used the Hutchinson’s niche concept by means of the Outlying Mean Index (OMI) analysis. The OMI analysis enable us to observe the environmental variables defining the ecological niche of the harmful species among the community. Secondly, we used the subniche theory to highlight the environmental variables defining the subniches in cases of high and low abundance of HABs with an estimation of the biological constraint restricting the species’ subniche. This was undertaken using the Within Outlying Mean indexes (WitOMI) calculated under environmental conditions promoting high (H) and low (L) abundance bloom. Thirdly, we used the Indicator Species Concept from the Indicator Species Analysis (ISA) to link the biological restriction with potential competing or indicator species. We combined a data set from the French National Phytoplankton and Phycotoxin Monitoring Network (REPHY), the Velyger network (oyster monitoring program) and satellite imagery. A total of 44 stations, over the period of 1998–2017 using 50 taxonomic units. 36 taxa had significant niche and were mostly distributed along nutrient and salinity gradients. The two species of interest L. chlorophorum and A. minutum seemed to have similar affinity for summer-like environmental conditions and both used a marginal habitat compared to the rest of the community. A. minutum had a larger niche due to a greater affinity to the estuarine-like conditions. The subniche of the two species had a similar response to the environmental variation; their respective abundance was partly caused by greater environmental restrains. Their success in abundance appeared to be linked to local hydrodynamics which increases or reduces resources. On the other hand, the biotic pressure exerted upon A. minutum and L. chlorophorum were antagonistic. A possible competitor assemblage was exposed but the analysis was inconclusive. The methodological limitations were discussed as well as a perspective for future similar studies.

有害浮游植物种类的分布，频率和强度受到环境条件变化的影响。在布列斯特湾，亚历山大细叶藻一直是与毒素生产相关的几种有害藻华（HAB）的源头，导致麻痹性贝类中毒（PSP）。此外，Lepidodinium chlorophorum在比斯开湾局部引起绿水和缺氧。先前的研究表明，L。chlorophorum的成功与可能的竞争排斥有关。因此，应考虑浮游植物的组成和环境条件。这项研究的目的是在时空尺度上评估栖息地条件和群落结构的变化与HAB物种的发生的综合影响。为了进行调查，我们首先通过离群均值指数（OMI）分析使用了Hutchinson的利基概念。OMI分析使我们能够观察到环境变量，这些变量定义了社区中有害物种的生态位。其次，我们使用亚生物位理论来强调环境变量，该变量定义了高和低HABs情况下亚生物位的水平，并估计了限制该物种亚生物位的生物学限制。这是通过使用在促进高（H）和低（L）丰度水华的环境条件下计算的外部平均数指数（WitOMI）进行的。第三，我们使用了指标物种分析（ISA）中的指标物种概念，将生物学限制与潜在竞争物种或指标物种联系起来。我们结合了来自法国国家浮游植物和植物毒素监测网络（REPHY），Velyger网络（牡蛎监测计划）和卫星图像的数据集。在1998-2017年期间，共有44个站点使用了50个分类单位。36个分类单元具有显着的生态位，并且大部分沿营养盐分分布。感兴趣的两种 我们使用了指标物种分析（ISA）中的指标物种概念，将生物学限制与潜在竞争物种或指标物种联系起来。我们结合了来自法国国家浮游植物和植物毒素监测网络（REPHY），Velyger网络（牡蛎监测计划）和卫星图像的数据集。在1998-2017年期间，共有44个站点使用了50个分类单位。36个分类单元具有显着的生态位，并且大部分沿营养盐分分布。感兴趣的两种 我们使用了指标物种分析（ISA）中的指标物种概念，将生物学限制与潜在竞争物种或指标物种联系起来。我们结合了来自法国国家浮游植物和植物毒素监测网络（REPHY），Velyger网络（牡蛎监测计划）和卫星图像的数据集。在1998-2017年期间，共有44个站点使用了50个分类单位。36个分类单元具有显着的生态位，并且大部分沿营养盐分分布。感兴趣的两种 在1998-2017年期间，共有44个站点使用了50个分类单位。36个分类单元具有显着的生态位，并且大部分沿营养盐分分布。感兴趣的两种 在1998-2017年期间，共有44个站点使用了50个分类单位。36个分类单元具有显着的生态位，并且大部分沿营养盐分分布。感兴趣的两种L. chlorophorum和A. minutum对类似夏季的环境条件似乎具有相似的亲和力，并且与社区的其他部分相比都使用了边缘生境。由于对河口状条件的亲和力更大，因此小min曲霉具有较大的生态位。这两个物种的亚生态位对环境变化具有相似的响应。它们各自的丰度部分是由于更大的环境约束所致。他们大量的成功似乎与增加或减少资源的局部流体动力学有关。另一方面，生物压力施加在小菜曲霉和绿球藻上是对立的。暴露了可能的竞争对手组合，但分析没有定论。讨论了方法学上的局限性以及未来类似研究的前景。