IFREMER-Centre de Bretagne, ODE/DYNECO, Plouzané, France; IFREMER-Centre de Bretagne, ODE/DYNECO, Plouzané, France.
IFREMER-Centre de Bretagne, ODE/DYNECO, Plouzané, France.
Harmful Algae. 2020 Mar;93:101785. doi: 10.1016/j.hal.2020.101785. Epub 2020 Mar 8.
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.
浮游植物物种的分布、频率和强度受到环境条件变化的影响。在布雷斯特湾，亚历山大藻曾引发过多次与毒素产生有关的有害藻华（HAB），导致麻痹性贝类中毒（PSP）。此外，绿裸甲藻在比斯开湾局部地区引发绿水和缺氧现象。先前的研究表明，绿裸甲藻的成功与其可能的竞争排斥有关。因此，应该考虑浮游植物的组成和环境条件。本研究旨在评估在时空尺度上，生境条件和群落结构变化与有害物种赤潮发生之间的综合影响。为了进行调查，我们首先使用 Hutchinson 的生态位概念，通过离群均值指数（OMI）分析来实现。OMI 分析使我们能够观察到有害物种在群落中的生态位所定义的环境变量。其次，我们使用亚生态位理论来突出高（H）和低（L）赤潮丰度情况下定义亚生态位的环境变量，并估计限制物种亚生态位的生物约束。这是通过在促进高（H）和低（L）赤潮丰度的环境条件下计算的离群均值指数（WitOMI）来实现的。第三，我们使用指示物种分析（ISA）中的指示物种概念将生物约束与潜在的竞争或指示物种联系起来。我们结合了来自法国国家浮游植物和藻毒素监测网络（REPHY）、Velyger 网络（牡蛎监测计划）和卫星图像的数据。在 1998 年至 2017 年期间，总共 44 个站点，使用了 50 个分类单元。36 个分类群具有显著的生态位，主要分布在营养盐和盐度梯度上。两种感兴趣的物种绿裸甲藻和亚历山大藻似乎对夏季型环境条件有相似的亲和力，并且与群落的其他部分相比，它们都使用了边缘栖息地。由于对河口型条件的亲和力更强，亚历山大藻的生态位更大。这两个物种的亚生态位对环境变化的反应相似；它们各自的丰度部分是由于更大的环境限制。它们在丰度上的成功似乎与增加或减少资源的局部水动力有关。另一方面，亚历山大藻和绿裸甲藻受到的生物压力是拮抗的。暴露了一个可能的竞争组合，但分析结果并不明确。还讨论了方法学限制以及对未来类似研究的展望。
