As an estuary being restored, the Scheldt (Belgium/The Netherlands) offers an interesting setting to study the response of organisms and ecosystems to changing conditions. In this regard, this study specifically deals with the spatio-temporal distribution and possible genetic differentiation among the species complex Eurytemora affinis (Copepoda, Calanoida). Until the 1990s, E. affinis typically occurred downstream the estuary. In parallel to water quality improvement, E. affinis since recently also occurs upstream in the estuary and in some of the tributaries. In a former study, Gasmi et al. (2014), found little genetic differentiation between the upstream population and downstream one, which is probably at the origin of the upstream population. However, surprisingly, two different genetic entities of the E. affinis complex were present: one in the main stream of the Scheldt estuary and one in its tributaries. This present work aims at understanding how independent tributaries, situated at opposite sides of the estuary, can host a single genetic entity while another one is present only in the main estuary. A dense sampling in the main stream and the two main tributaries was made in May 2014 (12 locations) and four ISSR primers producing 78 polymorphic loci were used to perform a molecular analysis. Bayesian and hierarchical analysis revealed that the results are more mixed and the different genetic entities are less well delimited than reported in our former study based on samples collected in 2012. A genetical mix between tributary and upstream populations is now observed. This suggests that a homogenization process of the E. affinis populations is in progress in parallel to the improvement of water quality. These results are discussed and several explanations are proposed.

随着河口的恢复，Scheldt（比利时/荷兰）为研究生物和生态系统对不断变化的条件的响应提供了一个有趣的环境。在这方面，本研究专门针对时空分布和可能的遗传分化，研究了复杂的Eurytemora affinis（Copepoda，Calanoida）物种。直到1990年代，嗜血链球菌通常发生在河口下游。在平行于水质改善，E. AFFINIS因为最近也发生在河口和某些支流的上游。在以前的研究中，Gasmi等人。（2014），发现上游种群和下游种群之间几乎没有遗传分化，这可能是上游种群的起源。然而，令人惊讶的是，血友病菌有两个不同的遗传实体复杂的存在：一个在Scheldt河口的主流和一个在其支流。本工作旨在了解位于河口相对两侧的独立支流如何容纳单个遗传实体，而另一个支流仅存在于主要河口中。2014年5月（在12个地点）对主流和两个主要支流进行了密集采样，并使用了四个产生78个多态性位点的ISSR引物进行了分子分析。贝叶斯和层次分析表明，与我们以前的研究（基于2012年收集的样本）所报告的结果相比，结果的混合程度更高，不同的遗传实体的界限也不太清楚。现在观察到支流和上游种群之间的遗传混合。这表明，改善水质的同时还进行了大肠杆菌的种群。讨论了这些结果并提出了几种解释。