Mesozooplankton structural responses in a shallow temperate estuary following restoration measures

Estuaries are extremely variable and unstable ecosystems subject to a wide range of influences, both natural and anthropogenic. Therefore, assessing the consequences of human impacts is crucial to predict and prevent changes in its communities. The Mondego estuary represents a good example of an impacted coastal system since the beginning of the 1990s until now and hence it has been subject to several physical interventions in an attempt to recover the ecosystem status. The effects of one of the latest intervention that took place in May 2006 were assessed using a monitoring programme carried out subsequently (2006–2009) and compared to a zooplankton database covering the period prior to this intervention (2003–2006). Using five sampling stations, the post-intervention period presented a higher total mesozooplankton density mainly of estuarine species. A station downstream of the intervention zone showed higher abundances of Acartia tonsa when it was previously dominated by the marine congener Acartia clausi. In general, at downstream sampling stations, communities of the two main channels became more homogeneous. However, results should be interpreted with care since during this period, the Mondego estuary experienced climatic variability that could mask or emphasize community responses. This paper contributes to understand the role of zooplankton communities in estuarine systems highlighting the importance of integrating natural, climatic and anthropogenic changes for a better understanding of ecosystems.