Reconfiguration of a benthic assemblage after drought: outcomes from a long term study where native species lose and invasive species win

Background/Question/Methods

Climate change may have great effects on biodiversity at different ecological levels and spatial scales. Recently, there is also evidence that an increase in extreme climatic events can be particularly important in ecological, social and economic terms. Indeed, extreme climatic events such as droughts and floods are predicted to become more intense, more frequent and longer lasting. In this study a long data set (from 2004 to 2012) assessing the annual dynamics of the molluscan fauna present in the River Minho (NW of the Iberian Peninsula) provided us with an opportunity to show the consequences of the strong 2005 drought on this faunal group. The main aim of this study was to give a perspective of the impacts provoked by this disturbance and their devastating consequences in the native molluscan fauna and how an invasive species can take advantage of this situation. In addition we aim to: i) determine the extent and nature of change in the molluscan assemblage as a result of this disturbance in terms of density, biomass and diversity; ii) determine the species resilience and iii) discuss possible implications in terms of conservation and ecosystem functioning.

Results/Conclusions

The resulted effects of the 2005 drought were responsible for significant alterations in the molluscan fauna (e.g. distribution, diversity, density and biomass). After 2006 native species such as Bithynia tentaculata, Lymnaea peregra, Valvata piscinalis, Anodonta anatina, Pisidium amnicum, Potomida littoralis and Unio delphinus decrease significantly without any sign of recovery; whereas the invasive species Corbicula fluminea rapidly recovers from this disturbance. According to our results, the 2005 drought was responsible for a complete alteration of the molluscan fauna present in this river with important changes in ecosystem processes and functions. A related trend could take place in similar aquatic ecosystems and future ecological and conservation studies have to include the impacts provoked by strong droughts and the possible interactions with non-indigenous invasive species. Indeed, the resilience of native mollusc species to drought appears to be very low and since future climatic scenarios predicted an increase in the frequency and severity of this kind of disturbance several of these native species are threatened with local extinction.