Response of a littoral macroinvertebrate assemblage to a persistent hydrological drought in a permanent mountain shallow lake from northwestern Spain

Correspon Abstract – Current projections predict an intensifi cation of hydrological drought as a consequence of climate change, but we know very little about the potential effects on aquatic communities. La Baña (SW León Province, Spain) is a mountain lake suffering from increased water seepage due to geological reasons. This has caused since 2005 a situation of hydrological drought, with pronounced reduction of lake area in late summer. The aim of this study was to assess the effects of this drought on the littoral macroinvertebrate assemblage. Macroinvertebrate samples were collected in 2005 (before the drought events became apparent), 2006 and 2014, as well as in a nearby temporary pond (only in 2014). The most evident change shown by the assemblage at La Baña was a drop in richness values. Rarefaction curves showed that richness in the lake in 2014 was, for an equivalent sampling effort, only slightly higher than that in the temporary pond, and much lower than that in the lake in 2005 or 2006. However, the assemblage composition did not shift toward a fauna typical of temporary waterbodies. The results might indicate that the resistance of the assemblage was high enough to prevent changes in the first moments (differences between 2005 and 2006 were small), but not after nine years of sustained summer drought.