Benthic fauna of Banyoles Lake (NE Spain)

Summary

The characteristic karstic morphology of the Banyoles Lake (with four main basins) and its subterranean water inflow are the origin of the different thermic stratification and dissolved oxygen conditions in each one of their basins. This fact determines the benthic fauna of each basin.

We can distinguish three different situations. The first one is the permanent meromictic basin III with a profundal benthic community composed only of Chaoborus flavicans.

In basin IV at 13–14 m depth a low oxygen concentration exists since July to November. The benthic community is present from February until October with low species richness and densities. Chaoborus flavicans and chironomids are the most abundant macroinvertebrates.

Finally basin I has rich benthic fauna, due to the very short anoxia period (one month). At 20 m deep, the macroinvertebrates are dominated by Oligochaeta, Chironomidae and Chaoborus. At 12 m chironomids are the most abundant, then Oligochaeta, Chaoborus and Gammaridae. In the upper sublittoral zone (5 m), benthos is still more diverse, with large amounts of chironomids and the presence of Ephemera. There is also a clear substitution of the Chydoridae (mainly Leydigia) by the cladoceran Iliocryptus with depth.