Depth related distribution of benthic macrofauna in a Costa Rican crater lake

On two different opportunities the distribution and diversity of the benthic macrofauna was studied at different depths in the Laguna del Cerro Chato crater lake, Alajuela, Costa Rica. For both surveys, the deep samples had significantly lower species diversity and evenness than the shallow samples. There was a drop in species diversity and evenness at 6 m, followed by an increase at 9 m. This pattern is associated with fluctuations in the lake's thermocline. Chironomids were the most abundant organism in both surveys and the genus Chironomus dominated at all depths. Analysis of the elements Ca, Cu, S, N, Fe, P and percentage of organic matter in the bottom sediments did not show a clear bathymetrical distribution. However, at a depth of 9 m the increase in both N content and percentage or organic matter could be related to the increase in abundance of organisms.