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Substrate and depth preferences of macroinvertebrates along a transect in a Pyrenean high mountain lake (Lake Redó, NE Spain)

Abstract:

We studied the macrozoobenthos along a transect in Lake Redó (Pyrenees), within the framework of the European programme MOLAR (Mountain Lake Research). Samples were taken at 2-metre intervals at depths from 4 to 20 metres by SCUBA divers. Two kinds of samples were taken, individual stones (three replicates) and cores (three replicates) from the soft sediment areas. In the deeper areas, samples were taken with an Ekman grab. All the samples were taken on the same date (15 July 1997). Using the Mantel autocorrelogram analysis two discontinuities were found in the stony bottom community. The first was at 4 m, and distinguishes the littoral from the sublittoral community, and the second was at 14 m, coincident with the lower part of the thermocline in summer. The layer is characterized by the fact that it receives less than 10% of surface incident light, by greater accumulation of detritus on stones and by the disappearance of macroscopic algae covering stones down to this depth. Several species preferred soft bottom areas (Oligochaeta, Micropsectra radialis and Pseudodiamesa nivosa, among the chironomids), while others were more abundant on the stones (Radix peregra, Plectrocnemia laetabilis, Psectrocladius octomaculatus). These results should be useful in aiding interpretation of data from subfossil records from cores taken in the lake. © Asociación Española de Limnología.