THE SIZE ABUNDANCE DISTRIBUTION AND TAXONOMIC COMPOSITION OF PLANKTON IN AN OLIGOTROPHIC, HIGH MOUNTAIN LAKE (LA-CALDERA, SIERRA-NEVADA, SPAIN)

In this paper we describe the main features of the size-abundance distribution and taxonomic structure of plankton in an oligotrophic, high mountain lake (La Caldera, Sierra Nevada, Spain). The distribution is characterized by a discontinuity in the size range between ̃2000 and 32 000 μm3 (cell volume). Phytoplankton are numerically dominated by the cyanobacteria Cyanarcus sp., followed by the chrysophyte Chromulina nevadensis and the diatom Cyclotella ocellata. Some microplanktonic species such as the diatom Navicula radiosa were observed sporadically. The size spectrum and composition of the zooplanktonic community are dominated by the copepod Mixodiaptomus laciniatus. On considering biomass, however, the maximum values are associated with the largest size classes, dominated by the cladoceran Daphnia pulex. Both the size structure and taxonomic composition of the planktonic community studied are consistent with expectations based on theories relating the pattern of energy flow and trophic status in lakes. © 1990 Oxford University Press.