Abstract

The lacustrine zooplankton of Chile is characterized by a low abundance of daphniid cladocerans and a predominance of calanoid copepods, thus making up a zooplankton community quite different from that described for North American lakes. To explain this pattern, this study investigates the role of the oligotrophy, and the resulting high transparency of a considerable number of locations. Due to low levels of dissolved organic carbon, viz., Daphniidae are exposed to ultraviolet radiation. Chilean lakes located between 39° and 51°S were studied, and maximum depth, mixing depth, trophic status, and dissolved organic carbon concentrations were measured and considered. The results obtained revealed that daphniids were abundant in oligo-mesotrophic lakes with shallow mixing depth. Thus, daphniid abundance is directly associated with chlorophyll-a concentration as an energetic resource, but also with sufficient depth, because this last condition provides protection against the penetration of ultraviolet radiation. © Koninklijke Brill NV, 2006.