Comparative study of the planktonic communities of three lakes of contrasting trophic status at Hope Bay (Antarctic Peninsula)

Abstract

Three water bodies of contrasting trophic status located at Hope Bay (Antarctic Peninsula) were studied during the summer of 1999, analysing all of their planktonic communities (zooplankton, phytoplankton and bacterioplankton) and their main limnological features. Important differences associated with their trophic conditions were found among lakes. At one extreme of the gradient, in the most oligotrophic lake (Lake Chico), the nektobenthic copepod Boeckella poppei and the rotifer Philodina gregaria were dominant in the open waters, and copepods presented a single reproductive event (univoltine life cycle); phytoplankton exhibited the lowest densities, dominated by nanoplanktonic Chrysophyceae and picocyanobacteria. In the meso-eutrophic Lake Boeckella, B. poppei, the dominant zooplankter, exhibited a multivoltine life cycle; phytoplankton were mainly represented by nanoplanktonic species of Volvocales, alternating with flagellate Chrysophyceae, and a great abundance of picocyanobacteria. In the hypertrophic Pingüi Pond, zooplankters were exclusively represented by bdelloid rotifers and ciliates; phytoplankton samples included some strictly planktonic species (Volvocales), a great proportion of picocyanobacteria and many typically benthic species (oscillatorians and diatoms) due to the shallowness of the water body. Bacterioplankton densities did not show important differences among lakes, but fluctuations, probably associated with a top-down control, were observed in the hypertrophic pond. This paper constitutes the first survey concerning all the planktonic compartments of water bodies of different trophic status at Hope Bay, describing the relative contributions of autotrophic and heterotrophic components to their food webs.