A first quantification of the overall biomass, from phytoplankton to birds, of a Mediterranean brackish lagoon: revisiting the ecosystem of Lake Ichkeul (Tunisia)

Abstract

The primary focus of this investigation was to evaluate the relevance of the first attempt to conceptualize the Ichkeul aquatic ecosystem. This 'draft model', published in 1994, was the conceptual working basis of a multidisciplinary research programme undertaken at Ichkeul Lagoon between 1993 and 1995 by a French-Tunisian-German team. The research programme was intended as the basis for devising conservation measures for the lagoon, and the data collected by the research team are used here to assess the validity of the draft model. A related goal is to make the unpublished data from the multidisciplinary study available to other researchers to improve knowledge of Mediterranean wetlands. We have compiled the biomasses of all functional groups recorded during the multidisciplinary study and compared them with the assumptions about biomass relationships in the draft model. Previously collated biomass data for seagrasses and benthic invertebrates collected from July 1993 to April 1994 are complemented by biomass estimates of phytoplankton, zooplankton, fishes and waterfowl from the same period. Thus, for the first time, biomasses of all major components of the Ichkeul aquatic community, from phytoplankton to birds, are presented together. Comparisons of these data with the qualitative biomass estimates in the draft model reveal important shortcomings in the earlier work. Biomasses of zooplankton and benthic invertebrates were underestimated in the draft model, while the biomass of migratory waterfowl was overestimated. This study is an important step towards providing the baseline information required for sound management and conservation decisions regarding the lagoon.