Daphnia magna Straus Living in an aerated sewage lagoon as a source of chitin : Ecological aspects.

As a means of determining the suitability of microcrustaceans living in aerated lagoons as a source of chitin, the biomass of these animals was measured twice monthly from October 1993 to November 1994 in a lagoon receiving the waste waters of the town of Differdange (G.D. of Luxembourg). The production and chitin content of Daphnia magna Straus, the dominant species of the zooplanktonic community (by number and biomass), were assessed over the same period. From December to February, the microcrustacean biomass was low, varying from 0.035 to 0.440 g.m(-2). High biomass values were observed in April and June (about 4.3 g.m(-2)) as a consequence of phytoplankton blooms and an increase in temperature. In November, despite the scarcity of algal food, the Daphnia magna biomass peaked up to 5.5 g.m(-2) due to the ability of these organisms to use bacteria and detritus for food. Throughout the sampling period, the Daphnia magna biomass far exceeded the Cyclops spp biomass. Fluctuations in the daily chitin production of Daphnia magna paralleled the biomass fluctuations of the species, with maximum values measured in April (1.9 g.m(-2).day(-1)) and June (4.8 g.m(-2).day(-1)). The chitin content of Daphnia magna ranged from 2.9 to 7.0\% of the total body dry weight. By the summation of the daily chitin productions of the species, the annual chitin production of Daphnia magna was estimated at 11.5 g.m(-2).year(-1). This figure is compared with the chitin production of other crustaceans in the natural environment. Prospects for using Daphnia magna living in the studied aerated sewage lagoon as a source of chitin are discussed.