Zooplankton food limitation and grazing impact in a eutrophic brackish-water tropical pond (Cote d'Ivoire, West Africa)

Gut fluorescence, feeding and egg production rates of zooplankton assemblag es were measured in a shallow, eutrophic brackish-water pond for 24 days. B rachionus plicatilis, Hexarthra intermedia and Apocyclops panamensis succes sively developed and exhibited differences in food selectivity. Rotifers se lected small particles but also had a preference for larger particles (15-2 1 mu m, Equivalent Spherical Diameter, ESD). B. plicatilis appeared less se lective than H. intermedia, which fed mostly on particles <6 mu m. A. panam ensis adults showed a selectivity for 6-21 mu m ESD particles. Laboratory e xperiments suggested that A. panamensis adults were able to shift from sest on to carnivorous feeding, depending on the availability of these food reso urces. Measurements of gut fluorescence and grazing gave comparable ingesti on rates. Rotifers displayed the highest ingestion rates (up to 486% body C d(-1)). Despite high total phytoplankton and seston biomasses, the high in gestion rates and selective grazing of rotifers induced auto food-limitatio n phenomena and caused major changes in seston abundance and size structure . Grazing impact was less important when A. panamensis dominated.