Zooplankton grazing on [methyl-3H]thymidine-labeIled natural particle assemblages: determination of filtering rates and food selectivity

SUMMARY. 1. The grazing of methyl-³H]thymidine-labelled bacteria by zooplankton was studied in Lake Norrviken. Sweden.
2. Animals did not ingest bacteria attached to large colonies of the cyanobacterium Microcystis wesenbergii Kom. but small aggregates of hacteria and free bacteria were readily consumed.
3. Diaphanosoma brachyurum (Liévin). Daphnia cucullata Sars. and Daphnia galeata Sars grazed free bacteria more quickly than aggregates, but Endiaptomus gracilis (Sars), Chydorus sphaericus Müll. and Bosmi- na coregoni s.l. Baird grazed the aggregates more readily.
4. Filtering rate determinations varied from LA to 123 μl ind. ⁻¹h ^{− 1}for various species.