Abstract
Behavioural observations were made on two copepods, Eurytemora herdmani and Acartia hudsonica, presented with 18 dissolved L-amino acids the concentrations of which ranged from 10−8 M to 10−2 M. The onset and duration of the swarming behaviour were determined by the structure and concentration of a restricted number of molecules, which differed depending on the copepod species. Dicarboxylic amino acids were the most stimulatory agent for E. herdmani, whereas A. hudsonica responded preferentially to aliphatic amino acids. Both the feeding and swarming of A. hudsonica could be induced by the same kind of molecules. The threshold sensitivity of the copepods appeared to be compatible with the natural concentrations of the dissolved free amino acids measured at sea. These findings are discussed with reference to the chemically mediated interactions between phytoplankton and zooplankton.
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