Title: Evaluation of synchrony of feeding behaviour in individual Acartia hudsonica (Copopoda, Calanoida)
Abstract: Variability in individual feeding behaviour of Acartia hudsonica was studied in 34 samples, each of 100 individuals.The samples were collected during 3 day-night cycles from a large experimental seawater system in Norfolk, Virginia, USA.Fluorometric measurements were made to determine gut pigment contents and evacuation rates, from which ingestion rates and daily rations were calculated.Results show that gut contents were almost always < 1.2 ng pigment copepod-'.Coefficients of variation (CV) calculated for each sample, w h ~c h were used as indices of synchrony, were always < 7 0 %.The highest frequency of synchronized behaviour was observed, independent of time, in individuals from bottom samples.At night, the probability of obtaining any particular CV in individuals from bottom or surface was the same.About 45 % of individuals displayed moderately high contents (0.2 to 0.5 ng) both day and night, but the percentage of copopods with >0.5 ng pigment increased from 16 % in the day-time to 42 D/o at night.This non-uniform pattern of gut contents suggests the copepods were feeding in short-term episodes which were perhaps more frequent at night.Since food was in excess at all times at all depths, and experimental temperatures did not vary, light was probably the principal factor controlling the observed feeding periodicity.