Abstract
During investigations of relationships between food concentrations and rates of egg production by the marine copepod
Anomalocera ornata Sutcliffe, we discovered an artifact that may be common in such experiments. Although rates of egg production by individual copepods were highly variable and rates exhibited no relation to food concentration offered during experimental incubations, egg production rates of up to 338 eggs·female
−1·day
−1 were obtained with natural phytoplankton and up to 83–128 eggs female
−1·day
−1 with unialgal phytoplankton cultures. However, concurrent measurements of ingestion rates in experiments with cultures revealed that the copepods were not eating. This suggested that food used to produce eggs during experiments had been ingested in the sea prior to capture. To test this, we offered
14C-labelled mixtures of diatoms and rotifers to five copepod species, and measured the lag period for labelled eggs to appear. Times for maximum measured values of counts per minute per egg were 9.5 h for
Acartia tonsa Dana, 16.5 h for
Centropages veliflcatus De Oliviera, 65.5 h for
Labidocera aestiva Wheeler, 89 h for
Centropages typicus Krøyer, and 91 h for
A. ornata. C. typicus and
A. ornata continued to produce eggs in filtered seawater for periods of 66.8 and 44.5 h, respectively. We concluded there is considerable interspecific variability in the lag period for conversion of ingested food to egg production in marine copepods, and this lag time must be known in order to interpret relationships between food and copepod egg production.