Abstract
The effects of temperature and food concentration on the egg production rate (EPR) of the tropical calanoid copepod Acartia amboinensis were studied from the coastal waters of the central Red Sea in March 2017. In the first experiment, adult females were incubated in glass bottles that were pre-filled with screened seawater containing a natural assemblage of phytoplankton. In the second experiment, the species were incubated in glass bottles that were enriched with different concentrations of Chaetoceros muelleri along with natural assemblages of phytoplankton. Both the experimental setups were then exposed to different temperatures (21, 24, 27, 30 and 33 degrees C). The daily EPR varied significantly across different temperatures and the various food concentrations (p < 0.05). Within the natural food assemblage (Exp. 1), the EPR increased gradually to a peak mean of 13.7 eggs female(-1) d(-1) at 27 degrees C, then declined as temperatures increased (at 30 and 33 degrees C). In the second experiment when the water was enriched with algal culture, EPRs were significantly greater (maximum EPR: 63.9 eggs female(-1) d(-1) at 27 degrees C) than those incubated in ambient water with natural food (maximum EPR: 17.4 eggs female(-1) d(-1) at 21 degrees C). The hatching rate fluctuated between 42.4% and 88.6%. The present study revealed that the EPR of Acartia amboinensis responded rapidly to changes in food availability, suggesting an extreme food limitation in the central Red Sea.