Effects of Temperature and Food Concentration on the Population Recruitment of Acartia bifilosa (Copepoda, Calanoida): Implications for the Over-Summering Life History Strategy in Jiaozhou Bay

Abstract

To obtain a clear understanding of the over-summering life history strategy of the dominant species A. bifilosa in the Jiaozhou Bay, the effects of high temperature and food concentration (represented by chlorophyll a, Chl a) simulating in situ summer conditions on the reproduction and post-embryonic development of A. bifilosa were studied. We found that the A. bifilosa population did not disappear from the seawater column in summer, and its abundance increased from June to July, and then sharply declined in August. Both temperature and food concentration had a significant influence on the reproduction of A. bifilosa. The results showed that 20 °C could not trigger the decline in population abundance and the resting egg strategy, and 28 °C was the upper threshold of A. bifilosa in the Jiaozhou Bay. Higher food concentration was essential for A. bifilosa to maintain population recruitment at a higher temperature. Nauplii could develop to adults in the higher-food-level treatments (10 and 15 μg/L Chl a). However, nauplii could not develop to copepodite at 28 °C with 5 μg/L Chl a. Neither temperature nor food concentration could induce resting eggs, and no resting eggs were detected in our study. A principal components analysis showed that temperature plays a more vital role than food concentration in determining the population recruitment of A. bifilosa. We suggest that A. bifilosa populations could sustain the high-temperature season independent of producing resting eggs in the Jiaozhou Bay, and implications for the over-summering life history strategy of A. bifilosa in the Jiaozhou Bay should be further discussed.