2018 年 13 巻 3 号 p. 95-103
The calanoid copepod Acartia steueri Smirnov, 1936 is a dominant embayment species in the temperate coastal waters of Sagami Bay, Japan and food concentration in the embayment area varies abruptly. In this study, we examined the biological responses of A. steueri in the embayment following an abrupt decrease in food concentration and subsequent starvation in the laboratory. Unlike other neritic species, A. steueri survived for 18 days and continued to produce eggs for 15 days under starvation. Dry weight, carbon weight, and C/N ratio of A. steueri under the high food condition were much higher than those of other Acartia copepods, while prosome length and nitrogen weight of A. steueri were similar. The length–weight relationship of A. steueri was atypical for marine planktonic copepods. Oil-like droplets, similar to the oil sac in oceanic copepods, were observed in the body cavity of A. steueri raised at the high food condition for more than 10 days. In the field, the rapid accumulation of lipids during sporadic high food conditions might contribute to continue the metabolism and egg production under low food conditions until they encounter favorable food conditions again. Thus, the survival strategy to abrupt changes in food concentration or starvation might support the population of A. steueri in the embayment.