Seasonal population dynamics, production, and feeding of the chaetognath Aidanosagitta crassa in a temperate eutrophic inlet

抄録

Once-to-twice weekly sampling at nocturnal high tide for a year enabled us to detail the seasonal population dynamics, production, and feeding of the chaetognath Aidanosagitta crassa in a eutrophic inlet of the Inland Sea of Japan. The population density fluctuated from 1.0 ind (or 0.0029 mg C) m⁻³ to 3,370 ind (or 14.69 mg C) m⁻³, with a small, protracted peak in winter and a large, sharp peak in summer. The population consisted of 3 subpopulations, each of which produced 6–7 generations, yielding a total of 19 generations. In most generations, the mortality was notably higher in the egg to small juvenile (body length: ca. 2 mm) stage and in the adult stage than in the large juvenile stage. Basic population parameters, e.g., time to first maturity (range: 32–71 d), minimum size for reproduction (4.0–8.9 mm), mean body length of mature adults (5.5–10.4 mm) and life span (34–96 d), were negatively correlated with temperature. The specific growth rates (0.07–0.22 d⁻¹) were a positive function of temperature, yielding an annual population production rate of 91.49 mg C m⁻³ y⁻¹. Only one third of A. crassa contained prey in the gut, and their feeding habit was completely carnivorous, with preference for progressively larger prey with their growth. Estimated carbon weight-specific feeding rates (0.01–0.81 d⁻¹) sustained net growth with a mean gross growth efficiency of 45% in warm seasons (≥ca. 15°C). This highly intensive survey of the A. crassa population serves as a benchmark for intra- and interspecific comparisons of ecophysiological and population parameters.