Temperature-Dependent Population Dynamics, Production, and Feeding of the Chaetognath Aidanosagitta crassain a eutrophic Temperate Inlet

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 crassain a eutrophic inlet of the Inland Sea of Japan. The population density fluctuated from 1.0 individual (or 0.0029 mg C) m^-3to 3,370 individuals (or 14.69 mg C) m^-3over an annual temperature range of 8.9–28.2ºC, with a small, but protracted peak in winter and a large, sharp peak in summer. There were always three separable size groups or subpopulations, each of which produced 6–7 generations, yielding a total of 19 generations. The time to first maturity (range: 32–71d), minimum size for reproduction, mean body length of mature adults, and life span (range: 34–96 d) were negatively correlated with mean water temperature at which each generation developed. The specific growth rate of each generation, varied from 0.07 to 0.22 d^-1, was a positive function of temperature, and the population’s annual production rate was 91.49 mg C m^-3y^-1. This chaetognath displayed a preference for progressively larger preyas they grew, but with no strict taxonomic preference when the prey size was suitable. Mean prey numbers in the guts and predicted temperature-dependent digestion times provided estimates of feeding rates (0.69–11.4 prey ind^-1d^-1) and of carbon weight-specific feeding rates (0.01–0.81 d^-1), both of which fluctuated largely in seasonal temperature variations. Assuming the annual mean gross growth efficiency to be 45%, which was attained in warm seasons, the A. crassapopulation would have consumed only a small part (<5.9%) of annual zooplankton prey production. The prominent early summer population peak declined in mid-summer and fall, which could be attributable to gelatinous predators.