Abstract
We aimed to identify spatial variability in estuarine trophic pathways and to elucidate their role as a nursery for juvenile fishes along Chikugo River estuary, Japan. First, we investigated distribution of larval and juvenile fishes and their diets. Using estuarine-dependent species as a model, we analyzed diets of Japanese sea bass (Lateolabrax japonicus) and conducted copepod distribution and gut fluorescence studies. To evaluate the nursery functions of spatially variable food webs, we used several indices: copepod biomass, feeding intensity, gut content biomass, growth rates, RNA/DNA ratio, condition factor, and starvation status of sea bass larvae and juveniles. We identified four different spatial distribution patterns of fishes: oligohaline, mesohaline, euryhaline, and polyhaline. Copepod assemblages and diets of fishes were completely different among the regions. Gut chlorophyll a and phaeopigment indicated that copepods in the oligohaline region depend on a detrital food web, while in the euryhaline region they depend on an algal food web. The oligohaline region had maximum turbidity, nutrients, chlorophyll pigments, and copepod biomass, and sea bass juveniles had higher feeding intensity, gut content biomass, RNA/DNA ratio, growth rate, and condition factor and lower starvation rates. This suggests that the oligohaline region, supported by a detrital food web, is an important nursery that positively influences fish growth and condition.
Published Version
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