Effects of experimental duration and density of Japanese dace <Emphasis Type="Italic">Tribolodon hakonensis</Emphasis> on the strength of trophic cascades on benthic algae |
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Authors: | Osamu Katano |
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Institution: | (1) National Research Institute of Fisheries Science, Fisheries Research Agency, Komaki, Ueda, Nagano 386-0031, Japan |
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Abstract: | To analyze density-mediated indirect effects through trophic cascades caused by Japanese dace Tribolodon hakonensis on the algal biomass and growth of ayu Plecoglossus altivelis altivelis, (freshwater fish belonging to Salmoniformes), I introduced zero, five, ten, and 20 dace with and without ayu into experimental
pools. Ayu fed predominantly on benthic algae, whereas dace fed on both invertebrates and algae. The percentage of algae in
the food content of dace was correlated with the number of dace in a pool. In the experiment lasting 8 days, trophic cascades
on algae were not clear. In contrast, when the experimental duration was extended to 20 days, the number of gastropods and
ephemeropteran nymphs was negatively correlated with the number of dace, consequently increasing the algal biomass and ayu
growth through trophic cascades. Compared with pools with five dace, the presence of ten and 20 dace had similar gross effects
on the number of algivorous invertebrates and algal biomass and greater gross effects on the ayu growth. The significant increase
in ayu growth in pools with ten and 20 dace strongly suggests that small positive effects on algal growth by dace accumulated
and extended to ayu during a 20-day experimental period. These results indicate the importance of analyzing interactions between
the density and behavior of the top predator and the experimental duration on the intensity of trophic cascades. |
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Keywords: | Density effect Food chain Indirect effect Interspecific relationship Stream fish |
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