Abstract
We examined the potential advantage of the association of Hemicyclops species with decapod burrows in their avoidance from fish predators through gut-content analysis of fishes collected from the estuary of the Tama River, Japan, and an experiment applying model burrows. The small gobiid species Pseudogobius masago, collected from an area dominated by burrows of the ocypodid crab Macrophthalmus japonicus, showed a high frequency of Hemicyclops gomsoensis in their guts relative to the other co-occurring fish species. In the experiment, no significant difference was observed in the numbers of H. gomsoensis eaten by the goby between the treatments with and without the model burrows. Another goby, Acanthogobius flavimanus, from an area dominated by burrows of the mud shrimp Upogebia major, showed very low frequencies of H. gomsoensis in their guts, as compared with those in P. masago. They had also ingested H. spinulosus and H. ctenidis, in spite of the overwhelmingly high abundance of H. gomsoensis in the burrows. The number of H. gomsoensis eaten by A. flavimanus was significantly lower in the treatments with the model burrows than in the absence of burrows. Since A. flavimanus was the most dominant demersal fish in the study area, H. gomsoensis seemed to avoid predation from this potentially strong predator by inhabiting the decapod burrows. H. ctenidis and H. spinulosus seemed to avoid predation by trespassers by inhabiting the smaller burrows of polychaetes, but this strategy may be less efficient against large predators that feed on polychaetes.
