Predatory impact of an epiphytic hydrozoan in an upwelling area in the Bay of Coliumo (Dichato, Chile)

The natural diet of the epiphytic hydrozoan Obelia geniculata has been studied in an upwelling area in the Bay of Coliumo (Dichato, Chile) during two 24-h cycles. Number of prey per predator and predatory density have been measured. In both cycles more than 78% of the diet consisted of eggs of invertebrates and faecal pellets. Compared with other species of hydrozoans studied in a similar way, O. geniculata had a heterogeneous diet and a capture rate which was scarcely related to the peaks of abundance of its prey. This catch rate was between 632×103 and 10 393×103 prey m−2 day−1, which corresponds to a mean ingestion rate of 113% of the hydranth biomass per day. These results indicate the importance of small-sized benthic suspension feeders in upwelling systems.