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

The natural diet of the epiphytic hydrozoan Obelia geniculata has been stud ied in on upwelling area in the Bay of Coliumo (Dichato, Chile) during two 24-h cycles. Number of prey per predator and predatory density have been me asured. In both cycles more than 78% of the diet consisted of eggs of inver tebrates and faecal pellets. Compared with other species of hydrozoans stud ied 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 x 10(3) and 10 393 x 10(3) 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 suspe nsion feeders in upwelling systems. (C) 2000 Elsevier Science B.V. All righ ts reserved.