Ecology of Gymnodinium aureolum. II. Predation by common heterotrophic dinoflagellates and a ciliate

Abstract

We investigated whether the common heterotrophic dinoflagellates Gyrodinium dominans, Oxyrrhis marina, Pfiesteria piscicida, Polykrikos kofoidii, Protoperidinium bipes and Stoeckeria algicida, and the naked ciliate Strombidinopsis sp., were able to feed on the mixotrophic red-tide dinoflagellate Gymnodinium aureolum (GenBank accession no. FN392226). We also measured the growth and ingestion rates of G. dominans, O. marina, P. kofoidii, and Strombidinopsis sp. on G. aureolum as a function of prey concentration. We calculated grazing coefficients by combining field data on abundance of small Gyrodinium spp. (25 to 35 mu m in cell length) and Strombidinopsis spp. (>70 mu m) and co-occurring G. aureolum with laboratory data on ingestion rates obtained in this study. G. dominans, O. marina, P. kofoidii, and Strombidinopsis sp. were able to feed on G. aureolum, whereas P. piscicida, P. bipes, and S. algicida were not. The maximum growth rates of G. dominans, a marina, Strombidinopsis sp. and P. kofoidii on G. aureolum were 0.92, 0.71, 0.44 and 0.11 d(-1), respectively. However, the maximum ingestion rates of G. dominans on G. aureolum (2.0 ng C predator(-1) d(-1)) were comparable with that of P. kofoidii (2.3 ng C predator(-1) d(-1)), but much lower than that of Strombidinopsis sp. (69.7 ng C predator(-1) d(-1)). Calculated grazing coefficients for small heterotrophic Gyrodinium spp. and large Strombidinopsis spp. on G. aureolum were up to 0.40 d(-1) and 0.25 d(-1), respectively (i.e. up to 33 and 22% of G. aureolum populations were removed by small Gyrodinium and Strombidinopsis populations in 1 d, respectively). The results of the present study suggest that small Gyrodinium spp. and Strombidinopsis sp. sometimes have considerable grazing effect on populations of G. aureolum.