Feeding by common heterotrophic protist predators on seven Prorocentrum species

Abstract

Species belonging to the dinoflagellate genus Prorocentrum are known to cause red tides or harmful algal blooms. To understand the dynamics of a Prorocentrum sp., its growth and mortality due to predation need to be assessed. However, there are only a few Prorocentrum spp. for which heterotrophic protist predators have been reported. We explored feeding by the common heterotrophic dinoflagellates Gyrodinium dominans, Oxyrrhis marina, Pfiesteria piscicida, Oblea rotunda, and Polykrikos kofoidii and the naked ciliate Strombidinopsis sp. (approx. 90 pm cell length) on the planktonic species Prorocentrum triestinum, P. cordatum, P. donghaiense, P. rhathymum, and P. micans as well as the ben thic species P. lima and P. hoffmannianum. All heterotrophic protists tested were able to feed on the planktonic prey species. However, O. marina and O. rotunda did not feed on P lima and P. hoffinannianum, while G. dominans, P. kofoidii, and Strombidinopsis sp. did. The growth and ingestion rates of G. dominans and P kofoidii on one of the seven Prorocentrum spp. were significantly different from those on other prey species. G. dominans showed the top three highest growth rates when it fed on P. triestinum, P. cordatu in, and P. donghaiense, however, P. kofoidii had negative growth rates when fed on these three prey species. In contrast, P. kofoidii had a positive growth rate only when fed on P. hoffmannianum. This differential feeding on Prorocentrum spp. between G. dominans and P. kofoidii may provide different ecological niches and reduce competition between these two common heterotrophic protist predators.