• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.14 no.3
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• pp.189-194
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• 2009

To investigate the difference in the ecological niches between Pfiesteria piscicida and Pfiesteria-like species (Cryptoperidininopsis brodyi and Stoeckeria algicida), we have observed the feeding behavior of three potential predators on abalone larvae and measured the survival rates of abalone larvae as a function of initial predator concentration. When the predators were mixed with abalone larvae, P. piscicida and C. brodyi became active and exhibited attacking behavior on abalone larvae within a few seconds. They could ingest whole soft body of abalone larvae using a peduncle. In contrast, feeding and attacking behavior were not observed from S. algicida. Survival rates in abalone larvae decreased with an increase of the initial concentration of P. piscicida and C. brodyi. These results indicate that Pfiesteria and Pfiesteria-like species displaying the very same shape and size have different ecological niche in the marine food webs, which implies that identification to species level is definitely important to understand and discriminate the ecological roles of them.

• ALGAE
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• v.29 no.2
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• pp.153-163
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• 2014

Mesodinium rubrum is a cosmopolitan ciliate that often causes red tides. Predation by heterotrophic protists is a critical factor that affects the population dynamics of red tide species. However, there have been few studies on protistan predators feeding on M. rubrum. To investigate heterotrophic protists grazing on M. rubrum, we tested whether the heterotrophic dinoflagellates Gyrodiniellum shiwhaense, Gyrodinium dominans, Gyrodinium spirale, Luciella masanensis, Oblea rotunda, Oxyrrhis marina, Pfiesteria piscicida, Polykrikos kofoidii, Protoperidinium bipes, and Stoeckeria algicida, and the ciliate Strombidium sp. preyed on M. rubrum. G. dominans, L. masanensis, O. rotunda, P. kofoidii, and Strombidium sp. preyed on M. rubrum. However, only G. dominans had a positive growth feeding on M. rubrum. The growth and ingestion rates of G. dominans on M. rubrum increased rapidly with increasing mean prey concentration < $321ngCmL^{-1}$, but became saturated or slowly at higher concentrations. The maximum growth rate of G. dominans on M. rubrum was $0.48d^{-1}$, while the maximum ingestion rate was 0.55 ng C $predator^{-1}d^{-1}$. The grazing coefficients by G. dominans on populations of M. rubrum were up to $0.236h^{-1}$. Thus, G. dominans may sometimes have a considerable grazing impact on populations of M. rubrum.