Growth and grazing rates of the prostomatid ciliate Tiarina fusus on red-tide and toxic algae

We investigated growth and grazing rates of the prostomatid ciliate Tiarina fusus when feeding on several species of red-tide and/or toxic algae (RTA). T. fusus ingested the dinoflagellates Lingulodinium polyedrum, Scrippsiella trochoidea, Heterocapsa triquetra, Prorocentrum minimum, Amphidinium carterae, and the raphidophyte Heterosigma akashiwo, but rarely consumed the dinoflagellate Ceratium fusus, and did not feed on the dinoflagellate Prorocentrum micans. T. fusus exhibited positive growth on L. polyedrum, S. trochoidea, and H. akashiwo. Specific growth rates of T. fusus increased rapidly with increasing density of L. polyedrum, S. trochoidea, and H. akashiwo before saturating between 500 and 1000 ng C ml(-1). Maximum specific growth rate of T, fusus feeding on L. polyedrum (0.47 d(-1)) was much higher than when feeding on S. trochoidea (0.13 d(-1)) or H. akashiwo (0.10 d(-1)). Threshold prey concentrations (where net growth = 0) for L. polyedrum, S. trochoidea, and H. akashiwo were 34 to 160 ng C ml(-1). Maximum ingestion rates of T. fusus on L. polyedrum, S. trochoidea, and H. akashiwo were 23.4, 10.2, and 6.5 ng C predator(-1) d(-1), respectively, while maximum clearance rates were 4.5, 0.2, and 0.6 mul predator(-1) h(-1), respectively. T. fusus exhibited comparable or higher maximum growth, ingestion, and clearance rates than previously reported for the mixotrophic dinoflagellate Fragilidium cf. mexicanum or the heterotrophic dinoflagellates Protoperidinium cf, divergens and P. crassipes, when grown on the same prey species. Grazing coefficients calculated by combining field data on abundances of T. fusus and co-occurring RTA with laboratory data on ingestion rates obtained in the present study suggest that T. fusus sometimes has a considerable grazing impact on the populations of H. akashiwo.