Growth and grazing rates of the marine planktonic ciliate Strombidinopsis sp. on red-tide and toxic dinoflagellates

We investigated growth and grazing rates of Strombidinopsis sp. when feeding on several species of red-tide and/or toxic dinoflagellates. Strombidinopsis sp., one of the largest aloricate choreotrichs so far reported, grew well on Lingulodinium polyedrum, Gymnodinium sanguineum, Scrippsiella trochoidea, Cochlodinium polykrikoides, and Prorocentrum minimum, but failed to grow on Amphidinium carterae. Specific growth rates of Strombidinopsis sp. increased rapidly with increasing prey density up to ca. 100 ng C ml(-1), but were saturated or increased slightly at higher concentrations. Maximum specific growth rates of Strombidinopsis sp. on various prey species were 1.38 day(-1) for C. polykrikoides, 1.27 for G. sanguineum, 1.06 for P. minimum, 0.83 for L. polyedrum, and 0.67 for S. trochoidea. Threshold prey concentrations (where net growth = 0) were 12-38 ng C ml(-1). Maximum ingestion and clearance rates of Strombidinopsis sp, were 353 ng C grazer(-1) day(-1) and 110 mu l grazer(-1) h(-1), respectively. Strombidinopsis sp. exhibited higher maximum growth, ingestion, and clearance rates than the mixotrophic dinoflagellate Fragilidium cf. mexicanum or the heterotrophic dinoflagellates Protoperidinium cf. divergens and P. crassipes, when grown on the same prey species. In addition, the sequence of prey species arranged according to growth response of Strombidinopsis sp. differed considerably from those of Fragilidium cf. mexicanum, Protoperidinium cf. divergens, and P. crassipes.