Lack of accumulation of paralytic shellfish poisoning (PSP) toxins in the tintinnid ciliate Favella taraikaensis feeding on the toxic dinoflagellate Alexandrium tamarense

Abstract

To clarify the fate of paralytic shellfish poisoning (PSP) toxins in planktonic food webs, toxin contents of the planktonic ciliate Favella taraikaensis feeding on Alexandrium tamarense and of the surrounding seawater were examined in laboratory experiments using high-performance liq- uid chromatography fluorometric detection. During 5 or 6 d incubation periods in 3 replicate experi- ments, F. taraikaensis actively ingested A. tamarense and reached 8 to 17-fold initial density values. At the end of the incubation, the toxin concentration of the suspension consisting mostly of F. taraikaensis, which had increased by feeding on A. tamarense, was much lower than that of A. tamarense cells. The toxin content of pure F. taraikaensis, which was analyzed based on 165 to 200 individuals of F. taraikaensis directly taken from the suspension, was also lower than the cellular tox- icity of A. tamarense. Toxin concentration in filtrates of the F. taraikaensis suspension was signifi- cantly higher than that in filtrates of the suspension containing only A. tamarense. Furthermore, the total toxin concentration in the F. taraikaensis suspension (particulates plus the filtrate) was almost equivalent to that in the A. tamarense suspension in each trial. We conclude that the PSP toxins of A. tamarense are not accumulated in F. taraikaensis over 24 h in the course of predator-prey inter- actions, and the toxins are rapidly excreted from the cell body of the ciliate.