Growth and grazing response of a ciliate feeding on the red tide dinoflagellate Gyrodinium aureolum in monoculture and in mixture with a non-toxic alga

Abstract

The effect of the red tide dinoflagellate Gyrodinium aureolum on the growth of the tintinnid ciliate Favella ehrenbergii was studied The ciliate is unable to sustain growth with this alga as the only food source, Irrespective of concentration. Ciliate survival decreases at very high concentrations of G. aureolum probably due to toxic substances exuded from G aureolum to the medium. This assumption is supported by the fact that growth of the ciliate is not affected by even very high concentrations of a non-toxic dinoflagellate, Heterocapsa triquetra. However, direct attempts to demonstrate toxic effects of exudates, using filtrates of dense cultures of G. aureolum, failed. Growth and grazing experiments were also carried out in which the ciliate was fed mixtures of G, aureolum and H tliquetra at relatively low algal concentrations. The growth of the ciliate was unaffected until G. aul-eolum accounted for about 7 0 % of the total biomass. In cases where G. aureolum accounted for about 90% of the algal biomass, the growth rate of the ciliate was reduced by less than 25%. Grazing experiments demonstrated that F. ehrenbergii cannot selectively avoid ingestion of G. aureolum.

Effects of the toxic haptophyte Prymnesium parvum on the survival and feeding of a ciliate: the influence of different nutrient conditions

“…Similar relationships have been reported between ciliates and other toxic phytoplankton species (Verity & Stoecker 1982, Hansen 1995. That is, ciliates can thrive among algae producing potent exotoxins, as long as the density of these algae is low and the algae do not dominate the phytoplankton assemblage.…”

Effects of Heterosigma akashiwo (Raphidophyceae) on protist grazers: laboratory experiments with ciliates and heterotrophic dinoflagellates

“…Capriulo & Carpenter 1983, Levinsen & Nielsen 2002, Johansson et al 2004 . Survival of protist grazers at low concentrations of otherwise toxic algae was seen in one other study of H. akashiwo (Verity & Stoecker 1982), as well as in studies of Prymnesium parvum (Rosetta & McManus 2003) and various dinoflagellates (Hansen 1989, Jeong & Latz 1994, Hansen 1995, Kamiyama 1997, Kamiyama & Arima 1997. Decreasing abundance of potential consumers with increasing algal density constitutes a negative feedback, which would promote further accumulation of harmful algal cells.…”

Ecology of Gymnodinium aureolum. I. Feeding in western Korean waters

“…The results of the present study indicate that the Korean strain of Gymnodinium aureolum is not toxic. However, a morphologically similar dinoflagellate, Karenia mikimotoi, is a known toxin producer (Gill & Harris 1987, Hansen 1995, Smolowitz & Shumway 1997, and accurate differentiation between these species is important.…”