Effects of Olisthodiscus luteus on the growth and abundance of Tintinnids

The effects of the red tide flagellate Olisthodiscus luteus Carter on the growth of two tintinnid species, Tintinnopsis lubulosoides Meunier and Favella sp. (Clap. & Lach.) Jorg., were measured in batch culture. T. tubulosoides and Favella sp. grew at rates equivalent to 1.2 (10°C) and 2.0 (20°C) population doublings per day, respectively, when offered nutritionally adequate phytoplankton species. The growth rates of both tintinnid species were reduced in the presence of 10²–10³ O. luteus cells · ml^-1 in multialgal treatments. Growth rate inhibition was proportionately greater at higher O. luteus densities. Lethal effects were observed for both tintinnid species at O. luteus concentrations of 5x10³ cells · ml^-1 in multi-algal treatments. T. tubulosoides mortality occurred at all O. luteus concentrations in unialgal culture. O. luteus-conditioned medium did not substantially inhibit tintinnid growth when combined with acceptable food species, suggesting that toxicity is induced by ingestion or direct contact with O. luteus cells, or by exposure to a short-lived exudate. In agreement with these results, an inverse relationship between O. luteus concentration and tintinnid abundance was observed in Narragansett Bay, Rhode Island, over a two year period. The small lorica diameter of the species apparently inhibited by these O. luteus blooms suggests a detrimental effect independent of cell ingestion. In addition to the absolute concentration of O. luteus cells, the availability of nutritionally adequate algal food may be an important factor determining the impact of O. luteus blooms on tintinnid populations.Contribution no. 5048 from the Woods Hole Oceanographic Institution