The Influence of Grazing by two Acartia Species on Olisthodiscus luteus CARTER

Abstract. The grazing of Acartia hudsonica and Acartia tonsa was observed on cultures of Olisthodiscus luteus and Dunaliella tertiotecta presented alone and in combination. Feeding on D. lertiolecla by both Acartia species increased directly with concentration but was always lower at equivalent food concentrations when O. luteus was present. In mixed phytoplankton cultures, A. hudsonica fed on both species at low O. luteus concentration, only on D, lertiolecla at intermediate levels and stopped feeding at highest O. luteus concentrations. A. tonsa showed a variable but similar result. These studies indicate the possible role of these dominant herbivores on the dynamics of O. luteus populations.