Key points are not available for this paper at this time.
In order to experimentally investigate feeding by mixotrophic dinoflagellates, we developed protocols for the use of live protistan prey as markers of ingestion. CMFDA (5-chloromethylfluorescein diacetate), a vital green fluorescent stain, was used to label cultures of photosynthetic nanoflagelIates, a diatom, and an oligotrichous ciliate. Cryptophytes were not readily stained with CMFDA, but phycoerythrin-containing members of this phylum havo a distinct yellow-orange fluorescence and thus can be used unstained to demonstrate ingestion. M'ith these complen~entary techniques, we qualitatively demonstrated feeding by the dinoflagellates Ceratium furca, G)/~nnodinium sanguineum, Gj,rodinium estuariale, Prorocentrum n ~~n i m u m (= mariae-lebouriae) and Peridinium brevipesin natural dsscmblages from Chesapeake Bay, USA. LVe also used CMFDA-stained Isochrysis galbana (Prymncsiophyta) and unstained Cryptomonas sp (Cryptophyta) in laboratory and field studles, respectively, to examine prevalence of feeding by C estuariale as a function of prey dens~ty However, determination of in situ grazing rates for m~xotrophic dlnoflagellates proved difficult, as only a small percentage of cells contained labeled food vacuoles follolving short incubations (5 4 h) with stained prey added at tracer concentrations. The use of CMFDA-stained cells and phvcoerythrincontaining prey as markers of ingestion should also be applicable to species-specific feeding studies with other phagotrophic protists and micro-metazoa. The protocols prescmtcd here have advantaqas over the use of fluorescent microspheres or fluorescently labeled heat-killed algae (FLA) for investigating grazing or predation because many micrograzers do not readily ingest, or discriminate agalnst. inert particles.
Li et al. (Mon,) studied this question.