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Aquatic Microbial Ecology

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AME 10:139-147 (1996)  -  doi:10.3354/ame010139

Ingestion of fluorescently labeled and phycoerythrin-containing prey by mixotrophic dinoflagellates

Li A, Stoecker DK, Coats DW, Adam EJ

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 nanoflagellates, a diatom, and an oligotrichous ciliate. Cryptophytes were not readily stained with CMFDA, but phycoerythrin-containing members of this phylum have a distinct yellow-orange fluorescence and thus can be used unstained to demonstrate ingestion. With these complementary techniques, we qualitatively demonstrated feeding by the dinoflagellates Ceratium furca, Gymnodinium sanguineum, Gyrodinium estuariale, Prorocentrum minimum (= mariae-lebouriae) and Peridiniumbrevipes in natural assemblages from Chesapeake Bay, USA. We also used CMFDA-stained Isochrysisgalbana (Prymnesiophyta) and unstained Cryptomonas sp. (Cryptophyta) in laboratory and field studies, respectively, to examine prevalence of feeding by G. estuariale as a function of prey density. However, determination of in situ grazing rates for mixotrophic dinoflagellates proved difficult, as only a small percentage of cells contained labeled food vacuoles following short incubations (<= 4 h) with stained prey added at tracer concentrations. The use of CMFDA-stained cells and phycoerythrin-containing prey as markers of ingestion should also be applicable to species-specific feeding studies with other phagotrophic protists and micro-metazoa. The protocols presented here have advantages 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 against, inert particles.

Chesapeake Bay . Ciliates . CMFDA-labeled protists . Cryptophytes . Dinoflagellates . Grazing . Mixotrophy

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