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

Abstract

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.

Spatial and temporal aspects of Gyrodinium galatheanum in Chesapeake Bay: distribution and mixotrophy

“…Although G.galatheanum is an obligate phototroph (Li et al, 1999), it is able to ingest a variety of nanoplankters, including phycoerythrin-containing cryptophytes (Li et al, 1996). In this present study, we dealt with the ingestion of the phycoerythrin-containing cryptophytes, because they usually co-occur with G.galatheanum in the Bay and because they are easily detected microscopically due to their orange fluorescence.…”

“…Slides were stored frozen at -20°C and subsequently examined with epifluorescence microscopy at room temperature (Zeiss filter set 487709; BP450-490 exciter filter, FT 510 dichromatic beam splitter, and LP520 barrier filter). Gyrodinium galatheanum and orange-fluorescent cryptophytes were enumerated at 400ϫ (Li et al, 1996).…”

“…In 1994, we noticed red tide patches caused by a small (<20 µm) non-thecate photosynthetic dinoflagellate in mesohaline waters of Chesapeake Bay (Li et al, 1996). Isolates of this species were identified as Gyrodinium galatheanum (Brauud) Taylor 1995 (synonym, Gymnodinium galatheanum) using scanning electron microscopy (Steidinger, personal communication).…”

“…Field and laboratory experiments have demonstrated that it is able to eat a variety of other protists, including cryptophytes, with which it commonly cooccurs in Chesapeake Bay (Li et al, 1996). Mixotrophy (i.e.…”

“…Mixotrophy (i.e. simultaneous nutritional mode of heterotrophy and autotrophy) appears common among dinoflagellates (Sanders and Porter, 1988;Bockstahler and Coats, 1993a;Jacobson and Anderson, 1996;Li et al, 1996), and has been proposed to contribute to their success under varying environmental conditions (i.e. light and nutrient limitation) (Stoecker et al, 1997).…”