Journal of Plankton Research Vol.23 no.3 pp.303-318, 2001
© Oxford University Press 2001
Use of the Food Vacuole Content Method to Estimate Grazing by the Mixotrophic Dinoflagellate Gyrodinium Galatheanum on Cryptophytes
1 Horn Point Laboratory, University Of Maryland Center For Environmental Science, Cambridge, Md 21613 And 2 Smithsonian Environmental Research Center, Box 28, Edgewater, Md 21037,Usa
3 Present Address: Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Ma 02543-1049, Usa
We measured in situ grazing rates of the mixotrophic dinoflagellate Gyrodinium galatheanum (Braarud) Taylor 1995 on populations of phycoerythrin-containing cryptophytes in Chesapeake Bay. Rates were estimated from instantaneous food vacuole contents, in situ temperatures, cryptophyte abundances and experimentally determined digestion rates. Laboratory digestion experiments showed that specific digestion rate constants increased sigmoidally with temperature, but were unrelated to the initial food vacuole content when it was <0.46 cryptophytes dinoflagellate1. These results allowed us to establish an empirical model to estimate in situ ingestion of cryptophyte prey by G. galatheanum. The estimated rates ranged from 0 to 0.26 cryptophytes dinoflagellate1 day1, corresponding to daily ingestion of 012.29 pg carbon, 02.48 pg nitrogen and 00.34 pg phosphorus dinoflagellate1. Estimated daily consumption of cryptophyte biomass by G. galatheanum was equivalent to 012% of body carbon, 013% of body nitrogen and 021% of body phosphorus. Estimated in situ clearance rates for cryptophytes ranged from 0 to 0.27 µl dinoflagellate1 day1, representing daily removal of 04% of the cryptophyte standing stock. Although G. galatheanum may increase its growth rate through phagotrophy, it appears to have little grazing impact on cryptophyte prey populations.
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