Taxon-specific analysis of microzooplankton grazing rates and phytoplankton growth rates

摘要

We performed laboratory experiments to test the accuracy of using HPLC to estimate taxon-specific grazing and growth rates obtained by the dilution technique. In seven of nine experiments, this technique underestimated microzooplankton grazing rates. The average estimated grazing rates were 52% of the true grazing rates for chlorophyll a and 33% for taxon-specific pigments. With the food sources Phaeodactylum tricornutum, Isochrysis galbana, Gymnodinium sp., and Emiliania huxleyi, the clearance rates for Oxyrrhis marina were between 2 x 10~(-3) and 7 x 10~(-3) ml grazer~(-1) d~(-1), at initial food concentrations of ～5x 10~3 cells ml~(-1). At higher food concentrations (1 x 10~5 cells ml~(-1)) clearance rates decreased to ～ 1 x 10~(-4) ml grazer~(-1) d~(-1). In field experiments performed in September 1991 and March 1992 in Monterey Bay, California, 21-55% of the phytoplankton standing stock was consumed daily by microzooplankton grazing. The underestimation of grazing rates in the laboratory experiments implies that rates obtained in field incubations may be in error.