MEPS 226:27-33 (2002)  -  doi:10.3354/meps226027

ABSTRACT: The application of the dilution method to productive coastal waters has been limited, in part by difficulties in interpreting the nonlinear grazing dynamics. A split-function model of microzooplankton grazing is used to adapt the dilution method for analysis of mesotrophic and eutrophic systems. Phytoplankton growth rate µ and microzooplankton grazing rate g are obtained using the conventional analysis with dilutions sufficient to ensure that grazing rate is proportional to phytoplankton concentration. When phytoplankton concentration is sufficiently great, dilution experiments indicate that grazing becomes independent of phytoplankton concentration (i.e. grazing is saturated). A straightforward calculation yields the phytoplankton concentration P_s that saturates grazing. The saturated grazing is G_s = gP_s. Grazing balances primary production when the phytoplankton concentration is P_b = gP_s/µ. In productive waters, determination of P_s is important because microzooplankton grazing becomes an increasingly irrelevant constraint on exponential phytoplankton growth as the phytoplankton concentration further exceeds P_b. Data were analyzed from a dilution experiment conducted in a mesotrophic coastal lagoon in New South Wales, Australia. Values of µ, g, P_s, and G_s were 0.53 d^-1, 0.65 d^-1, 3.8 µgchl l^-1, and 2.5 µgchl l^-1 d^-1, respectively. In this particular experiment the in situ phytoplankton concentration exceeded P_b by a factor of 1.7.

KEY WORDS: Microzooplankton grazing · Dilution method · Nonlinear models · Zooplankton · Phytoplankton growth · Saturated grazing