Collected reprints: Abstract 2787

Collected reprints

Abstract

Tackx, M.L.M.; Daro, M. H. (1993). Influence of size dependant 14C uptake rates by phytoplankton cells in zooplankton grazing measurements. Cah. Biol. Mar. 34: 253-260

C14 is currently used to label natural phytoplankton food in zooplankton grazing experiments. Carbon content per unit volume and rate of carbon uptake both decrease with cell size, following different regressions. When working with multi species phytoplankton assemblages, this physiological property results in a disproportional distribution of tracer to phytoplankton carbon biomass. Because most zooplankton organisms select certain sizes of cells, this disproportionate distribution of tracer results in bias of clearance rates determined on the total phytoplankton population with the 14C method. This paper combines experimentally determined clearance rates of the copepods A. tonsa and T. longicornis measured on natural particulate matter distributions in combination with theoretical calculations of the 14C clearance rates. It is shown that in these examples, clearance rates measured by the 14C method would underestimate the grazing pressure on the phytoplankton carbon stock by 7 to 24%.


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