Using dilution grazing assays to measure size fractionated phytoplankton mortality rates across the freshwater-to-marine continuum

Abstract

There is a need for a unified grazing method that can be used across the freshwater-to-marine continuum. To accomplish this, this research utilized dilution grazing assays across the freshwater-to-marine continuum and across the oligotrophic-to-hypereutrophic gradient by measuring size fractions of dilution-based mortality. This was investigated by using 0.7 {micro}m and 0.2 {micro}m prefiltered water and major ion solutions (MIS) as diluent media for use in the Landry-Hassett grazing bioassays run in lake, river, estuarine (riverine and lagoonal), and oceanic shelf systems. Because MIS does not include vitamins that would be in prefiltered natural water, vitamin effects on grazing rate determination were also investigated for the MIS bioassays. Results show that the dilution grazing method can be broadly applied across the freshwater-to-marine continuum and across trophic gradients.