Microbial control of live/dead zooplankton ratio in sevastopol bay

Abstract

To explain higher fraction of live zooplankton in heavily polluted and eutrophic Sevastopol Bay comparing with cleaner adjacent waters, a hypothesis has been proposed and tested experimentally that more intensive bacteria-driven decomposition of dead organisms in the bay reduced their pool and, as a result, increased the live-to-dead zooplankton ratio. In the experiment, a heat-killed batch culture of the copepod Calanipeda aquaedulcis was used as a substrate for decomposition by natural microbial communities from the waters of different pollution status. Bacterioplankton abundance and in situ decomposition rate of copepod carcasses were shown to be about 3-fold higher in the bay (1.3 × 106 cells ml-1 and 0.13 day-1, respectively) while an approximation of zooplankton non-predatory mortality rates gave equal values for both the sites (about 0.046 day-1). These findings call for revising the ways of interpreting the results of zooplankton viability assays in their relation to water pollution status.