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.
Highlights
Zooplankton have been widely shown to suffer from non-predatory mortality owing to starvation, diseases, injuries, parasites, harmful algal blooms, environmental stresses (Carpenter et al, 1974; Murtaugh, 1981; Byron et al, 1984; Burns, 1985; Ianora et al, 1987; Kimmerer, McKinnon, 1990; Hall et al, 1995; Delgado, Alcaraz, 1999; Gomez-Gutierrez, 2003; Tang et al, 2006; Dubovskaya, 2009; Elliott, Tang, 2011)
Material and Methods To estimate microbial abundances and conduct decomposition experiments in situ, seawater samples were collected at two stations in Sevastopol Bay and adjacent, open waters (Fig.2)
Under steady-state conditions (μ = m, constant NL) in the model population, fraction of live organisms (FLO) depends on ND and, on the ratio between the nonconsumptive mortality rate (m) of live zooplankton and the decomposition rate (d) of copepod carcasses
Summary
Zooplankton have been widely shown to suffer from non-predatory mortality owing to starvation, diseases, injuries, parasites, harmful algal blooms, environmental stresses (Carpenter et al, 1974; Murtaugh, 1981; Byron et al, 1984; Burns, 1985; Ianora et al, 1987; Kimmerer, McKinnon, 1990; Hall et al, 1995; Delgado, Alcaraz, 1999; Gomez-Gutierrez, 2003; Tang et al, 2006; Dubovskaya, 2009; Elliott, Tang, 2011). Recent studies of live and dead planktonic copepods in Sevastopol bay and adjacent coastal waters (Litvinyuk et al, 2011) have revealed a surprising pattern: average annual fraction of live organisms (FLO) in highly polluted and eutrophic waters of the bay was significantly higher than one in the cleaner offshore area (Fig. 1).
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