Impact of improved bottom hypoxia on zooplankton community in shallow eutrophic lake

Abstract

Key-words:oxygen condition, hypoxia, zooplankton, copepod, brackish lakeWe followed changes in the abundance of meso-and microzooplankton after an existing bottom hypoxia improved by the introduction of water with high oxygen content into the bottom. Mesozooplankton, calanoid copepod Acartia hudsonica showed ten times higher abundance under high oxygen condition at the bottom than under control where there was less oxygen at the bottom. On the other hand, during summer when microzooplankton such as rotifers and small cyclopoid species Oithona spp. were dominant, no difference in their distribution pattern and abundance was observed. Results have suggested that oxygen concentration at the bottom is one important factor determining the abundance and distribution of mesozooplankton even in local-scale probably by providing bottom refuge, but not for microzoooplankton. Since spring season is important for recruitment of many commercial fish juveniles, the distribution of oxygen in the lake seems very important for the fish stock in the lake.

Zooplankton Community Responses to Oxygen Stress

“…This is consistent with our results, which showed that most rotifers seemed to prefer low oxygen conditions, and the smaller Cladocera were more resistant to oxygen depletion than the larger daphnids. The results from field studies also suggest that decreased meta-and hypolimnetic oxygen concentrations resulted in a shift in zooplankton from large to smaller species [14,18,19]. We observed a similar pattern of changes in zooplankton community structure as a result of oxygen stress, regardless of trophic status, which indicated that oxygen stress is one of the most important factors altering zooplankton structures.…”

Combined effects of elevated epilimnetic temperature and metalimnetic hypoxia on the predation rate of planktivorous fish

“…The effect seems to be the result of the fact that the presence of meta- and hypolimnetic hypoxia decreased the mean depth selected by Daphnia but not by the fish. The greater predation rate of the fish in hypolimnetic hypoxia confirmed the results of outdoor enclosure experiments (Wright and Shapiro, 1990; Field and Prepas, 1997; Chang et al ., 2013) but contradicts the results from the single indoor experiment (Larsson and Lampert, 2011). Two possible explanations for the opposing results are most likely.…”

“…Experimental evidence is less consistent. While three field studies confirmed that decreased meta- and hypolimnetic oxygen concentrations resulted in a shift from large- to intermediate-bodied Daphnia (Wright and Shapiro, 1990; Field and Prepas, 1997; Chang et al ., 2013), a single indoor study (Larsson and Lampert, 2011) revealed the opposite effect, which was attributed to a decreased mortality risk in the presence of metalimnetic hypoxia, because Daphnia is more tolerant of lower oxygen concentrations than most pelagic fish species (Weider and Lampert, 1985; Klumb et al ., 2004; Stanley and Wilson, 2004; Vanderploeg et al ., 2009a, 2009b). However, the experimental design of the study conducted by Larsson and Lampert (2011) did not allow verification of the possibility that either the fish’s acclimation to hypoxia or the shrinking thickness of the metalimnion (due to the increased temperature of the epilimnion) would increase the mortality risk caused by planktivorous fish at a low oxygen concentration in the metalimnion.…”