Combined Effects of Turbulence and Different Predation Regimes on Zooplankton in Highly Colored Water—Implications for Environmental Change in Lakes

Abstract

In aquatic ecosystems, predation is affected both by turbulence and visibility, but the combined effects are poorly known. Both factors are changing in lakes in the Northern Hemisphere; the average levels of turbulence are predicted to increase due to increasing wind activities, while water transparency is decreasing, e.g., due to variations in precipitation, and sediment resuspension. We explored experimentally how turbulence influenced the effects of planktivorous fish and invertebrate predators on zooplankton when it was combined with low visibility caused by high levels of water color. The study was conducted as a factorial design in 24 outdoor ponds, using the natural zooplankton community as a prey population. Perch and roach were used as vertebrate predators and Chaoborus flavicans larvae as invertebrate predators. In addition to calm conditions, the turbulent dissipation rate used in the experiments was 10−6 m2 s−3, and the water color was 140 mg Pt L−1. The results demonstrated that in a system dominated by invertebrates, predation pressure on cladocerans increased considerably under intermediate turbulence. Under calm conditions, chaoborids caused only a minor reduction in the crustacean biomass. The effect of fish predation on cladocerans was slightly reduced by turbulence, while predation on cyclopoids was strongly enhanced. Surprisingly, under turbulent conditions fish reduced cyclopoid biomass, whereas in calm water it increased in the presence of fish. We thus concluded that turbulence affects fish selectivity. The results suggested that in dystrophic invertebrate-dominated lakes, turbulence may severely affect the abundance of cladocerans. In fish-dominated dystrophic lakes, on the other hand, turbulence-induced changes in planktivory may considerably affect copepods instead of cladocerans. In lakes inhabited by both invertebrates and fish, the response of top-down regulation to turbulence resembles that in fish-dominated systems, due to intraguild predation. The changes in planktivorous predation induced by abiotic factors may possibly cascade to primary producers.

Effects of mixing on the pelagic food web in shallow lakes

“…Härkönen et al . () showed that under turbulent condition with low visibility, planktivorous fish increase their predation on copepods. They explain this result to a lower escape ability of copepods, thus making them more vulnerable to fish predation.…”

Effects of turbulence on alkaline phosphatase activity of phytoplankton and bacterioplankton in Lake Taihu

“…Turbulence generation The submerged wave-maker pumps described earlier, fixed under surface water by strong magnets, were used to generate turbulence simulate to the ones induced by natural wind waves as demonstrated in previous studies (Clarke et al, 2005;Pekcan-Hekim et al, 2013;Härkönen et al, 2014). The pump frequency was set to 1 Hz and the turbulence generated was monitored and measured by an acoustic Doppler velocimeter (ADV, 10 MHz ADVField; Sontek/YSI, San Diego, California, USA).…”

Mesocosms with wavemakers: A new device to study the effects of water mixing on lake ecology

“…in mesocosms with turbulent conditions. Different studies showed the negative effects of turbulence on cladocerans and calanids (Sluss et al 2008;G.-Toth et al 2011;Striebel et al 2013;Harkonen et al 2014) but the cyclopids Cyclops vicinus and Mesocyclops leuckarti grow better in turbulent conditions (G. -Toth et al 2011).…”

“…The management objectives are to improve water quality, that is, in most cases, to obtain density destratification to alleviate problems linked to bloom-forming cyanobacteria (Steinberg 1983;Hawkins and Griffiths 1993;Visser et al 1996;Burford and O'donohue 2006;Oberholster et al 2006;Hudnell et al 2010;Upadhyay et al 2013). Research objectives encompass the broad study of the effects of mixing depth and background turbidity on phytoplankton species (Diehl et al 2002), and more precisely, the consequences of destratification and the mixing intensity on bacteria and plankton (Reynolds et al 1983;Weithoff et al 2000;Becker et al 2006;Read et al 2011), sediment resuspension on phytoplankton biomass and plant nutrient concentration (Ogilvie and Mitchell 1998), effects of turbulence on plankton community composition or on predation (Huisman et al 2004;Sluss et al 2008;Pekcan-Hekim et al 2013;Striebel et al 2013;Harkonen et al 2014;Zhou et al 2015). Table 1 summarizes the operating principles of these devices as well as the physical processes involved.…”

“…Water circulation with a pump (Sluss et al 2008;Pekcan-Hekim et al 2013;Harkonen et al 2014;Zhou et al 2015) Water discharge through submerged pumps Generation of turbulence in the water column by the water circulation 2001; Anbarsooz et al 2013). The originality of our system relates to its adaptation for research in freshwater ecology.…”