Fish-mediated plankton responses to increased temperature in subtropical aquatic mesocosm ecosystems: Implications for lake management

Abstract

Although it is well established that climate warming can reinforce eutrophication in shallow lakes by altering top-down and bottom-up processes in the food web and biogeochemical cycling, recent studies in temperate zones have also shown that adverse effects of rising temperature are diminished in fishless systems. Whereas the removal of zooplanktivorous fish may be useful in attempts to mitigate eutrophication in temperate shallow lakes, it is uncertain whether similar mitigation might be achieved in warmer climates. We compared the responses of zooplankton and phytoplankton communities to climate warming in the presence and absence of fish (Aristichthys nobilis) in a 4-month mesocosm experiment at subtropical temperatures. We hypothesized that 1) fish and phytoplankton would benefit from warming, while zooplankton would suffer in fish-present mesocosms and 2) warming would favor zooplankton growth but reduce phytoplankton biomass in fish-absent mesocosms. Our results showed significant interacting effects of warming and fish presence on both phytoplankton and zooplankton. In mesocosms with fish, biomasses of fish and phytoplankton increased in heated treatments, while biomasses of Daphnia and total zooplankton declined. Warming reduced the proportion of large Daphnia in total zooplankton biomass, and reduced the zooplankton to phytoplankton biomass ratio, but increased the ratio of chlorophyll a to total phosphorus, indicating a relaxation of zooplankton grazing pressure on phytoplankton. Meanwhile, warming resulted in a 3-fold increase in TP concentrations in the mesocosms with fish present. The results suggest that climate warming has the potential to boost eutrophication in shallow lakes via both top-down (loss of herbivores) and bottom-up (elevated nutrient) effects. However, in the mesocosms without fish, there was no decline in large Daphnia or in total zooplankton biomass, supporting the conclusion that fish predation is the major driver of low large Daphnia abundance in warm lakes. In the fishless mesocosms, phytoplankton biomass and nutrient levels were not affected by temperature. Our study suggests that removing fish to mitigate warming effects on eutrophication may be potentially beneficial in subtropical lakes, though the rapid recruitment of fish in such lakes may present a challenge to success in the long-term.

Countergradient variation concealed adaptive responses to temperature increase in Daphnia from heated lakes

“…Lower predation seems unlikely given data obtained from the same system reveals that lake heating resulted in increased fish predation pressure on zooplankton (Ejsmont‐Karabin and Węgleńska 1988; Hillbricht‐Ilkowska and Zdanowski 1988 a ), and warm water discharge generally attracts planktivorous fish resulting in increased fish density (Świerzowski and Godlewska 2001). Moreover, higher temperatures are generally known to increase fish predation on zooplankton, especially on large‐bodied cladocerans (e.g., Gliwicz 1994; Brucet et al 2010; He et al 2018). Fish in heated lakes have increased growth rates, and in some species increased fertility, in comparison with fish from non‐heated lakes (Thorslund 1971).…”

“…In situ, we compared the D. longispina complex communities (composed of three hybridizing species: D. galeata , D. longispina , and D. cucullata ) inhabiting either heated lakes or non‐heated control lakes nearby. Reduced body size in Daphnia can be caused directly by temperature increase (due to the physiological advantage of size reduction, Kozłowski et al 2004), or indirectly by temperature‐mediated increase in planktivorous fish predation (e.g., Brucet et al 2010; He et al 2018). Fish predation has a particularly strong impact on body size in zooplankton communities (Brooks and Dodson 1965).…”

Increased Nitrogen Loading Boosts Summer Phytoplankton Growth by Alterations in Resource and Zooplankton Control: A Mesocosm Study

“…We also calculated the densityweighted body mass of the zooplankton community and the biomass ratio of cladocerans to copepods to assess the predation strength of fish on zooplankton as large-sized individuals and taxa with low mobility (e.g., cladocerans) were more sensitive to fish predation (Jackson et al, 2007;Jeppesen et al, 2011). These metrics (when combined) are considered to be good indicators of top-down control and are widely used in long-term monitoring, cross-system lake comparison, and mesocosm studies (Gyllström et al, 2005;Jackson et al, 2007;Jeppesen et al, 2011;Liu et al, 2018;He et al, 2018He et al, , 2021.…”

Application of a Hybrid Optimized BP Network Model to Estimate Water Quality Parameters of Beihai Lake in Beijing

“…As an issue of national concern, numerous studies in lakes have been paid more attention regarding their physical, chemical (e.g., total nitrogen [17], total phosphorus [18], heavy metals [19], etc. ), and biological (e.g., phytoplankton [20], aquatic fish [21] and aquatic plant [22] etc.) parameters, as well as the influences of land use [23] and eutrophication [24].…”