Bottom-up and top-down effects on phytoplankton communities in two freshwater lakes

Abstract

The relative importance of bottom-up versus top-down effects in aquatic ecosystems remains a longstanding and ongoing controversy. To investigate these effects on phytoplankton communities in freshwater lakes, phytoplankton and zooplankton were sampled, and physical-chemical variables were measured during spring and summer in two important freshwater lakes in northern China: Nansi Lake and Dongping Lake. The redundancy analysis results showed that phytoplankton density and biomass were regulated by physicalchemical variables (bottom-up effects) and predation (top-down effects) together, and the former was more prominent in both lakes. However, the correlation analysis indicated that the top-down effects of zooplankton on phytoplankton were not significant in spring and summer in both lakes, while the bottom-up regulation of physical-chemical variables on phytoplankton had different patterns in the two lakes. In Nansi Lake, the bottom-up effects of physical-chemical variables on phytoplankton were weaker in summer than that in spring due to the abundant nutrients in summer. In Dongping Lake, the bottom-up effects of physical-chemical on phytoplankton were significant both in spring and summer, and the dominant bottom-up control factor shifted from total nitrogen in spring to total phosphorus in summer, with an increased ratio of nitrogen to phosphorus due to changes in limiting factors. In the two studied lakes, with fish culture, the bottom-up effects of phytoplankton on zooplankton were more important than the top-down effects of zooplankton on phytoplankton. These results demonstrate the interactions between phytoplankton and zooplankton and highlight the importance of phytoplankton regulation in freshwater lakes, which has implications for the effective management of freshwater lake ecosystems.

Spatial distribution of zooplankton in response to ecological dynamics in tropical shallow lake: insight from Lake Malombe, Malawi

“…Similar findings have been reported in other African tropical lakes such as Lake Chad and Lake George, Lake Kariba (Talling 1986;Moyo 1991). As observed in other studies, the low temperature can lead to a decrease in zooplankton density in the Lake (Brucet et al 2010;Cremona et al 2020;Li et al 2020;Pomati et al 2020). In early HDS, Chl-a develops when nutrients are available and when temperatures are high.…”

“…Hallegraeff (2010) suggested that phytoplankton is the primary producer in the complex food web system and this phytoplankton also produces Oxygen and organic matter through photosynthesis. This mechanism provides a better connection between primary producers with more advanced consumers in the food webs and provides a crucial link in the aquatic food web system (Li et al 2020). The changes in zooplankton density as seasonal changes are predominately influenced by physicalchemical (bottom-up effects) and predation (top-down effects) through the aquatic food web (Lv et al 2011;Muhid et al 2013;Li et al 2020).…”

The Role of Environmental Processes and Geographic Distance in Regulating Local and Regionally Abundant and Rare Bacterioplankton in Lakes

“…Other environmental variables (e.g., nutrients and pH) that were not investigated and so were not accounted for in the models could explain some of the variation. Biological impacts such as grazing and virus infection were also not taken into account but have previously been shown to have impacts on bacterioplankton communities ( Tijdens et al, 2008 ; Shurin et al, 2012 ; Li et al, 2020 ). Finally, the lakes in the study crossed multiple different environmental, chemical, and physical gradients and the interaction of these gradients may confound results.…”

Plankton population dynamics and methylmercury bioaccumulation in the pelagic food web of mine-impacted surface water reservoirs

“…Unlike GR and SCR, which had small-dominant zooplankton assemblages, AR and CR contained higher abundances of large copepods and cladocera, which may explain the presence of planktivorous fish. In addition to connecting the planktonic food web to predatory fish, planktivorous fish can provide a top-down control on the plankton assemblage and density in lakes (Li et al, 2020 ). Predation by fish could explain why zooplankton abundance is relatively low in AR and CR despite high phytoplankton diversity in AR and abundance in CR.…”

“…However, we found no correlation between biomass densities of phytoplankton or cyanobacteria and zooplankton, suggesting that the zooplankton population is not limited by food availability. Predation by planktivorous fish and carnivorous zooplankton is likely an important top-down control on zooplankton density that obscures the relationship between the phytoplankton and zooplankton communities (Sinstro, 2010 ; Li et al, 2020 ).…”