Abstract
Network analyses of biological communities allow for identifying potential consequences of climate change on the resilience of ecosystems and their robustness to resist stressors. Using DNA metabarcoding datasets from a three-year-sampling (73 samples), we constructed the protistan plankton co-occurrence network of Lake Zurich, a model lake ecosystem subjected to climate change. Despite several documentations of dramatic lake warming in Lake Zurich, our study provides an unprecedented perspective by linking changes in biotic association patterns to climate stress. Water temperature belonged to the strongest environmental parameters splitting the data into two distinct seasonal networks (October–April; May–September). The expected ecological niche of phytoplankton, weakened through nutrient depletion because of permanent thermal stratification and through parasitic fungi, was occupied by the cyanobacterium Planktothrix rubescens and mixotrophic nanoflagellates. Instead of phytoplankton, bacteria and nanoflagellates were the main prey organisms associated with key predators (ciliates), which contrasts traditional views of biological associations in lake plankton. In a species extinction scenario, the warm season network emerged as more vulnerable than the cold season network, indicating a time-lagged effect of warmer winter temperatures on the communities. We conclude that climate stressors compromise lake ecosystem robustness and resilience through species replacement, richness differences, and succession as indicated by key network properties.
Highlights
Protists are essential for lake ecosystems because their roles as primary producers, decomposers, or consumers contribute to biomass fluxes among different trophic levels [1,2]
Our study aims at filling this void by analyzing the protistan plankton co-occurrence network of a large freshwater lake, subjected to climate change effects
Irradiance by sunlight was naturally higher in the warm season, chlorophyll concentrations and Secchi depths were lowest, which is a clear indication that phytoplankton could not establish stable populations
Summary
Protists are essential for lake ecosystems because their roles as primary producers, decomposers, or consumers contribute to biomass fluxes among different trophic levels [1,2] Such interactions are essential components that define the function of an ecosystem. Singular samplings of individual sites only provide a snapshot of a specific moment in time of the protistan community under study, and, do not allow to infer the complex interactions in these communities and their reaction to habitat changes. Addressing such topics requires data collected in timeseries studies [9]. The vast majority of time-series studies of protistan freshwater
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