# Sustained Heatwaves Reshape the Phytoplankton–Zooplankton Community Structure in Freshwater Ecosystems: A Case Study of Shengjin Lake

## TL;DR

Sustained heatwaves in Shengjin Lake changed the plankton community structure, favoring heat-tolerant species and altering interactions between plankton.

## Contribution

This study provides empirical evidence of how sustained heatwaves reshape freshwater plankton communities in a natural lake setting.

## Key findings

- Cyanophyta dominated during heatwaves, while Bacillariophyta became dominant during acclimation.
- Zooplankton shifted from Rotifera to Cladocera and Copepoda dominance during heatwaves.
- Water temperature contributed 33.83% and 38.70% to zooplankton and phytoplankton community changes, respectively.

## Abstract

Extreme climate events caused by global climate change pose a huge threat to freshwater ecosystems. As the frequency and intensity of heatwaves increase, sustained heatwaves may increase their certainty in ecosystems, which may affect phytoplankton and zooplankton, the key components of freshwater ecosystems. Sustained heatwaves can lead to shifts in plankton community structure, driven by changes in immigration patterns and life history strategies, potentially resulting in altered functional characteristics of phytoplankton and zooplankton in aquatic ecosystems. However, research on the effects of sustained heatwaves on plankton has mostly been conducted in laboratories, with less data from studies in natural water bodies. Therefore, in order to understand this ecological process in natural lakes, this study investigated the phytoplankton and zooplankton in Shengjin Lake during the summer heatwave in 2022. The results show that sustained heatwaves significantly alter the composition of plankton communities: Cyanophyta dominated during the heatwave period, while Bacillariophyta replaced Cyanophyta as the dominant group during the heatwave acclimation period. For zooplankton, the community shifted from being dominated by Rotifera to being dominated by Cladocera and Copepoda. Water temperature is a key driving factor affecting plankton communities, with contribution rates of 33.83% and 38.70% to the changes in zooplankton and phytoplankton communities, respectively. The connectivity of plankton co‐occurrence networks and keystone species change dynamically with heatwaves. Sustained heatwaves can exert thermal selective pressure on plankton communities, favoring the survival of individuals or species with stronger high‐temperature tolerance and potentially inducing acclimation or other adaptive responses. These results provide data support for studying the impact of sustained heatwaves on plankton communities and also provide a new perspective for the management and protection of freshwater ecosystems under climate change.

The sustained heatwave has shaped the plankton community structure and led to high‐temperature domestication of some of the plankton. Plankton communities have the ability to resist heatwave stress. The sustained heatwave has altered the interrelationships between plankton.