Experimental warming and browning influence autumnal pelagic and benthic invertebrate biomass and community structure

Abstract

1. Globally, lakes are warming and browning with ongoing climate change. These changes significantly impact a lake's biogeochemical properties and all organisms, including invertebrate consumers. The effects of these changes are essential to understand, especially during critical periods after and before the growing season, that is, autumn and spring, which can determine the composition of the invertebrate consumer community.2. In this study, we used a large-scale experimental pond system to test the combined effect of warming (+3°C) and increased input of terrestrial and coloured dissolved organic carbon (gradient of 1.6-8.8 mg/L in the ambient and 1.6-9.3 mg/L in the warm)-which causes browning-on zooplankton and benthic macroinvertebrate biomass and composition during the autumn and the following spring.3. Total zooplankton biomass decreased with warming and increased with browning, while total zoobenthos did not respond to either treatment. Warming and browning throughout the autumn had no overall interactive effects on zooplankton or zoobenthos. Autumnal warming decreased total pelagic consumer biomass, caused by a decrease in both Rotifera and Copepoda. In contrast, there was no effect on overall benthic consumer biomass, with only Asellus sp. biomass showing a negative response to warming. An autumnal increase in dissolved organic carbon led to increased total pelagic consumer biomass, which was related to increases in Daphnia sp. biomass but did not affect zoobenthos biomass. While we expected zooplankton and zoobenthos biomass to follow responses in primary and bacterial production to treatments, we did not find any relationship between consumer groups and these estimates of resource production. 4. Our results suggest that consumer responses to warming and browning during autumn may lead to less overarching general changes in consumer biomass, and responses are mostly taxon-specific.