Data from: Warming advances top-down control and reduces producer biomass in a freshwater plankton community

Global warming has been shown to affect ecosystems worldwide. Warming may,
for instance, disrupt plant herbivore synchrony and bird phenology in
terrestrial systems, reduce primary production in oceans, and promote
toxic cyanobacterial blooms in freshwater lakes. Responses of communities
will not only depend on direct species-specific temperature effects, but
also on indirect effects related to bottom-up and top-down processes.
Here, we investigated the impact of warming on freshwater phytoplankton
community dynamics, and assessed the relative contribution of nutrient
availability, fungal parasitism, and grazing therein. For this purpose, we
performed an indoor mesocosm experiment following seasonal temperature
dynamics of temperate lakes and a warmed (+4°C) scenario from early spring
to late summer. We assessed phytoplankton biomass, C:N:P stoichiometry and
community composition, dissolved nutrient availabilities, fungal parasite
(i.e., chytrid) prevalence, and zooplankton abundance. Warming led to an
overall reduction in phytoplankton biomass as well as lower C:P and N:P
ratios, while phytoplankton community composition remained largely
unaltered. Warming resulted in an earlier termination of the diatom spring
bloom, and an epidemic of its fungal parasite ended earlier as well.
Furthermore, warming advanced zooplankton phenology, leading to an earlier
top-down control on phytoplankton in the period after the spring bloom.
Linear model analysis showed that most of the observed variance in
phytoplankton biomass was related to seasonal temperature dynamics in
combination with zooplankton abundance. Our findings showed that warming
advanced grazer phenology and reduced phytoplankton biomass, thereby
demonstrating how bottom-up and top-down related processes may shape
future phytoplankton dynamics.