Many plant and algal communities respond to warming with shifts towards more carbon-rich species and growth forms, thus diluting essential elements in their biomass and intensifying the stoichiometric mismatch with herbivore nutrient requirements. The dataset is from a 95-day mesocosm experiment on the spring succession of an assembled plankton community in which we manipulated temperature (ambient vs. +3.6°C) and presence vs. absence of two types of grazers (ciliates and Daphnia) in a 2x2x2 factorial design with 3 replicates of each treatment (= 24 mesocosms in total). All mesocosms were initially stocked with low amounts of 6 phytoplankton taxa and were spontaneously colonized by an additional 6 taxa over the course of the experiment.

At ambient temperatures, a typical spring succession developed, where a moderate bloom of nutritionally adequate phytoplankton was grazed down to a clear-water phase by a developing Daphnia population.

Warming accelerated initial Daphnia population growth but speeded up algal growth rates even more, triggering a massive phytoplankton bloom of poor food quality (i.e. high carbon to phosphorus ratio of phytoplankton biomass). Consistent with the predictions of a stoichiometric producer-grazer model, accelerated phytoplankton growth promoted the emergence of an alternative system attractor, where extremely low phosphorus content of abundant algal food eventually drove Daphnia to extinction. Where present, ciliates slowed down the phytoplankton bloom and the deterioration of its nutritional value, but this only delayed the regime shift. Eventually, phytoplankton grew out of grazer control also in presence of ciliates, and the Daphnia population crashed. The results support the notion that warming can exacerbate the stoichiometric mismatch at the plant-herbivore interface and limit energy transfer to higher trophic levels.

One replicate of the 'ambient temperature, Daphnia present, ciliates absent' treatment failed. The dataset therefore consists of data from 23 mesocosms including measurements of the following variables: water temperature, chlorophyll a concentration (a proxy for total phytoplankton biomass), abundances of ciliates and Daphnia (no. of individuals per volume), the concentrations of soluble reactive phosphorus (SRP) and total phosphorus (TP), the carbon to phosphorus ratio (C_P) of seston, and the proportional contribution of different phytoplankton taxa to total phytoplankton biovolume.

The zenodo folder (see link https://doi.org/10.5281/zenodo.4715500 below) contains the Matlab and excel files that were used to run a dynamical mathematical model of the study system that were used to generate the model output shown in Figs. 2, 6 and 7 of the publication.

See descriptions in the methods section of the publication.

The frequency of sampling differed between different variables as described in the 'Read me.txt' file. Half the SRP samples from day 19 were lost.