Experimental design
Forty square polyethylene containers (around 100 L, 55×45×40cm, l ×w ×h) were used as mesocosms and exposed to eight experimental treatments in a full factorial design (a control and three factors: shading, nutrient loading and herbivory, each with two levels), with five replicates for each treatment (FigureS1), assigned randomly to the containers. The two selected light intensity levels were full sunlight (S0, high light intensity) and 25% sunlight (S1, low light intensity with shading). The two nutrient loading treatments consisted of nutrient loading (E1) and no external nutrient loading (E0) to the water column. Two snail herbivory treatments, one with (H1) and one without (H0) extra snails added. The experiment lasted for 58 days, from January 26 to March 18, 2021. Tap water was added bi-weekly to the containers to compensate for evaporation.