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.