1. Predators can exert nonconsumptive effects (NCEs) on prey, which often take place through prey behavioural adjustments to minimize predation risk. As NCEs are widespread in nature, interest is growing to determine whether NCEs on a prey species can indirectly influence several other species simultaneously, thus leading to changes in community structure.

2. In this study, we investigate whether a predator can exert NCEs on a foundation species and indirectly affect community structure.

3. Through laboratory experiments, we first tested whether the predatory marine snail Acanthina monodon exerts negative NCEs on larviphagy (consumption of pelagic larvae) and phytoplankton filtration rates of the mussel Perumytilus purpuratus, an intertidal foundation species. These hypotheses stem from the notion that mussels may decrease feeding activities in the presence of predator cues to limit detection by predators. Afterwards, a field experiment tested whether the presence of A. monodon near mussel beds leads to higher colonisation rates of invertebrates that reproduce through pelagic larvae (expected under a lower larviphagy in P. purpuratus) and to a lower algal biomass on P. purpuratus shells (expected under a lower metabolite excretion in the mussels), thereby changing the community structure of the species typically found in P. purpuratus beds.

4. The laboratory experiments revealed that waterborne cues from A. monodon limit the larviphagy and filtration rates of P. purpuratus. In turn, the field experiment showed that A. monodon cues led to greater abundances of barnacles and bivalves and a lower algal biomass in P. purpuratus beds, thus altering community structure.

5. Overall, this study shows that a predator can indirectly affect community structure through NCEs on an invertebrate foundation species. As invertebrate foundation species are ubiquitous worldwide, understanding predator NCEs on these organisms could help to better understand community regulation in systems structured by such species. 12-Feb-2021

Descriptions of how the data were collected are written in full in the Methods section of the manuscript.

The data is saved as three separate files contain the results of laboratory and field based experiments. The experiments used the same two treatments: predator presence (A+) and absence (A-). 

1. Larviphagy_rate_data.xls contains the results of a laboratory experiment in which we tested the larviphagy rate of Perumytilus purpuratus (number of larvae eaten per individual per hour) under Acanthina monodon presence (A+) and absence (A-).

2. Filtration_rate_data.xls contains the results of a laboratory experiment in which we tested the phytoplankton filtration rate of P. purpuratus (litres of water filtered per individual per hour) under A. monodon presence (A+) and absence (A-).

3. Field_experiment_data.xls contains the results of a field manipulative experiment in which we determine the community structure of species associated to P. purpuratus beds under A. monodon presence (A+) and absence (A-). The density of the associated invertebrate species was calculated as the number of organisms per experimental unit. The algal biomass was quantified as algae wet weight (mg) per experimental unit.