Predation intensity is negatively related to plant species richness in a benthic marine community

Plant biodiversity affects primary productivity and resource utilization in terrestrial and aquatic ecosystems, and may also influence other key ecological processes such as predator–prey interactions. We tested the hypotheses that predation intensity is negatively related to plant species richness, and that prey density is positively related to plant species richness. We performed one field and one mesocosm experiment based on a benthic estuarine food web to measure the effects of macroalgal species richness on the predation of a herbivorous amphipod by a carnivorous fish. In the mesocosm experiment, prey mortality was significantly lower in the 5 species algal polyculture than in the average monoculture, suggesting that increasing algal richness decreased predation intensity. In the field experiment, prey colonization and density were positively related to algal richness in the presence of a diverse guild of predators. Combined, these results suggest that primary producer richness can influence animal community structure and food web dynamics, emphasizing the need for biodiversity-ecosystem functioning research in realistic, multitrophic systems.