Interactions between sea urchin grazing and prey diversity on temperate rocky reef communities

Abstract

While we frequently observe that increasing species richness within a trophic level can increase the rates of predation or herbivory on lower trophic levels, the general impacts of prey diversity on consumption rates by their predators or herbivores remains unclear. Here we report the results of two field experiments that examined how subcanopy sessile species richness affects rates of consumption by sea urchins. We crossed a natural gradient of species richness in a benthic subtidal community of understory macroalgae and sessile invertebrates against two experimental gradients of urchin density (0–50 and 0–14 individuals) in 0.5-m2 fenced plots. We found that the percent cover of macroalgae and invertebrates consumed by urchins was greater at higher levels of sessile prey species richness. However, this positive association between prey richness and sea urchin consumption was only apparent at low urchin densities; at high urchin densities nearly all algal and invertebrate biomass was consumed irrespectiv…

Keywords

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