Interactive effects of depth and marine protection on predation and herbivory patterns

Abstract

ABSTRACT: The establishment of marine protected areas (MPAs) worldwide has shown thatclosure of areas to fishing results in major changes in the structure of marine ecosystems. Theremoval of high-order consumers by fishing has both direct and indirect effects that can lead toimportant changes in the strength of trophic interactions. Although the effects of marine protec-tion on biological interactions are beginning to be understood, our knowledge is largely restrictedto shallow-water assemblages. However, depth gradients are also characterised by significantdifferences in the intensity of trophic linkages, and these may be interacting with any effectsderived from protection. In this study, the individual and combined effects of depth and marinereserve protection on predation and herbivory were determined across 3 regions in the NWMediterranean (Catalunya, Mallorca and Menorca) using juvenile urchins and palatable algae asbioassays. Marine protection did not strongly influence fish herbivory, which generally decreasedwith depth. We found no evidence of depth-related changes in predation rates or the size ofpredatory fishes, but there was a strong effect of protection on predation rates that was onlyconsistently observed across regions in shallow water (5 m depth), but not at greater depths(15 and 30 m). This increase in predation of sea urchins within MPAs in shallow waters can haveimportant community-wide consequences, as herbivorous sea urchins are commonly most abun-dant in these shallow habitats and predator−urchin interactions have important cascading effectson algal communities.KEY WORDS: Marine reserves · Sea urchins · Macroalgae · Mediterranean Sea · Fish herbivory ·