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O’Brien JM, Scheibling RE, Krumhansl KA
Positive feedback between large-scale disturbance and density-dependent grazing decreases resilience of a kelp bed ecosystem
Large-scale perturbations may alter the effects of subsequent disturbances to drive unanticipated shifts in community structure. O’Brien and colleagues examine how large-scale disturbances that defoliate kelps beds on the Atlantic coast of Nova Scotia modify the grazing dynamics of the small gastropod Lacuna vincta. Field observations and a manipulative experiment demonstrate that kelp thinning disproportionately increases snail density and grazing intensity on remaining kelp, a phenomenon reflected in variation in grazing intensity across sites as a function of standing kelp biomass. Heightened grazing enhances the indirect impact of L.vincta on kelp by increasing tissue loss with subsequent large storms. This positive feedback may reinforce or accelerate observed losses of kelp biomass and facilitate turf-forming algae on rocky reefs.