Unravelling the impact of harvesting pressure on canopy-forming macroalgae.

Canopy-forming macroalgae create a specific surrounding habitat (the matrix) with their own ecological properties. Previous studies have shown a wide range of responses to canopy removal. Magnitude and strength of the effects of harvesting are thought to be context-dependent, with the macroalgal matrix that can either soften or exacerbate the impact of harvesting. We experimentally examined in situ the effect of harvesting on targeted commercial species, and how these potential impacts might vary in relation to its associated matrix. We found that patterns of recovery following the harvesting disturbance were variable and matrix specific, suggesting that local factors and surrounding habitat characteristics mediated the influence of harvesting. The greatest and longest effects of harvesting were observed for the targeted species that created a dominant and monospecific canopy on their site prior to the disturbance. Another relevant finding was the important natural spatiotemporal variability of macrobenthic assemblages associated with canopy-forming species, which raises concern about the ability to discriminate the natural variability from the disturbance impact. Finally, our results support the need to implement ecosystem-based management, assessing both the habitat conditions and ecological roles of targeted commercial species, in order to insure the sustainability of the resource. The effects of canopy removal on macrobenthic communities from rocky shores were examined, taking into account the matrix associated to the harvested canopy-forming macroalgae. The greatest effects of harvesting were observed for the species that created a dominant monospecific canopy prior to the disturbance. The results demonstrate the importance of implementing ecosystem-based management, assessing both the habitats conditions and ecological roles of targeted commercial species. [ABSTRACT FROM AUTHOR]