Patterns of recovery of intertidal organisms after compounded anthropogenic disturbances

Abstract

Coastal habitats are exposed to increasing human and natural disturbances, including extraction of organisms and extreme climatic events. Patterns of recovery (i.e. convergence towards an unmanipulated control) of the structure of benthic assemblages, the total number, and the abundance of individual taxa were examined over a period of 15 mo after the end of a previous experiment. In that experiment, crossed manipulations of levels of mussel harvesting and of the temporal patterns of storm-related mechanical disturbance (in terms of changes in variance but not in the overall intensity) were performed on north Portugal rocky shores. Effects of past disturbances were mostly detected at 3 and 9 mo after the end of disturbances, while no significant differences between unmanipulated and treated assemblages were present after 15 mo. These findings confirm that intertidal assemblages subjected to even extreme combinations of past disturbances can recover in a relatively short time. Important effects present after 3 to 9 mo were associated with the timing of disturbance, likely depending on interactions with life-history traits such as peaks in reproduction and recruitment. Contrary to theories considering disturbances as opportunities for some organisms to replace competitors that dominate space in undisturbed conditions, we observed changes in the abundances of the same taxa rather than their replacement. The present evidence contributes to the understanding of how multiple anthropogenic pressures affect the ability of intertidal assemblages to recover after disturbance.