Acclimating across healthy and degraded reefs

Abstract

As a result of human activities, many environments are becoming fragmented into areas with different community compositions and selective regimes. The coral reefs of Fiji for example, are divided into ‘fished areas’ (fragments subjected to fishing and trampling) and ‘protected areas’ (fragments with little human pressure) that occur in close proximity and now have differing community compositions and selective regimes. Theory predicts that the species able to survive in such conditions should have highly plastic genotypes allowing them to acclimatise to diverse habitats without the time lag required for local adaptation. Here we use two species -Epinephelus merra (a small grouper) and Sargassum polycystum C. Agardh (a brown macroalga)- which are found in both fished and protected reefs, to investigate this plastic response and understand how these species cope in healthy versus degraded environments. We found that the fish E. merra exhibits plasticity in diet and feeds lower in the food chain in fished reefs than similarly sized conspecifics in protected reefs. The seaweed S. polycystum exhibits plasticity in defensive traits and is able to induce increased defenses in response to being partially consumed. In addition, we found that dense stands of S. polycystum increased the survival and growth of both recruit-sized and mature-sized S. polycystum ramets, suggesting that Sargassum beds protect conspecifics from grazing by herbivorous fishes and construct conditions that facilitate their growth. Implications for management are discussed.