Conservation gone wrong: Marine Protected Areas and Coral Reefs

Marine Protected Areas (MPAs) are widely considered from a conservationist perspective to be the most appropriate and effective way of preserving the structural complexity of marine habitats and in preventing overfishing and consequent decline in fish stocks. If one was to transfer this understanding to coral reef habitats we’d assume that MPAs would be largely beneficial in protecting the diversity within these rich havens. However, in the face of climate driven impacts a study by Graham et al. in 2007 found that the lagged impacts on coral reef fish species are enhanced by assignation of MPAs. The study assessed the long term impacts of the bleaching events on species, their size structure and the effectiveness of MPAs by investigating sites that were fished and those under conservation. The 1998 event reduced coral cover over these sites by 90% and upon revisiting the sites in 2005, recovery had only reached 7.5% overall. The results showed that juvenile species were most affected by long term impacts and the slope of species size decreased significantly, as juvenile species rely heavier on coral cover for shelter and protection from predation. The implications for a loss in juvenile species are severe considering that these species ensure future stable population size. While all sites (both fished and protected) showed a marked decrease in juvenile species the study found that greater predator biomass in MPAs (as these are the targeted species in sites with active fishing) actually results in higher predation rates on the vulnerable juvenile species, ultimately increasing the severity of the lag effect. Looking at species specifically, surgeonfishes (Acanthuridae) and parrotfishes (Scaridae) which generally span a large number of size classes showed a significant loss of size variation as juvenile habitat was destroyed.

The interesting findings from this study raises questions about the efficacy of conservation techniques in coral reefs. As is well known, in the face of climate change bleaching events are only to become more frequent, longer lasting and severe as enhanced teleconnective processes between the atmosphere and oceans (such as el Niño events) also become more frequent. Despite this however, one must consider whether the lag impacts on species size composition after bleaching events pose more threats than overfishing does in general? Though the paper doesn’t weigh up these considerations it will be interesting to see if there has been further thought on the effectiveness of MPAs in light of long term bleaching impacts.