While Marine Protected Areas (MPAs) are an important tool for conservation and protection of reefs they may not be enough to hedge against climate change according to research published in the journal Global Change Biology.
MPAs have been praised for their ability to mitigate stressors like nutrient enrichment, sedimentation, and overfishing. MPAs offer zones of suppressed physiological stress protecting resilient key source populations and providing a healthy source of recruits to already degraded populations. The success coral reef MPAs have had for restoring fisheries and trophic structures led to optimism that they would be useful tools for conservation in the face of climate change.
Warming global sea temperatures pose a serious risk to thermally sensitive ecosystems like coral reefs. High temperatures have been correlated with slow coral growth, increased prevalence of diseases, and mortality from coral bleaching. Reef-building corals already live near their upper thermal limits so if warming continues at a similar rate most coral taxa would be at risk of exceeding their upper limit in 100 years.
The authors tested whether or not MPAs mitigate temperature-associated coral loss and whether MPA design factors promoted resilience. They compared the effect of temperature on coral cover from 298 tropical MPAs (37 ͦN – 37 ͦS) to adjacent unprotected areas using a 21-year dataset.
The study found that MPAs fail to protect against thermal stress; despite the reduction of various physiological stressors resilience to thermal stress does not increase. When water temperatures are optimal tropical MPAs lead to an average increase of coral cover of 1-2% per year. Unfortunately, the benefits of MPAs are only realized after 4-14 years of protection. This questions the efficacy of creating new MPAs in regions of medium to high susceptibility if warming continues at its current rate.
The authors offer two suggestions to MPA managers hoping to protect reefs against climate change. First is to focus conservation efforts on protecting reefs with a history of moderate temperature variability because they are more resilient and acclimated to thermal stress. Second, is to design MPAs on a larger scale. Managers should design MPAs to be larger than an acceptable percentage of anomaly events so that it is guaranteed to contain unaffected populations within their boundaries.
When faced with the current climate changes crisis the local conservation measure of creating MPAs is not suitable to improve a reef’s resilience to globally increasing thermal levels. The study suggests that effectively managing coral reef systems will require complementing local measures with global measures aimed at reducing anthropogenic activities responsible for climate change.