By Emily Darling
Protected areas that control local stressors are a hallmark strategy for species protection. However the global impacts of climate change don’t stop at the boundaries of protected areas. Nevertheless, a popular conservation narrative is that reducing local stressors can buffer ecosystems against the global impacts of climate change. This narrative is especially poignant since we can usually only make positive change at local levels by reducing exploitation and pollution or slowing habitat loss. But is this enough? Given the unpopular politics of curbing global carbon emissions and the reality of committed warming over future decades, it is critical to evaluate if managing local stressors will protect ecosystems in the face of climate change.
Beginning in the 1960s, a series of no-take Marine National Parks were created along the Kenyan coastline to recover marine resources and support tourism. With effective enforcement from the Kenyan Wildlife Service, there are now more abundant and diverse coral reef communities and healthier ecosystem processes inside the reserves. In fact, Kenya’s marine reserves are some of the most effective in the western Indian Ocean. Does this mean that Kenya’s protected areas are more resilient to climate change? Not necessarily.
In 1998, an El Niño heat wave intensified throughout the western Indian Ocean and resulted in the warmest ocean temperatures ever recorded, provoking mass coral bleaching that killed over 40% of corals throughout the region. Widespread bleaching affected corals both inside and outside of Kenya’s National Marine Parks. The Kenyan coastline provided a timely natural experiment to understand the role of no-take reserves and local stressor management in the face of a major climate disturbance. Surprisingly, coral communities protected within marine reserves were the most harmed by bleaching and nearby fished reefs were less affected. We discovered that was because of the different types of coral species on protected versus fished reefs. Within the protected reserves, we saw more coral species that were vulnerable to bleaching. Reserves provided a safe harbor for sensitive branching and plating corals from the effects of fishing, but these were the same corals that were highly sensitive to death by bleaching. On the other hand, fished reefs had tougher corals that could survive the marine heatwave – likely because fished reefs had already lost their sensitive species after decades of fishing pressure.
By digging into the different types of coral species on fished and unfished reefs, we revealed important shifts in coral communities both before and after bleaching. Importantly, marine reserves were extremely vulnerable to the impacts of coral bleaching and the loss of climate-sensitive branching and plating corals from these reefs had resulted in smaller and flatter coral communities. This adds to the growing evidence that underwater architecture is being lost on coral reefs around the world (even inside marine reserves), threatening reef biodiversity and ecosystem services in the future.
While marine reserves can’t protect corals from climate change, they can allow reefs to recover from catastrophic events. Several recent studies have shown that recovery from climate change is faster within notake marine parks in the Bahamas, and that in Belize, the protection of algae-eating herbivorous fishes inside marine parks can maintain key ecosystem processes for coral recovery. In these models, coral recovery is highest when local management is combined with global actions to curb carbon emissions.
This is hopeful news, but unfortunately recovery is not happening everywhere. In Kenya, corals did not recover faster within marine reserves compared to fished reefs. Even 16 years after the 1998 mass bleaching event, Kenyan reserves have only recovered half of their pre-bleaching coral, and these are different types of corals than were there before bleaching. Yet reserves provide the only safe harbor for rare and climate-sensitive species (like competitive corals that partially recover from bleaching only inside reserves) – although this increases the susceptibility of protected reefs to future climate events. In situations where climate is the knock-out punch, there might not be enough time to manage for recovery.
There is mounting evidence that marine reserves cannot protect coral reefs from climate change. In some cases, protected areas will even experience greater mortality from climate impacts. What can we do with limited resources to ensure conservation success? Should we protect the healthiest ecosystems or restore the degraded? How can we make local management more effective to tackle a warming and more acidic ocean?
Portfolios of different conservation options for climate adaptation can give coral reefs the best chance to survive and adapt to climate change. From the lessons learned in Kenya, the impacts of climate change have swamped the effects of local management. Kenyan reefs are expected to keep getting hit by climate change in the future. Here, we should focus on local fisheries management that can sustain climate-tolerant resources and ecosystem services. We can also find and cultivate unusually healthy species or habitats that show signs of climate adaptation or acclimation. Marine reserves to protect coral diversity will be best suited to places of natural climate refugia (i.e., areas of the oceans that can escape the worst impacts of climate change). For example, coral reefs in northern Mozambique occur in the ‘climate shadow’ of Madagascar and have been largely protected from large marine heatwaves and mass bleaching in the western Indian Ocean. Refugia can also make wise investments for coral restoration of degraded areas.
Coral reefs in Kenya, like tropical reefs all over the world, face urgent threats. To maintain the carbonate backbone of these unique and important ecosystems, we need to think outside of the box and consider new portfolios of conservation strategies in a changing climate. At stake is an ecosystem with immense biological diversity that provides resources for half a billion people. Coral reefs are at the frontier of how we try to protect and help ecosystems adapt to the pressures of climate change. If we can make a difference for coral reefs, we can make a difference for the planet.
Côté IM and ES Darling. 2010. Rethinking Ecosystem Resilience in the Face of Climate Change. PLoS Biology 8:e1000438.
Darling ES, TR McClanahan and IM Côté. 2013. Life histories predict coral community disassembly under multiple stressors. Global Change Biology 19: 1930-1940.
Darling ES, McClanahan TR and IM Côté. 2010. Combined effects of two stressors on Kenyan coral reefs are additive or antagonistic, not synergistic. Conservation Letters 3: 122-130.