BONN, Germany (Landscape News) — Marine protected areas cover about 4 percent of ocean surface. They are designed to protect vulnerable ecosystems from overfishing, pollution and mining, and are important for the conservation of thousands of unique species, including whales, dolphins, porpoises and polar bears. Next to that, they provide ecosystem services that sustain the fisheries on which millions of people depend.
Studies have suggested that marine protected areas can also help to strengthen the resilience of ocean species and ecosystems in the face of climate change. For example, the protection of coral reefs against overfishing and pollution would make them less vulnerable to warming, and better able to recover after climate-related disturbances such as heavy storms.
This may well be wishful thinking, warns a recent article in Nature Climate Change. If greenhouse gas emissions are not reduced, most of the marine protected areas will become uninhabitable for many species. This is based on an analysis of 8,263 marine protected areas across the globe by an international research team headed by John Bruno, biology professor in the College of Arts and Sciences at the University of North Carolina.
To predict the impact of human-induced climate change on protected ecosystems, they modeled sea surface temperatures and oxygen concentrations in a business as usual scenario and in a scenario with reduced greenhouse gas emissions (known as RCP8.5 and RCP4.5 respectively).
- Warming waters
In a business as usual scenario, mean sea-surface temperatures within marine protected areas are projected to increase 0.034 degrees Celsius per year. In this scenario, 99 percent of the world’s marine protected areas will warm by more than 2 degrees C by 2100.
- A threat to marine life
When the maximum summertime temperature of the water exceeds the temperature that an organism can tolerate, the survival of the species is at risk. By 2050, most tropical marine protected areas will reach critical thresholds that will be intolerable for many species.
- Reduction in oxygen
Human induced climate change does not only lead to higher sea-surface temperatures, but also to a reduction in oxygen concentration. This is doubly problematic, because rising temperatures increase the oxygen demand of many sea organisms.
- Some move, others disappear
Many species that occur in marine protected areas have small populations and low genetic diversity, which reduces their adaptive capacity and makes them extra vulnerable to climate change. Due to the rising water temperature and associated reduction in oxygen concentration, some species will go extinct, while others will shift their ranges to higher latitudes, resulting in altered species compositions.
- Changing food-webs
Changes in species compositions will also change ocean food-webs, which is likely to have significant consequences for fisheries.
Although the authors support the further expansion of marine protected areas, they emphasize they will only be effective in combination with drastic reductions in greenhouse gas emissions.