What impacts will climate change and ocean acidification have on coral reefs and people?

Coral reefs: a key element for oceans and people

Did you know that over 25% of marine life, that is to say 2 million ocean species, depend on coral reefs for food and shelter? This is even more impressive when we know that reefs cover less than 1% of the earth’s surface and less than 2% of the bottom of the oceans!

Life in the ocean depends on coral reefs.  People also benefit from healthy coral ecosystems in a variety of ways that we call "ecosystem services."  For instance, coral reef fish help feed local communities and provide jobs for many fishermen. Coral reefs also are at the basis of many different types of material, from medicine (e.g. treatments for some cancer and HIV) and even jewellery and cement, sometimes to the detriment of the reef ecosystem. Coral reefs also are beautiful; this is why many tourists and people vacation near coral reefs where they participate in  recreational activities, like scuba-diving and snorkeling, which in tun, create jobs and contribute to the economy. Last but not least, healthy coral reefs protect our coasts from erosion and waves associated with extreme weather events.

Credit: Mountains in the Sea 2004. NOAA Office of Ocean Exploration; Dr. Les Watling, Chief Scientist, University of Maine

Coral reefs face many (environmental) threats

In the Anthropocene, coral reefs face some threats that are directly or indirectly related to human activities. 

Direct anthropogenic (human-caused) pressures include destructive fishing practices and overfishing, but also careless tourism (don't touch the corals!), coral mining and local pollution. These impacts can be tackled by changing practices and behaviors toward more sustainable practices, like sustainable fishing and tourism for instance. For more information on this issue, do not hesitate to read the Reefs at Risk Revisited report by the World Resource Institute.

Coral reefs also feel pressure from indirect anthropogenic environmental threats, like climate change. Climate change and increased CO2 concentrations in the atmosphere have two main impacts on oceans, and thus on coral reefs: (1) elevation of sea surface temperature and (2) ocean acidification. Here's what we wrote recently about this (from Pendleton et al.) :

"Ocean acidification, climate change, and other environmental stressors threaten coral reef ecosystems and the people who depend upon them. New science shows that these multiple stressors interact and may affect numerous physiological and ecological processes in complex ways. The interaction of multiple stressors and ecological complexity may mean that the negative affects on coral reef ecosystems will happen sooner and be more severe than previously thought. Yet, most research on the effects of global change on coral reefs focus on one or few stressors and pathways. Based on a critical review of the literature, we call for a regionally targeted strategy of mesocosm-level research to address this complexity and provide more realistic predictions about coral reef impacts in the face of global environmental change. We believe similar approaches are needed for other ecosystems that face global environmental change."

The complexity of our human relationship with coral reefs

Coral reefs exist in a delicate balance between: a) accretion, where corals build the hard structure of coral reefs (through the process of calcification), and b) erosion, where organisms (known as bioeroders) and ocean processes (which can be made worse by decalcification that can be caused by ocean acidification) combine to destroy the three-dimensional integrity of the reef. In this figure, from our paper in Frontiers in Marine Science, the inner circle depicts the key non-human organisms in coral reefs ecosystem. The top of the outer circle highlights the functions and services provided by coral reefs (ecosystem functions, ecosystem services and ecosystem properties) while the bottom describes the key characteristics of a healthy reef. The four "corners" of the figure represent the four key types of pressures that reefs face: ocean acidification, rising temperatures, local stressors (e.g. overfishing), and other major global stresses like those caused by hurricanes.  When coral reefs are healthy and stressors are low, processes of reef calcification outpace the loss of reefs caused by decalcification and erosion. Before the Anthropocene, coral reefs spread throughout many tropical regions. Calcification outpaced, or at least kept up with, decalcification. During this time, coral reefs provided important ecological services to humans and non-human organisms, alike. More recently, however, the combined effects of a variety of human activities has increased stresses on coral reefs to the point where the natural process of calcification can no longer keep pace with coral reef loss.  As a result, coral reefs are degraded and dying in many places and more coral reef loss is expected as carbon dioxide builds in the atmosphere. 

Holistic representation of coral reefs: their constitution, evolution of (im)balances, ecosystem services, environmental pressures, etc.

Online access to publication:

Click here to learn more about who depends most on coral reefs