Global Warming a “Death Sentence” for Coral Reefs

coral2In April, I spent a sun-soaked week in Santa Lucia, a beach town on Cuba’s northern coast. At the encouragement of the locals, I went snorkeling in the nearby coral reef (one of the longest in the world). I was amazed by the diversity of sea life.  Among other creatures, I saw snappers, needlefish, and even a barracuda!

But, due to a phenomenon known as “coral bleaching”, these creatures and their habitat are under increasing threat. Coral bleaching occurs when coral expels the colorful algae (zooxanthalle) living in its tissues. The tissues becomes transparent and “the coral’s bright white skeleton is revealed”. Although bleached corals are not yet dead, most “begin to starve once they bleach”, as the zooxanthalle “provide up to 90% of the energy corals require to grow and reproduce”. Thus, unless conditions return to normal, most bleached corals eventually die and decay.

So why does coral expel algae? According to an expert at the Australian Institute of Marine Science, “any environmental trigger that affects the coral’s ability to supply the zooxanthellae with nutrients for photosynthesis will lead to expulsion”. These triggers could include changes to water salinity, quality (from urban and agricultural runoff), and sedimentation (from underwater activity or massive dust storms). They could also include oxygen starvation or diseases/infections in the coral.

However, the most common cause of coral bleaching is a rise in sea temperatures—from global warming, el Niño etc. In fact, a temperature increase of a mere 1 degree Celsius for four weeks can trigger bleaching. If these temperatures “persist for longer periods (eight weeks or more), coral begin to die”.

For example, in 2005, the US lost half of its Caribbean coral reefs when the waters near the Virgin Islands and Puerto Rico produced a “thermal stress…greater than the previous 20 years combined”. Similarly, in 1998, 50% of the Great Barrier Reef suffered bleaching as “sea temperatures on the…Reef were the highest ever recorded“. But the most severe bleaching from warm water has occurred in the Indian Ocean. Consequently, “up to 90% of coral cover has been lost in the Maldives, Sri Lanka, Kenya, Tanzania, and the Seychelles”.

This large-scale coral bleaching poses a significant environmental problem. Although reefs comprise less than 1% of the earth’s underwater ecosystem, they shelter a full 25% of marine species. Specifically, they provide “spawning, nursery, refuge, and feeding areas for a large variety of organisms, including sponges, cnidarians, worms, crustaceans, molluscs, echinoderms, sea squirts, sea turtles, and sea snakes”. If these species dwindle, there will be “a tremendous cascade effect for all life in the oceans” potentially leading to a “complete collapse of the marine ecosystem”.

Such an outcome would also put humans in hot water. According to the United Nations, approximately “1 billion people, largely in developing countries, rely on fish as their primary animal protein source”. A further 3.2 billion consume fish for over 15% of their animal protein. Ocean fisheries also provide direct employment to about 45 million people and indirect employment to 180 million people. Add in their families and a full 540 million people “depend on some aspect of catching, farming, processing, or distributing fish for their economic wellbeing”. Furthermore, coral and marine life are a “significant attraction for the tourism industry”. In fact, “many Caribbean countries get nearly half their gross national product from visitors seeking tropical underwater experiences”. Given these realities, experts suggest that, “If the reefs vanished… hunger, poverty, and political instability could ensue.”

Of further note, “reef structures play an important role as natural breakwaters”. They help minimize the impact of waves from storms (e.g. cyclones, hurricanes, or typhoons) on coastal communities and beaches.  Many also believe that corals could be home to the next medical breakthrough. Though 95% of the ocean remains unexplored, scientists have already discovered key treatments for asthma, arthritis, and cancer in the so-called “underwater pharmacy”.

Regrettably, as the climate changes, “coral bleaching is predicted to become more frequent and severe”. In fact, the IPCC’s moderate warming scenarios (B1 to A1T, 2°C by 2100) forecast that “corals on the Great Barrier Reef are very likely to regularly experience summer temperatures high enough to induce bleaching”. This has led some experts to predict that “most of the world’s coral reefs could be killed within our lifetime”.

To avert such a future, non-profit organizations are taking both proactive and reactive measures. They are encouraging others to lower their carbon footprints and to lobby their public officials for comprehensive climate legislation. They are collaborating with countries to establish marine protected area networks. Moreover, they are working to increase the resiliency of coral reefs by developing, sharing, and implementing science-based strategies to “better respond to bleaching events”.

For more information on coral bleaching, and how you can help, please contact the Nature Conservancy, the World Wildlife Fund, the National Wildlife Federation, or our partners, the Ocean River Institute, the Living Planet Aquarium, and the Blue Ocean Society for Marine Conservation.

Flickr photo credit: Only Point Five