The Inevitable Loss of Coral Reefs Due to Global Warming

The concentration of carbon dioxide (CO2) in the atmosphere and the warming of the water are some of the impacts on these ecosystems.

Coral reefs are the most biodiverse marine ecosystems, making them some of the most biologically complex and valuable on the planet.

Increasing levels of greenhouse gas pollution, due to the burning of coal, oil and gas, are driving up average global temperatures and accelerating the loss of coral reefs.

Corals are animals that live in symbiosis with zooxanthellae, algae with high photosynthetic activity; therefore, they form a very productive ecosystem by providing food and protection to numerous marine animals. They occupy only 0.2% of the ocean floor, but are home to more than a quarter of all known marine species. For this reason they are sometimes called the “rainforests of the sea”.

The result of more than 50 million years of evolution, coral reefs are one of the most fragile and complex systems of biodiversity on Earth.

According to the World Conservation Monitoring Center or UNEP-WCMC, from an economic point of view, it has estimated that coral reefs generate up to US$375 billion annually in goods and services, which include protection of the coastline against erosion and storms, form a food supply, economic resources to human populations living in their vicinity and also provide protein and basic components for many life-saving medicines.

Their destruction represents a threat, as a healthy reef can annually supply more than 15 tons of fish and shellfish per square kilometer, enough to feed 2,500 people.

The concentration of carbon dioxide (CO2) in the atmosphere and the warming of the water are some of the impacts on these ecosystems. As CO2 emissions increase, its dissolution in the sea increases, the water becomes more acidic and the concentration of carbonates decreases.

This is very important because corals and other organisms use carbonates, in the form of calcium carbonate, to form their skeletons. After all, reefs are geological formations built from the accumulated skeletons of animals and plants.

The International Panel on Climate Change (IPPC) estimates that rising temperatures will cause the extinction of between 70% and 90% of coral reefs by 2050.

Rising temperatures and coral reefs

A report published in 2021 by the Global Coral Reef Monitoring Network warns that in the last decade, globally, 14% of coral reefs have been lost, which means 11 700 km2 due to the increase in sea surface temperature.

Loss of coral reefs. Source: Pixabay

Current estimates suggest that it could take hundreds of years for the reefs to recover. Rising sea temperatures cause corals to die, because corals are extremely sensitive and can only live in water temperatures between 18°C and 30°C.

Global warming affects the health of the oceans in general, they still absorb almost 50% of the CO2 generated by man, resulting in increased acidity, so the oceans are becoming more saturated and acidic.

High temperatures and acidity change the chemistry of the oceans, causing corals to expel their symbiotic algae, bleach and die, notable in Australia's Great Barrier Reef. When coral reefs die, the fish that live in them also die, causing chains of extinction, as their death disrupts the entire food chain in tropical waters.

Coral bleaching

Rising ocean temperatures can cause massive coral bleaching, which occurs when coral polyps (very simple cylindrical animals that resemble anemones), stressed by heat or ultraviolet radiation, expel the symbiotic algae that live in the coral tissues. When the algae are expelled, the coral turns white. These algae provide the coral with most of its food and oxygen.

In 2005, there was bleaching of up to 95% of corals in the Cayman Islands, Jamaica, Cuba and the French West Indies.

Australia's Great Barrier Reef is the largest reef in the world, stretching 2500 km, and has already suffered three bleaching events in 2014, 2016 and 2020. These events are estimated to have affected 86% of the corals on the surface of the reef

Negative impacts on coral reefs lead to declining biodiversity, reduced coastal protection and reduced income from fisheries and tourism, as globally many people depend partly or wholly on reefs for their livelihoods. Economic losses could be in the billions of dollars. If global warming continues, the next generation will not see coral reefs.

Research by the Global Coral Reef Monitoring Network stated in 2019 that despite some irreversible data, 2% of their coral cover shows that they can be restored and are still resilient, so combined efforts by governments, societies, businesses and individuals can prevent and reverse worse effects to reefs.

A great alternative to protect coral reefs is to protect and enhance ecosystems that absorb greenhouse gases. The loss of some ecosystems, especially forests and wetlands, contribute a significant amount of carbon dioxide and other greenhouse gases to the atmosphere, impacting these wonderful marine ecosystems.

Sources consulted:

Guldberg, O. “Climate change, coral bleaching and the future of the World's coral reefs” edited by Greenpeace in July 1999, ISBN 90-73361-52-4. https://archivo-es.greenpeace.org/espana/Global/espana/report/cambio_climatico/el-cambio-climatico-y-los-arre.pdf

The Coral Reef Alliance (CORAL) (2014) CORAL REEFS AND GLOBAL CLIMATE CHANGE. https://coral.org/wp-content/uploads/2014/02/climatechange_esp1.pdf

Elvira, E. (2004) Coral reef fishes at risk from climate change. Trofeo Pesca 131: 110-111.

Responsible Journal (2021) Global warming has caused irreversible loss of coral reefs. https://diarioresponsable.com/noticias/31927-el-calentamiento-global-ha-causado-una-perdida-irreversible-de-arrecifes-de-coral