Coral reef resilience key to support the underwater cities threatened by climate change

The world is figuring out how to move forward in the face of the COVID-19 pandemic by finding newer ways to support economic development, animal and human well being, and ecosystem integrity. As the priority in many parts of the world is to stay home, safe and healthy, work continues to address the ongoing crisis of nature loss which also threatens long-term health and prosperity. In fact, nature, now more than ever, is sending warning signals calling for our attention.

One such warning is from the Great Barrier Reef along Australia’s northeast coast. In March 2020, the area suffered a third mass coral bleaching event in five years due to increasingly warmer temperatures recorded in February 2020.

There have also been reports that widespread bleaching in the first quarter of the year has also occurred in East Africa.

Coral reef scientists predict that bleaching events will be more frequent, more widespread and more severe. For instance, the 2017 Coral Bleaching Futures report by the United Nations Environment Programme (UNEP) predicted, “Increasingly coral bleaching would be among the greatest threats to coral reefs due to climate change.” Annual Severe Bleaching (ASB) is projected to occur within this century for 99 per cent of the world’s coral reefs. The average projected year of ASB is 2043, the report adds.

Great barrier reef, feb 2017. Photo by The Ocean Agency / Coral Reef image bank

A report by the Intergovernmental Panel on Climate Change published in October 2018 warns that, even if we collectively manage to stabilize global surface temperatures to 1.5°C above pre-industrial levels, 70 to 90 per cent of coral reefs will be lost by the middle of this century.

Leticia Carvalho, Head of UNEP’s Marine and Fresh Water Branch says: “Scientists have been telling us for a while that coral bleaching events would become more frequent with anthropogenic climate change and warming oceans. Unfortunately, their worst predictions have come to pass. Mass coral bleaching events are like nature’s fire alarm, a stark reminder that climate change is happening and is already impacting our societies and global ecosystem”.

To date the Great Barrier Reef—a UNESCO World Heritage Site, known for its vast mosaic patterns of reefs, islands and coral cays visible from space—has suffered six mass bleaching events due to warmer than normal ocean temperatures: in 1998, 2002, 2006, 2016, 2017 and now 2020. A statement by the Great Barrier Reef Marine Park Authority shows climate change remains the single greatest challenge to the Reef. It is home to the world’s largest collection of coral reefs, with 400 species of coral, 1,500 species of fish and 4,000 types of mollusk.

Bleaching occurs when coral—tiny animals that secrete calcium carbonate for protection—become stressed by factors such as warm water or pollution. As a result of the stress, they expel the microscopic symbiotic algae called zooxanthellae, which reside within their tissues. The corals then turn ghostly white; they become ‘bleached’ (watch these coral bleaching explainer videos). The zooxanthellae are the primary food source for corals. If the algae do not return to the corals as soon as possible (or if temperatures get warmer), the corals can die as it happened in the Great Barrier Reef in 2016 and 2017.

Corals have been observed to glow in luminescent colours—blue, yellow and purple— to protect themselves, like a sunscreen, during extreme ocean heat waves before they die. The phenomenon has sparked the Glowing Gone Campaign in which UNEP has partnered with The Ocean Agency, among other leading ocean conservation organizations.

“It is important to remember bleached corals are not dead corals — on mildly or moderately bleached reefs there is a good chance most bleached corals will recover and survive this event. Equally, on severely bleached reefs, there will be higher mortality of corals,” adds the statement from the lead management agency for the Reef. However, some pockets of the Reef remain unaffected.

Coral reefs, like underwater cities, support a quarter of all marine life – potentially up to 1 million species. They provide at least half a billion people with food security and livelihoods. They also protect coastlines from increasing damage by buffering shorelines against waves, storms and floods, preventing loss of life, property damage and erosion.

“Understanding the different responses of coral reefs to bleaching events is critical for managing coral reefs in a changing climate. Coral reefs are naturally resilient ecosystems, and have been observed to recover well after mortality events if they are given the chance to and other stressors are reduced. This means better water quality, reduced pollution, and sustainable fishing,” says Ms Carvalho.

Supporting coral reefs to be resilient entails reducing coral reef vulnerability to climate change and other stressors.

The bleaching event comes at a time when this year’s World Environment Day, celebrated on June 5, is focused on biodiversity. The day calls for increased awareness and understanding of what biodiversity is and how it provides the vital services that sustain all life on earth. Coral have the highest biodiversity of any ecosystem on the planet—even more than a tropical rainforest.

Further, coral protection speaks to the UN Decade on Ecosystem Restoration (2021-2030) geared towards the restoration of degraded and destroyed ecosystems to fight the climate crisis and enhance food security, water supply and biodiversity.