Fourth global mass coral bleaching event triggered : What does it mean?

THE FOURTH global mass coral bleaching event has been triggered by extraordinary ocean temperatures, the US National Oceanic and Atmospheric Administration (NOAA) said last week. This could have serious consequences for ocean life and millions of people who rely on coral reefs for food, jobs, and coastal defence.

What are corals and coral reefs?

Corals are animals, which are sessile, meaning they permanently attach themselves to the ocean floor. They use their tiny tentacle-like hands to catch food from the water and sweep it into their mouths. Each individual coral animal is known as a polyp and it lives in groups of hundreds to thousands of genetically identical polyps that form a ‘colony’.

Corals are largely classified as either hard coral or soft coral. It is the hard corals that are the architects of coral reefs — complex three-dimensional structures built up over thousands of years. “Unlike soft corals, hard corals have stony skeletons made out of limestone that are produced by coral polyps. When polyps die, their skeletons are left behind and used as foundations for new polyps,” according to a report by NOAA.

What is the significance of corals?

Coral reefs are crucial ecosystems as thousands of marine species can be found living on one reef. Scientists believe there could be millions of undiscovered species of organisms living in and around reefs.

Every year, reefs provide about $2.7 trillionin goods and services, according to a 2020 estimate by the Global Coral Reef Monitoring Network, Reuters reported. More than 500 million people across the world depend on coral reefs for food, income, and coastal protection.coral reef scan absorb up to 97% of the energy from waves, storms, and floods, which prevents loss of life and property damage. Therefore, the absence of coral reefs would result in severe ramifications for both marine life and humans.

What is coral bleaching?

Most corals contain algae called zooxanthellae — plant-like organisms — in their tissues. Corals and zooxanthellae have a symbiotic relationship. While corals provide zooxanthellae a safe place to live, zooxanthellae provide oxygen and organic products of photosynthesis that help corals to grow and thrive. Zooxanthellae also give bright and unique colours to corals.

Corals are very sensitive to light, temperature, and pollution, and even a small change in their surroundings can stress them. When stressed, they expel zooxanthellae and turn entirely white. This is called coral bleaching.

Coral bleaching doesn’t necessarily lead to the death of corals. It rather reduces the reproductivity of corals and makes them more vulnerable to fatal diseases due to lack of nutrients. If the bleaching is not too severe, corals have been known to recover.

Global mass bleaching of coral reefs happens when significant coral bleaching is confirmed in the Atlantic, Indian, and Pacific oceans, according to a report published by The Conversation. Such events are a relatively new phenomenon. The first one took place in 1998 in which 20% of the world’s reef areas suffered bleaching-level heat stress. The next two global bleaching events occurred in 2010 (35% of reefs affected), and between 2014 and 2017 (56% of reefs affected).

What is happening right now?

NOAA has confirmed that the fourth global bleaching event is currently underway. Nearly 54 countries, territories, and local economies — from the US, Saudi Arabia to Fiji — have confirmed bleaching, according to a report by The New York Times. The Great Barrier Reef of Australia — the largest in the world—is witnessing its most severe bleachingevent. reef sin the western indian ocean, including Tanzania, Kenya, and off the western coast of indonesia have also been affected.

In total, more than 54% of the world’s coral reef areas have experienced bleaching-level heat stress in the past year, and that number is increasing by about 1% per week, Derek Manzello, the coordinator of NOAA’S Coral Reef Watch program, told the NYT.

Why is it happening?

Although there can be several reasons for coral bleaching, the key driver behind the ongoing global event is higher ocean temperatures.

Since mid-march 2023, the average sea surface temperature (SST) has been abnormally high. In March this year, it reached a record monthly high of 21.07 degree Celsius, according to the EU Copernicus Climate Change Service (C3S). Temperatures are soaring mainly because of the rising emissions of heat-trapping greenhouse gases (GHGS) such as carbon dioxide and methane. Nearly 90% of the extra heat trapped by GHGS has been absorbed by the oceans — that is why they have become so warm.

Corals begin to bleach when surrounding waters become at least 1 degree Celsius warmer than the maximum average temperature and persist for four or more weeks, according to scientists.

The situation has been exacerbated by El Niño, a weather pattern which is associated with warmer oceans, which developed in June 2023. Now that it is weakening and a cooling La Niña may set in by the end of the year, the global mass coral bleaching event may not last very long.

The full impact of the event will not be known for a while but scientists have said that it is the most severe yet.