Ocean temperatures in Australia’s Great Barrier Reef now hottest in 400 years: What a new study says
- August 11, 2024
- Posted by: OptimizeIAS Team
- Category: DPN Topics
Ocean temperatures in Australia’s Great Barrier Reef now hottest in 400 years: What a new study says
Sub : Env
Sec :Eco system
Context: According to a new study, Water temperatures in and around Australia’s Great Barrier Reef have risen to their warmest in 400 years over the past decade, placing the world’s largest coral reef under threat.
What are coral reefs?
Corals are essentially 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 mouth. 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 NOAA.
Coral reefs, also referred to as “rainforests of the sea”, have existed on the Earth for nearly 450 million years.
Why are coral reefs important?
Coral reefs have a crucial role in marine ecosystems.
Important habitat: Thousands of marine species can be found living on one reef. For instance, “the Great Barrier Reef contains over 400 coral species, 1,500 fish species, 4,000 mollusc species and six of the world’s seven sea turtle species”, according to a report by the Natural History Museum. Research has shown that there could be millions of undiscovered species of organisms living in and around reefs.
Economic Imp: These massive structures also provide economic goods and services worth about $375 billion each year. More than 500 million people across the world depend on coral reefs for food, income and coastal protection from storms and floods.
Protection: Coral reefs can absorb up to 97% of the energy from waves, storms, and floods, which prevents loss of life, property damage, and soil erosion.
What are the findings of the study?
A group of scientists at universities across Australia drilled cores into the coral and, much like counting the rings on a tree, analysed the samples to measure summer ocean temperatures going back to 1618.
Combined with ship and satellite data going back around a hundred years, the results show ocean temperatures that were stable for hundreds of years began to rise from 1900 onwards as a result of human influence, the research concluded.
From 1960 to 2024, the study’s authors observed an average annual warming from January to March of 0.12 degree Celsius per decade.
Since 2016, the Great Barrier Reef has experienced five summers of mass coral bleaching, when large sections of the reef turn white due to heat stress, putting them at greater risk of death. (Widespread mass bleaching of the Great Barrier Reef was first seen in 1998 and happened again in 2002016, 2017, 2020, 2022 and now in 2024)
These summers were during five of the six warmest years in the last four centuries, the study showed.
Great Barrier Reef (GBR)
- The GBR is the world’s largest coral reef system. It’s located in the Coral Sea off the coast of Queensland, Australia.
- The Great Barrier Reef is a site of remarkable variety and beauty on the north-east coast of Australia. It contains the world’s largest collection of coral reefs, with 400 types of coral, 1,500 species of fish and 4,000 types of mollusc. It also holds great scientific interest as the habitat of species such as the dugong (‘sea cow’) and the large green turtle, which are threatened with extinction.
The GBR is a UNESCO World Heritage site and was inscribed in 1981.
- In 2023, the UNESCO Heritage Committee refrained from listing Australia’s Great Barrier Reef as a site “in danger” but warned that the world’s biggest coral reef ecosystem remained under “serious threat” from pollution and the warming of oceans.
What is Coral Bleaching?
- When corals face stress by changes in conditions such as temperature, light, or nutrients, they expel the symbiotic algae zooxanthellae living in their tissues, causing them to turn completely white. This phenomenon is called coral bleaching.
- The pale white colour is of the translucent tissues of calcium carbonate which are visible due to the loss of pigment-producing zooxanthellae.
- Bleached corals can survive depending on the levels of bleaching and the recovery of sea temperatures to normal levels.
- If heat pollutions subside in time, over a few weeks, the zooxanthellae can come back to the corals and restart the partnership but severe bleaching and prolonged stress in the external environment can lead to coral death.
- Over the last couple of decades, climate change and increased global warming owing to rising carbon emissions and other greenhouse gases have made seas warmer than usual.
- Coral bleaching has occurred in the Caribbean, Indian, and Pacific oceans regularly.
Mass Coral Bleaching:
- To officially declare a global mass bleaching event, widespread bleaching must be observed in three major ocean basins: the Atlantic, Pacific, and Indian Oceans.
Fourth Mass Coral Bleaching Event:
- The current coral bleaching event is part of a global trend, identified as the fourth mass coral bleaching event, which has affected over 50 regions worldwide since 2023.
- Triggered by elevated sea surface temperatures due to an ongoing El Niño event, this phenomenon threatens marine biodiversity, as corals act as crucial ecosystems for various marine species.
- Historical data from global events in 1998, 2010, 2014, and 2017 highlight the recurring and severe nature of these bleaching events, emphasizing the urgent need for effective marine environmental management.
Previous Mass Coral Bleaching:
- First Mass Bleaching: It occurred in 1998 when the El Niño weather pattern caused sea surfaces in the Pacific Ocean to heat up; this event caused 8% of the world’s coral to die.
- Second Mass Bleaching: This event took place in 2002. In the past decade, however, mass bleaching occurrences have become more closely spaced in time, with the longest and most damaging bleaching event taking place from 2014 to 2017.
- Third Mass Bleaching: The event that took place between 2014-17 affected reefs in Guam in the Western Pacific region, the North, South-Pacific, and the Indian Ocean.
Coral reef:
- Corals are invertebrate animals belonging to a large group of colourful and fascinating animals called Cnidaria.
- Each coral animal is called a polyp, and most live in groups of hundreds to thousands of genetically identical polyps that form a ‘colony’.
- Coral polyps host a microscopic symbiotic alga called zooxanthella that photosynthesizes just like plants, providing food to the coral.
- Coral is generally classified as either hard coral or soft coral.
Importance of Coral Reefs:
- Coral reefs, often described as the “rainforests of the sea,” play a vital role in marine life by providing essential habitat, food, and breeding grounds for numerous marine organisms.
- The health of coral reefs is directly linked to the broader ecological balance and biodiversity of the oceans.