The Great Barrier Reef’s recovery

The highest levels of coral cover, within the past 36 years, has been recorded in the northern and central parts of Australia’s Great Barrier Reef (GBR), according to the annual long-term monitoring report by the Australian Institute of Marine Science (AIMS). The researchers behind the report have warned, however, that this could be quickly reversed owing to rising global temperatures. 

What are coral reefs?

• Largest living structures on the planet -Corals are marine invertebrates or animals which do not possess a spine. Each coral is called a polyp and thousands of such polyps live together to form a colony, which grow when polyps multiply to make copies of themselves.
• Types of Corals- Corals are of two types hard corals and soft corals. Hard corals extract calcium carbonate from seawater to build hard, white coral exoskeletons. Hard corals are in a way the engineers of reef ecosystems and measuring the extent of hard coral is a widely-accepted metric for measuring the condition of coral reefs. Soft corals attach themselves to such skeletons and older skeletons built by their ancestors. Soft corals also add their own skeletons to the hard structure over the years.
• Services provided by Corals- Coral reefs support over 25% of marine biodiversity even as they take up only 1% of the seafloor. The marine life supported by reefs further fuels global fishing industries. Besides, coral reef systems generate $2.7 trillion in annual economic value through goods and service trade and tourism.

What does the new report say?

• Reefs are resilient- The report states that reef systems are resilient and capable of recovering after disturbances such as accumulated heat stress, cyclones, predatory attacks and so on, provided the frequency of such disturbances is low.
• Increase in overall coral cover- The new survey shows record levels of region-wide coral cover in the northern and central GBR since the first ever AIMS survey was done. Coral cover is measured by determining the increase in the cover of hard corals. The hard coral cover in northern GBR had reached 36% while that in the central region had reached 33%. Meanwhile, coral cover levels declined in the southern region from 38% in 2021 to 34% in 2022.
• Reasons for coral growth-The record levels of recovery, the report showed, were fuelled largely by increases in the fast-growing Acropora corals, which are a dominant type in the GBR. Incidentally, these fast growing corals are also the most susceptible to environmental pressures such as rising temperatures, cyclones, pollution, crown-of-thorn starfish (COTs) attacks which prey on hard corals and so on. Also, behind the recent recovery in parts of the reef, are the low levels of acute stressors in the past 12 months — no tropical cyclones, lesser heat stress in 2020 and 2022 as opposed to 2016 and 2017. 

Persistent Issues

• Climate change-induced stress - Besides predatory attacks and tropical cyclones, scientists say that the biggest threat to the health of the reef is climate change-induced heat stress, resulting in coral bleaching.
• Increase in Ocean Temperature- According to the UN assessment in 2021, the world is going to experience heating at 1.5°C in the next decade, the temperature at which bleaching becomes more frequent and recovery less impactful.
• Increase in marine heatwaves - The report says that the prognosis for the future disturbance suggests an increase in marine heatwaves that will last longer and the ongoing risk of COTs (crown-of-thorn starfish) outbreaks and cyclones. 

What do you understand by corals? Explain the threats which are leading to coral bleaching?