From UPSC perspective, the following things are important :
Prelims level : Corals, Coral Bleaching
Mains level : Great Barrier Reef
A joint report by the International Union for Conservation of Nature (IUCN) and UNESCO’s World Heritage Centre (WHC) expressed concern about the status of the Great Barrier Reef (GBR) in Australia, recommending that it “be inscribed on the List of World Heritage in Danger.”
About Great Barrier Reef
- Australia’s Great Barrier Reef is the world’s largest reef system stretching across 2,300 km and having nearly 3,000 individual reefs.
- It hosts 400 different types of coral, gives shelter to 1,500 species of fish and 4,000 types of mollusc.
- 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.
- In Australia, the Barrier Reef, in pre-COVID times, generated $4.6 billion annually through tourism and employed over 60,000 people including divers and guides.
What does the new report say?
- The current report surveyed 87 reefs in the GBR between August 2021 and May 2022.
- 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.
- 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.
- Acropora 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.
Does this mean the reef is out of the woods?
- 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 earlier.
- 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.
- The concern is that in the past decade, mass bleaching events have become more closely spaced in time.
- The first mass bleaching event occurred in 1998 when the El Niño weather pattern caused sea surfaces to heat, causing 8% of the world’s coral to die.
- The second event took place in 2002.
- But the longest and most damaging bleaching event took place from 2014 to 2017. Mass bleaching then occurred again in 2020, followed by earlier this year.
Back2Basics: Coral Reefs
- Corals are marine invertebrates or animals which do not possess a spine.
- They are the largest living structures on the planet.
- 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.
- 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. These growing multiplying structures gradually form coral reefs.
How do corals bleach?
- Corals share a symbiotic relationship with single-celled algae called zooxanthellae.
- The algae prepares food for corals through photosynthesis and also gives them their vibrant colouration.
- When exposed to conditions like heat stress, pollution, or high levels of ocean acidity, the zooxanthellae start producing reactive oxygen species not beneficial to the corals.
- So, the corals kick out the colour-giving algae from their polyps, exposing their pale white exoskeleton and leading to coral starvation as corals cannot produce their own food.
- Bleached corals can survive depending on the levels of bleaching and the recovery of sea temperatures to normal levels.
- Severe bleaching and prolonged stress in the external environment can lead to coral death.
Try this PYQ:
Consider the following statements:
- Most of the world’s coral reefs are in tropical waters.
- More than one third of the world’s coral reefs are located in the territories of Australia, Indonesia and Philippines.
- Coral reefs host far more number of animal phyla than those hosted by tropical rainforests.
Which of the above statements is/are correct?
(a) 1 and 2 only
(b) 3 only
(c) 1 and 3 only
(d) 1 and 3 only
Post your answers here.
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