[Environment] Coral reefs – recent findings

Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals like calcareous algae, gastropods, green algae, sino bacteria, oyester, mollusca etc found in marine waters. Coral reefs are often called “rainforests of the sea” as they form some of the most diverse ecosystems on Earth. Despite occupying less than 0.1% of the world’s ocean surface, they provide a home for 25% of all marine species!


Conditions required for coral reef formation:
  • They are found in clear tropical ocean water usually between 30N to 30S latitudes
  • The water temperature must be between 20-25C
  • Coral reef can form to depth of 90 meters since at this depth algae can form food through photosynthesis.
  • Coral are not found near mouth of river where lots of sediments are unloaded into ocean.
  • Coral are formed only in saline water with almost 27ppp (parts per million).
Types of Coral reefs:
  1. Fringing reef: A coral reef which is attached to the shore is known as fringing reef. eg Andaman Nicobar, Lakshadweep, Coast of Florida
  2. Barrier Reef: A lagoon formed between continent and corals are known as barrier reef. eg Great barrier reef of Australia
  3. Atoll: A ring shaped coral reef formed by barrier reef over long period of time is known as atoll. eg Tobalu Island.
Recent Findings:
A recent study taken up by a team of researchers from the Zoological Survey of India (ZSI), Chennai, brought to light the serious threat of extinction the coral reef colonies and mangrove forests in the Palk Bay are facing. At present, only two per cent of the coral reefs survive in the area.

Global warming, siltation, release of untreated raw sewage into the water bodies and overgrowth of algae were stated to be the three important reasons for the possible disappearance of coral colonies and its associated organisms from the Palk Bay area.

The study showed that release of untreated raw sewage from the nearby areas into the water bodies, which ultimately drained into the sea, led to diseases in coral colonies, due to which they died. The mix of sewage water into the sea water had a cascading effect, resulting in coral colonies being covered with an increased growth of algae. This also led to the disappearance of corals.

At present, a small colony of bolder corals, a resilient species, is only found in the Palk Bay region.

“A decade ago, the entire region used to be filled with a lot of life forms and it was a paradise for researchers. But, today, the place is totally deserted,”.

Apart from these problems, the conflicts of interest between the traditional fishermen and the trawler operators also took a toll on the biodiversity of the Palk region.

Australian scientists have discovered the molecular mechanism that leads to mass death of corals worldwide as the Earth’s climate changes. Coral bleaching is one of the most devastating events affecting coral reefs around the planet, which is triggered by rising water temperature.It occurs when the coral & its symbioyic algae come heat-stressed, and the algae, which feed the corals, either die or are expelled by the coral.Now, scientists from the ARC Centre of Excellence for Coral Reef Studies and James Cook University have revealed that a complex cascade of molecular signals leading up to the self-inflicted death of corals and their symbiotic algae is triggered as sea water begins to warm.

Sadly, more than three-quarters of the corals in the Caribbean Sea have been lost in the past 35 years and half the cover in Australia’s Great Barrier Reef has died since 1960.

A report released by the International Coral Reef Symposium has stated that more than 85% of reefs in the “Coral Triangle” (covering Indonesia, Malaysia, Papua New Guinea, the Philippines, The Solomon Islands and East Timor) is under threat from pollution, sedimentation, overfishing and climate change.

But there is one factor emerging as the biggest threat to the reefs, that is being called “climate change’s equally evil twin.” This factor is he rising acid levels in oceans.

Acidic oceans

Like global warming, ocean acidification to is driven by is driven by excessive levels of carbon dioxide.

Oceans absorb about a quarter of the carbon dioxide in the atmosphere, forming carbonic acid. This increases sea acidity. Scientists initially assumed that the carbon dioxide absorbed by the water would be sufficiently diluted as the oceans mixed shallow and deeper waters.


But most of the carbon dioxide and the subsequent chemical changes are being concentrated in surface waters. Higher acid levels make it tough for coral skeletons to form and lead to its deterioration.


Oceans’ rising acid levels have emerged as one of the biggest threats to coral reefs, acting as the “osteoporosis of the sea” and threatening everything from food security to tourism to livelihoods.

Some attempts to address the problem are already under way. Instruments that measure changing acid levels in the water have been installed in some areas to warn oyster growers when to stop the flow of ocean water to their hatcheries.


But that is only a short-term solution, say scientists. The most critical element is reducing carbon emissions.

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