- Coral reefs serve many roles within the marine ecosystem. Also, they are important to the way our global ecosystems work as well.
- However, anthropogenic activities such as pollution, overfishing, destructive fishing practices using dynamite or cyanide, collecting live corals for the aquarium market, mining coral for building materials, and global warming are causing depletion of coral.
- Marine ecosystem has been impacted negatively by these factors.
- Coral reefs are most important constituents of marine ecosystem are being degraded due to multiple factors, which has called for urgent conservation efforts.
Corals and coral reefs
- Corals are calcareous rocks which are formed from the skeletons of minute sea animals, called polyps.
- The polyps extract calcium salts from sea water to form hard skeletons which protect their soft bodies. Further, accumulation of these skeletons forms corals.
- The corals live in colonies and develop on skeletons of dead polyps. These tubular skeletons grow upwards and outwards as a cemented calcareous rocky mass, collectively called corals.
- The shallow rock which is created by these depositions is called reef which evolves into islands on maturity.
Types of Corals
- There are two kinds of corals which are hard and soft corals.
- Hard corals (Scleractinia) such as brain, star, staghorn, elkhorn and pillar corals secrete rigid calcium carbonate exoskeletons (or corallites) that protect their soft delicate bodies.
- Soft corals (Gorgonians) such as sea fans, sea whips, and sea rods lack an exoskeleton.
Causes of depletion of coral reefs
- Coral polyps are very sensitive organisms. The increase in PH of oceans due to ocean acidification caused by global warming and even influx of large amount of fresh water has the ability to destroy coral reefs.
- Land-based runoff and pollutant discharges from dredging, coastal development, agricultural and deforestation activities, and sewage treatment plant operations contain sediments, nutrients, chemicals, insecticides, oil, and debris which are corrosive and harmful in nature.
- Nutrient levels of ocean water increase when pollutants enter water which promotes the rapid growth of algae and other organisms.
- This leads to reduction in Biological Oxygen Demand (BOD) leading to death of corals.
2. Oil Spills
- Oil spills leads to damaging of eggs of coral polyps and immature deaths of adult corals.
- If oil spills occur when corals are spawning, the eggs and sperm can be damaged as they float near the surface before they fertilize and settle. Oil pollution also disrupt the reproductive success of corals
3 .Catching of fishes
- Coral reefs are often destroyed when coral heads and brightly-colored reef fishes are collected for the aquarium and jewelry trade.
- Bottom trawling involves dragging heavy weighted nets across the sea floor, in an effort to catch fish.
- It often leads to destruction of coral reefs which are essentially habitats of fishes. This method of fishing is often used for fishing by commercial companies because large number of fishes is caught by this method.
- Dynamite or other heavy explosives are detonated to startle fish out of their hiding places which leads to indiscriminate killing of other species and can crack and stress corals so much that they expel their zooxanthellae.
- It involves spraying or dumping cyanide onto reefs in order to stun and capture live fish.
- It kills coral polyps and degrades the reef habitat affecting other species such as zooxanthellae.
4. Ocean Acidification
- Ocean acidification causes coral bleaching at large scale. It occurs due to formation of carbonic acid when the carbon-di-oxide reacts to the water on the surface of the oceans.
- Decrease in PH of water leads to coral bleaching as corals expel the algae (zooxanthellae) living in their tissues causing the coral to turn completely white.
5. Increase in Sea-surface temperature
- It also leads to coral bleaching as corals expel zooxanthellae due to high temperature of ocean water.
- Hot water streams and effluents for industries and global warming are important factors behind it.
6. Influx of fresh waters
- Corals survive in saline or brackish water. When large amount of fresh water influxes it leads to destruction of coral habitats.
Why are coral reefs important to the ecosystem?
- Maintaining marine and coastal ecosystem: Coral reefs are the pillars on which marine and coastal ecosystems are built. They keep plants, fish, and animals They clean up our water and protect our coasts.
- Coastline protection: Coral reefs protect coastlines from the damaging effects of waves and tropical storms.
- Coastal cities depend on the coral reefs to provide a buffer to wave action and storm surges.
- The Great Barrier Reef is aptly named because it provides a barrier against the destructive ocean forces that would have otherwise eroded the coastline of the continent.
- Coral reefs stabilize mangroves and seagrass beds, providing habitats, oxygen, and vegetation for inland species besides humans.
- Habitat and protection: They provide habitats and shelter for thousands of marine organisms.
- Water filtration: Corals and spongesare often filter feeders, which consume particles from the water that surrounds them. This filtration then enhances the clarity and quality of the ocean’s waters.
- Water health: Coral reefs help with nutrient recycling, assist in carbon and nitrogen-fixing, and provide nitrogenand essential nutrients for the diverse array of life that exists within the marine food chain.
Major Coral reef systems and conservation efforts
Conservation of Great Barrier Reef
- Australia's Great Barrier Reef is the world's seven natural wonders and has been accorded as the World Heritage Area and the largest coral reef system.
- It is the biggest living structure on the planet which sprawls over a 344,400 square kilometers.
- It is located off the Queensland coast and is composed of 3000 individual reef systems, 760 fringe reefs, 600 tropical islands and more than 300 coral cays.
- It is a network of marine sanctuaries having unparalleled ecological importance.
- It provides refuge for an astounding variety of marine life, plants and animals ranging from ancient sea turtles, reef fish and 134 species of sharks and rays, to 400 different hard and soft corals and a plethora of seaweeds.
- It has unique biodiversity in form of turquoise waters, kaleidoscopic corals, abundant life and over 900 islands.
- Australia and WWF together have started to conserve the great barrier reef which is essentially a wild life habitat.
Methods used for conservation of Coral Reefs
Various efforts are being made to conserve coral reef system across the world.
1. Direct transplantation
- It includes transplanting coral colonies or fragments without intermediate nursery phase.
2. Coral gardening
- It includes transplanting coral fragments after an intermediate nursery phase.
3. Larval enhancement
- It includes reproduction of coral using sexually derived coral larvae to release or outplant at restoration site, after intermediate holding phase which can be in- or ex-situ.
- This methods includes larval propagation, sexual propagation, larval seeding and assisted breeding.
4. Substratum addition
- It includes addition of artificial structures for purposes of coral reef restoration. These structures are engineered/artificial structures, various brand names such as BioRock, EcoReef, ReefBall and Mars Spiders.
Coral Reefs in India and their conservation
- In India, coral reefs are restricted mainly in seven regions of India, such as:
- Coral reefs in Goa coast
- Coral reefs in Kerala coast
- Coral reefs in Palk Bay
- Coral reefs in Gulf of Kuchh
- Coral reefs in Gulf of Manner
- Coral reefs in Lakshadweep islands
- Coral reefs in Andaman and Nicobar islands
Relocation of coral reefs in Maharashtra
- Recently Maharashtra government has decided to relocate coral reefs off the coast of Mumbai for coastal road projects.
- The eight-lane highway is being envisaged to connect the northern suburb of Kandivali to the southern end of the city at Marine Drive.
- It is a 9.98-km section of the coastal road from Marine Drive to the Bandra-Worli sea link.
- The expert groups have identified eight areas having smaller colonies of corals including Haji Ali Section which have been protected under Schedule I of the Wildlife Protection Act, 1972.
- The Union Environment Ministry and the Maharashtra government have granted permission to translocate the coral colonies instead of burying them during the land reclamation process.
Coral Conservation in Gulf of Mannar
- Gulf of Mannar Marine National Park is comprised 23 islands, two of which are now submerged.
- The remaining 21 have been divided into four island groups namely Mandapam in the north, followed by Keelakarai, Vembar and the Thoothukudi groups going south.
- The Gulf of Mannar National Park have the coral islands adjacent to the coast from Rameswaram to Thoothukudi.
- During a global mass bleaching event in 2017, 2 percent of corals had died but after that different projects were launched to conserve these coral reefs, these shows a comparative recovery.
- Invasive Alien species and pollution has been touted as major reasons for coral bleaching apart from ocean acidification and global warming.
Coral Conservation in Gujarat
- Coral Reef Recovery Project was launched in 2008 by Gujarat Government and Wildlife Trust of India.
- It was supported by Gujarat Forest Department and Tata Chemicals Limited (TCL) to develop and implement appropriate strategies.
- The project aimed for the conservation of the Mithapur Reef, which is situated 12 kilometres south of the Gulf of Kachchh in Gujarat.
- The project envisioned for the creation of a model public-private-managed coral ecosystem of international standards.
- It used global benchmarks to restore degraded reefs through activities including coral transplantation and natural recruitment.
- Fragments of Acropora (Corals) were broken off the donor colonies and were implanted on moveable substrates and stabilized.
- The stabilised coral fragments were transported, covering a distance of more than 1500 kms from Lakshadweep to Mithapur.
- The coral fragments were stabilized with Lakshadweep water which was gradually acclimatized to the local sea water.
- These fragments were finally immersed into the natural surrounding and transplanted.
Coral reefs are also known as the ‘Rainforests of the Seas’ due to ecosystem services provided by them apart from largest variety of flora and fauna supported by them. These ecosystem supports marine ecosystem in different ways and hence are crucial for their existence. Government must take steps to conserve coral reefs to achieve Sustainable Development Goals such as Life Below Water (SDG 14) and Responsible consumption and production pattern (SDG 12).