07 Jan

Cnidaria: Corals

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• Fire Corals (Millepora Boschmai)

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• Why in news?
  • Largest deep-sea coral reef to date is mapped by scientists off the US Atlantic Coast (Jan 2024)
• What is Coral?
  • Corals are colonial organisms made up of Individual polyps. Coral ‘Polyps’ are tiny animals related to anemones and jellyfish.
  • They fall under phylum Cnidaria and the Class Anthozoa. They have a sac like body and an opening, or mouth, encircled by stinging tentacles. They use calcium and carbonate ions from water to form a hard-cup shaped skeleton of calcium carbonate. This skeleton protects the soft, delicate body of Polyp. Most skeletons have clear bodies i.e. their skeletons are white like human bones.
  • Understanding Symbiotic Relationship between Coral (Polyp) and Algae
    • Algae zooxanthellae provide nutrients through photosynthesis activities.
    • Corals provide protected environment, steady supply of carbon dioxide, for photosynthesis and phosphorus to
  • Other Source of Nutrition for Corals
    • In addition to the symbiotic relation with algae, most corals capture and consume live prey ranging from microscopic zoo-planktons to small fish, depending on the Coral size.
  • Useful Video: What is Coral: Coral: What is it?

Types of Corals

• Hard Coral and Soft Corals
  • Only hard corals form reef: They produce rock-like skeleton made up of calcium carbonate. These skeletons contribute towards making reefs. They rely on algae (zooxanthellae) living within their tissues for nutrition and energy to build their skeleton. They therefore live in shallow clear water to allow sunlight to reach the algae.
  • Soft Corals, such as sea fans and sea whips, look like colorful plants or graceful trees and are not reef building as they don’t form hard calcified skeleton of many reef-building corals. They only produce small amount of calcium carbonate which help them remain in shape. They may or may not be in symbiotic relations with zooxanthellae.
• Cold Water Corals/Deep water Corals
  • Though majority of coral reefs are found in tropical and sub-tropical waters, there are also deep-water corals in colder regions.
    • They are mostly stony (hard) corals but can also include soft corals like sea fans.
    • They are not dependent on Zooxanthellae for energy. They filter out food particles out of water for energy.
    • They provide habitat for sharks, swordfish, sea stars, octopus, shrimp, various types of fish etc.
  • Largest Deep-Sea Coral Reef to date is mapped by Scientists off the US Atlantic Coast (Jan 2024)
    • It extends for about 499 kms from Florida to South Carolina and at some point is upto 109 kms wide.
  • Scientists predict that deep reef cover more of the ocean floor than tropical reefs. 75% of world’s ocean floor is still unmapped in high resolution.
• Coral Reefs
  • These are larger underwater structure composed of the skeletons of Corals. Reefs are built by coral polyps as they secrete layers of Calcium carbonate from under their skin. These skeletons made from calcium carbonate, protect the coral animals from predators and also offer a substrate on which new Coral Polyps can attach themselves.
  • Coral reefs grow best in warm water and they prefer a shallow range with lots of sunlight for their symbiotic algae.
  • Classification of Coral Reefs based on their location: Fringing, Barrier, Atolls and Patches
    • Fringing Reefs grow near the coastline around islands and continent They are separated from the shore by narrow, shallow lagoons. They are the most common types of reefs that we see.
      • E.g. reefs of Andamans.
    • Barrier Reefs are also parallel to coastline but are separated by deeper, wider lagoons. At their shallowest point, they can reach the water’s surface forming a ‘barrier‘ to navigation. The great barrier reef of Australia is the largest and the most famous of the barrier reefs.
      • g. in reefs in Nicobar and Lakshadweep.
    • Atolls are rings of corals that create protected lagoons and are usually located in the middle of the They are generally formed when islands surrounded by fringing reefs sink into the sea or the sea level rises around them. The fringing reefs continue to grow and eventually form circles with lagoons inside. Atolls are like circular barrier reefs but without their central land mass.
      • E.g. Atolls of Lakshadweep and Nicobar.
    • Patch reefs are small, isolated reefs, that grow up from the open bottom of the island platform or continental shelf. They usually occur between fringing reefs and barrier reefs. They vary greatly in size and rarely reaches the surface of the water.

• Where are Coral Reefs located globally?
  • Coral reefs are found in more than 100 countries of the world. Most of these reefs are located between the Tropic of Cancer and Tropic of Capricorn.
  • Great Barrier Reef, located off Australia’s East Coast is the largest coral reef in the world.
  • Important Coral Reef Areas of India include Andaman and Nicobar Islands, Lakshadweep Islands, the Gulf of Mannar and finally the Gulf of Kutch in the order of their species diversity.

• Great Barrier Reefs
  • It contains the world’s largest collection of Coral Reefs and is world’s most extensive coral reef ecosystem. It is a site of remarkable variety and beauty on north-eastern Coast of Australia.
    • Size: It stretches more than 2,300 kms and has some 2,500 individual reefs of varying sizes and shapes, and over 9,00 islands. It is extremely rich in biodiversity – it has 400 types of corals, 15,00 species of fish, and 4,000 types of molluscs.
  • The entire ecosystem was inscribed as World Heritage Site in 1981, covering an area of 348,000 sq. km and a length of 2,300 km.
  • But the Reef system is facing severe environmental threats.
    • Recently, World Heritage Committee have tried to downgrade the reef’s World Heritage Status to “in danger” because of the damage caused by climate change. But, Australia has prevented this by garnering enough international support.
    • Factors threatening Reef:
      • Rising sea temperature
      • Thermal extremes
    • The state of the ecosystem has become very poor here due to rising sea temperatures and thermal extremes. This is negatively impacting abundance and health of many species groups, including corals, invertebrates, some bony fishes, marine turtles and seabirds.
• Significance of Coral Reefs
  • Biodiversity Protection: Coral reefs are believed to have highest biodiversity of any ecosystem on the planet – even more than the tropical rain forests. They occupy less than 1% of the ocean floor but is home to 25% of marine life. They are sometimes also known as ‘The tropical rainforest of the Oceans’.
    • They also provide substrate for mangroves.
  • Economic Benefits: The value of goods and services provided by Coral reefs is estimated to be $2.7 trillion per year.
  • Coral reef provide millions of people with food, medicine, protection from storms, and revenue from fishing and tourism.
  • They are also the largest biogenic CaCO3 producer.
• Threats: As per Global Coral Reef Monitoring Network (CCRMN), in the last decade, world has lost 14% of its Coral.
• Key Factors:
  • Man-Made Causes
    • Pollution, Ocean Acidification,
      • Eutrophication -> Deoxygenation -> Dead As per a recent study, deoxygenation has emerged as the biggest threats in recent years.
    • Overfishing, Unsustainable Tourism, and Poor Coastal Management
    • Mechanical Damages
    • Thermal Pollution
    • Climate Change
      • As per the GCRMN report, the reefs all over the world are under relentless stress due to warming caused by climate change.
      • Higher sea surface temperatures have also become a factor for coral
  • Natural disturbance such as violent storms, El Nino Southern Oscillation, epizootics
• Coral Bleaching
  • • When Corals are stressed by changes in conditions such as temperature, light, or nutrients, they expel the symbiotic algae living on their tissues, causing them to turn completely white.
    • It has emerged as one of the major reasons for coral reef destruction. For e.g. in 1998, it caused the loss of 8% of the world’s corals.

1) FIRE CORALS (MILLEPORA BOSCHMAI)

• Fire corals are colonial marine organisms that look like a real coral. Technically they are not corals. They are more closely associated with Hydra and other hydrozoans.
• Millepora Boschmai: It is a critically endangered species of fire coral. As per the IUCN’s latest update the fire Coral (Millepora Boschmai) may be possibly extinct.
• The scientific name Millepora is derived from several small pores on the surface of these coral They are usually yellow green or brown in color.
• Habitat: Generally found in Murky inshore waters and display a tolerance for siltation. Often found in clear offshore sites.
• Distribution: Indonesia, Gulf of Chiriqui in Panama Pacific
• Possibly extinct from: Australia, India, Indonesia, Malaysia
• Threats
  • Illegal Trade: Collected for decoration and jewellery trade.
  • Global warming and related bleaching effect: though to have completely disappeared from the majority of marine.