Coral polyps are little, fleshy sea anemones that live in tropical and subtropical oceans and seas. They share a symbiotic relationship in shallow waters with a species of microscopic algae called Zooxanthellae, which gives them a vivid color. Only 0.0025 % of the ocean floor is made up of corals, but they are responsible for producing half of the oxygen on Earth and absorbing more than a third of the carbon dioxide released by burning fossil fuels. More than 75% of the world's corals are currently threatened by a range of stressors, including climate change, overfishing and destructive fishing, coastal development, pollution, and degradation. This article will explain to you about Corals which will be helpful in preparing the Environment Syllabus for the UPSC Civil Service exam.

Coral Polyps

• A coral polyp is an invertebrate that can range in size from the size of a pinhead to up to a foot.
• Each polyp has a mouth surrounded by stinging tentacles and a sac-like body.
• The more or less extendable tentacles that gather food are equipped with nematocysts, which are specialized stinging structures that paralyze prey.
• The polyp creates a strong, cup-shaped skeleton using calcium carbonate (limestone) from seawater.
• The sensitive, delicate body of the polyp is shielded by its skeleton.

Corals - Types

Hard (Stony) Corals

• The construction of the coral reef depends heavily on hard coral. They build themself a hard skeleton.
• Hard coral polyps secrete calcium carbonate (limestone) skeletons that will eventually harden into rock.
• Elkhorn coral and brain coral are examples of hard coral.
• Hard corals are regarded as hermatypes, which are corals that form reefs.
• For their existence, these corals are dependent on a particular type of algae called zooxanthellae that inhabits their tissues.

Soft Corals

• Soft corals frequently resemble trees and vegetation. They don't have stony skeletons like hard coral since they are breakable.
• They develop wood-like cores for stability and protection.
• These cores are composed of structural proteins like gorgonin and other proteins found in animal horns and nails.
• Ahermatypes are the name given to these varieties of coral (non-reef building corals).
• Sea fingers or sea whips are two types of soft coral found in the Bahamas and Caribbean.
• Additionally, zooxanthellae and this form of coral do not always work together symbiotically.

Deep - Sea Corals

• Up to 6,000 meters (20,000 feet) below the ocean's surface, in the deepest depths, is where deep-sea coral can be found.
• These corals require extremely cold water and little to no sunlight to survive.
• Like shallow species, these corals can exist as a single polyp or as many, dwelling in intricate colonies made up of many species.
• These species may flourish in a wide range of waterways all over the world because they don't need sunlight or warm water to grow.
• Even in waters as cold as -1 degrees Celsius, they have been discovered.
• These corals don't have zooxanthellae since they don't require sunlight to survive.

Ideal Conditions for Coral Growth

• Shallow water: Corals must grow in shallow areas of water. The coral's surface should not be more than 80m above the water's surface.
• Sunlight: Zooxanthellae require adequate sunlight to perform photosynthesis.
• The semi-hard or hard surface is required for coral polyp skeleton compaction, cementation, and solidification.
• Beautiful coral polyps die in areas with sediment-filled waters. This is due to the presence of sediments and opaque water, which restricts the passage of sunlight to the algae, which sustains their life.
• Temperature: Coral reefs are in direct contact with warm oceanic waters. The water temperature should be around 20 degrees. As a result, coral reefs predominate on the eastern coasts of continents.
• Salinity: The slight salt in ocean waters is extremely important for the development of coral polyps. The polyps extract calcium from the waters to protect their skeletons. Hence, mild salinity is a necessity for coral reefs to flourish.
• Nutrients: Corals flourish in sea waters because ocean waves support the constant supply of rich nutrients. Coral polyps multiply faster when supplied with nutrients.

Coral Reefs

• Coral reefs are large underwater structures made up of the skeletons of coral, which are colonial marine invertebrates.
• In other words, the huge colonies of corals are referred to as coral reefs.
• Coral reefs are built and maintained by thousands of tiny animals known as coral "polyps," which are related to anemones and jellyfish.
• Corals are cemented calcareous rocky masses that grow upwards and outwards as tubular skeletons.

*To know more about the topic, click this link Coral Reefs

Coral Bleaching

• When corals lose their brilliant colors and turn white, this is known as coral bleaching.
• Bleaching or the paling of coral color occurs when:
  • the density of zooxanthellae decreases and/or
  • the concentration of photosynthetic pigments inside the zooxanthellae decreases.
• Coral is brilliant and colorful due to zooxanthellae, a type of microscopic algae.
• The zooxanthellae live in a mutually beneficial relationship within the coral, one assisting the other to survive.
• When coral is stressed by changes in conditions such as temperature, light, or nutrients, they expel the symbiotic algae living in their tissues, causing them to turn completely white.

*To know more about the topic, click this link Coral Bleaching

Corals - Significance

• Rich Biomass: As coral reefs are found in the shallow water of tropical or subtropical regions they are characterized by high biomass production & rich floral & faunal activity.
• Erosion Barrier: Corals are a natural protective barrier against erosion.
• High-quality Proteins: Some corals are a source of high-quality proteins.
• Hotspot of Marine Biodiversity: Coral is a large hot spot of marine biodiversity & fishery resources.
• Calcium Carbonate Producer: Corals are the largest producer of biogenic calcium carbonate.
• Substrate for Mangroves: They provide substrate for mangroves.
• Habitat: Coral reefs provide habitat for a large variety of animals & plants including avifauna.
• Coral play a remarkable role in the in situ or conservation of marine biodiversity.
• Medicinal Application: Coral is used as a bone substitute in reconstructive bone Surgery as pores & channels are some corals that resemble that of human bone.
• Source Of Food Supply: Fish that live in and around coral reefs provide a healthy source of protein to billions of people, the majority of whom live along coastlines.

Threats to Corals

Overfishing

• A study shows that Overfishing has destroyed 55 percent of the world's coral reefs.
• Overfishing of deep-water commercial fish and vital reef species has resulted from rising demand for food fish and tourism.
• Overfishing of certain species near coral reefs has the potential to disrupt the biological balance and biodiversity of the reef.
• Overfishing of herbivorous fish, for example, can result in excessive algal growth.
• When fish numbers decline, especially those that eat algae, algae can grow out of control, suffocating corals.

Climate Change

• In a decade, global warming has killed 14 % of the world's coral reefs, and more will be wiped away if ocean temperatures continue to rise.
• The greatest danger to coral reefs is climate change.
• Since pre-industrial times, anthropogenic greenhouse gas emissions have produced a 1°C increase in global surface temperature.
• As a result of this, unprecedented mass coral bleaching episodes have occurred, making coral reefs one of the most vulnerable ecosystems on the planet.
• Corals eject the symbiotic algae dwelling in their tissues, which are responsible for their color when environmental factors such as temperature change.
• Bleaching can occur when one coral that has been bleached for an extended period of time will finally perish.

Destructive Fishing Method

• Explosive fishing, cyanide fishing, and other practices devastate the fragile coral reef and make them unsustainable.
• The fish are stunned with dynamite and cyanide, making them easier to catch.
• Fishermen claim they have no other choice if they want to compete with trawlers and overcome a lower fish supply due to earlier overfishing.
• These procedures rarely select or target specific fish species, and they frequently result in the death of coral reefs.
• Damage to the coral reef habitat on which the fish rely will lower the area's productivity, further affecting fishermen's livelihoods.

*To know more about the topic, click this link Threats to coral reefs

Conservation of Corals

• Environmental Protection Act: Environmental Protection Act, 1986 prohibits the use of corals and Sands from the beaches & coastal water for Construction & other purposes.
• Green Coast Project: In Asia, where the 2004 tsunami left a trail of destruction, WWF and other environmental organizations have begun work on the "Green Coast" coastal restoration project. India is participatory in the Green Coast Project.
• Coastal Regulation Zone: Coastal regulation zone rules (CRZ) ban the collection and destruction of corals along with dredging and underwater blasting in and around the coral formations.
• Protected Areas And National Parks: Concepts of marine protected areas & marine national parks help in coral conservation.
• For example, Flist national marine park Gulf of Mannar (Gujrat), Great Nicobar Biosphere Reserve, and Mahatma Gandhi Marine National park (Andaman) are playing an important role in the Conservation of corals.
• Paris Agreement: India has ratified the Paris agreement and became the 62nd country in the world to do so, a step toward Climate change mitigation.
• Kyoto Protocol: The Kyoto Protocol is a global agreement that extended the 1992 United Nations Framework Convention on Climate Change, which obligates signatory states to cut greenhouse gas emissions.
• India has ratified the second commitment period of the Kyoto protocol (2013-20).

Conclusion

Apart from potentially hosting the world's most diversified ecosystems, coral reefs are essential for a variety of reasons. They protect coastlines from wave action and tropical storms, provide habitat and refuge for many marine animals, are a source of nitrogen and other vital nutrients for marine food chains, aid in carbon and nitrogen fixation, and aid in nutrient recycling. However, coral bleaching has been documented in various sites around the world this year. If sea surface temperatures continue to rise, coral bleaching will become more common and severe, reducing coral reefs' ability to adapt and supply many of the services that people rely on.