Coral reefs are one of the most biologically diverse marine ecosystems on Earth. Coral reefs play an important role in marine ecosystems and support the habitats of flora and fauna in the sea. The vast diversity of animal and plant species that contribute to its system is increasingly at risk due to climate change. India with its coastline extending over 7,500 km and subtropical climatic conditions has very few coral reef areas.
Polyps vs. Coral vs. Coral Reefs?
Polyps are tiny microscopic marine animals.
When polyps die, their skeletons are left out.
These left-out skeletons made up of Calcium carbonate are called simply coral or coral reef.
These coral reefs grow higher and higher, and later coral islands form.
Ideal conditions for coral growth
Corals thrive in tropical waters between 30°N and 30°S latitudes.
Theideal depths for coral growth are 45 m to 55 m below sea surface, where there is abundant sunlight available.
The temperature of the water should be around 20-27°C.
Clear salt water is suitable for coral growth, while both fresh water and highly saline water are harmful to polyp growth.
An adequate supply of oxygen and microscopic marine food, called plankton, is essential for growth and existence. As the food supply is more abundant on the seaward side, corals grow more rapidly on the seaward side.
From where do Polyps get food?
Most of the Polyps give habitat to algae called "Zooxanthellae" on their tissues.
Polyps and Algae have a mutual symbiosis relationship.
Polyps provide nutrients and habitat to Algae and help in the photosynthesis process.
Zooxanthellae supply photosynthesis products such as carbohydrates to coral polyps.
Zooxanthellae also provide beautiful colors to coral.
Many polyps also get some food from floating ocean minerals directly.
Coral reefs found in India?
India is recorded to have around 7,517 km of coastline but only 6,100 km represents the mainland coastline. The three major types of coral reefs found in India are fringing, barrier, and atolls.
Coral reefs in India are found in a lot of areas including the Gulf of Kutch, Gulf of Mannar, Palk Bay, Andaman & Nicobar, and Lakshadweep Islands. The Gulf of Kutch in the northwest has some of the most northerly reefs in the world.
Patches of coral reefs are also found in Ratnagiri, Malvan, and Redi, south Bombay, and at the Gaveshani Bank located in the west of Mangalore.
Corals running parallel to the shore are found at Quilon near the Kerala coast to Enayem in Tamil Nadu. On the east coast, between Parangipettai (south of Cuddalore) and Pondicherry, corals are found in abundance. When it comes to island corals, the Andaman and Nicobar Islands and Lakshadweep Islands are rich with flourishing corals.
Types of coral reefs in India
India has three major prevailing types of coral reefs:
1. Fringing reefs
Fringing reefs evolve and develop near the continent and remain close to the coastline. These reefs are separated from the coastline by small, shallow lagoons. They are the most commonly found reefs in the world.
2. Barrier reefs
Barrier reefs are found offshore on the continental shelf. They usually run parallel to the coastline at some distance. A deep and wide lagoon is located between the coastline and the barrier reef.
3. Atolls
Atolls are formed on mid-oceanic ridges. They are shaped circularly or elliptically are surrounded by seas on all four sides and have shallow waters in the center called a lagoon.
Formation of Lakshadweep Islands (Atoll Formation)
The basic coral reef classification scheme described above was first proposed by Charles Darwin and is still widely used today.
Darwin theorized that fringing reefs began to grow near the shorelines of new islands as ecological conditions became ideal for hard coral growth.
Then, as the island began to gradually subside into the sea, the coral was able to keep pace in terms of growth and remained in place at the sea surface, but farther from shore; it was now a barrier reef.
Eventually, the island disappeared below the sea surface, leaving only the ring of coral encircling the central lagoon; an atoll had formed.
Distribution of Coral Reefs
The majority of reef-building corals are found within tropical and subtropical waters. These typically occur between 30° north and 30° south latitudes.
The Indonesian/Philippines archipelago has the world’s greatest concentration of reefs and the greatest coral diversity.
Other areas of reef concentration are the Great Barrier Reef of Australia, the Red Sea, and the Caribbean, the latter having a much lower diversity than all major Indo-Pacific regions.
World’s major coral reef regions:
Caribbean/Western Atlantic
Eastern Pacific
Central and Western Pacific
Indian Ocean
Arabian Gulf
Red Sea
Why is the survival of corals and coral reefs important to human and marine life?
Corals are important to marine life because of the following reasons:
The health of the marine ecosystem is dependent on corals.
They support a wide range of ecosystems and hence, are called the rainforests of the ocean.
Corals provide a place to live for a huge variety of fish.
Corals are a primary source of food in the marine ecosystem.
Importance of coral reefs:
Sustain biodiversity: Ecologically, coral reefs are important because they are the counterpart to the tropical rain forest in terms of species diversity and biological productivity in the Ocean. Coral reef enables the formation of associated ecosystems which allow the formation of essential habitats, fisheries, and livelihoods.
Protect coastlines: Coral reefs protect coastlines from the damaging effects of wave action and tropical storms.
Nutrition and Habitat: Coral reefs provide habitats and shelter for many marine organisms. They are the source of nitrogen and other essential nutrients for marine food chains and assist in carbon and nitrogen fixing
Economic: The fishing industry depends on coral reefs because many fish spawn there and juvenile fish spend time there before making their way to the open sea. The Great Barrier Reef generates more than 1.5 a billion dollars every year for the Australian economy, from fishing and tourism.
Climate change record: In addition, coral reefs are climatologically important because they provide an accurate long-term record of climate change and help extend our knowledge of seasonal climate variability in many remote tropical oceans.
Coral Reefs Bleaching
Coral reef ecosystems worldwide have been subject to unprecedented degradation over the past few decades. Disturbances affecting coral reefs include anthropogenic and natural events.
Recent accelerated coral reef decline seems to be related mostly to anthropogenic impacts (overexploitation, overfishing, increased sedimentation, and nutrient overloading).
Natural disturbances that cause damage to coral reefs include violent storms, flooding, high and low-temperature extremes, El Nino Southern Oscillation (ENSO) events, etc.
Coral bleaching occurs when the relationship between the coral host and marine algae, which give coral much of their color, breaks down. Without the marine algae, the tissue of the coral animal appears transparent and the coral’s bright white skeleton is revealed. Coral reef bleaching is a common stress response of corals to many of the various disturbances mentioned above.
Corals begin to starve once they bleach. While some corals are able to feed themselves, most corals struggle to survive without their algae. If conditions return to normal, corals can regain their algae, return to their normal color, and survive. However, this stress is likely to cause decreased coral growth and reproduction, and increased susceptibility to disease.
Bleached corals often die if the stress persists. Coral reefs that have high rates of coral death following bleaching can take many years or decades to recover.
Causes of Coral Bleaching
As coral reef bleaching is a general response to stress, it can be induced by a variety of factors, alone or in combination.
It is therefore difficult to unequivocally identify the causes of bleaching events.
The following stressors have been implicated in coral reef bleaching events.
Temperature
Coral species live within a relatively narrow temperature margin and therefore, low and high sea temperatures can induce coral bleaching. Bleaching events occur during sudden temperature drops accompanying intense upwelling episodes, seasonal cold-air outbreaks etc.
Solar Irradiance
Bleaching during the summer months, during seasonal temperature and irradiance maxima often occurs disproportionately in shallow-living corals and on the exposed summits of colonies.
Subaerial Exposure
Sudden exposure of reef flat corals to the atmosphere during events such as extreme low tides, ENSO-related sea level drops or tectonic uplift can potentially induce bleaching.
Fresh Water Dilution
Rapid dilution of reef waters from storm-generated precipitation and runoff has been demonstrated to cause coral reef bleaching.
Other causes include the increase in the concentration of inorganic Nutrients, sedimentation, oxygen starvation caused by an increase in zooplankton levels as a result of overfishing, ocean acidification, changes in salinity, sea level change due to global warming, cyanide fishing etc.
Spatial and Temporal range of Coral Reef bleaching
Mass coral moralities in coral reef ecosystems have been reported in all major reef provinces since the 1870s.
The frequency and scale of bleaching disturbances hasincreased dramatically since the late 70’s. This is possibly due to more observers and a greater interest in reporting in recent years.
More than 60 coral reef bleaching events out of 105 mass coral moralities were reported during 1979-1990, compared with only three bleaching events among 63 mass coral moralities recorded during the preceding 103 years.
Methods of coral restoration:
Biological restoration: Biological restoration uses various methods involving coral growth and transplanting to assist the restoration of a coral reef. It includes:
Asexual propagation: It involves the transplanting of coral fragments or larger colonies from a donor reef site to a reef of choice, most commonly a degraded reef.
Coral Gardening: Coral gardening is the process of collecting, growing and reattaching coral fragments at a degraded reef site.
Structural restoration: Structural restoration generally involves the construction of artificial reefs, sinking of wrecks, or relocation of rocks/dead coral heads. The goal is to increase the amount of reef structure and habitat available for the corals and other reef organisms to grow on.
Physical restoration: Physical restoration involves addressing the conditions in which the corals are growing to improve their health, growth rates, or reproductive ability. These methods have generally been developed more recently, and some are still in the experimental stages.
Laws protecting the coral reefs of India
The Ministry of Environment, Forest and Climate Change makes and ensures the guidelines and laws protecting coral reefs are followed properly. The State Wildlife Department takes care of the corals if the coral reef region comes under a protected area.
All marine resources are protected under the Coastal Regulation Zone (CRZ) of 1991. It provides protection to all coral reefs under the CRZ1 category of the law. Specific Section 7 (2) of the CRZ states that no hotels or resorts are to be made on coral reefs. The mining and quarrying of coral reefs are banned in some states, except for scientific purposes.
Coral reefs have sustained life for over a million years. Its diverse ecosystem keeps marine life running. It would not be in our best interest to interfere with the coral reefs. Conservation methods should therefore be taken to protect these beautiful polyps. Laws should be strictly enforced and if not followed, penalties should be imposed swiftly. It is in our best interest to protect our corals from eroding and withering away. Let’s make a pact to do what we can to protect them, today.
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