Treasures of the Ocean
What are corals and why are they important?
Aside from containing the most diverse ecosystems on the planet, coral reefs are important for many different reasons.
Coral reefs and atolls are an essential part of the world’s marine ecosystem. Occupying less than 0.1% of the planet’s ocean surface, these calcium carbonate structures support life for at least 25% of all marine species.
Enchanting and diverse, coral reefs in the Maldives and beyond are fundamental to the fishing industry, shoreline protection and tourism. Their importance is beyond measure but their survival is under threat from climate change, ocean acidification and other forms of pollution.
What are corals and how do they reproduce?
Often called ‘rainforests of the sea’, coral reefs are underwater ecosystems built by colonies of tiny animals and held together by calcium carbonate. The coral structures consist of polyps that belong to a group of sea animals known as cnidaria - which also contains sea anemones and jellyfish. To protect the polyps, the corals secrete a hard, carbonate exoskeleton, forming the reefs that pulsate with the rhythms of nature.
Polyps range in size from a pinhead to 30 cm in diameter and form a symbiotic relationship with algae. Dependent on sunlight for survival, the algae organisms live within the tissues of the polyps.
Neither plant nor rock, polyps are translucent animals that reproduce sexually by either internal or external fertilization. The fertilized eggs are released on mass. When an egg and sperm meet they form a larva known as planula. The baby coral looks like a small jellyfish and can drift in the water for weeks before finding a new home with the coral structures.
Coral spawning happens at the same time each year and is influenced by the lunar cycle. This allows divers the opportunity to witness a spectacular phenomenon of nature, along with all the fish and predators that come to feed on them.
Coral reefs grow best in shallow water that admits a generous amount of sunlight, forming a brilliant and surreal display of shapes and colors, the likes of which only nature is capable of producing.
Reefs are home to a large variety of animals, including fish, cnidarians, worms, molluscs, sea urchins, sea cucumbers, sea urchins, sea squirts, sea turtles, sea snakes and crustaceans such as lobsters, shrimp and crabs.
Aside from snorkelers and divers, mammals are rare on coral reefs, with visiting cetaceans such as dolphins being the main exception. A few of these species feed directly on coral while others feed on the reef’s algae.
How do corals eat and how are they formed?
While most of corals nutrients come from their symbiotic existence with algae, they can also fish for food too. A coral polyp captures small fish and plankton by waving its tentacles out from its body. The surface of each tentacle has thousands of stinging cells that stun and kill prey before it passes into their mouth …Gulp!
How are corals formed?
The British naturalist Charles Darwin, originator of ‘the theory of evolution’, was the first to discover how reefs and atolls were formed during the South American ‘voyage of the Beagle’ in 1835.
Darwin’s theory starts with the formation of volcanic islands formed tens of millions of years ago. As the islands subsided beneath the water coral grew to create a fringing reef. In the case of atoll reefs, as found in the Maldives, a shallow lagoon was formed between the land and the main reef.
Darwin predicted that underneath each lagoon would be the remains of the original volcano. Subsequent drilling has proved his theory correct.
There are three main types of coral reef:
Atolls: As found in the Maldives, atolls are large, ring shaped reefs with a lagoon in their middle. The islands that form on atolls are usually rich in vegetation and easily spotted by towering coconut and palm trees. Atolls are underwater islands or islands that sink. Atolls develop on the sea surface on islands that sink or subside.
Fringing reefs: These lie close to land and are fairly narrow shallow and recently formed. They are often separated from the coast by a channel of water that is sometimes incorrectly called a lagoon.
Barrier reefs: Broader than fringe reefs, barrier reefs are separated from the coast by a stretch of water that can be several miles wide and tens of meters deep. Sandy islands covered in vegetation often form upon these reefs, creating the perfect base for divers and snorkelers.
How fast do corals grow?
Even under ideal conditions large coral structures tend to grow slowly. They exhibit a wide and often bizarre range of shapes. For instance, sub massive corals look like clumps of stubbed out cigar and have no secondary branches. Table corals look like their namesake and often have fused branches. Foliose coral have broad, plate like portions rising in spirals like spinning wheels. Massive corals are ball shape or boulder like and can be small as an egg or large as a house.
Massive corals increase in size slowly, from between 0.5cm and 2cm per year. However, when the conditions are ideal, some species can grow as much as 4.5cm per year. In contrast to the larger species, branching colonies tend to grow faster, and when conditions are near perfect, can grow vertically by as much as 10cm per year.
Where are corals found?
Corals are found throughout the oceans, from deep, cold waters to shallow tropical waters and are estimated to cover 0.1% of the oceans surface, or about half the size of France. The Indo-Pacific region, which includes the Indian Ocean, Pacific Ocean, Red Sea and Southeast Asia account for 91% of this total. The Atlantic and Caribbean coral reefs account for 7.6%.
Shallow water reefs form only in a zone extending approximately 30 degrees north to 30 degrees south of the equator. The polyps that are the living flesh of coral reefs thrive best in warm waters and struggle to survive at depths below 50 meters. The ideal temperature for most coral reefs is around 26 – 27degrees centigrade.
However, there are rare exceptions. Reefs in the Persian Gulf have adapted to temperatures of 13 degrees centigrade in winter and 38 degrees centigrade in summer. Likewise, deep-water coral forming reefs as far north as Norway are known to exist, though little is known about them.
Coral reefs are also rare along the west coasts of Africa and the Americas, due primarily to strong coastal currents that cause sea temperatures to plunge. Corals also struggle to form along the coastline of South Asia – from the Myanmar and Bangladesh borders to the eastern tip of India as well as the coasts of northeastern South America and Bangladesh due to fresh water release from the Amazon and Ganges rivers.
Coral reefs are located in tropical oceans near the equator. Here is a list of destinations to start planning you next travels to and explore the underwater rainforests of our planet.
• Numerous reefs scattered across the Maldives
• The Great Barrier Reef—largest, comprising over 2,900 individual reefs and 900 islands stretching for over 2,600 kilometers (1,600 mi) off Queensland, Australia
• The Mesoamerican Barrier Reef System—second largest, stretching 1,000 kilometers (620 mi) from Isla Contoy at the tip of the Yucatán Peninsula down to the Bay Islands of Honduras
• The New Caledonia Barrier Reef—second longest double barrier reef, covering 1,500 kilometers (930 mi)
• The Andros, Bahamas Barrier Reef—third largest, following the east coast of Andros Island, Bahamas, between Andros and Nassau
• The Red Sea—includes 6000-year-old fringing reefs located around a 2,000 km (1,240 mi) coastline
• The Florida Reef Tract—largest continental US reef and the third largest coral barrier reef system in the world, extends from Soldier Key, located in Biscayne Bay, to the Dry Tortugas in the Gulf of Mexico
• Pulley Ridge—deepest photosynthetic coral reef, Florida
• The Philippines coral reef area, the second largest in Southeast Asia, is estimated at 26,000 square kilometers and holds an extraordinary diversity of species. Scientists have identified 915 reef fish species and more than 400 scleractinian coral species, 12 of which are endemic.
• The Raja Ampat Islands in Indonesia's West Papua province offer the highest known marine diversity.
• Bermuda is known for its northernmost coral reef system, located at 32.4° N and 64.8° W. The presence of coral reefs at this high latitude is due to the proximity of the Gulf Stream. Bermuda has a fairly consistent diversity of coral species, representing a subset of those found in the greater Caribbean.
• The world's northernmost individual coral reef so far discovered is located within a bay of Japan's Tsushima Island in the Korea Strait.
• The world's southernmost coral reef is at Lord Howe Island, in the Pacific Ocean off the east coast of Australia.