Coral & Coral Reefs

Kindly compiled by James Harvey from The Reef-World Foundation (please scroll down for scientist profile)


© WiseOceans

© WiseOceans

Corals are the main component of tropical reefs with over 800 recognised species globally to date. They are unique in that they are formed of a symbiotic relationship of an animal (the polyp) and a plant (marine algae called Zooxanthellae) living within the calcium carbonate skeleton. This symbiotic relationship is mutually beneficial and without the other, one cannot survive on its own for long. Their 3D environment can be home for up to 4,000 species of fish and although coral reefs only occupy less than 1% of the marine environment, more than 25% of all known marine creatures live here.


Corals are found all around the world but are restricted to two distinct zones. Cold water corals occur at temperatures of -3°C-14°C and are generally found at depths of 39m+ compared to their warm water counterparts found in shallow warm waters in temperature ranges of 20–31°C and in a salinity range of 32–40‰. These circum-tropical (30°N – 30°S) species are found along the coasts and shorelines of tropical islands and continents and require sunlight for photosynthesis. This means that they are usually limited to a maximum depth of around 60m but have been found deeper.

Food Plankton from the water column but also energy is provided from the symbiotic algae living within the calcium carbonate structure of the polyp itself.

Size A colony of coral polyps can grow anywhere from 1cm to 3 meters over their lifetime.

Lifespan Corals have been around for 240 million years but their more typical lifespan is up to 30 years per colony. Many modern day living reefs (collection of corals) are estimated at being 6000-9000 years old.

Interesting Facts

  • As the Great Barrier Reef can be seen from space this makes it the largest animal in the world!
  • Coral reefs support over a million animal and plant species combined.
  • Their economic value exceeds US $ 375 billion a year which is more than the GDP of Thailand or Hong Kong.
  •  Many new medical applications and medicines have originated from coral reefs such as those to help treat cancer, arthritis, human bacterial infections, Alzheimer’s disease, heart disease, viruses, and other diseases.
  • The stinging cells found on corals (nematocysts or cnidocysts) are the fastest reaction in the animal kingdom.
  • Almost half a billion people, 8% of the total global population, live within 100 kilometres of a coral reef.
  • 32 of the 34 recognised animal Phyla are found on coral reefs compared to only 9 Phyla in tropical rainforests.

Reef Scene © James Harvey

Reef Scene © James Harvey

Reef Scene © James Harvey

Reef Scene © James Harvey


Corals reproduce in a number of ways but the most common method is sexually (some reproduce asexually) and via broadcast spawning, meaning that male and female corals release their gametes into the water column.

© Mark Bol

© Mark Bol

© Mark Bol

© Mark Bol

Feeding & Hunting

Corals polyps are often equipped with stinging tentacles that are able to immobilise or even kill its prey. The tentacle then contracts and brings the prey into the mouth of the coral polyp to be digested in the stomach. The energy from digesting this can be shared to other neighbouring polyps through a tunnel network called the gastrovascular canals.

Check out “Receding Reefs:  The Greatest Threat to Coral Reefs” infographic 

© Abbie Hine

© Abbie Hine


There are many natural threats to corals such as storms, waves, tsunamis and natural predators such as the Crown of Thorns seastar (Acanthaster planci) but anthropogenic influences such as climate change and fishing pressures from unsustainable techniques such as dynamite and cyanide fishing are also extremely detrimental. In 2011, it was estimated that 75% of the world’s reefs are potentially threatened by human activity. This ranges from coastal development and destructive fishing practices to overexploitation of resources, marine pollution, and runoff from inland deforestation and farming. Coral reefs in SE Asia, the most species rich location on earth, is the most threatened region with more than 80% of the corals here at risk.

Conservation Status & International Protection

It is estimated that 19% of the world’s coral have been lost to date. Currently less than 2% of the world’s oceans are protected under law and yet only a very small percentage of these areas are coral reefs. 27% of the world’s reefs are already inside Marine Protected Areas (MPA’s) but it is estimated that only 6% of that is properly protected and effective.

ReefPosterFinal_A3How can people help?

It depends where you are in the world but if you are near reefs you could always volunteer and help lobby for better protection from destructive fishing techniques or poorly controlled tourism. Coastal development in tropical areas is a major threat to the coral reefs and people in a position of power need to act on enforcing existing laws set up to protect coral reefs and near marine ecosystems. If coral reefs are not on your doorstep but you eat fish from abroad, check to see if they are sustainably caught and if you are going on holiday check that your resort or hotel is also acting in a sustainable way and not negatively impacting the local reefs or nearby marine ecosytems. If you are going diving then have a look at the Green Fins project for guidance first. You can always take part in beach clean-ups wherever you are in the world as marine litter is a transboundary problem and affects the world over.

Interested in working in Coral Reef Conservation? Visit Wise Work!

WiseOceans best practice suggestions:

    • Never stand on or touch the coral
    • Always keep your distance – divers maintain neutral buoyancy, snorkelers keep your feet up off the coral
    • Do not disturb or harass the marine life
    • Support qualified professional and environmentally friendly hotels
    • Care for corals by helping reduce global warming
    • Do not collect or purchase coral; in most countries collecting, buying and importing coral is illegal
    • Take all your litter home
    • Take home only photographs and memories

Scientist Profile: James Harvey


The Reef-World Foundation

Year(s) Founded

Reef-World – 1999

Funding bodies

Rufford Small Grants Foundation UNEP, IUCN-MFF Initiative.

Description/Background of work


9540675The Reef-World Foundation was the brainchild of Anne Miller, the founder and current Trustee of the charity. The roots of Reef-World started in 1993 in Phuket Thailand and has grown to working alongside the governments of Thailand, Malaysia, Indonesia, Philippines, Vietnam and the Maldives whilst supporting various departments of the United Nations. There have since been a variety of projects Reef-World have been involved in ranging from educational and teaching programmes to developing project monitoring techniques such as our Green Environmental Assessment Rating System – GEARS. Reef-World are the UNEP designated International Coordinators of the Green Fins project since 2008 and currently has its headquarters in Anglesey, Wales, UK with a sub-office in the Philippines.


The concept of Zoox came from the symbiotic relationship in corals. The marine algae, Zooxanthellae, provides nutrition and energy to its host partner the coral polyp. Zoox Ltd provides human and financial resources to Reef-World enabling it to support the International Coordination of Green Fins. Zoox is a registered UK business and has been going since 2010. Zoox also provides Training courses that are run both independently and alongside the Zoox Experience Programme (ZEP), with course titles including Marine conservation and Diving, Blue Carbon and Marine Monitoring. The ZEP is an 8 week placement designed to give the successful applicant a better understanding of marine conservation while focussing on the individuals experience and professional development to increase their chances of getting a job in this competitive sector.

Importance of work

8468137Through both Zoox and Reef-World, we have managed to successfully train four government departments in marine conservation techniques and approaches. We have done this primarily through implementation of the Green Fins approach in conjunction with the United Nations Environment Programme. Green Fins is helping to protect coral reefs against the threats associated with the tourism industry, the world’s fastest growing industry. Marine tourism is both an opportunity and a threat, and through our approaches to environmental protection, we have managed to enhance the sustainability of potentially damaging marine recreational activities. This in turn has secured the jobs of many local communities for years to come while allowing corals to flourish and continue to provide the ecosystem services we need the world over.

Web links

Volunteer /Paid Work Opportunities

Reef-World  – We are starting our first Internship placement this year. The placement is for a reasonably qualified individual to work for 6 months in our Asia office in the Philippines to support the various projects that we are involved in. To see more please visit the Reef-World Intern page.

Return to SeaSense or learn more about other Invertebrates