Coral reefs are some of the most diverse and valuable ecosystems on Earth. They occupy less than 0.1% of the world’s ocean surface but support over 25% of all marine species. Coral reefs also provide food, income from tourism, and shoreline protection from waves and storms to over half a billion people. Here are some quick facts about coral reefs:
Summary
– Coral reefs are formed by coral polyps, which are tiny marine invertebrates.
– They require clear, shallow water to get sunlight for symbiotic algae called zooxanthellae.
– The largest coral reef is the Great Barrier Reef off the coast of Australia.
– Other famous reefs include the Mesoamerican Reef, New Caledonia Barrier Reef, and Red Sea Coral Reef.
– Reefs face threats like climate change, pollution, overfishing, and tourism.
What are coral reefs?
Coral reefs are underwater structures made of calcium carbonate secreted by coral polyps. Corals are marine invertebrates in the phylum Cnidaria, which includes jellyfish and anemones. They typically live in compact colonies of many identical individual polyps.
Most corals have a symbiotic relationship with single-celled algae called zooxanthellae. The coral provides the algae with shelter and compounds they need for photosynthesis. In return, the algae produce oxygen and help the coral remove wastes. This relationship with algae gives corals their color and provides them with 90% of their nutrients.
Corals can only thrive in warm, clear, shallow water that allows sunlight to reach their symbiotic algae. The typical depth limit for most tropical reefs is around 90 feet. Corals cannot survive in murky water or at depth, so reef-building occurs mainly in shallow tropical waters.
Where are the most famous coral reefs?
There are hundreds of coral reefs around the tropical islands and coastlines of the world. But several iconic reefs stand out for their immense size, diversity, and global significance. Here are some of the most famous coral reefs on Earth:
| Reef | Location | Description |
|---|---|---|
| Great Barrier Reef | Australia | The largest coral reef system in the world at over 1,400 miles long. Home to over 1,500 species of fish and 400 species of coral. |
| Mesoamerican Reef | Caribbean | The second largest reef in the world stretching over 700 miles from Mexico through Belize, Guatemala, and Honduras. Extensively diverse with 65 species of coral and over 500 fish species. |
| New Caledonia Barrier Reef | South Pacific | A long barrier reef in the Coral Sea off New Caledonia. Over 1,500 kilometers long with tremendous diversity and home to 750 fish species. |
| Red Sea Coral Reef | Red Sea | Located between Africa and the Arabian Peninsula, home to over 300 species of coral and 1,200 species of fish within just 4.5% of the total ocean surface. |
Other famous and highly diverse reefs include the Florida Reef off the Florida Keys, the Mariana Trench Reefs in the Western Pacific, the Maldives Reefs in the Indian Ocean, and the Great Chagos Bank in the British Indian Ocean Territory.
The Great Barrier Reef
The Great Barrier Reef is the world’s most extensive coral reef system and arguably the most famous. It stretches for over 1,400 miles off the northeast coast of Australia along the state of Queensland. Comprised of over 2,900 individual reefs and 900 islands, it can be seen from outer space. It’s so large that it is considered the world’s largest single structure made by living organisms.
The reef includes vast shallow lagoon areas, smaller patch reefs, branching channel reefs, ribbon reefs, and offshore reefs that descend over 2,000 feet. This variety of habitats supports astounding biodiversity with over 1,500 fish species, 411 species of hard coral, 4,000 types of mollusk, and 240 species of birds. Giant clams, sea turtles, dolphins, and sharks are common.
The Great Barrier Reef Marine Park was established in 1975 and declared a UNESCO World Heritage Site in 1981. It welcomes over 2 million visitors per year and contributes over $5.4 billion annually to the Australian economy through fishing and tourism.
However, rising ocean temperatures have caused extensive “bleaching” events leading to coral death, putting the reef’s future at risk. Other threats include agricultural runoff, invasive species, illegal fishing, coral disease, and tropical cyclones. Intensive conservation efforts aim to protect this natural wonder.
The Mesoamerican Reef
The Mesoamerican Reef is the world’s second largest barrier reef extending over 700 miles from the northern tip of the Yucatan Peninsula down through the coasts of Mexico, Belize, Guatemala, and Honduras. It runs parallel to the coastline, separated by a channel averaging 30-40 miles wide.
This reef has tremendous diversity with over 65 species of coral and more than 500 fish species identified. Vibrant sponges, sea turtles, rays, and sharks also inhabit the reef. It includes the longest barrier reef in the Western Hemisphere and the Belize Barrier Reef Reserve System, a UNESCO World Heritage Site.
The Mesoamerican Reef faces threats from coastal development, overfishing, tourism, pollution, and climate change impacts like coral bleaching, but conservation efforts aim to protect it. It provides essential habitat, resources, and storm protection for coastal communities in Central America.
The New Caledonia Barrier Reef
New Caledonia is a French territory in the Coral Sea off the east coast of Australia. It’s surrounded by the world’s longest double barrier reef, which extends over 1,500 kilometers along the coastline. The New Caledonia Barrier Reef encloses a huge lagoon between the outer reef and the mainland.
This South Pacific reef has tremendous marine biodiversity with over 750 fish species identified so far. Corals and fish from diverse regions mingle, including species from Australia, Indonesia, and the Philippines. Threatened green and hawksbill sea turtles nest on the reef’s islands and feed in the lagoon and channels.
The reef faces threats from nickel mining on land leading to increased sedimentation that can smother and kill corals. Other risks include bleaching from climate change, pollution, and overfishing. Parts of the reef are protected within the Natural Park of the Coral Sea established in 2014.
The Red Sea Coral Reef
The Red Sea separates the coasts of Africa and the Arabian Peninsula. Despite making up just 4.5% of the Indian Ocean’s area, the Red Sea contains extensive shallow coral reefs with tremendous biodiversity.
Over 300 species of coral have been identified in the Red Sea. About 10% are endemic and found nowhere else on Earth. Its reefs also support over 1,200 species of fish, with 20% of these endemic. Other marine life includes manta rays, sea turtles, dolphins, and sharks.
Many fringing reefs line the Red Sea coastlines, while offshore reefs and coastal islands host lagoons and interior patch reefs. But rising temperatures have led to mass coral bleaching. Other threats include coastal development, tourism, and shipping impacts.
The Red Sea Coral Reef is protected within various Marine Protected Areas in Egypt, Saudi Arabia, Jordan, Israel, and Djibouti.
Threats to coral reefs
Coral reefs globally face a range of human and environmental threats that have caused extensive reef decline in recent decades. Major threats include:
- Climate change – Rising ocean temperatures cause coral bleaching as stressed corals expel their symbiotic algae. Mass bleaching can lead to widespread coral death.
- Pollution – Runoff carrying sediments, fertilizers, and toxins can damage reef health.
- Overfishing – Excessive fishing alters food webs and depletes key herbivores needed to control algae.
- Destructive fishing – Practices like dynamite and cyanide fishing kill corals.
- Coastal development – Ports, seawalls, dredging, and filling destroy reefs.
- Tourism – Uncontrolled tourism damages corals through anchoring, touching reefs, or collecting coral.
- Invasive species – Invasive algae or animals introduced through ballast water or aquarium releases can harm native reef species.
Conservationists work to reduce these threats and make reefs more resilient through tools like Marine Protected Areas, fishing regulations, pollution controls, tourism management, and coral restoration.
Conclusion
Coral reefs are biodiversity hotspots that support immense marine life but are threatened worldwide. The largest and most famous reef is certainly Australia’s iconic Great Barrier Reef. But other globally significant reefs include the extensive Mesoamerican Reef, the New Caledonia Barrier Reef, and the highly diverse Red Sea Coral Reef.
Protecting the world’s remaining healthy coral reefs is crucial but challenging in the face of escalating climate change impacts and other human activities. Targeted conservation and restoration efforts aim to save these unique ecosystems and the many communities that rely on them before it’s too late.
