The Mesoamerican Barrier Reef System (MBRS), also called the Great Mayan Reef or Great Maya Reef, is an area in the ocean that spans 1,126 kilometers (700 miles) along the coasts of four countries: Mexico, Belize, Guatemala, and Honduras. It begins at Isla Contoy, the northernmost point of the Yucatán Peninsula, and extends south to Belize, Guatemala, and the Bay Islands of Honduras. This reef system is the second-longest in the world.

Location

This area includes several protected places and parks, such as Punta Cancún, the Belize Barrier Reef, Arrecifes de Cozumel National Park, Hol Chan Marine Reserve (Belize), Sian Ka'an biosphere reserve, and Cayos Cochinos Marine Park. Belize’s coastline, which includes the Belize Barrier Reef, holds about 30% of the Mesoamerican Barrier Reef System (MBRS). Mexico has the largest share of the MBRS, Honduras has a significant portion, and Guatemala has the smallest share of the MBRS coastline.

The MBRS begins near Isla Contoy at the northern end of the Yucatán Peninsula in Mexico and continues south along the Riviera Maya, covering areas such as Cancún, Playa del Carmen, Tulum, Cozumel, and the southern tip of Quintana Roo, including Banco Chinchorro and Xcalak. It then extends south along Belize’s eastern coast, passing many cayes and atolls, and reaches the northeast part of Honduras. The MBRS is the largest barrier reef in the Western Hemisphere and the second largest in the world after Australia’s Great Barrier Reef. It is much less studied and recognized compared to other major reefs.

Biodiversity

The reef system is home to more than 65 species of stony coral, 350 species of mollusk, and more than 500 species of fish. Many species live in or near the reef system that are endangered or protected. These include five types of sea turtles (green sea turtle, loggerhead sea turtle, leatherback turtle, hawksbill turtle, and olive ridley turtle), the queen conch, the West Indian manatee, the splendid toadfish, the American crocodile, the Morelet's crocodile, the Nassau grouper, elkhorn coral, and black coral.

The reef system is home to one of the world's largest populations of manatees, with about 1,000 to 1,500 manatees. Some northern areas of the reef system near Isla Contoy are home to the largest fish on the planet, the whale shark. These animals usually stay alone but gather in groups to feed and mate.

Threats

The Mesoamerican Barrier Reef System is listed as critically endangered by the IUCN Red List of Ecosystems. In the last 50 years, this ecosystem has faced many dangers, such as hurricanes, rising water temperatures, ocean acidification, pollution, overfishing, invasive species like lionfish, and disease in corals and urchins.

The reef is being harmed by lionfish (Pterois volitans and Pterois miles), which come from the Indo-Pacific region. These fish harm the reef by eating nearly all species that help maintain it, such as cleaner shrimp and other animals that eat algae. Algae help keep corals clean and healthy. Lionfish can eat up to 90% of these helpful species in a small area within months, which can quickly destroy a reef. Important fish like lobster are also harmed because lionfish eat so much.

Coastal erosion is a major threat to the reef, made worse by human actions like cutting down trees, unsustainable tourism, and building along the coast. This erosion causes more sediment to enter the water, which reduces the light corals need to grow through photosynthesis, making them weaker.

Climate change has become a major problem for the reef. Higher ocean temperatures can cause coral bleaching, a process where corals lose the algae that provide them with energy and color. This weakens corals and makes them more likely to get sick or die. Ocean acidification, another effect of climate change, reduces the availability of carbonate ions that corals need to build their skeletons, weakening reef structures over time. Along with sediment and nutrients from the land, these stressors have caused corals like Siderastrea siderea and Pseudodiploria strigosa to grow more slowly and become less resilient. Poor coral health harms the reef’s structure and the homes of many sea creatures, such as fish, marine turtles, and invertebrates, which threatens the reef’s biodiversity.

Conservation Efforts

Multiple programs are working to protect and restore the Mesoamerican Barrier Reef System to address threats it faces. Groups like the Mesoamerican Reef Fund, the Healthy Reefs Initiative, and the World Wildlife Fund use strategies to reduce erosion, pollution, and overfishing. These programs support sustainable fishing, control pollution, and monitor the reef to lower local pressures and improve the reef's ability to survive.

Working together across national borders has helped reduce threats that affect multiple countries. Projects such as the Integrated Transboundary Ridges-to-Reef Management Project involve Mexico, Belize, Guatemala, and Honduras. These efforts combine methods like controlling sediment runoff, creating marine protected areas, and involving local communities. These actions have improved water quality and reduced overfishing. However, challenges remain in managing activities on land that cause sediment and pollution.

Local communities are helping by taking part in reef restoration, such as growing and moving coral. Sustainable tourism, like guided marine conservation tours, and public awareness campaigns also help reduce human harm to the reef. These combined actions aim to reduce immediate dangers and strengthen the reef’s ability to survive in the future.