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Thursday, June 1, 2023

Warming of Caribbean Waters Endangers Coral Reefs in Costa Rica

The coral reefs of Costa Rica are slowly dying. Last year, many locations throughout the Caribbean Sea recorded surface temperatures that broke all records. Southern Caribbean divers here saw some coral turn white and then later die beneath a blanket of quick-growing seaweed. But warm waters are not the only factor killing the reef; chances are you might be playing a part.

Reef-building corals do not live alone. Corals are little animals that, under the right conditions, slowly make their own little shelters out of calcium. The tiny tentacles of each coral animal, or polyp, grab minute sea life drifting by to eat and survive. But these wee creatures could not build a reef without help. So they share their shelter with some plants.

The petite plants photosynthesize sunlight and receive a sheltered place to live. The wastes the plants produce nurture the corals with just what they need to make reef. All reef-building corals depend on plants that, in turn, rely on the corals. This mutually beneficial relationship demonstrates one of the most fantastic examples in nature of what is called symbiosis.

When things heat up, the coral and plants do not get along. Rising water temperatures cause coral to kick out their roommates.

Without the plants, the corals turn white, a phenomenon divers and coral researchers call “bleaching.” The corals cannot live for very long without their plant buddies, but if the waters cool enough the plants return and the reef grows.

Reefs grow so well that they are the biggest animal-made structures on the planet.

The barrier reef growing off Costa Rica’s southernmost Caribbean coast, known as Long Shoal to area residents, stretches for several kilometers offshore of the Gandoca-Manzanillo National Wildlife Refuge and north toward the fringing reef off Cahuita.

Some of the many patch reefs growing inshore toward the beach from the barrier reef are larger than a city block. Other patch reefs, some just a few fin kicks off the beaches, are about as big as your dinner table.

Reefs Provide

A lot of things on your dinner table in Costa Rica might have arrived there with the help of the coral reef. Many lobsters, fish, shellfish, shrimp, crabs and others spend at least part, if not all, of their life cycles hiding within the protection of the coral. Coral reefs are the most diverse marine ecosystems on earth, and an enormous number of species, from sponges to dolphins, depend on them for food. When not eating reef species, people studying them gain insight that leads to many medical advances, such as artificial bone.

Without the reefs, many surfers and divers would simply go elsewhere. Reefs cause waves to break overhead in a spectacular fashion; Puerto Viejo’s Salsa Brava wave, created by the coral reef below, is considered by many surfers to be one of the best in the world. There are many other surfing waves –reef breaks – in the southern Caribbean region, which draw a lot of surfers, who in turn bring a lot of money into the country.

Divers also come for the reef and its accompanying marine life, and, like surfers, spend money on transportation, accommodations, food and services all over the country.

Not only does the reef provide food and tourism income, it also protects Costa Ricans from tsunamis, massive waves usually caused by earthquakes. Manzanillo residents who were here for the devastating big shake of 1991 recall watching a massive tsunami break offshore over the Long Shoal barrier reef. The wave spending its deadly energy on Long Shoal reef is probably why parts of the southern coast received a slowly rising wave of foam and not a high-speed, crushing impact.

The reefs also create shallow pools and lagoons that are protected from surf and are perfect for swimming. These reefs and pools together form what many people consider to be the most beautiful beaches in Costa Rica.

Reefs under Threat

This source of food, money, medicine, beaches and protection for the nation is now under threat. Rapid development of the tourism industry is leading to harmful waste dumping, bush cutting and wetland draining. Irresponsible agriculture does the same thing. All affect the reef with increased sediments in the water. Sediments make the water murky and prevent the reef from growing. The plants that live with coral need plenty of light, which can only pass through clear water. Cutting forest and draining land for habitation stops a natural filtration process. Dirty water reaches the reef in hours instead of spending time oozing through the land, which filters much of the sediments.

Another major threat for corals in Costa Rica is water that is too warm. Last year was the worst Caribbean bleaching I have seen in more than 20 years diving the region. Much of the bleached coral is colored again this year, but some of it has died for good.

Bleaching corals were documented throughout most of the Caribbean Sea by the end of the summer last year, the warmest year on record for this body of water.

This year, the Caribbean Sea is heating up as the northern hemisphere’s summer advances. According to the U.S. National Oceanic and Atmospheric Administration (NOAA), parts of the northern Caribbean are already as hot as they normally would be at the end of summer. Costa Rica’s waters usually remain warmer longer than in the northern Caribbean, and cool off when the winds of November blow down water from the north. That’s still months of summer heating to come, which does not bode well for Costa Rica’s Caribbean reef or the marine life and people who depend on it.

Don’t think dying coral doesn’t affect the Pacific coast of Costa Rica. Reef-building coral does not usually grow on the western side of continents because of ocean circulation patterns, but here in Costa Rica, Pacific divers know that plenty of coral grows on the rocks in some areas and that there are even some rare eastern tropical Pacific patch reefs. These Pacific corals provide habitat for little fish that bring in the big stuff Pacific sport fishers and divers come to see. Without Pacific corals and all the fish they bring, Costa Rica would have to buy a lot more seafood from other countries.

Many think global warming is the cause of the unprecedented warming of the Caribbean Sea. The phenomenon is thought to also cause more frequent warmings of the eastern tropical Pacific, a phenomenon known as El Niño. Previous El Niños have caused massive bleachings in all of Costa Rica’s Pacific coral areas, from Guanacaste in the north to CocosIsland in the south, including some local species extinctions.

This negatively affects diving, sport and commercial fishing, dolphin and whale watching and tourism in general.

But even if the sea does not heat up, unchecked development and overfishing off the Caribbean and Pacific coasts will continue to damage the reefs. Already the reef sections off the southern Caribbean’s Puerto Viejo are mostly dead, and that happened long before last year’s bleaching.

Possible Solutions

Inside the waters of the Gandoca-Manzanillo National Wildlife Refuge and Cahuita National Park, the marine life clearly appears healthier to divers than it does outside, evidence that earthquake damage and agricultural runoff are not the only factors hurting the reef. But even in protected Manzanillo waters, where locals are allowed to hunt but there are no “no-take zones,” most divers admit that overfishing has factored into local sons knowing they will never make catches as big as their fathers. Will the next generation even get to see live coral reef?

The most important things we can do to save Costa Rican reefs involve slowing water contamination. If tourists, travel agents, guidebooks and newspapers began checking the wastewater treatment systems of the hotels and operators they patronize and write about, businesses would clean up their act fast.

A certification for sustainable Costa Rican fisheries would help to ensure that future generations of Ticos have the chance to eat local seafood and dive the reef, as well as keep tourists coming back. The independent, global, nonprofit Marine Stewardship Council ( offers an example of such certification.

We can all do our part. Leaving more bush around waterways helps to filter more sediment, preventing it from reaching the reef.

Creating more no-take zones would leave crucial nursery areas for countless species. And divers, snorklers and beachgoers can take care to not touch, stand on or fin the highly stressed corals.



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