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Saturday, September 30, 2023

Coral Bleaching a Sign of Sickness

WHILE surfers are appearing from the jungle and towns, divers have disappeared from the country’s Caribbean region, many migrating to the Pacific. The first rains and waves are falling on the southern Caribbean coast, wrapping up an excellent summer dive season of clear, calm waters. But this summer, the ocean revealed a cause for concern under the transparent blue: much of the living coral has been bleached white.The famous coral reefs of Cahuita, Punta Uva and Manzanillo are under serious stress. Healthy reef-building corals get their color from algae that live in their little coral houses with them. Stress in the form of water that is too warm or full of sediments or pollution causes these tiny upside-down jellyfish in a cup to kick out their little alga buddies when they don’t have enough food to go around. The corals then turn white. This is called coral bleaching. A dive to any of the many patch and fringing reefs revealed many coral colonies white as bone. The bleaching was especially evident in brain coral, star corals and solitary corals. There are still many live corals, but at least one or two, often more, are bleached within sight from any spot you drop down. Imagine putting spots of white paint throughout your favorite coral reef photo and you get the idea of what it looks like. The dying coral is disconcerting to see on the normally vibrant and colorful underwater landscape.Coral bleached white is not dead, just sick. If conditions improve in time, the corals allow algae to move back in and the reef starts to grow again, little by little. Most of Costa Rica’s coral dive sites, both Pacific and Caribbean, have bleached and rebounded before, but each time it seems they come back a little less than what they were. Isla del Coco National Park has lost entire species to coral bleaching in the recent past.Of the three coral bleachings I have now seen on the southern Caribbean coast, this is the worst. One way a bleaching becomes permanent is when the surface of the bleached-white coral is taken over by a different kind of algae, one that smothers any coral below it. Often the white coral will turn a light shade of blue, then brown, and then the coral is dead. Much of the lettuce and fire coral that used to cover the tops of the shallow reefs are dead and brown. There are fewer fish and other sea life as a result. At least the deep reef slopes and walls of the offshore barrier reef of Manzanillo seem unaffected. A quick search on Caribbean coral bleaching will reveal that the entire sea is in the throes of a massive bleaching, probably due to global warming. This has led many people to think that the bleaching is beyond control. But it is well proven that coral exposed to elevated sedimentation and pollution bleaches faster and quicker, and is more likely to die.Growing development weakens the coral with dumping of waste into the rivers, streams and creeks. Many hotels in the southern Caribbean region still do not have adequate septic or waste systems.New drainage trenches continue to kill the soil’s ability to filter the water. If you doubt this, just take a look at the coral.Divers are starting to drop on the Pacific coast as the rains taper off. Caño and Cocos islands report good conditions and some sun starting to be seen. For diving information or to contribute to this report, call 835-6041, email or


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