Arcing around Punta Cahuita, the arrecife de Cahuita, or Cahuita reef, comprises six square kilometres of coral, and is one of just two snorkelling reefs on this side of Costa Rica (the other is further south at the Refugio Nacional de Vida Silvestre Gandoca-Manzanillo). Corals are actually tiny animals, single-celled polyps, that secrete limestone, building their houses around themselves. Over centuries the limestone binds together to form a multilayered coral reef. The coral thrives on algae, which, like land plants, transform light into energy to survive; reefs always grow close to the surface in transparent waters where they can get plenty of sun. The white-sand beaches along this part of the coast were formed by shards of excreted coral.

Unfortunately, Cahuita’s once-splendid reef is dying, soured by agricultural chemicals from the rivers that run into the sea (the fault of the banana plantations), and from the silting up of these same rivers caused by topsoil runoff from logging, and the upheaval of the 1991 earthquake. The species that survive are common brain coral, grey and mushy like its namesake, moose horn coral, which is slightly red, and sallow-grey deer horn coral. In water deeper than 2m, you might also spot fan coral wafting elegantly back and forth.

This delicate ecosystem shelters more than 120 species of fish and the occasional green turtle. Lobsters, particularly the fearsome-looking spiny lobster, used to be common but are also falling victim to the reef’s environmental problems. Less frail, and thus more common, is the blue parrotfish, so called because of its “beak”; actually teeth soldered together. Unfortunately, the parrotfish is causing a few environmental problems of its own as it uses its powerful jaws to gnaw away at the coral’s filigree-like structures and spines.

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