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Marine life on the reefs
WBF09 - Sports - Dive
Marine life on the reefs
Night dives reveal hidden beauty
The fabled clear seas of The Bahamas are as much an illusion as they are a legend. Each gallon of water, apparently pure and lifeless, actually contains up to two million invisible plants and animals, making up a rich nutrient soup on which all offshore life depends.
The coral reefs survive by filtering out this abundance of foodstuff. Anyone who has ever dived at night will know the transformation that comes over a reef after dark, when what looked like a beautiful, ornate formation of rock in the daylight suddenly becomes a throbbing surface of tiny, voraciously feeding mouths.
“All sorts of exotic, nocturnal creatures come out that you wouldn’t otherwise see,” says Christina Zenata of Freeport’s Underwater Explorer’s Society. “There are squid, starfish, lobster (crawfish) and shrimps popping around. But the most exciting change is to the coral, because diving with a lamp is like taking your own little sun down, and all the colours, especially the reds that are almost grey in daylight, come flashing to life.”
Coral reefs are colonies of living polyps—simple, cylindrical creatures just like sea anemones and jellyfish, except that they secrete an outer skeleton of calcium carbonate. They thrive in water that rarely drops below 70°F, so most of The Bahamas should be too far north to support them. However, the Gulf Stream provides a flowing, warm-water sanctuary from the surrounding Atlantic, creating conditions so favourable that the 100-mile barrier reef east of Andros is the third-largest biological construction on earth (behind the barrier reefs of Australia and Belize).
Picturesque reef killers
Corals grow at different speeds. Star and brain corals average just an inch a year, while each antler-like tip of the staghorn coral extends four inches before branching in two. Like all the other corals, staghorns are eaten back almost as quickly as they grow.
Sharp-beaked parrotfish are the most picturesque of the reef’s destroyers. Ranging in colour from delicate cream and rose to vivid midnight blue, they crunch away at the hard surface to eat the algae that live inside with the polyp. Algae produce energy and food for the polyps, and in return get protection and nutrition from the polyp’s waste. They also give the coral its colour—the growing edges of corals are often colourless, because algae has not spread to them.
The symbiotic nature of the coral is another limiting factor on how far it can spread, restricting it to shallow, sunlit waters.
Sponges are even more primitive animals, but have a far greater range, from the surface of the reef to abyssal waters miles below the surface. They may be a few inches or ten feet across and vary in shape from indeterminate patches, clinging to rocks, all the way up to beautiful, lacey fans. Some have amazing inner lives. The huge loggerhead sponge has a labyrinth of internal cavities and passageways. As it grows it can trap up to several hundred pistol shrimp—named for the explosive sound of their snapping claws—inside these spaces, so that a loggerhead sponge often sounds as if there is a gunfight taking place inside.
Strange and stranger
Most reef animals are territorial to the point of foolhardiness. The yellow, black-striped sergeant major and numerous small, bright species of damselfish will attack divers and even, on occasion, the Caribbeanreef shark, which is at the top of the reef’s food chain. Another highly territorial fish is the grouper, a type of sea bass that is a staple of Bahamian cuisine. The most aggressive groupers are called supermales. Having started their life as females, they undergo a spontaneous sex change when they reach a certain size (usually about two feet in length), which allows them to defend a territory.
Curiously, the greater an animal’s reputation for being dangerous, the more timid it seems to be. Ferocious-looking moray eels are shy creatures, unless you get too close. The three stinging species of ray found in The Bahamas—the small, delicate yellow stingray, the hulking southern stingray and the even larger spotted eagle ray, with its eight-foot wingspan—strike only if pestered or stepped on.
There are many other saltwater habitats, from mangrove swamps to the open ocean. But coral reefs are home to more than 25 per cent of all marine life, in a dizzying variety of forms. Anyone who dives or snorkels in Bahamian waters can be confident of encountering some of the most surprising, resourceful and beautiful creatures in the whole of nature.
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