Coral Reefs




Tropical Coral Reefs For those of us who live in the far north, coral reefs represent an exotic paradise, a place where warm tropical currents and lazy days of relaxation are the norm. Under the water, divers have a similar expectation; that the water is always warm and clear, the sun streams through the waves leaving a trail of bright ripples on the sand. Friendly fish swim lazily over to watch the curious antics of human divers. Images of brilliant colours and wild shapes flood past the uninitiated eyes of the would-be diver. Check out these pictures and discover that it is all true! But it's also just a bit more complicated than you might think.
	Light in Water Before we get too far into the images, however, it's important to understand what the light does. As light passes through water, its color changes. The deeper you go, or the farther away from the light source, the less red, less orange, and less yellow there are in the light. Compare these two photographs of the same coralhead (cavernous star coral). The top one is lit with an electronic flash, the lower is taken in natural light. Whenever you see an underwater picture with lots of reds and oranges, it was probably lit with artificial light.
	Guess how this one was taken. No artificial light. This species is the regular star coral of the Caribbean. It is usually found in shallower water than the cavernous star coral, but has a similar look.
	Underwater Animals and Plants The blue tang eats plants on coral reefs in the Caribbean.The fish also has the common name "doctor fish" because of the sharp spine that is hidden in a slit (colored yellow) along the side of the tail. This recurved scalpel can be used to slash any would-be predator.
	Near the shoreline, the feel of the water changes. Strong rays of sunlight sparkle in ripples on the sand. Currents of water move the sand to form underwater dunes, and eelgrass nestles in the valleys or creates large hummocks.
	The graysby is the clown of the grouper family. Covered with spots and portraying a grumpy mouth it is very curious and watches divers from the protection of little caves in the coral.
	Blackbar soldier fish are members of the squirrelfish family and have huge eyes designed to see well at night. During the daytime, they hang around in or near caves where the light is dim and they are safe from predators. At night they move out into open water where their big eyes help them find their prey in the darkest hours.
	Cerianthid anemones are incredibly elegant, but are not easy to find. They are often in deep water and live in muddy-sandy areas. The tubes in which they live are usually stuck fast to a sunken rock or shell, so when a diver approaches they disappear down the tube in zero time.
	The delight of most divers on a coral reef, these little Christmas tree worms are literally underwater worms. They live in tubes that they secrete onto corals, which then grow over the tubes, making them into permanent worm homes. These creatures are both exquisitely beautiful and delicate. Often a diver is tempted to touch one, but to no avail. The worm can sense the diver's approaching finger, and winks away into the tube. Patience will, however, be rewarded as the worm is likely to reappear in a moment.
	OK, OK, so you want to see some sharks. This species is the silvertip, an Indo-Pacific form of requiem shark that is lively, quick, and curious. On one expedition, they were so abundant that we had difficulty getting them to move away from the boat so we could jump in without danger.
	In the Caribbean, the most common shark that divers encounter is probably the Caribbean reef shark. These are also requiem sharks. The name comes from their unpleasant habit of sometimes eating people. In this case we were making a film documentary for Discovery channel and had tempted the sharks in with lots of dead fish and bloody guts. This female was about 2.5 meters (8 feet) long and had a bad attitude.
	Another Caribbean reef shark, this one did not have the same difficult personality and was easy to get along with. We had found this one in a cave resting in a "sleeping" position. This and a few other requiem sharks can rest on the bottom. Most other species of sharks must swim to continue breathing.

Contact us: alan@kivu.com