Life on a Coral Reef
CORAL REEFS HAVE an amazing variety of marine life, from teeming multitudes of brightly colored fish to giant clams wedged into rocks. Every bit of space on the reef provides a hiding place or shelter for some animal or plant. At night, a host of amazing creatures emerge from coral caves and crevices to feed. All the living organisms on the reef depend for their survival on the stony corals which recycle the scarce nutrients from the clear, blue, tropical waters. People, as well as animals, rely on coral reefs for they protect coastlines, attract tourists'money, and some island nations live on coral atolls. Sadly, in spite of being one of the great natural wonders of the world, coral reefs are now under threat. Destruction is caused by reefs being broken up for building materials, damaged by snorkelers and divers touching or treading on them, dynamited by fishermen, ripped up by souvenir collectors, covered by soil eroded by the destruction of rain forests, and polluted by sewage and oil spills.
FRILLY LETTUCE
Sea slugs are related to sea snails but do not have shells. Many sea slugs living on coral reefs feed on corals, but the lettuce slug feeds on algae growing on the reef by sucking the sap from individual cells. Chloroplasts, the green part of plant cells, are then stored in the slug's digestive system where they continue to trap energy from sunlight to make food. Many other reef sea slugs are brightly colored to warn that they are dangerous and recycle the stings that they eat from the coral's tentacles.
LIVING IN HARMONY
Clown fish which shelter in anemones live on coral reefs in the Pacific and Indian Oceans. Unlike other fish, clown fish are not stung by their anemone home. The anemone's stings are not triggered because chemicals taken from the anemone are carried in the clown fish's slimy coat. Clown fish seldom venture far from their anemone home for fear of attack bv other fish. There are different kinds of clown fish, some living only with certain kinds of anemones.
DATE MUSSEL
Many different clams live on coral reefs. This date mussel makes its home by producing chemicals to wear a hole in the hard coral. Like most clams, the mussel feeds by collecting food particles from water passing through its gills.
NOTORIOUS STARFISH
The crown-of-thorns starfish devours the soft parts of a gorgonian coral. Like many other starfish, it feeds by turning its stomach inside out, making enzymes to digest its prey. Plagues of these starfish attacked Australia's Great Barrier Reef in the 1960s and 1970s, killing large numbers of corals.
COLORFUL CUCUMBER
. One of the most colorful kinds of sea cucumber lives on or close to reefs in the Indo- Pacific region. Sea cucumbers are echinoderms (pp.18-19), like starfish, sea urchins, and sea lilies. The sea cucumber puts out its sticky tentacles to feed on small particles of food. Once the food has stuck onto the mucus on the tentacle, it is placed inside the mouth and the food removed.