Page 57 - French Polynesia
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R eef-building or hermatypic corals urchins, sponges, and other forces and or- damage them or erode the sediments in
live only in the photic zone (above ganisms act as bioeroders, breaking down which they are rooted, while the mangroves
50 meters), the depth to which sufficient coral skeletons into fragments that settle and sea grass protect the coral from large
sunlight penetrates the water, allowing into spaces in the reef structure or form influxes of silt, fresh water and pollutants.
photosynthesis to occur. Coral polyps do sandy bottoms in associated reef lagoons. This level of variety in the environment
not photosynthesize, but have a symbiotic Many other organisms living in the reef benefits many coral reef animals, which, for
relationship with zooxanthellae; these community contribute skeletal calcium car- example, may feed in the sea grass and use
organisms live within the tissues of polyps bonate in the same manner. Coralline algae the reefs for protection or breeding.
and provide organic nutrients that nourish are important contributors to reef structure
the polyp. in those parts of the reef subjected to the R eefs are home to a large variety of ani-
greatest forces by waves (such as the reef mals, including fish, seabirds, sponges,
B ecause of this relationship, coral reefs front facing the open ocean). These algae cnidarians (which includes some types of
grow much faster in clear water, which strengthen the reef structure by depositing corals and jellyfish), worms, crustaceans
admits more sunlight. Without their sym- limestone in sheets over the reef surface. (including shrimp, cleaner shrimp, spiny
bionts, coral growth would be too slow lobsters and crabs), mollusks (including
to form significant reef structures. Corals C oral reefs form some of the world’s cephalopods), echinoderms (including star-
get up to 90% of their nutrients from their most productive ecosystems, providing fish, sea urchins and sea cucumbers), sea
symbionts. complex and varied marine habitats that squirts, sea turtles and sea snakes. Aside
support a wide range of other organisms. from humans, mammals are rare on coral
R eefs grow as polyps and other or- Fringing reefs just below low tide level reefs, with visiting cetaceans such as dol-
ganisms deposit calcium carbonate, have a mutually beneficial relationship phins being the main exception. A few of
the basis of coral, as a skeletal structure with mangrove forests at high tide level these varied species feed directly on corals,
beneath and around themselves, pushing and sea grass meadows in between: the while others graze on algae on the reef.
the coral head’s top upwards and outwards. reefs protect the mangroves and seagrass
Waves, grazing fish (such as parrotfish), sea from strong currents and waves that would
