Page 7 - The British Big Four

R eef-building or hermatypic corals live act as bioeroders, breaking down coral skel- rooted, while the mangroves and sea grass
only in the photic zone (above 50 me- etons into fragments that settle into spaces protect the coral from large influxes of silt,
ters), the depth to which sufficient sunlight in the reef structure or form sandy bottoms fresh water and pollutants. This level of vari-

penetrates the water, allowing photosynthe- in associated reef lagoons. Many other or- ety in the environment benefits many coral

sis to occur. Coral polyps do not photosyn- ganisms living in the reef community con- reef animals, which, for example, may feed

thesize, but have a symbiotic relationship tribute skeletal calcium carbonate in the in the sea grass and use the reefs for protec-

with zooxanthellae; these organisms live same manner. Coralline algae are important tion or breeding.

within the tissues of polyps and provide or- contributors to reef structure in those parts
ganic nutrients that nourish the polyp. Rof the reef subjected to the greatest forces
eefs are home to a large variety of ani-
B ecause of this relationship, coral reefs by waves (such as the reef front facing the mals, including fish, seabirds, sponges,
grow much faster in clear water, which
open ocean). These algae strengthen the cnidarians (which includes some types of

reef structure by depositing limestone in corals and jellyfish), worms, crustaceans (in-

admits more sunlight. Without their sym- sheets over the reef surface. cluding shrimp, cleaner shrimp, spiny lob-

bionts, coral growth would be too slow to C oral reefs form some of the world’s sters and crabs), mollusks (including cepha-
form significant reef structures. Corals get most productive ecosystems, provid- lopods), echinoderms (including starfish,
up to 90% of their nutrients from their sym- sea urchins and sea cucumbers), sea squirts,

bionts. ing complex and varied marine habitats that sea turtles and sea snakes. Aside from hu-

R eefs grow as polyps and other organ- support a wide range of other organisms. mans, mammals are rare on coral reefs, with
isms deposit calcium carbonate, the ba- Fringing reefs just below low tide level have visiting cetaceans such as dolphins being
a mutually beneficial relationship with man- the main exception. A few of these varied

sis of coral, as a skeletal structure beneath grove forests at high tide level and sea grass species feed directly on corals, while others

and around themselves, pushing the coral meadows in between: the reefs protect the graze on algae on the reef.

head’s top upwards and outwards. Waves, mangroves and seagrass from strong cur-

grazing fish (such as parrotfish), sea urchins, rents and waves that would damage them

sponges, and other forces and organisms or erode the sediments in which they are