What are coral reefs?
Some
of the biodiversity of a coral reef
Coral
reefs are aragonite structures produced
by living organisms, found in shallow,
tropical marine waters with little to
no nutrients in the water. High nutrient
levels such as that found in runoff
from agricultural areas can harm the
reef by encouraging the growth of algae.
In most reefs, the predominant organisms
are stony corals, colonial cnidarians
that secrete an exoskeleton of calcium
carbonate (limestone).
The accumulation
of skeletal material, broken and piled
up by wave action and bioeroders, produces
a massive calcareous formation that
supports the living corals and a great
variety of other animal and plant life.
Although
corals are found both in temperate and
tropical waters, reefs are formed only
in a zone extending at most from 30°N
to 30°S of the equator; although
the reef-forming corals do not grow
at depths of over 30 m (100 ft) temperature
has less of an effect on distribution
but it is generally accepted that no
corals exist in waters below 18 °C.
