Ecology
and biodiversity
Coral
reefs support an extraordinary biodiversity;
although they are located in nutrient-poor
tropical waters. The process of nutrient
cycling between corals, zooxanthellae,
and other reef organisms provides an
explanation for why coral reefs flourish
in these waters: recycling ensures that
fewer nutrients are needed overall to
support the community.
Cyanobacteria also
provide soluble nitrates for the coral
reef through the process of nitrogen
fixation. Corals absorb nutrients, including
inorganic nitrogen and phosphorus, directly
from the water, and they feed upon zooplankton
that are carried past the polyps by
water motion (Castro and Huber, 2000).
Thus, primary productivity on a coral
reef is very high, which results in
the highest values per square meter,
at 5-10g C m-2 day-1. Producers in coral
reef communities include the symbiotic
zooxanthellae, coralline algae, and
various seaweeds, especially small types
called turf algae, although scientists
disagree about the importance of these
particular organisms (Castro and Huber,
2000).
Coral reefs are home
to a variety of tropical or reef fish,
such as the colorful parrotfish, angelfish,
damselfish and butterflyfish. Other
fish groups found on coral reefs include
groupers, snappers, grunts and wrasses.
Over 4,000 species of fish inhabit coral
reefs (Spalding et al., 2001).
Reefs are also home
to a large variety of other organisms,
including sponges, Cnidarians (which
includes some types of corals and jellyfish),
worms, crustaceans (including shrimp,
spiny lobsters and crabs), molluscs
(including cephalopods), echinoderms
(including starfish, sea urchins and
sea cucumbers), sea squirts, sea turtles
and sea snakes. Aside from humans, mammals
are rare on coral reefs, with visiting
cetaceans such as dolphins being the
main group. A few of these varied species
feed directly on corals, while others
graze on algae on the reef and participate
in complex food webs (Castro and Huber,
2000; Spalding et al., 2001).
A number of invertebrates,
collectively called cryptofauna, inhabit
the coral rock substrate itself, either
boring into the limestone surface or
living in pre-existing voids and crevices.
Those animals boring into the rock include
sponges, bivalve molluscs, and Sipunculans.
Those settling on the reef include many
other species, particularly crustaceans
and Polychaete worms (Nybakken, 1997).
Due to their vast biodiversity,
many governments world-wide take measures
to protect their coral reefs. In Australia,
the Great Barrier Reef is protected
by the Great Barrier Reef Marine Park
Authority, and is the subject of many
plans and pieces of legislation, including
a Biodiversity Action Plan.
Algae
and coral reef
Researchers have found evidence of algae
dominance in locations of healthy coral
reefs. In surveys done around largely
uninhabited US Pacific islands, algae
consists of a large percentage of the
surveyed coral locations. The algae
population consists of turf algae, coralline
algae, and macroalgae.
