the opportunity to show your children the beautiful underwater
corals. There are only 20% of the corals left
in the Caribbean that were here 50 years ago! Going.. going ....
Corals belong to the animal kingdom, and are
members of the same group of animals as jellyfish and sea anemones
(Phylum: Cnidaria). The actual coral animal or 'polyp'
is soft bodied, with tentacles like a sea anemone. The main difference
is that corals secrete an external calcium carbonate skeleton
and sea anemones do not. This hard skeleton forms the framework
of coral reefs. The tiny coral polyps occupy little cups or corallites
in the massive skeleton. Corals can be colonial or solitary and
there are several hundred species, some are large and branching
and grow rapidly at a rate of up to 10cm per year, while others
are mound shaped, growing slowly at only 1cm per year.
addition to the hard corals, there are a variety of soft corals
like this common sea fan (Gorgonia ventalina). The calcium carbonate
skeleton of soft corals is located within their bodies, allowing
them to move with the wave action. Sea fans typically grow so
that the wave action is moving over the broad plane of their bodies,
so all of the sea fans in an area will be oriented in the same
building corals live in symbiotic association with zooxanthellae,
single celled algae, which live in the tissue of the corals. The
zooxanthellae produce the oxygen, that the corals need
to survive, by photosynthesis; in return the algae are protected
from grazing species and can access the nutrients that the coral
excretes - a mutually beneficial association.
feed on zooplankton with the use of their tentacles. During daylight
they mostly remain within their protective skeleton to avoid predation,
but at night the tentacles are extended to allow them to feed.
colonies grow by having the polyps bud off new polyps asexually.
New colonies are established by the fragmentation of skeletal
pieces or through the settling of planktonic coral lava on a hard
substrate. The lava are the result of sexual reproduction.
do corals need to grow? There are six major factors that limit
coral reef development; water temperature and salinity, depth,
light, sedimentation and emergence into air.
Coral reefs are only found between about 30 degrees north and
south of the equator, where the water temperature is at least
70 degrees F, and optimal reef development occurs in waters where
the mean annual temperatures are around 75 degrees F.
Corals are intolerant of salinities that deviate significantly
from that of seawater and gaps will occur in reefs where, for
example, freshwater from a river enters the sea.
Depth is also critical, coral reefs will not develop in water
that is deeper than about 50-70m, and they grow most energetically
at depths of 25m or less. Light, which is related to depth of
water, is necessary for the zooxanthellae to photosynthesize.
Without light the photosynthetic rate is reduced and with it the
corals ability to secrete calcium carbonate.
Corals also require clear water - sediment clogs their
feeding structures and smothers them. For this reason corals usually
grow most actively in areas of strong wave action, such as the
windward side of a reef, where sediment is prevented from settling
on the colonies.
Finally corals reefs are limited in an upward direction by emergence
into air. Most corals are killed by long exposure to air and so
their upward growth is limited to the level of the lowest tides.
Coral Reef Monitoring Network
for seafood is so great in the Caribbean that many reefs are severely
over fished, throwing off the delicate balance essential to the
survival of the reef ecosystem. Too many nutrients and not enough
plant-eating fish cause algae to overgrow and smother corals.
can we help our coral reefs?
Plant vegetation barriers along rivers and shorelines
to reduce runoff.
Force government agencies to establish moorings for boats to pick
up and tie to, instead of damaging corals with their anchors.
Pick up trash along beaches and in other coastal areas.
Refrain from buying souvenirs, jewelry, or ornaments made of coral.
Snorkel, dive, and anchor with care so as not to crush reef organisms.
Buy only captive-bred aquarium fish
Request seafood that have been sustainably harvested. Eat less
Support education and research on coral reefs as well as reef-friendly
--A new study paints a grim picture of the health of coral reefs
across the Caribbean. In the past three decades, the amount of
coral cover has dropped about 80 percent, according to researchers
in the journal Science. A team of U.K. scientists compiled data
from 263 separate reef sites in the Caribbean for this week's
report, which they called the most extensive coral study ever
of the region.
Some of the causes are natural, such as disease and weather damage.
Hurricanes, for example, can break coral tissue, making it more
susceptible to diseases.
But much of the problem can be traced to humans. "The man-made
causes, the ones we can do something about, need to be taken extremely
"A lot of the important causes come from things people are
doing on land, like pollution, sedimentation resulting from development
and deforestation. They have very serioust repercussions".