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Basics of the Coral Reef
xxThere
is coral and there are coral reefs. Corals occur in all
oceans—frigid and warm water. Reef building corals
occur only in warm water, tropical-like conditions.
xxCoral
can be hard or soft, i.e. stony or octocoral (gorgonians).
Stony corals secrete the massive, calcium carbonate (limestone)
skeleton of the reef. Octocorals secrete a leather-like
substance called gorgin. Hard corals are the rock-like,
hard surfaces of the reef. Gorgonians are most often mistaken
for plants and you see them dreamily waving about in the
currents. |
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How do they grow?
xxThe basic coral structure is the polyp. The polyp is a two-layered animal comprised of an epidermal outer layer and gastrodermal inner layer. The polyp has an opening that serves both as mouth and anus making these creatures some of the few in the world who can perhaps kiss their own butts.
xxThe gastrodermis of the hard coral is the home of zooxanthellae (I’ll call them, zooxs). Hard corals and zooxs enjoy a symbiotic relationship. Zooxs are algae who take in CO2 given off by the polyps and use this for their own enjoyment. Zooxs give back O2 for the polyps. Zooxs also take in calcium from the seawater and deposit it as the calcium carbonate, reef skeleton providing for the hard substrate growth of the reef. Corals that do not have zooxs cannot create massive coral reefs.
xxCorals house colonies of polyps that create the largest biological structures in the world. The largest coral reef, Great Barrier Reef off northeastern Australia, is much, much larger than the Amazon rain forest.
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Coral Nutrition
xxCoral
are carnivorous. They eat plankton. Coral nematocysts
sting and capture the abundant meroplankton living on
a reef. Meroplankton are creatures that spend only part
of their lives as plankton. The meroplankton hang out
near the surface at night. Hence corals feed primarily
at night and therefore night dives are when you get to
see the profusion of polyp feeding activity on a coral
reef. These meroplankton provide only 5-10% of the corals'
nutritional needs. Zooxs supply the rest. |
Corals Sting!
xxNematocysts, the stinging parts
of the coral, cannot differentiate very well between you and
the plankton that they want to eat (see Coral Nutrition, above).
If you get too close and rub up against them, they will sting
you. The sting is almost
always irritating and often can make the rest of your dive quite
miserable. On some occasions serious reactions to the sting
occurs resulting in the need to get to a doctor ASAP.
xxDon’t touch the coral!
xxTouching the coral also damages
them and can lead to the death of the part of the coral that
is touched.
xxBeginner photographers
are most notorious for inadvertently brushing up against the
coral. It can be frustrating to be almost in position for a
wonderful shot and tempting to allow yourself to rest against
the coral to get that shot. Obtaining a nice photo to view at
home can be rewarding but don’t let the act of getting
that photo cause an injury to yourself or destroy a piece of
the home where that photo was taken. Please become buoyancy
proficient before tackling underwater photography or at least
try being satisfied with fewer winning shots while you learn
to control your buoyancy.
Coral reef info for Virgos and other statisticians among you:
- Coral reefs generally form on the eastern sides of major
continents. (Due to the coriolis
effect.)
- Water temperature needs to be a minimum of 65° F. Ideal is 77° to 84°. (That’s Puerto Rico where, in the past one year, I measured a water temperature cycle of a low of 77° and a high of 83°!!)
- They need a salinity of 32-36ppt (parts per thousand) to grow. Therefore coral reefs do not occur where fresh water rivers (which are unsalted) flow into the ocean nor do they occur in the Persian Gulf where salinity is greater than 36ppt.
- They must have at least 15-20% surface light penetration. Coral reefs exist as deep as 300 feet but most live above 80 feet.
- Sustainable coral reef surplus production is only 2-3%. That is, the amount of fish that can be harvested from a reef without resulting in harmful effects.
- Gorgonians do not have zooxs.
- Moderate wave action renews plankton supply, promotes oxygenation and prevents sedimentation, which can choke out the zooxs.
What creates a danger to the coral reefs?
xxAnything that prevents the zooxs
from maintaining their health will be a detriment to the coral
and cause them to die out. Run off chemicals from farming will
do this. Pollution from the presence of excessive population
close to the coasts harms the reefs. Excessive sediment
in the water from construction and from poor farming
practices will limit light penetration. Ocean warming can bring
the temperature too high. Over harvest of reefs’ marine
life will harm the reef. In some places of the world, fishermen
use dynamite to stun the fish. This brings the fish to the surface
for an easy harvest. Cyanide can also be used for this purpose.
Of course, not much reef remains where these practices are done.
Want more information about coral reefs?
xxThe following
are very good web sites dedicated to informing the public about
coral reefs:
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