| What
is Coral? |
By:
Mohamed Habib
What
we commonly call corals includes a
variety of types of organisms that
biologists refer to as coelenterates
or cnidarians. One of the main physical
characteristics of this group is that
they all have a single body cavity
and opening, a coelenteron, that doubles
both for the ingestion of food and
for the release of digested wastes.
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Another
characteristic is that corals and other
coelenterates have stinging cells, or nematocysts,
that are normally carried within special
cells on the animal's surface. When potential
food prey is present in the water, the coral
ejects these stinging cells to entangle
or poison the prey, which the coral can
then consume.
Although
the term "coral" is often used
in a general sense, it usually refers to
reef or hard corals, which are more formally
called scleractinians.
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These are the corals that may form large
coral heads and which are the primary
building blocks of coral reefs in tropical
oceans.
The common characteristic of this group
is the secretion of a basal skeleton
of calcium carbonate as the mineral
aragonite. |
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The
livng portion of this group usually has
its radial symmetry divided into multtiples
of six, which is most apparent in the numbers
of tentacles that surround each polyp. This
pattern is also shown in the pattern of
the calyx, (plural=calyces) or cup, which
is secreted by each polyp, and which remains
after the live tissue is cleaned from a
coral skeleton.
Each
calyx is divided by a number of septa, again
usually in multiples of six, which look like
sharp ridges radiating from the center of
the calyx.
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In life, however, this coral shows
the white colouration of its polyps
and feathery tentacles, which
resemble thousands of small white
flowers.
The term "corals" often
includes other varieties of coelenterates
that have somewhat different characteristics
than scleractinian corals. |
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| The
largest of these groups are the octocorals
which includes both hard and soft forms
and the gorgonians or horny corals.
Their common characteristic is that,
instead of being in multiples of six
like the hard corals, the structures
of their polyps, such as tentacles,
grow in multiples of eight. The tentacles
of these octocoral polyps are pinnate
or feather-like.
The
most common hard octocoral is the organ
pipe coral, which grows from a deep
red skeleton which is formed by parallel
rows of tubes. In life, however, this
coral shows the white coloration of
its polyps and feathery tentacles, which
resemble thousands of small white flowers.
The
soft octocorals have many features in
common with the hard corals. Most grow
as upwardly facing polyps, contain symbiotic
zooxanthellae and have tentacles and
nematocysts that may be used in food
capture. The primary difference is that
the soft corals do not lay down an external
hard skeleton that remains as a permanent
structure after the coral dies.
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Instead,
the soft corals get their structure
and body support from calcium
carbonate spicules that are deposited
within their body walls. These
corals may look like quite drab
leather-like gray-green sheets
on the reef surface, or they can
be very colorful and beautiful,
such as the dendronepthid or ‘teddy
bear’ corals which have
a crown of red to orange tentacles
on a translucent white stalk. |
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A
reef coral can be a single polyp and
calyx, but in most cases reef corals
grow as colonies with hundreds, even
thousands of polyps and calyces on the
same coral skeleton. The variety of
forms that are created by this colonial
growth make up some of the most beautiful
structures to be found in nature. These
structures can range from delicate,
branching bushes and arbors, to robust
tables, intricate flower-like leaves,
multiple starbursts, branching fingers
and massive boulders that have brain-Iike
fissures on their surface. The variety
of shapes is determined by the pattern
of budding of new polyps from older
polyps as the coral grows, and whether
the polyps become separated or continue
to share a common mouth within the original
ring of tentacles.
The
calcium carbonate skeleton also varies
substantially in density and strength
according to the coral species. Some
corals have very dense skeletons and
can resist a great deal of wave disturbance,
while others are light and porous
and are restricted to the calm waters
of embayments. However, these porous
corals have the advantage of having
faster growth rates and may have live
tissue penetrating the coral skeleton.
This tissue within the skeleton gives
these corals a greater ability to
recover from stresses which may kill
off the coral surface tissue.
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Because
of their flower-like appearance,
corals were classically referred
to as "zoophytes", indicating
that they were recognized as animals,
but had many external characteristics
of plants in their patterns of
growth. Now we know that this
original descriptive term was
quite valid, but for a different
reason. |
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Coral
biologists have long recognized that
all hard corals with rapid growth rates
contain massive numbers of single celled
algae called zooxanthellae within the
cells of the coral tissue. These algal
cells appear under the microscope as
yellowish-brown spheres, and they are
extremely abundant in the coral tissue,
normally numbering millions of cells
per square centimeter of coral surface.
The zooxanthellae provide the major
colouration of most living hard corals
and many soft corals, which usually
appears as shades of brown or green.
The actual functional relationship of
these internal algae to the coral has
been studied intensively and was a subject
of controversy for many years. Coral
biologists always recognized that the
presence of the intracellular algae
was necessary for hard corals to achieve
the rapid growth rates which enable
them to reach massive sizes and form
coral reefs. Most non-reef forming or
solitary corals, although they have
similar calcium carbonate skeletons,
do not contain zooxanthellae and do
not grow to large sizes.
The
question remained as to how the association
between the corals and their zooxanthellae
might aid or benefit either of the partners?
When rapid growth occurs, an animal
produces metabolic carbon, phosphorus
and nitrogen wastes that must be removed
or they will poison the growth process.
Corals, being very simple organisms,
have no specialized structures for such
waste removal. However, the abundant
zooxanthellae within the coral tissue
provide a mechanism for removing wastes
and therefore permit rapid coral growth.
The waste products produced by the coral
tissue are the raw materials used for
photosynthesis by the zooxanthellae
and thus are kept from rising to toxic
concentrations.
The
zooxanthellae, on the other hand, benefit
by having a ready supply of nutrients
for photosynthesis. This is an example
of what is termed mutualistic symbiosis,
where both partners benefit from being
joined in a close association.
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| Look
But Leave |
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By:
Hesham Tomoum
Few are the people who know that
regardless of what type they are,
shells serve the same purpose
all around the world: they clean
out impurities and make the water
cleaner. In this sense we can
say that shells do a lot more
good living than as an ashtray
or a side lamp in the corner of
a restaurant.
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Shell
shapes often have more than one purpose.
Some are streamlined to make burrowing
through mud or sand easier. Some bivalves
are heavily ridged to help them stay
anchored. Still other shells grow long
spines to catch seaweed and coral for
camouflage. Mollusks are the scientific
name of the soft bodied creatures that
make their shells from calcium they
get from either their food or the water
they dwell in. When a tiny mollusk hatches
from its egg, it comes into the world
a homeowner: a tiny shell that grows
with it as it grows. Each different
species of mollusk makes a shell that's
unique. Within a species, there can
be distinct differences in shells. Things
like food, climate, environment and
genetics all play a part in making each
shell somewhat different in size, colour,
or shape.
Shell trade has been banned in many
countries around the world. Law Number
102 for preserving the Egyptian Environment
in article # 2 states: Damaging or removing
any living organisms or natural features
and resources, such as shells, corals,
rocks, or soil for any purpose is forbidden.
HE the Governor of the Red Sea has issued
a local decree regarding the same subject
which prohibits selling, buying and
trafficking shells within the boundaries
of the Red Sea Governorate. Some tourists
and visitors are not aware of the fact
that carrying shells in their suit cases
while traveling back to their countries
can lead to unnecessary delay and inconveniences.
Confiscating the shells would be the
minimum action taken against them by
the airport police.
As
a tourist or as a resident in the Red
Sea you might encounter shells or stuffed
marine animals displayed on the pavements.
If you admire the beauties and the natural
resources of the Red Sea then it would
be your obligation to express your discontent
to the person who is committing such
a violation. Furthermore, you could
assist in stopping this illegal trade
by notifying the Rangers of the Red
Sea by calling them on # 548339.
Most
divers have collected some shells at
a certain time in their past and this
is a fact that is hard to deny. In the
last few years, and after learning the
negative aspects of such actions a lot
of divers are becoming environmentally
aware. Most of the dive training organizations
are educating the new generation of
divers about the environment and how
to preserve the natural resources. Personally,
and since I used to work for an environmental
NGO, I cannot but pull over the car
upon seeing any of the shell sellers
and take all that they display and hand
it to the Rangers.
What you see in the picture is what
has been collected by an individual
from the streets of Hurghada during
the past two months. I believe it is
up to you and me to stop or even assist
in stopping this negative trade. If
however nothing is done and shell sellers
are left in the streets, we will all
be speaking about the beautiful shells
that we used to see while diving in
the Red Sea and this is a very real
possibility.
Though
some of the Red Sea Shells are now hard
to see underwater and they are nearly
extinct, the situation now is way better
than what it used to be 6 or 7 years
ago. For those who do not know, there
used to be specialized shops in the
Red Sea that sold shells and stuffed
marine life. Thanks to the laws and
the support of both the local government
and caring individuals this has stopped.
This
is a call for you all to assist in stopping
this trade by reporting the violators
in order to preserve the natural resources
of the Red Sea.
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Environment: