In the past, New Providence has
experienced an epidemic of food poisoning from the Conch sold at Potter's
Cay, Arawak Cay and Fort Montagu. The disease causing organism has been
identified as Vibrio parahaemolyticus, a salt
water gram- negative bacterium naturally and commonly found in warm
marine and estuarine environments. In the States, infection is commonly
caused by eating raw Oysters.
The Queen or Pink Conch (Strombus gigas)
is a gastropod mollusc - a big sea snail. It begins life as a tiny egg,
one of thousands laid by the female between March and September as part of
an egg mass containing half a million eggs or more. The Conch larva -
called a veliger, hatches after three to five days and swims up into the
water to become part of the plankton.
eggs are laid in a string of jelly which is moved from side to side
to form a firm egg mass 4 to 6 inches long. The eggs hatch in 3-5
The Conch egg mass is laid
in the sand
The Conch veliger has two rounded lobes fringed with
tiny hairs which beat beat back and forth. They help to move the larva
through the water and create a water current sending tiny food particles
in towards the mouth. The
veliger stands little chance of survival - which is why the Conch lays so
In the plankton, the eggs are totally at the
mercy of the ocean's currents. In the three weeks that the veliger exists,
many of them will become food for larger filter feeding reef organisms,
corals, sponges, crinoids and even some other molluscs!
Those that are not eaten will only survive if at the
end of the three weeks, they fall to the seafloor in shallow water. Many
will fall into the ocean depths where they will find no food. Some
however, will descend into beds of Sea grass where they stand at least a
small chance of survival.
Descent to the sea floor is not necessarily
immediate. It has been shown that the Conch larvae must 'sample' the
correct food organisms in the water before it starts to descend. Chemicals
produced by specific bottom living micro-organisms known as diatoms will
trigger the Conch's metamorphosis, providing a 'settlement cue' . This is
clearly a valuable survival strategy, as it ensures that the Conch will
descend into the correct environment for survival.
On the sea bed, the veliger goes through a period of
metamorphosis or change in which the lobes disappear and it develops a
long snout and a foot with a claw. It buries itself in the sand at this
stage where it lives for about a year on very small algae.
When the Conch develops its shell, it is rounded
without the characteristic lip of the mature Conch.
It is known at this stage as a 'roller', as it will roll about in the surf
unlike a mature Conch which is stabilised by its lip. At seven months of
age, the roller's shell is some four centimeters long.
It takes almost another three years before the Conch
reaches its full mature size. At this stage it is growing its lip - the
wide shell edge that protects the animal's body as it 'hops' about in the
Sea grass. At first the edge of the lip is thin and fragile, but it
gradually thickens over the next few years. An old Conch with a thick lip
may be six or seven years old. By this time it will have acquired a
variety of hitch hikers on its shell, Bryozoans, algae, and even juvenile
Unlike many snails, the Conch is either male or
female. Without seeing the body of the Conch out of its shell, it is
almost impossible to tell the sex of an animal. If the body is removed
from the shell, the male is seen to have a small 'arm' extending from
above the right eye, while the female has a groove extending from the base
of the foot right up into the shell.
outside of the shell is covered by a horny brown periostracum - which will
eventually peel off after a Conch shell has been dead and laying about in
the sun. The inside of the shell however, is covered with a thin layer of
crystalline calcium carbonate known as nacre. This is the same substance
with which an Oyster coats an irritant grain of sand to form a
pearl. The Conch can also produce pearls, although much more rarely
than Oysters. The Conch pearls are much more variable in both shape
Conchs mate in the summer, with large numbers
gathering together. The male sits just behind the female and extends its
'arm' up underneath the female's shell to deposit sperm close to the eggs.
Following mating, the egg mass is left on the sand.
In many parts of the Caribbean, the Conch's habitat
is limited by relatively small areas of shallow water. In such places the
Conch have been over-fished and become almost a delicacy. I was astonished
by the price of Conch in Saint Lucia when I ordered a meal at a 'native'
Even in the Bahamas, the Conch is no longer found in
any numbers close to large centres of population.
For further exploration of the over-fishing theme, go to my page 'Harvesting
The Conch is a wonderful resource, but one which
could go the way of far too many of Mankind's food resources with
continued over harvesting. It would be tragic for the Conch to reach
'endangered species' status. Let us hope that with wise and sensible
management of the Conch and its environment, it never will.