Environmental Engineering Reference
In-Depth Information
other countries spread from Seychelles in the
west to India in the North to Malaysia in the east,
all having over 200 species of coral recorded.
Coral reef is the housing complex of a wide
spectrum of fauna. It has been documented that
as many as 300 animal species may live together
on a single reef. The giant clam (
Islands, etc. Coral reefs occur in and around 20
Islands between Tuticorin and Pamban in the
Gulf of Mannar and Palk Bay.
6.3.1 Types of Coral Reefs
sp.)
measuring up to a metre in length and weighing
over 150 kg is an important species of reef eco-
system, but overharvesting and poaching have
greatly reduced their numbers. These clams also
possess zooxanthellae in large numbers in the
colourful tissues that line the edges of the shell.
The bubblegum corals are another surprise to the
reef community. They are octocorals belonging
to the phylum cnidaria, which also includes stony
corals and jelly
Tridacna
On the basis of the structure and their relationship
to the underlying geologic features, coral reefs
can be divided into three categories. They are
fringing reefs, barrier reefs and atolls (Fig.
6.21
).
1.
Fringing reefs
: These are found very close to or
near the newly formed volcanic islands as well
as surrounding the continental landmasses.
They are located directly offshore and project
outward to the sea, e.g., the Caribbean reef.
sh. Despite forming enormous
tree-like structures, the trunk and branches of
bubblegum corals are not corneous or calcareous
like most branching octocorals. Instead, the
branches are accumulation and near fusion of
microscopic sclerites made of calcite.
Crabs, moray eels, colourful reef sh, poi-
sonous stone
2.
Barrier reefs
: These reefs act as barrier sep-
arated by a lagoon from the landmass, with
which they are associated. Those surrounding
volcanic islands are formed from subsiding
islands with fringing reefs. The lagoon forms
between the island and the reef. The largest
barrier reef is the Great Barrier Reef of Aus-
tralia, which runs over 2,000 km along the
north-eastern coast of Australia to New Gui-
nea. It is so large that it is visible from space
shuttle. The second largest barrier reef is
located in the Caribbean Sea off the coast of
Belize.
sh, spiny sea urchins, seahorses,
shrimps, lobsters, sponges and various life forms
are found in the coral reef ecosystem. Global
pattern of coral
sh diversity has been
examined in detail. The biodiversity of coral reef
reef
shes
show patterns of distribution and diversity at all
scales ranging from global to regional to local. At
the largest scale, diversity appears to be princi-
pally controlled by the interaction of tectonic and
geomorphological events with evolution and
dispersion processes. At a regional level, water
parameter like turbidity and current strength,
perhaps requiring differential adaptation at the
larval stage, may control the species distribution
pattern. At a local level, diversity is in
shes covers a wide array of species. Reef
3.
Atolls
: These reefs are somewhat circular in
shape with a centrally located lagoon.
According to Darwin, they are formed in areas
where barrier reefs subside below sea level,
whereas according to Alexander Agassiz, they
are formed on the top of the cones of sub-
merged volcanoes, leaving only the reef
around a central lagoon. But in any of the case,
the lagoon remains connected to the open sea
by breaks in the reef. Over time, the reefs may
become eroded or exposed to wind action or
waves. These physical processes sometimes
give rise to formation of islands surrounding
the lagoons, which is perhaps the depositional
feature of sand carried by the wind or wave
action. More than 300 atolls are present in and
around Paci
uenced
by the habitat characteristics such as depth, het-
erogeneity and complexity. Because of the
vagaries of larval distribution and recruitment,
the assemblages to be found at a site are quite
variable, although the extent of these variations
probably differs among species and areas.
In the Indian subcontinent, coral reefs are
concentrated in regions like Gulf of Mannar,
Andaman and Nicobar
fl
c and Indian Ocean, whereas 10
atolls are present in Atlantic Ocean as the
water is too cool or turbid.
Islands, Lakshadweep
