FORESTS OF THE SEA: Coral reefs are called the rain forests of the sea
owing to their diverse and productive nature. They are found in the
warm, clear, shallow waters of tropical oceans worldwide.
A coral is a structure built by a polyp. A polyp is a small
invertebrate animal that lives in the sea. It belongs to the same group
of animals as Sea Anemones, Jellyfish and Corals. Most polyps live in
large colonies. The soft body of a coral polyp is about the size of a
Corals breed by both sexual and asexual reproduction. The newborn
coral larva resulting from fertilization of eggs and sperms is called a
planula. It is only the size of the head of a pin and it floats in the
sea till it finds something hard to latch onto and develop in to a
Polyps also reproduce asexually by budding, where an identical polyp
sprouts out of the polyp's side. Broken pieces of corals that land on a
suitable substrate also may begin growing and produce a new colony.
Bubble coral (Plerogyra Sp)
Corals feed on particles and organisms like zooplankton in the water
column. They use two methods of prey capture: They catch their food
using the tentacles that they have round their mouths.
These tentacles have poisonous stingers called nematocysts. Some
corals will trap prey in sticky mucus on their tentacles and move the
prey into the mouth. Most corals feed at night.
However, an alga known as Zooxanthellae provides important sources of
nutrition to reef building corals. Zooxanthellae are unicellular - i.e.
body made of one cell -, yellow-brown algae, which live within the
Nutrients supplied in the form of photosynthetic products by the
zooxanthellae make it possible for the corals to grow and reproduce
quickly enough to create reefs.
In turn, the coral provides protection and access to light for the
zooxanthellae. Relationships like this in which both parties benefit are
called symbiotic. Because of the need for light, corals containing
zooxanthellae only live in ocean waters less than 100 meters deep.
There are two types of corals, hard and soft. Hard corals have an
internal, rock-like, chalky (calcium carbonate) skeleton that remains
when they die and have six tentacles in the polyp.
Soft corals have eight tentacles on their polyps. They are soft or
leathery in texture and have limestone pieces embedded in the body
instead of a solid skeleton.
Huge colonies of hard corals form coral reefs. The corallite is the
part of the skeleton deposited by one polyp. The calcium carbonate is
secreted at the base of the polyps.
The living coral colony is found to completely cover this hard,
stony, branching calcium carbonate structure, which is continuously
deposited by the living colony, making this structure bigger. When coral
polyps die, another polyp, which latches itself on to this structure,
will grow on top of the old one.
Brain coral (Diplolria labrynthiformis)
While corals form the reef structure, algae living in the reefs
cement various corals together with compounds of calcium, other
organisms such as tube worms and molluscs contribute to the reef by
leaving behind their hard skeletons.
A coral colony may consist of thousands of polyps. An entire colony,
many meters in diameter, can start out as a single polyp.
Coral reefs consist of many diverse species of corals. Many corals
have different growth forms and shapes and come in many colours. Common
names for corals refer to the shape of their colonies. There are orange
cup corals. (Tubastrea coccinea) and golf ball corals (Favia fragum).
They can also be meandroid in which corallites form a series within
the same walls, as in the Pillar Coral species (Dendrogyra cylindrus).
There are massive, staghorn or branching, plating, encrusting, columnar,
corymbose and foliacious (leaf or vase-like).
Coral reefs start out small and grow about half an inch a year, but
if undisturbed by man they can grow to be quite large. The tan parts of
the reefs that one observes are the shells of dead coral polyps and the
colorful parts are the living reefs. Coral polyps construct many
different types of reefs.
The three basic types of coral reefs are fringing reefs, barrier
reefs and atolls. Fringing reefs are coral reefs that grow in shallow
waters and border the coast closely or are separated from it by a narrow
stretch of water.
Fringing reefs consist of several zones that are characterized by
their depth, the structure of the reef, and its plant and animal
Barrier reefs are those that are separated from land by a lagoon.
These reefs grow parallel to the coast and are large and continuous. The
Great Barrier Reef off the northeast coast of Australia is 150 km wide
and 2000 km long.
The third type of reefs is the atolls. Coral Atolls are rings of
coral that grow on top of old, sunken volcanoes in the ocean. They begin
as fringe reefs surrounding a volcanic island; then, as the volcano
sinks, the reef continues to grow, and eventually only the reef remains.
Purple and white branching hard coral
There are two types of atolls, deep sea atolls that rise from deep
sea and those found on the continental shelf.
Coral bleaching is the whitening of coral colonies due to the loss of
symbiotic zooxanthellae from the tissues of polyps. This loss exposes
the white calcium carbonate skeletons of the coral colony
Reefs provide food and shelter to fish and invertebrates Sponges,
such as Cliona, cause bioerosion in corals. Sponges inhabit corals for
the purpose of protection from predators.
Crustaceans, like crabs, shrimp, and lobsters, fish like Reef Sharks,
groupers, clown fish, eels, parrotfish, snapper, and also scorpion fish,
turtles, sea snakes, snails, and mollusks like octopuses, nautilus, and
clams, are found in coral reef environments. Birds also feast on coral
Corals play a very important role in that they control the amount of
carbon dioxide in the ocean water by trapping carbon dioxide in the
In addition, coral reefs are very important because they provide a
barrier between the ocean and the shore and protect the coasts from
strong currents and waves.
Coral reefs of Sri Lanka
A total of 183 species of stony corals divided among 68 genera have
been recorded from Sri Lanka. Almost 400 species of reef and
reef-associated species have been identified during the reef surveys
conducted by NARA. This is from a total of nearly 1000 known reef and
Sri Lankan reefs also support many species of invertebrates including
commercially important species of spiny lobsters, shrimps and crabs and
marine flora such as sea grasses and algae. Dolphins, whale sharks and
sea turtles have also been sighted among inshore and offshore reefs.
Table coral (Acropora hyacinthus)
The growth of coral reefs around Sri Lanka is influenced mainly by
the monsoons, which have a major impact on the level of turbidity and
fresh water input into the coastal waters.
Only 2% of the shoreline of Sri Lanka has true coral reefs. Most
fringing reefs are found on the south-western, southern and eastern
In the south they are found at Hikkaduwa, Unawatuna and Weligama. In
the eastern seaboard, they are found, in Trincomalee going up to
Kuchchiveli (Pigeon Island). Well developed off shore coral reefs occur
from Kalpitiya northwards to Mannar.
Coral reefs around the Jaffna Peninsula are less developed and occur
mainly around the coastal islands. There are Barrier reefs off Vakarai
and Silvaturai on the east coast. They are the true coral habitats
consisting of live coral as well as calcareous substances, sandstone and
Only two coral reef areas have been afforded legal protection so far.
The Hikkaduwa Marine Sanctuary is located in the southern province and
is one of the most popular tourism sites in Sri Lanka.
It is the first national marine sanctuary and was established in
1979. The Bar Reef, located west of the Kalpitiya Peninsula near
Puttalam lagoon, was declared a marine sanctuary in 1992.
Because many coral reef organisms can tolerate only a narrow range of
environmental conditions, the slightest change in the reef environment
may have detrimental effects on the health of entire coral colonies.
These changes generally fall within two categories: natural
disturbances and anthropogenic, or man made, disturbances. Because of
the important ecological and economic roles that coral reef communities
play, an understanding of the stresses and dangers to the reefs is
Most near shore reefs in Sri Lanka have been severely damaged due to
human activities. The major causes are coral mining, destructive fishing
methods, uncontrolled harvesting and pollution.
Cup coral (Tubastraea coccinea)
The increased amount of earth and sand, from land-clearing areas,
that comes with run off carries large amounts of sediment. High levels
of nutrients from agricultural areas or septic systems, as well as many
pollutants such as petroleum products or insecticides are also
detrimental to the reefs.
It can be direct sedimentation onto the reef or an increase in the
turbidity of the water due to eutrophication, which is a condition
resulting from excess nutrients flowing into the water (e.g. Hikkaduwa).
The water becomes green or brown, gives off bad odour and the
resulting decrease in the amounts of light reaching corals will destroy
Water treatment plants and large power plants are the cause of much
damage to coral reefs by altering water temperatures by their discharge
of extremely hot water into the coastal waters.
Coral reefs also receive much damage from both commercial and private
vessels. Anchor damage to coral reefs is also common during fishing
operations and when boats are anchored within reef lagoons.
The leakage of fuels into the water and the occurrences of spills by
large tankers are extremely damaging to local corals.
It has also been found that the anti-fouling bottom paints used by
many boats contribute to the formation of toxic concentrations of
Tributyl tin (TBT) and several other chemical compounds, which may be
harmful to corals or other coral species.
Wastewater and bilge water are dumped overboard from ships. As a
result of these, coral reef lagoon areas of Hikkaduwa, Weligama and
Negombo lagoon have become highly polluted.
Highly efficient fishing techniques, introduced recently, such as the
bottom-set nets to catch spiny lobsters and reef fish cause, severe
damage to coral reefs.
Blast fishing using explosives is also commonly practiced in many
parts of the country, being most prevalent in the southern coastal
waters in the Galle District.
Distribution of coral reefs in Sri Lanka.
In some areas fish traps with small mesh diameters are used to catch
even the small juvenile fish. Not only do these practices kill all fish
in the affected areas but they also severely damage the corals.
Muro-ami netting pounds the reefs with weighed bags to scare fish out
of crevices. Trawling also directly damages the corals. These methods
are generally non-selective and large numbers of other species, along
with undersized target species, are swept up in nets or are killed by
poisons or explosives in the process.
Major damage is caused by the extraction of living and dead coral for
the lime industry, which is subjected to some degree of control now,
especially after tsunami.
More damage is caused by the over harvesting of exotic reef resources
such as ornamental fish for export and for tourism related activities.
There are between 200 and 300 marine species of fish and
invertebrates that are being exported by the aquarium trade With regard
to fisheries export products, ornamental fish exports are rated as the
third highest in volume and value, after prawns and lobsters. Due to
over fishing, reef fish populations have been greatly reduced in some
The removal of large numbers of reef fish has caused the loss of a
natural balance in coral reef ecosystems and has allowed more
competitive organisms, such as algae, which were once controlled by
large fish populations, to become dominant on the reefs.
Corals are also very popular as decorations. This is very damaging
because a large amount of the healthiest corals are selected for curio
shops by commercial collectors
Due to their beauty coral reefs brings much income from tourism. The
Hikkaduwa Marine Sanctuary is one of the places which attracts tourists
most. Hikkaduwa's reefs are being gradually worn down.
Snorkeling on coral reefs causes damage to corals with branching
species being the most susceptible. Snorkelers and divers often stand on
reefs walk over corals in the shallows.
Reef working at low tide is very popular among tourists. This causes
lot of damage to corals in areas with highly developed cover of fragile
A status report published by NARA assessed the degree of damage and
threats to various coral reefs of Sri Lanka. According to the report, in
the Bar Reef Marine Sanctuary the shallow the coral areas are partially
damaged while the deep coral areas are in good condition.
The Crown of Thorns Starfish, destructive fishing, uncontrolled
harvesting and boat anchors, cause the damage.
The Chilaw corals are partially damaged owing to destructive fishing
and uncontrolled harvesting. Negombo reefs are mostly in good condition
though some damage is evident in the inshore reefs.
The inshore reefs from Ambalangoda to Hikkaduwa are degraded while
the offshore reefs are in relatively good condition The Hikkaduwa Marine
Sanctuary is partially degraded owing to sedimentation, boat anchoring,
reef trampling, pollution, use of glass bottom boats and increase of
Halimeda, which is a large green algae that is threatening several other
reefs as well including Pasikuda. It is a calcareous algae in that it
deposits calcium carbonate in its tissues.
When the algae die, it leaves a limestone 'skeleton' behind. Galle
including the Rumasssala reef, Unawatuna and Weligama are under
different degrees of degradation while Polhena, in Matara, is heavily
degraded due to the seasoning of coconut husks. The Great and Little
Basses are relatively undegraded but uncontrolled harvesting takes
There are several natural disturbances, which cause significant
damage to coral reefs. The most recognised of these events are
hurricanes or typhoons, which bring large and powerful waves to the
These storm waves cause large corals to break apart and scatter
fragments about the reefs. In addition, these storms generally bring
heavy rain, which increases runoff and sedimentation. Tsunamis are
another natural force that damages coral reefs.
The impact of the tsunami in 2004 was highly varied, ranging from
almost unaffected to extreme damage.
Almost total destruction of a reef was seen at Dutch Bay off
Trincomalee town. Most damage observed was mechanical, with breakage of
fragile corals, notably Acropora and Montipora spp., and larger massive
colonies toppling over.
There was also damage caused by rubble, which dated back to a mass
coral mortality in 1998, triggered by rising sea temperature. The impact
on fish populations were most likely the loss of fish habitat. Some
smothering has been observed.
Severe damage on the coast was observed where coral mining in the sea
has been rampant. Currently, specific laws relating to corals are
included in the Fauna and Flora Protection Act, the Coastal Conservation
Act, the Marine Pollution Prevention Act and the Fisheries and Aquatic
The provisions of the Customs Ordinance relating to export of
prohibited goods apply by extension. In relation to pollution in
general, particularly water pollution, the National Environment Act may
be cited as well.
Pictures Courtesy: IUCN