1. CSEC GEOGRAPHY
CORAL REEFS AND MANGROVES ECOSYSTEMS
MR JOHNSON
NOVEMBER 2019
CORAL REEFS
What is a Coral Reef
A coral reef is a hard, rocky ridge built up from the sea by many tiny coral animals. It is one of
the richest ecosystems on Earth and is sometimes called the ‘rainforest of the sea’. Some living
reefs are several million years old.
Why are coral reefs valuable ecosystems?
Coral reefs are extremely important ecosystems providing a range of benefits. An estimated 500
million people depend on coral reefs for food, coastal protection, building materials and income
from tourism. About 30 million people are totally dependent on coral reefs for their livelihoods
or because they live on atolls. The main benefits of coral reefs include the following:
 Coastal protection: coral reefs act as buffer zones providing vital shoreline protection
from storms and tsunamis. The shallow water above a reef forces waves to break early

2. before reaching the mainland shore. This reduces coastal erosion and risk of flooding.
Corals also provide sheltered conditions for the growth of mangroves, which themselves
are important breeding grounds for fish.
 Beach development: The erosion of coral reefs creates the white sand that typically forms
the beaches of tropical coastlines. Some of this sand is extracted for the construction
industry to make cement.
 Ecological Benefits: Coral reefs are extremely diverse ecosystems. They provide a home
to over 25% of all known marine fish. One hectare of reef off Southeast Asia was found
to support over 2000 species of fish! Coral reefs are important breeding grounds for fish
offering shelter and food.
 Economic benefits: The global value of the world’s coral reefs has been estimated at
almost US $30 billion each year! In Hawaii alone, the benefits associated with tourism,
fishing and biodiversity amount to US$ 360 million a year. Coral reefs are extremely
important commercial fishing grounds providing some 25% of the total fish catch of low-
income countries. It is estimated that coral reef fisheries in East Asia feed over 1 billion
people. Coral reefs are extremely popular tourist destinations, providing a huge source of
income and employment for thousands of people. Millions of people visit the Caribbean
each year to enjoy its tropical beaches and coral reefs. Coral reefs are increasingly valued
for medicinal purposes. Scientists believe that some of the chemicals released by corral
species for self-protection could have applicants for the treatment of some viruses and
cancers.
Formation of coral reefs
Corals are formed by millions of coral polyps, tiny animals resembling overturned jellyfish!
They use excess carbon dioxide in the water, converting it into limestone to form solid reefs.
Corals need particular conditions in order to develop, survive and thrive. They grow best in
sunny, shallow, warm and clear water conditions. This explains why they are only found in
certain parts of the world.
The main factors controlling the development of corals are water temperature, depth, salinity and
turbidity together with the presence of beneficial algae and fish.

3.  Temperature: Tropical corals only live in seawater that has an average temperature of
180
c and over. The ideal temperature is between 230
c and 250
c. Therefore, coral reefs are
mostly found in tropical latitudes. The exception is where warm ocean currents transfer
these conditions into subtropical regions such as Bermuda.
 Depth: corals feed on tiny algae, and they algae need light in order to photosynthesise
and grow. If there is not enough light, there can be no algae. This means that coral
develops only in relatively shallow water conditions where sunlight can penetrate the
water. In clear tropical waters coral can live as deep as 48m. Very few species are found
below this depth.
 Salinity: corals thrive in salty water where the salinity is between 30 and 40 parts per
thousand. They do not develop so successfully in areas where freshwater runoff enters the
sea at river mouths.
 Turbidity (water movement): some turbidity is necessary to distribute coral larvae, to
provide food and oxygenated water to the sedentary polyps, prevent smothering of the
polyps by sediment and to remove waste products. However, strong waves and currents
can inhibit or prevent coral reef formation. Under such conditions, sediment becomes
agitated reducing light and smothering coral and preventing feeding and respiration.
 Presence of beneficial algae and fish: Coral enjoys a symbiotic relationship with both
algae (zooxanthelae) and fish. This means that they benefit from their association with
one another. The algae live within the coral structures and up to 90% of the organic
materials produced through the process of photosynthesis is passed directly to the host
coral tissue. Fish are abundant in coral reefs, using them as sheltered breeding grounds.
Coral consume small fish using their tentacles to stun and kill the fish.

4. Types of Coral reef
Fringing reef – A fringing reef is a shallow-water feature found close to and running parallel to
the shore. These refs are associated with many of the islands in the Caribbean. A fringing reefs
reef forms from the gradual accumulation of coral in ideal environment. Between the reef and the
shore is a shallow lagoon that is rich in marine life.

5. Barrier reef- A barrier reef is a much larger feature than a fringing reef. It lies in deeper water,
much further out to sea. The Great Barrier Reef in Australia is the world’s best example of a
barrier reed. It runs for 2600 km off the east coast of Queensland and is made up of 3000
separate reefs and 900 islands. It has been designated a world heritage site. In the Caribbean
there is a barrier reef some 25km off the coast of Belize.
A coral atoll- A coral atoll is an isolated ring-shaped reef rising out of deep water. It is the
centre of an atoll is a lagoon. Coral atolls are largely concentrated in the Indian Ocean, for
example the Maldives.

6. Evolution of Coral Reefs according to Darwins theory of subsidence
Causes of Coral Reef Degradation
There are a number of potential threats to coral reefs
Pollution
Solid Waste Pollution-Sometimes solid wastes are carried to the sea by rivers, these solid waste
blocks the sunlight from reaching the reefs which are necessary for the corals growth and
development.
Sewage pollution- sewage pollution is one of the major causes of coral reef degradation. Sewage
is rich in nutrients that foster the growth of excess algae a process called eutrophication. The
algae take up most of oxygen that are essential to the corals growth. Other marine animals
include fishes are affected which need oxygen to survive. The algae also block the sunlight from
reaching the reefs.
Agricultural pollution- Some agricultural inputs (pesticides, herbicides, fertilizers) that are
widely used in the Caribbean end up reaching the sea by direct run-off. Run-off from farms
inland can enter the river system eventually reaching the sea. Organic fertilizers increase the

7. growth of nitrogen in seawater, causing an overgrowth of algae, which 'smothers' reefs by cutting
off their sunlight.
Tourism related activity
Tourism has contributed to major development in the Caribbean. However, tourism activities
have contributed to the degradation of many coral reefs in the Caribbean.
1. Clearing of land for construction of hotels, roads- the removal of trees have led to
erosion and subsequent sedimentation of sea water. Direct sediments from constructional
activities also results in sedimentation. Sedimentation blocks sunlight from reaching the
corals and also chokes the corals.
2. Collection of corals- Tourists collects corals for souvenir purposes. This practice is
causing a serious damage to coral reefs in the world.
3. Some boats anchor on reefs to allow scuba diving and viewing
4. Trampling by divers- During diving or snorkelling tourists trample the reef sometimes by
walking on it
Sedimentation
Sedimentation involves the discharge of sediment from the mouths of rivers into the sea.
Following heavy rainfalls river may discharge huge quantities of sediment into the sea causing
the water to become cloudy and reducing the penetration of sunlight. This can reduce
photosynthesis and cause corals to die.
Increased rates of sedimentation are often associated with land degradation, such as deforestation
or soil erosion. Whenever the bare soil is exposed it is vulnerable to being washed away.
Removal of coastal Mangroves
Coastal mangroves are well known as nurseries for many of the fish and other animals that later
populate the coral reefs. This direct interaction between coastal mangroves and coral reeds
means that the loss of mangroves inevitably affects the reefs. In addition, the mangroves filter
the run-off from the shore removing many pollutants and nutrients that would reach the reefs and
damage them. Once the mangroves are removed, the dangers from pollution and sedimentation
are greatly increased.

8. Destructive fishing practices
These include cyanide fishing, blast or dynamite fishing, bottom trawling, and muro-ami
(banging on the reef with sticks). Bottom-trawling is one of the greatest threats to cold-water
coral reefs. Dynamites that are used are so powerful that it can destroy the reefs. Cyanides that
remain in water can also kill coral polyps.
Sea Urchins
Sea urchins feed on algae and prevent the algae growing out of control and swamping the coral.
In Jamaica, disease wiped out of large numbers of sea urchins following a hurricane in 1983.
This has led to a lot of damage. Whilst the presence of sea urchins benefits coral reef
ecosystems, too many sea urchins can cause excessive burrowing. This demonstrates just how
fragile reefs are- they are ecosystems that can easily be thrown off-balance and suffer as a result.
Global Warming
Corals are very sensitive to temperature change. A rise of just 1-20
C can have a significant
impact on the health of the coral and cause them to turn white. This is called bleaching. In
August 2005, severe bleaching affected 50-95 per cent of coral colonies in the Lesser Antilles
and killed more than half.
Bleaching occurs when unicellular organisms called zooxanthellae, which normally live within
the corals, become stressed by rising temperatures and are expelled. It is the zooxanthellae that
gives the coral reef its colour. When they lose their colour, the corals become more susceptible to
death from starvation or disease.

9. Hurricanes
Hurricanes are common in the Caribbean during the summer months. Storm waves damage the
coral reefs and the heavy rains often wash large amounts of sediment into the seas, clouding the
normally clear waters. In 1980, Hurricane Allen reduced much of Jamaica’s reefs to rubble.
Plagues of starfish (Crown of Thorns Starfish)
Some starfish species can devastate coral reefs, killing up to 90% of reef-building corals. Plagues
of starfish may result from nutrients being washed into the sea from the land. These nutrients
may be linked to agricultural fertilizers.
Coral
Bleachi
ngA healthy
reef

10. Overfishing
Overfishing can lead to the loss of very important fish species. Parrot fish and sea urchins for
example are species that are in decline that protects coral reefs. Parrotfish are colourful and
voracious herbivores that spend up to 90% of their day eating algae off of coral reefs with their
beak-like teeth.
Crowns
of thorn
starfish

11. Mangroves
What are mangrove wetlands?
Mangrove wetlands or swamps are coastal ecosystems found in tropical and subtropical regions.
Mangroves are found extensively in the Caribbean as well as in many other regions around the
world. One of the largest mangrove swamps in the world is on Florida's southwest coast.
Mangrove swamps are characterised by halophytic (salt loving) trees, shrubs, and other plants
growing in brackish to saline tidal waters. These wetlands are often found in estuaries, where
fresh water meets salt water. They are famous for their dense maze of woody vegetation.
Caribbean mangrove wetland ecosystems
In the Caribbean there are three types of mangroves:
 Red mangroves: These are found closes to the sea and have their roots submerged at
high tide. They cope with high levels of salt by obtaining water from the ocean through a
process known as ‘reverse osmosis’. Inn this process, magnesium ions releases salt from
their roots enabling the plant to survive. The long arching aerial woody roots help anchor
the plant in the soft muddy sediment. It is through the roots that oxygen is obtained. The
roots also trap sediment helping to stabilize the coastal environment.

12. 
 Black mangroves: These are found further inland where conditions are saltier. They
cope by excreting the excess salt onto their leaves. Spongy structures called
pneumatophores protrude from the roots to stick out through the sediment rather like
periscopes. They can transfer oxygen direct to the roots.
 White mangroves: These are found further inland. Like the black mangroves they do not
have the extensive aerial root systems of the red mangroves. They also excrete salt onto
their leaves.

13. Mangroves swamps support a wide diversity of animals. They are constantly replenished with
nutrients that are transported by fresh water runoff from the land and flushed by the ebb and flow
of the tides. These ecosystems sustain billions of worms, protozoa, barnacles and oysters which
in turn feed fish and shrimp. These then support wading birds, pelicans, and the endangered
crocodile!
Why are mangrove wetlands important?
Mangrove wetlands are one the most important ecosystems in the world.
 Coastal protection: The dense tangle mangrove roots help to trap sediment. This created
an effective coastal defence against hurricanes, storm surges and tsunami. As sea level
rise due to global warming, mangroves will continue to grow and thrive, providing
lasting protection to coastal areas. If the mangroves are removed, the muddy sediment
quickly washes away leaving the coastline unprotected. In the tsunami of 2004, many
areas of Indonesia that were stull protected by their mangroves experienced relatively
little damage to human structures.
 Ecological (biodiversity) importance: Mangrove swamp provides valuable habitats for
many species of animal and fish which benefit from the calm, sheltered waters.
Mangroves are also very important to nearby coral reefs. They filter out silt and nutrients
that would otherwise go out to the reef, smothering the coral polyps and encouraging
algal growth. Mangrove swamps also serve as a breeding ground a nursery for young fish

14.  Socio-economic benefits: Mangrove swamps are popular tourist attractions despite the
biting insects! They are home to a wide variety of wading birds and crocodiles and
alligators. Mangroves provide many products and raw materials and they have significant
value for local communities.
Mangroves are mostly being destroyed to facilitate the construction of houses, hotels, roads and
industries.