Adaptations to life in the marine
environment
by Julia Hughes
Coral Reefs
Location of the Coral Reefs
Coral reefs can be found in 109 countries throughout the world (see figure 1 below) –
primarily located within the Tropic of Capricorn and the Tropic of Cancer, between 20o North
and 20o South of the equator – the Indo-Pacific, the Western Atlantic and the Red Sea. (Reef
Relief, May 2009)
The Indo-Pacific region is the largest and richest assemblage of coral reefs and stretches from
southeast Asia through Polynesia and Australia, heading eastwards across the Indian Ocean
and Africa. (Reef Relief, May 2009)
(Figure 1: Reef Relief, May 2009)
The Western Atlantic region (featured in blue in the figure above) is located from Florida to
Brazil and includes Bermuda, the Bahamas, the Caribbean, Belze and the Gulf of Mexico.
The Red Sea, located between Africa and Saudi Arabia as indicated in red in the figure
above, is the smallest region. (Reef Relief, May 2009)
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Characteristics of the Coral Reef
Coral reefs were first formed about 500 millions years ago and are the largest natural
structure in the world. The Great Barrier Reef alone measures more than 1,250 miles/2,013
km long and as much as 150 miles/242 km wide in some places and was formed about
500,000 ago with its present structure being around 8,000 years old. (Reef Ecology, May
2009)
They are the most diverse biological marine
ecosystem on our planet. Thousands of
seemingly alien life forms of a multitude of
bright colours and ever changing patterns
live within the coral reef. The coral reef
support over 4,000 species of fishes
throughout the tropics and is also the only
place that has examples of nearly every
group of organisms which represent a billion
years of evolution. (Reef Ecology, May
2009)
Over thousands of years, thin plates of
calcium carbonate are secreted by billions of
soft bodied animals called coral polyps that
consist of a tube and an oral disc or mouth
surrounded by tentacles that help catch
passing plankton. This secretion takes years
to grow just one inch of coral that can grow
(Figure 2: Reef Relief)
up to a foot in length. By living on top of
the limestone remains of former colonies, the polyps help create massive reefs, the formation
of which can be seen from outer space. (Reef Relief, May 2009)
Coral generally gets it colour from the algae zooxanthellae. This algae photosynthesises
carbon dioxide that gives off oxygen which is used by the coral polyps. (Reef Ecology, May
2009)
Corals live on the ocean bottom (see
figure 2 & 3 above and left). There are
two kinds - hard corals which have rigid
exoskeletons, or corallites, that protect
their soft delicate bodies such as staghorn,
brain, star, elkhorn and pillar corals and
soft corals or gorgonians that lack an
exoskeleton and sway with the currents,
such as sea whips, sea fans, and sea rods.
(Figure 3: Reef Relief)
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The delicate balance of the coral reef relies entirely on the interaction of these hard and soft
corals with sea life such as anemones, sponges, rays, lobsters, snails, crabs, turtles and
dolphins (see figure 4 below). (Reef Relief, May 2009)
(Figure 4: Reef Ecology)
Cold Water Coral Reefs
Cold water coral reefs are found globally in temperatures of between 4 – 13oC and do not
need light in order to function. They get their nutrients from passing currents, trapping
plankton and organic particles in their tentacles. The coverage of cold water coral reefs could
possibly equal or exceed that of warm water reefs (see figure 5 below for the areas marked in
blue). Norwegian waters alone cover c.2,000km2. The salinity range is between 32 and 38.8
o
/oo with depths of beyond 1,000m. It contains no symbiotic algae and has a growth rate of 4
– 25mm per year. The age of the living reef is up to 8,000 years. (UNEP, May 2009)
(Figure 5: TÖPKE, 2008)
Warm Water Coral Reefs
Temperatures are a lot higher than cold water at 20 – 29oC. They are found in sub-tropical
and tropical seas between 30oN and 30oS, covering 284,300km2 with Indonesia having the
highest coverage at 51,020km2 and the Great Barrier Reef with more than 30,000km2 (see
figure 5 above marked in red). The salinity range is 33 to 36 o/oo and has depths of 0 to 100m.
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Unlike the cold water coral reefs, these do contain symbiotic algae and nutrition wise, has
suspended organic matter. The reefs have a growth rate of up to 150mm per year are between
6,000 and 9,000 years old and have about 800 reef building coral species. (UNEP, May
2009)
Changing Environment of the Coral Reef
(Figure 6: Reef Ecology, 2009)
The Coral Reef is an extremely fragile environment. 25% of the coral reefs have been
damaged by human activity (see figure 6 above) that is leading to the potential extinction of
countless forms of unique tropical marine life. A further 30% are under serious threat from
global warming, destructive fishing practices, overfishing, commercial trading for the
aquarium trade, tourist souvenirs, curios and shell trade, jewellery and even certain
pharmaceuticals. (Reef Ecology, May 2009)
Cold water coral reefs are extremely fragile and vulnerable and the main threats come from
human activities in the form of bottom fisheries, trawling, oil and gas exploration and
production, placement of pipelines and cables as well as coral bleaching, pollution, research
activities and dumping. (UNEP, May 2009)
The main threat to the warm water coral reefs are human activities such overfishing and
fishing using dynamite and cyanide, pollution and sedimentation from land-based sources and
coastal development, tourism and anchoring. (UNEP, May 2009)
The pet industry target live food, rare fish and large polyped corals for the aquarium trade.
The removal of these species drastically alters the dynamics of this ecosystem and reduces
the essential reef habitat. With the loss of these fishes that feed on the algae, the algae will
continue to expand which in turn will smother and kill the coral. (Westmacott, 2000)
Under certain conditions and limited human exploitation, reefs may be able to restore their
once thriving community. To achieve this, the coral needs a solid submerged surface in
pollutant free, good quality water, free from algae where coral larvae can settle and grow.
This surface could potentially be the coral that has died through bleaching as the rock they
leave behind is an ideal substrate for new growth. (Westmacott, 2000)
Coral reef and mangroves working together
Coral reefs are directly affected by the health of mangroves swamps and sea grasses. The
roots help filter off silt, chemicals and other pollutants and produce nutrients-rich waters and
sediment by trapping decaying plant and animal matter. The mangroves also provides safety
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from predators and the hazards of the open ocean making it an ideal breeding and nursing
ground for plankton, invertebrates and other fish that migrate to and populate the reef before
settling on local reefs as adults. (Reef Ecology, May 2009)
Mangroves and Sea Grasses
(Figure 7: St John Beach, May 2009)
Unlike the coral reefs that are over 200 million years old, the Mangroves only date back 2000
years. There are about 69 species of Mangrove that exist worldwide, compared to the
millions of species that make up a coral reef. (WRAS, May 2009)
Mangroves (see figure 7 above) are trees and shrubs that live in a highly hostile environment
such as high salinity waterlogged soil and strong tidal waves and winds. They have adapted
to become salt-tolerant, growing to a height of 30 feet over a lifetime of between 20 and 30
years, with salt excreting glands in the leaves. (WRAS, May 2009)
They are located wherever there is a combination of marine and freshwater, much like waters
around the coral reefs. They replace saltmarshes in tropical and subtropical regions and are
most commonly found around the Florida Keys. They exist mainly in lagoons, extend
inwards up rivers and streams and near estuaries along tropical mudflats (see figure 8 below)
and like the coral reefs, they too are subjected to changes in water salinity. Because of their
ability to live in this type of environment, they have little competition from other plants.
(WRAS, May 2009)
(Figure 8: NESSThai, 2009)
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The mudflats are rich in nutrients, brought in by the tides, making it a very important feeding
ground for the molluscs and marine invertebrate that live there, emerging on high tide to feed.
(NESSThai, 2009)
During high tides they have high salinity whilst at low tide they are subjected to fresh water
from heavy rains. Water temperatures change with the ebb and flow of the tide together with
the changes in current from rivers. This also alters the supply of nutrients and oxygen to the
mangroves root system making them unique in the ability to survive in such a changeable
environment. (WRAS, May 2009)
They have four main survival techniques in order to survive the high salinity. Firstly they
filter out most of the salt via their roots, they absorb and retain a high quantity of water in
order to dilute the salt in their tissues, the leaves of the mangroves excrete salt through their
glands and finally they store salt in old bark and leaves that then take that salt with them
when they drop. (Soonabai, 2009)
(Figure 9: St John Beach)
Their seeds (see figure 9 left) fall from the trees and float on the
water until the root end absorbs enough water to weigh it down
and seed itself in the mud. They are very well adapted to
pollinate in the mud flats they grow in and their pneumatophores
or root extensions rise out of the mud in order to absorb oxygen.
Sea Grasses as well as the mangrove roots help to keep the
waters calm while the seedling root settles itself in the mud.
(WRAS, May 2009)
One of the ecological benefits of mangroves is that they help control erosion from tides and
storms. Another is to maintain healthy corals that require clean, clears waters. They do this
by providing a buffer to the corals by trapping sediment before the coastal run-off reaches the
open ocean and the coral reefs, preventing them being smothered by land-based soils.
(WRAS, May 2009)
Like coral reefs Mangroves provide an efficient network for feeding and breeding. Oysters
attach themselves to the roots of the mangroves at high tide. Fiddler crabs can be found
burrowing in the mud around the roots and the algae which cover the roots are fed on by
small baitfishes which are in turn fed on by larger gamefish such as trout, snook, tarpon, red
drum and red fish.
Another important player in the food web are sea grasses, flowering marine plants that
provide food and habitat for manatees, turtles sea urchins, sea cucumbers and filter-feeding
organisms and like the coral reef provides a safe nursery for lobster, pink shrimp and
snappers, to name a few.
Changing Environment of the Mangroves
There has been a decline in mangroves from 18.8 million ha in 1980 to 15.2 million ha in
2005 which is approximately 20% loss. (Ewing, 2008) Mangroves are often removed to
build mariculture farms and cut down to provide fuel and charcoal for lime production and
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household cooking. The wood of the mangrove tree is also used for house and other small
building projects within the local community. Coastal coral reefs are increasingly being
subjected to siltation and a decrease in water visibility as the mangroves are being cleared
through these types of activities. (WRAS, May 2009)
Estuaries & Saltmarshes
(Figure 10: NCCOS, May 2009)
Younger than coral reefs but older than mangroves, estuaries (see figure 10 above) can be
dated back to the ice age about 10,000 years ago. (estuaries.gov, Nov 08)
Estuaries are very similar to mangroves in that they too are a place where nutrient rich
freshwater rivers and streams, because of its lower density, flows above the salt water and
mix together becoming brackish as they flow into the ocean (see figure 11 below) and
whereas the mangroves are themselves the living entity that live within lagoons, etc, estuaries
semi-enclosed bays, lagoons, harbours and inlets that provide the area for the mangroves to
exist and like the mangroves, they also help protect water quality by filtering out pollution
and dirt. Plankton blooms occur on the seaward side. (EPA, 2009)
Figure 11 (Butler, 1993)
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River and tidal currents are very important in the mixing of the lower and upper layers of
water. This estuarine circulation, is a crucial factor and determins the high productivity of
estuaries. In the Northern hemisphere, sea-water flows clockwise when it enters the estuary
and the freshwater that flows down-river also moves clockwise, thus flowing to the other
side. This means that often one side of the estuary is saltier than the other. (DFO, 2007)
The salinity is about 0.5 ppt upstream in the estuary and up to 30 ppt downstream. The sea
on average is about 35 ppt. The zone where freshwater changes to saltwater is called a
pycnodine. (DFO, 2007)
An estuary is constantly changing as it accumulates sediments. As the water becomes
shallower and the estuary widens, the water flow decreases and deposits sediment on the
banks. As a consequence, mudflats may rise above the level of the highest tide through soil
accumulation and river flooding. (Waller, 1996)
Where marsh grasses take over mudflats, these areas will often become permanent
saltmarshes. In subtropical and tropical areas mangroves replace these saltmarshes as they
occupy a similar habitat and in some areas of the world, both mangroves and saltmarshes can
be found in the same region. (Waller, 1996)
In the more northerly regions, estuaries can become covered in ice for up to four months of
the year. While this helps to maintain water temperature, once this ice melts, it creates a
sudden increase in freshwater, contributing significantly to the variable salinity. (DFO, 2007)
As mentioned earlier that while mangroves provide protection from soil erosion, so do
estuaries. They act like huge sponges that buffer and protect upland areas from storm
damage and crashing waves by soaking up the excess flood waters and tidal surges that are
driven into shore by strong winds. (estuaries.gov, Nov 08)
The incoming tides that happens approximately every 12 hours, replenish the oxygen supply.
Without this the estuarine invertebrates and fish that live there would find it very difficult to
breathe, and they would eventually suffocate. The outgoing tides help carry away their
wastes that in turn gets put to use in the nearby ocean and elsewhere within the estuary.
(Butler, 1993)
The rise and fall of the tides - turbulence causes an upwelling of water that brings with it the
nutrients from the bottom of the estuary to the surface. (DFO, 2007)
Formation of an estuary
There are four types of estuary formations.
1)
Coastal Plain (figure 12 below) – river valleys were formed from the melting of
ancient glaciers, the sea level then rose and filled in these existing river valleys creating an
estuary – examples being Chesapeake Bay in Maryland and Narragansett Bay in Rhode
Island.
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(Figure 12: ONR, accessed 9 May 2009)
2)
Tectonic (see figure 13 below) – these are found mainly along fault lines such as San
Francisco Bay and are caused either by large pieces of land that sink into the earth following
an earthquake producing a basin below sea level that fills with seawater or where the land
surfaces fold together.
(Figure 13: ONR, accessed 9 May 2009)
3)
Bar-built (see figure 14 below) – these are formed when a sandbar, barrier or barrier
island, built up by ocean currents and waves in coastal areas, protect a shallow lagoon or bay
from the ocean – mainly off the Atlantic coastline of North Carolina and Massachusetts.
(Figure 14: ONR, accessed 9 May 2009)
4)
Fjords (see figure 15 below) – typically U-shaped valleys with steep sides that have
been forged by glaciers that are then filled with sea water when the glacier melts - mainly
found in Northern Europe, Canada and Alaska.
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(Figure 15: ONR, accessed 9 May 2009)
Habitat of the estuary
Estuaries have many different types of habitat, some being: coral reefs
 mangroves
 coastal marshes
 oyster reefs
 deepwater swamps and riverine forests
 kelp and other macroalgae
 rocky shores and bottoms
 soft shores and bottoms
 submerged aquatic vegetation
Like the coral reefs and mangroves, the sheltered waters of estuaries are an ideal habitat for
plants and animals that can sustain themselves in both fresh and salty water for example
horseshoe crabs and manatees as well as certain fish and shell fish that at some point in their
lives pass by, such as scallops, shrimp, and salmon. Estuaries also similarly provide a safe
haven and protective nursery for small fish, shellfish, migrating birds, and coastal shore
animals. (Butler, 1993)
The plants commonly found in estuaries, photosynthesis higher than intensive agriculture,
making them one of the most biologically productive ecosystems on Earth. Most of this
production is carried out by marsh plants and bottom-dwelling algae that grow in the
mudflats that are left uncovered at low tide and marshes of the estuaries and when they die
and decay, they get covered by protozoa and other microorganisms which provide food for
the small invertebrates, worms, snails, clams, oysters and shrimp, who are then eaten by fish
and other amphibians living there. (Butler, 1993)
Fauna of the estuaries
Similar to the fauna of the mangroves, there are very few species that are able to survive
totally in the changeable conditions of salinity, temperature, and water level of estuaries.
Most species migrate into estuaries during specific times of the year; spawning whitefish and
migrating sandpipers, for example. (Butler, 1993)
The majority of organisms, such as crustaceans, that are able to survive in this type of
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environment, living on or in the sediments, excrete the salt as rapidly as it's absorbed. (DFO,
2007)
Some species of marine animal groups have adapted physiologically to changing salinities
and in some estuarine areas the oyster, crab, shrimp and ragworm can be found in abundance.
Invertebrates, such as mussels, amphipods, clams and snails, thrive in the mudflats, using the
mud for protection against the elements and predators by burrowing down into the mud.
(Butler, 1993)
Challenges facing estuaries
Again, like the mangroves, it is mainly human activities that are upsetting the natural balance
and endangering the estuaries by living and building on the surrounding lands creating
greater pollution of the waters that harm the animals living there. (EPA, 2009)
Invasive species that are often introduced accidentally by humans find themselves competing
for shelter and food with native plants and animals and by doing so weaken the ecosystem.
(estuaries.gov, Jul 08)
Fauna of the Coral Reefs
Angelfishes
Classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Perciformes
Family: Pomacanthidae
Angelfishes are the classic coral reef fish with their bright colours and oval shaped bodies.
They belong to the family Pomacanthidae. They have deep disc like structure to their bodies
with a continuous dorsal fin, a prominent spine that extends over the lower gill cover from
their rear cheek and a tail that while may differ in shape according to each variety is always
oriented vertically. They are herbivores and mainly feed on aglae and sponges. (EPA, 2009)
There are several types of angelfish, some of which are listed below which have been taken
from Biological Indicators of Watershed Health website:Atlantic/Caribbean
Blue angelfish (juvenile) Holocanthus bermudensis
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Cherubfish Centropyge argi
French angelfish (juvenile) Pomacanthus paru
Queen angelfish Holocanthus ciliaris
Rock beauty Holocanthus tricolour
Indio-Pacific
Blue-girdled angelfish Pomacanthus navarchus
King Angelfish Holacanthus passer
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Cortez angelfish Pomacanthus zonipectus
Bluering angelfish Pomacanthus annularis
Lemonpeel angelfish Centropyge flavissimus
Scribbled angelfish Chaetodontoplus duboulay
The use of a variety of coloration distinguishes adults from juveniles. The colour "phases"
could also be an indication of sex, sexual maturity or even social rank. Some exhibit colour
changes as a defence mechanism or swell when alarmed in order to thwart the attack of a
would-be predator. Rapid colour changes also occur when preparing to take cover for the
night. Certain markings, stripes for example, act as a warning to predators that they may be
unsavoury to eat. (Library Think Quest)
Fishes that live in shallow waters and are active during the daytime can see a wide range of
colours and patterns, sometimes including ultraviolet which enables them to recognise their
own kind from a distance within the densely populated but clear water of the coral reef.
(Pitkin, 2009)
Many fishes are very territorial and will fiercely protect their feeding, breeding and nesting
site against any unwelcome intruders or competitors by spreading their fins and gill covers,
make excited movements and warning sounds. (Pitkin, 2009)
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Once an angelfish has hatched from its egg, the tiny transparent larval fishes spend between
10 to 100 days making its way to the open water and away from the reef, feeding on the
minute plankton around them. They travel these distances, facing the dangers of the open
ocean, in order to get away from the reefs predators and set up new territories elsewhere as
juvenile fishes. They arrive at their destination under the cover of darkness and until they
learn how to fit in. Until such time they remain extremely vulnerable to predators. Juvenile
angelfishes have a different colour pattern from the one they will acquire in maturity (see
figure 16 below) so that they are more readily accepted and blend in to their new
environment. (Pitkin, 2009)
A juvenile French angelfish Pomacanthus paru (left) and an
adult French angelfish (right). The colour patterns of juveniles
are spectacularly different to those of the adults. The young
fish's bold stripes may advertise the fact that they sometimes
act as cleaner fish to potential clients. (Left: Linda Pitkin,
Right: Brain Pitkin)
(Figure 16: Pitkin, 2009)
Jellyfish
Classification
Kingdom: Animalia
Phylum: Cnidaria
Class: Scyphozoa
Jellyfish are marine invertebrates that have a jelly like texture with a bell-shaped head and are
made up of ninety-five per cent water. They obtain their oxygen by diffusion so do not have
a respiratory system. Nor do they have a brain or central nervous system, instead support a
loose network of nerves located in the epidermis. They have stinging tentacles varying from
a severe to mild and temporary prickling or burning sensation. (Reef Ed, 2009)
They belong to the Scyphozoan class, and in turn the phylum Cnidaria that shares the same
type of skin cells which hold nematocycts or stinging cells which are basically used for
defense and food collection. There are two basic forms of cnidarians: the polyp form, such as
corals, and the medusa form of the jellyfish (see figure 17 below) and are made up of
Jellyfish are made up of a layer of epidermis, gastrodermis and a thick jellylike layer that
separates the epidermis from the gastrodermis called mesoglea. (Reef Ed, 2009)
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(Figure 17: ReefEd, 2009)
They drift in the current of the ocean, coming to rest in sheltered bays and estuaries. Their
hydrostatic skeleton swim by the rhythmic pulsing of their muscles that propels their bodies
in an up and down motion through the water. (Reef Ed, 2009)
Jellyfish feed on zooxantellae by trapping them in their tissues having attaching itself upside
down to sandy and muddy bottoms of their environment. Most though catch their food –
crustaceans, fish and minute planktonic organisms, in the tentacles either as it drifts by or by
wafting up their food by the movement of their bodies to within easy reach. They then move
the food up to their mouth in the centre of the bell-shaped body. (Reef Ed, 2009)
Jellyfish are dioecious – they are either male or female. To breed, the male and female both
release sperm and eggs into the water where the eggs are fertilized and grow into new
organisms. Jellyfish have a two-part life-cycle (see figure 18 below) – firstly in early forms
of life there is the polyp stage which is formed just after the egg and sperm combine. These
are very small and non free-swimming. They then go into their dominant stage by shedding
parts of their bodies which forms their familiar free-swimming bell-shaped animal - often
accompanied by small fish hiding amongst their tentacles for protection. (ReefEd, 2009)
(Figure 18: Wikipedia, 2009)
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Fauna of the Mangroves
Fiddler crab
Classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Decapoda
Infraorder: Brachyura
Family: Ocypodidae
Genus: Uca
(Figure 19:
Soonabai, 2009)
There are 62 known species of fiddler crabs (also known as the Calling Crab) in the world
and they are one of the most commonly seen animals in the mangrove, measuring in at
slightly over 2 inches wide. The males armour themselves with one fiddle shaped large
pincer or claw (see figure 19 above) which is used as a courtship display tool and one smaller
pincer which is used for feeding. If they lose the larger claw, the smaller one will become
larger while the lost claw regenerates as the smaller one. The female fiddler crab has two
equal regular sized pincers. They reabsorb their shells rather than shedding them as they
grow. (Soonabai, 2009)
Their eyes are mounted on long stalk which gives them a good panoramic view of the world
helping them detect predators from afar and spot potential mates and rivals. These crabs are
highly sensitive to movement so when a crab feels threatened it scuttles back to its burrow,
folding down its eyestalks into grooves along their body. (Tan, 2001)
While fiddler crabs are semiterrestrial, they prefer to bury themselves into the sand and mud
beaches located within the brackish intertidal zone, only coming out at low tide in order to
feed and court. (Soonabai, 2009)
Fiddler crabs are non-swimmers, preferring to breathe air so at high tide, they plug the
entrance of their burrows with balls of sand, trapping some air inside. However, they absorb
water from the wet sand through hairs on their legs as they still need water to keep their gill
chambers wet as well as to process their food. (Tan, 2001)
Fiddler crabs often change colour – the males do this during the mating season. Sometimes,
they may just change their appearance from night to day, making it difficult to identify one
species of Fiddler Crab from another. (Tan, 2001)
Fiddler crabs scoop up sand with the smaller of their pincer claws (in the male) into their
bristle-like mouthparts that they use to filter out the edible thin coating of detritus on the sand
grains, spitting out the leftovers as balls of sand that then line the entrance to their burrows.
This is a sure sign that a burrow is occupied by a fiddler crab. (Tan, 2001)
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They court by waving around their enlarge claw, tapping it on the ground to attract females
and fighting other males in order to impress. After a male has succeeded in persuading a
female to mate with him, they retire into his burrow. The female carries her eggs underneath
her body, remaining in the burrow for up to two weeks until she ventures out to release them
into the receding tide where the free-swimming larvae drift with the plankton for another two
weeks until they change into yet another form before settling down and developing into
Fiddler crabs. Their total life cycle lasts between 1 and 2 years. (Tan, 2001)
Fiddler crabs are prey to fish, large crabs, some mammals and birds. In the Indo-Pacific
region of the mangroves, the mangrove snake will hunt the crab by going into its burrow.
(Soonabai, 2009)
Mudskippers
Classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Perciformes
Family: Gobiidae
Subfamily: Oxudercinae
(Figure 20: Soonabai, 2009)
Mud skippers (see figure 20 above) are completely amphibious and live on the mud of the
mangroves shores. It has uniquely adapted to the intertidal environment by being able to hop
along the water’s edge alternating between exposure to air and submersion. They respire
under water and swim like a regular fish, gulping air when out of water while they skip along
the ground. (Soonabai, 2009)
They survive out of the water by calling on their reserve chamber of oxygen stored in their
gills. This is done by rotating their eyes, applying pressure to that cavity which reoxygenates
the water. This oxygen supply is depleted after only a few minutes and must be replenished
by burrowing into a pool of water. They can also absorb air through their skin so long as it
remain moist. (Soonabai, 2009)
They have a fused pelvic rear fin that they use as suckers when climbing trees, using their
pectoral fins as arms which also have little “elbows”. They can also use their muscular body
to flip themselves up to 60cm into the air. (Soonabai, 2009)
They have very noticeable highly mobile googly eyes that are perched on stalks on top of
their heads. The position of these eyes not only give them an increased field of view but
enables them to see both under and over the water at high tide by acting as periscopes giving
them a good 360o view. The eyes are kept moist by being retracted so that they can dip them
into the water that collects at the bottom of their eye socket. (Tan, 2001)
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They thermoregulate their body temperature by burrowing deeply into the soft sediment of
the mangrove mud. They do this also to avoid marine predators during high tide and to
breed. While in these condition of low oxygen concentrate they ensure they have a bubble of
air so that they can still breathe. (Soonabai, 2009)
They have an ability to change their colour to match their background, keeping them wellcamouflaged against any predators. (Soonabai, 2009)
When breeding, mudskippers are very territorial. They build deep nests in the mud where the
eggs are laid on the roof of the chamber of the burrow. The nesting area is aerated by the fish
taking large mouthfuls of oxygen down into the burrow. The eggs hatch into larvae and
remain in the nest until they start to form the basic shape of the mudskipper and then never
venture too far from the pool of water the nest has been made until they are big enough to
leave. (Tan, 2001)
Fauna of the Estuaries
Mussels
Classification
Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
(Figure 21: DFO, 2007)
Mussels that can tolerate salinities below 30o/oo penetrate far into the estuarine. (Waller,
1996)
Mussel or filibranchiates (which means that the filaments of their gills have interlocking
bunches of hairlike cilia) are closely related to oysters and scallops. (Encarta, 2009)
Ribbed Mussels (see figure 21 above) prefer brackish waters so are found mainly at low tide
in salt marshes. (DFO, 2007)
The wild mussels that live in estuaries have elevated levels of nutrients from land runoff,
which causes an increase in phytoplankton (microscopic plants) - the main food for these
filter-feeding mussels, however, mussels cannot tolerate freshwater for extended periods of
time. (ACWA, 2009)
Mussels filter our edible particles by drawing water into the shell. Any waste water gets
pumped out through a different opening. These opening are different in appearance, one
being fringed to restrict large fragments being drawn in, the other an oval. The mussel opens
slightly to feed but if it senses danger by detecting any unusual water movement, it closes up
very quickly. (Lilley, 2009)
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With the Blue Mussel, when the level of salinity becomes too low or the tide is out, it closes
its valves. On the reverse side, if the salinity rises too much it also closes up making itself
temporarily watertight. (DFO, 2007)
Life begins (see figure 22 below) when the male mussel expels its sperm that fertilizes the
females eggs when she siphoned them into her gills. She then broods for anything from two
to ten months as the eggs develop into tiny, strange looking larvae called glochidia. These
larvae can be from 0.05 to 0.50mm in diameter. When the larvae become mature they are
released into the water. A few of which out of the hundreds that are released, will find their
way and attach themselves to the gill, fins or body of its host fish. The glochidia form a cyst
as it becomes overgrown or encased by fish tissues. (Menunkatuck, 2004)
(Figure 22: Menunkatuck, 2004)
The juvenile mussel will then break out of its parasitic cyst stage after about one to ten
weeks, falling to the bottom where it burrows itself in. This whole cycle is the reason why
fish play a critical role in a mussel's survival. The fish host provides food and shelter for the
developing larvae and it provides its means of dispersal, making sure that the mussel larvae
ends up where it needs to be - upstream. (Menunkatuck, 2004)
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Adaptations to life in the marine environment
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The shells of the freshwater mussels that are found in estuaries are used in button making.
The pearls that are readily secreted are of low quality and are therefore used in making
inexpensive jewellery. Mussels are severely affected by chemical pollutants. (Encarta, 2009)
Flounder
Classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Pleuronectiformes
Family: Pleuronectidae
Genus: Pseudopleuronectes
Species: P. americanus
(Figure 23: Orange Beech Fishing)
The larval or young stages of the Winter Flounder start off as a typical looking fish. As it
grows, it undergoes a metamorphosis by settling on its side on the bottom, gradually moving
it’s right eye round to the left side (or the other way around). The mouth becomes askew (see
figure 24 below).
(Figure 24)
The markings of the Flounder also follows the same migration like it was tanned on the same
side. It is generally a dull brown on the top side, sometimes grey/green mottled effect or
olive when feeding over a bed of mussels with a white belly, occasionally displaying brown
or grey blotches. (DFO, 2007)
The flounder has a group of roughened scales or “prickles” above the pectoral fin that
protrude from the skin to the upper rear of the gill slit and along the anal fin. (Thrussell,
2006)
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Preferring the estuarine environment the Flounder can tolerant waters with low salinity and
temperature, and therefore is able to live as both a young and adult fish in estuaries and can
be found many miles past the upper estuary reaching far into pure freshwater rivers. Some
fish however choose a beach existence while keeping close to the river outflow. They are
also quite happy in only a few inches of water of the salt marsh creeks even in daylight by
burying themselves in sand. (Thrussell, 2006)
When in danger a young Flounder will bury themselves in the mud at low tide where they are
almost completely camouflaged.
To feed, they rise with the incoming tide flow into tidal creeks where food is plentiful.
(DFO, 2007)
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Book References
Waller Geoffrey, 1996, Sealife: A Complete Guide to the Marine Environment, Russel
Friedman Books CC, South Africa
Internet References
ACWA, Aquaculture Council of Western Australia,
http://www.aquaculturecouncilwa.com/species/mussels/habitat, [Accessed 10th May 2009]
Butler, R W et al, 1993, Hinterland Who’s Who,
http://www.hww.ca/hww2.asp?pid=0&id=226&cid=2, Her Majesty the Queen in Right of
Canada, represented by the Minister of the Environment
DFO, Department of Fisheries and Oceans, 2007, http://www.glf.dfo-mpo.gc.ca/os/byseaenmer/estuaries-estuaires-e.php#formation, Canada
Encarta, 2009, Mussel, Microsoft Encarta, Online Encyclopedia 2009,
http://encarta.msn.com, Microsoft Corporation
EPA – Environmental Protection Agency, April 2009, Biological Indicators of Watershed
Health, http://www.epa.gov/bioindicators/html/coral_reef_fish_angelfishes.html, Coral Reef
Fishes – Angelfishes, Chicago
EPA - United States Environmental Protection Agency, 2009, http://www.epa.gov, Exploring
Estuaries
estuarties.gov, July 2008, Life in an Estuary, http://www.estuaries.gov/, National Oceanic and
Atmospheric Administration (NOAA) [Accessed 9th May 2009]
Ewing Bob, 1 Feb 2008, Mangrove Loss Causes Environmental, Economic Concerns,
http://digitaljournal.com/article/249680/Mangrove_Loss_Causes_Environmental_Economic
_Concerns
Library Think Quest, http://library.thinkquest.org/27115/pages/coral/coral.html, Coral Reefs
[Accessed 9th May 2009]
Lilley Jane, British Marine Life Study Society, http://www.glaucus.org.uk/Mussels.htm,
[Accessed 11th May 2009]
HNC/D Animal Studies - Marine Studies
Adaptations to life in the marine environment
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NESSThai, Network for Environmentally- & Socially-Sustainable Tourism (Thailand),
Mangroves and Mudflats, http://www.geocities.com/~nesst/mangrove.htm, [Accessed 10th
May 2009]
ONR: Office of Naval Research, http://www.onr.navy.mil/focus/ocean/default.htm,
[Accessed 9th May 2009]
Pitkin, Linda, The Natural History Museum, 2009, http://www.nhm.ac.uk/natureonline/life/reptiles-amphibians-fish/reef-life/session3/, Life on the Reef
Reef Ecology, http://www.geocities.com/diver_drew/reefecology.html [Accessed 3rd May
2009]
Reef Ed,
http://www.reefed.edu.au/home/explorer/animals/marine_invertebrates/corals_and_jellyfish,
Corals and Jellyfish, [Accessed 9th May 2009]
Reef Relief, Protect Living Coral, http://www.reefrelief.org/coral_reef_body.shtml
[Accessed 3rd May 2009]
Soonabai Pirojsha Godrej Marine Ecology Centre, Mangroves,
http://www.mangroves.godrej.com/index.htm, [Accessed 10th May 2009]
St Johns Beach Guide, Mangroves, http://www.stjohnbeachguide.com/Mangroves.htm,
[Accessed 3rd May 2009]
Tan, Ria, April 2001, Mangrove and Wetland Wildlife at Sungei Buloh Wetland Reserve,
http://www.naturia.per.sg/buloh/
Thrussell Mike, 2006, World Sea Fishing, Flounder Profile,
http://www.worldseafishing.com/fishspecies/flounder.html
TÖPKE, Katrien, 18 December 2008, Marine Biodiversity Wiki,
http://www.marbef.org/wiki/Coral_reefs
UNEP, Cold Water Coral Reefs, http://www.unep.org/cold_water_reefs/comparison.htm
[Accessed 3rd May 2009]
Westmacott S, Teleki K, Wells S & West J M, 2000, The World Conservation Union,
Management of Bleached and Severely Damaged Coral Reefs, IUCN - Gland, Switzerland
and Cambridge http://cmsdata.iucn.org/downloads/coralen.pdf
WRAS Web Reef Advisory System,
http://datamanagement.reefcheck.org/factsheet.asp?surveyID=&issuecode=iMO&display=i
ntroduction, [Accessed 3rd May 2009]
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