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Coral reefs are wave-
resistant structures notable
for their great species
richness,
ecological complexity and
remarkable beauty
They are unique in being
formed entirely by the
biological activity
Often called rain forests of the sea, due to
their richest biodiversity. They occupy less
than 0.1% of the world’s ocean surface, but
provide home for 25% of marine species
ORIGIN OF REEFS
Subsidence theory – (Darwin-Dana)
Solution theory – (Semper-Murray)
Submerged bank theory
Glacial epoch theory - Daly
It involves understanding biotic
and abiotic factors influencing the
distribution and abundance of
living things of coral community
DISTRIBUTION
Corals occur throughout the oceans, but
colonial reef-building (hermatypic) corals are
confined to the tropics and sub-tropics where
calcification rates are greatly enhanced
Reefs grow best in warm, marine, shallow,
clear, sunny and agitated waters
LIMITING FACTORS
Latitude
Temperature
Light
Salinity
Turbidity & Sedimentation
Wave action
Aerial exposure
Coral reefs, just like any other ecosystem on our
planet, rely on a variety of biotic and abiotic
factors to keep them healthy and functional.
Without stable temperature, pH, light intensity,
water flow, salinity, and chemical composition of
sea water, coral reefs could not exist, but
without a stable trophic cascade, coral reefs
could not survive.
Biotic Factors
• Competitors
• Disease
• Predators
• Food availability
• Habitat availability
• Symbiotic relationships
Abiotic Factors
• pH
• Temperature
• Weather conditions
• Water availability
• Chemical composition of environment
• nitrates, phosphates, ammonia, O2, pollution
TYPES OF CORALS
Hard corals, also known as scleractinian and
stony coral, produce a rigid skeleton made of
calcium carbonate (CaCO3) in crystal form
called aragonite. Anatomic structures such
as septa, tentacles, and mesenteries are
found in sets of six, so hard corals are also
often termed hexa corals.
One of the characteristic feature of hermatypiccorals is the presence of unicellular algae(Symbiodinium microadriaticum) with in thegastrodermal tissue.
By their influence on coral growth andcalcification rates these symbiotic zooxanthellaeplay a fundamental role in the reef-buildingprocess
SOFT CORALS
Soft coral, also known as Alcyonacea and ahermatypic coral,
do not produce a rigid calcium carbonate skeleton and do not
form reefs, though they may be present in a reef ecosystem.
Anatomic structures such as tentacles and mesenteries are
found in sets of eight, so soft corals are often called
octocorals.
DIVERSITY OF CORAL REEFS
Reefs are home to a large variety of organisms, including
fish, seabirds, sponges, cnidarians (which includes some types of
corals and jellyfish), worms, crustaceans (including shrimp, cleaner
shrimp, spinylobsters and crabs), mollusks (including
cephalopods), echinoderms (including starfish, sea
urchins and sea cucumbers), sea squirts, sea turtles and sea
snakes.
Aside from humans, mammals are rare on coral reefs, with
visiting cetaceans such as dolphins being the main exception.
A few of these varied species fed directly on corals, while others
graze on algae on the reef.
Reef biomass is positively related to species diversity.
NUTRITION
Corals have developed several unique ways
of feeding; they receive nutrients from
symbiotic algae, capture particles such as
plankton, and take up dissolved substances
from the water.
In order to fully appreciate the importance of a
balanced ecosystem such as a coral reef, we
must first understand its trophic structure; the
organisms that make up each trophic level, and
the functions of each level in the maintenance
of a healthy reef.
TROPHIC STRUCTURE
Coral reefs are complex ecosystems that require a balanced
trophic structure to function properly and efficiently.
Imbalances can occur in this intricate trophic cascade
from the top down or the bottom up. For an example of
bottom-up effects, nutrient-rich agricultural run-off can
cause a massive increase in primary productivity (e.g.
algal blooms), the effects of which often cannot be
buffered by consumers fast enough to prevent a coral
reef ecosystem from collapsing.
There are three categories of organisms in every ecosystem: producers, consumers, and decomposers.
Primary consumers are herbivorous, whereas secondaryconsumers prey on herbivores and tertiary consumers eatother carnivores.
Decomposers are responsible for breaking down deadand decaying plant and animal matter into componentsthat are once again usable for growth by producers.
None of these three categories of organisms can existwithout the others in order to complete the cycle ofproduction, consumption, and decomposition.
PRIMARY PRODUCERS OF CORAL REEF
ECOSYSTEM
zooxanthellae in corals
filamentous algal scum (turf algae)
coralline (calcareous) algae
non-coralline seaweed
filamentous algae growing through the
upper layers of the porous reef rock
(endolithic algae)
benthic and interstitial diatoms
phytoplankton
herbivorous snails and
sea hares
most sea urchins
herbivorous crabs
green sea turtles
Chiton
Tiger cowrie
Consumers
- primary consumers
Phytoplankton and other single-celled primaryproducers are eaten by primary consumers.
Due to the large community of primary consumers oncoral reefs, phytoplankton levels in coral reef waterscan be 15-65% lower than in adjacent open oceanwaters.
Benthic grazers and some coral species feed byfiltering phytoplankton out of the water while othervertebrate and invertebrate grazers eat algae andseaweed; many species of parrotfish, surgeonfishand blennies have a diet that consists entirely ofcoralline, filamentous, and calciferous algae.
Secondary consumers
The animals in this trophic level feed on primaryconsumers and are consequently carnivorous.Secondary consumers in a reef ecosystem canbe divided into four main groups: (1) zooplankton feeders, (2) corallivores - organismsthat feed on coral tissue, (3) feeders on otherbenthic invertebrates, and (4) piscivores - fisheaters.
Plankton feeders can be small sessileinvertebrates like barnacles, corals like sunpolyps (Tubastrea sp.) and gorgonians, smalldamselfish or 15-ton whale sharks.
Corallivores can be sub-divided into polyp
eaters, coral scrapers, mucus feeders etc.
Many species of butterfly fish, damselfish
specialize in eating coral polyps
Some common coral scrapers are specific
species of triggerfish, parrotfish, blennies,
puffers, and butterfly fish.
Some animals that feed on coral mucus are
coral guard crabs and shrimps
Benthic invertebrates like mollusks,gastropods, worms, and crustaceans areeaten by many kinds of fish (e.g. goatfish,wrasses, triggerfish, etc.) and other largerinvertebrates
Piscivores are carnivores that eat fish; manyspecies of fish are piscivores as well assome mollusks and arthropods.
Tertiary (top) consumers
Tertiary consumers are large reef fish at the
top of the food chain that eat many smaller
fish. Some examples of top consumers in a
coral reef ecosystem are sharks, barracudas,
and moray eels. Marine mammals such as
dolphins and seals, and sea birds, if present,
are considered tertiary consumers, too.
Decomposers (and Detritivores)
Decomposers serve an extremely important function in allecosystems; they break down dead biological matter andwaste products and convert them into usable energywhile returning important materials to the environment.
The main decomposers in coral reefs are bacteria; thesebacteria play an integral part in the nitrogen cyclewhereby ammonia (NH4) is converted into nitrite (NO2)by bacteria in the genus Nitrosomonas, after which nitriteis then converted into nitrate (NO3) by bacteria in thegenus Nitrobacter.
The ultimate result is that levels of toxic wastes are keptvery low and that waste products are converted intocomponents that are available to producers in a readily-usable form.
Coral reefs are complex ecosystems thatrequire a balanced trophic structure to functionproperly and efficiently.
Imbalances can occur in this intricate trophiccascade from the top down or the bottom up.For an example of bottom-up effects, nutrient-rich agricultural run-off can cause a massiveincrease in primary productivity (e.g. algalblooms), the effects of which often cannot bebuffered by consumers fast enough to prevent acoral reef ecosystem from collapsing.
PRODUCTIVITY OF CORAL REEFS
The symbiotic arrangement between the algae
and corals results in nutrients being tightly
recycled with in coral reefs. This internal
nutrient cycling is of primary importance in
maintaining the productivity of the reef
The gross primary productivity ranges from
about 1500 to 5000 g.C/m2/year, values much
higher than those of open tropical Oceans
INTERNAL NUTRIENT RECYCLING
How can such rich community grow when the surrounding sea is unproductive?
IMPORTANCE OF CORAL REEFS
Protection from coastal erosion
Very high diversity = ecological stability
Source of important natural chemicals being researched as cures for cancer, arthritis, human infections, viruses, etc
Reef fisheries
Tourism
THREATS TO CORAL REEFS
There are two types of threats to coral reefs, anthropogenic and natural
Destructive and non-sustainable fishery practices
Coral bleaching – socio economic impacts, reef based tourism and fisheries
Coral mining – construction, lime industry, ornamental purposes
Pollution – agriculture, coastal development
Sedimentation - deforestation
CORAL BLEACHING
Coral bleaching
occurs when
symbiotic
zooxanthellae
algae is removed
or expelled
Associated with
high water
temperatures
Diseases – Black band, white band and red
band diseases were observed in corals
especially in shallow areas
In addition to the direct human interferences,
global climate change poses serious threat –
increase in temperature, and a possible
increase in the incidence of storms
Reefs are subjected to physical-erosion and bio-erosion
Physical erosion – intense wave action, currents, tropical storms
Bio erosion Removal of large no. of animals from reefs may
alter the ecology
Sea urchins graze up on the coral frame work
( fish, molluscs are over fished)
Crown of thorns star fish – Acanthasterplanci
( triton snail) Destruction of Great Barrier Reef
Others
As building material – Maldive islands
For ornamental purposes
Destructive fishing methods – dynamite, sodium cyanide
Anchoring – Reefs of Florida
