CORAL AND CORAL REEFS
Coral Reefs• Corals are marine invertebrates, which are animals, in the
phylum Cnidaria.
• Class Anthozoa (Anthos= flower, Zoa= animals) is exclusively
marine, and include sea anemones, stony corals, soft corals, sea
pens, sea fans and sea pansies.
• Anthozoa is the largest taxon of cnidarians; over six thousand solitary
and colonial species
• They typically live in compact colonies of many identical
individual polyps (which are animals as well, just very tiny).
• The group includes the important reef builders that inhabit
tropical oceans and secrete calcium carbonate to form a
hard skeleton.
• Coral polyps are translucent animals that form a living mat
over a calcium carbonate skeleton.
• Stony corals are the corals primarily responsible for laying
the foundations of, and building up, reef structures.
Key Characteristics of a Coral Reef?
• Colorful
• Extremely Diverse Life
• Located in Warm Water
• USUALLY located in Clear Water
• Water is Nutrient Poor
Interesting Facts about the Coral Reefs
• Though coral reefs cover less than 1% of the Earth’s surface, over 25% of all marine fish species find their homes in coral reefs.
• The average growth rate of a coral reef is less than 3 cm per year; hence it takes several years to form a large coral/area of coral
• Coral is an animal related to jellyfish (A Cnidarian)
CORAL
Anatomy of a Coral Reef
-Reefs are made when
each individual coral
organism – or polyp –
secretes a skeleton of
calcium carbonate
-Zooxanthallae (an
algae/protist) will
inhabit the Coral
General Characteristics• Coral polyps are tiny, soft-
bodied organisms related to
sea anemones and jellyfish.
• At their base is a hard,
protective limestone
skeleton called a calicle,
which forms the structure of
coral reefs.
• Reefs begin when a polyp
attaches itself to a rock on
the sea floor, then divides,
or buds, into thousands of
clones.
• Coral reefs are built from the
remains of stony or hard
corals
• Salt water: 34-37 ppt
• Hard substrate to settle on as larvae
• Food
• Oxygen
• NOT A PLANT, A PROTIST
• Sunlight
• Nutrients (nitrogen)
• Warm temperature:~20ºC
• Clear water
• Carbon dioxide
Factors necessary for coral reef formation:
Coral (animals) need: Zooxanthellae (algae)need:
Reef Formation• Reefs cover about 100,000 square miles of the world’s
shallow marine areas
• Located in shallow, tropical waters
• They grow gradually as the organisms that form their
living surfaces multiply, spread, and die, adding their
limestone skeletons to the reef.
• Millions of Stony coral polyps are the marine animals
responsible for building the hardened coral reefs you
see in the ocean
• Reefs are excretions of calcium carbonate produced
by each polyp
• New polyps secrete reef on top of older polyps
Reef Growth Forms
• Hard coral colonies generally exhibit one
of three basic growth forms:
1.Massive
2.Branching
3.Plate-like
1. Massive• These rely on sheer mass, growing into
huge sheet or boulder formations that tend
to make up the bulk of a reef
2. Branching
• These require a small area to anchor
themselves, but branch out into vast, tree-
like colonies
3. Plate-like
• Form flat expanses that overshadow other
corals and monopolize the available light
Zooxanthellae “ZO ZAN THEL I/A”
• Tiny algae that are photosynthetic
organisms live in the tissue of
each coral polyp, millions can live
in just one square inch of the
coral
• Provide a source of food to the
polyps
• Give corals their color
• Example of a mutualistic
symbiotic relationship
• This is why corals need sunlight
to grow
• Receives Food
• Receives Oxygen
• Receives protection
• Receives Carbon Dioxide
Mutualism
Coral (animals) need: Zooxanthellae (algae)need:
Organisms Contributions
• Mollusks and echinoderms add their
skeletal remains
• Grazing and boring organisms break
down coral skeletons into sand
• Coralline Algae bind the sand
Importance of Coral Reefs to the Environment
• The Reefs built by corals provides homes for millions of different species
• Involved in nitrogen fixation provides food to fish
• Photosynthesis of the Zooxanthallae absorbs carbon
• Nursery for different organisms.
Importance of Coral Reefs to Humans
• Coral reefs are widely used in the treatment of cancer, HIV, cardiovascular diseases and Asthma.
• Porous limestone skeletons of the corals have been used in grafting human bones.
• Important source for the fishing industry
• Protect coastlines from storm surges
• Stimulate economy through increasing tourism
Reef Distribution
Coral Reefs are found in all three of Earth’s oceans that have
portions in the tropics. (Pacific, Atlantic, and Indian). They are
scattered randomly, however.
Reef Distribution
• Grow in clear, sunlit,
shallow water
• Average salinity of 36 ppt
• Require warmer water
temperatures, as seen in
tropical and sub-tropical
areas
• Require little or no wave
action
• Little or no sedimentation
from river run-off
• The two main areas of
development that meet
these criteria are the
Indo-Pacific and
Greater Carribean
Belize – Great Blue Hole
Indo-Pacific Region
• Central and South
Pacific Ocean
• Greatest number are
in an area from
southern Phillipines
through western New
Guinea and Indonesia
• Red Sea are is cut off
from large water flow,
so has high number
of endemic species
Greater Caribbean Region
• Tropical, western
Atlantic
• Spans the entire
Caribbean Sea,
Bahamas, and south
Florida
PARTS
OF
REEFS
Parts of a
Reef
Parts of a Reef
• Reef Slope:
– or fore-reef, is the part that
faces the sea.
– The upper parts of the reef
slope are dominated by
branching coral colonies
and intermediate depths
by massive forms.
– These are the areas of the
reef with the greatest
diversity of species.
• Reef Crest
– Narrowest of the reef
zones
– Massive wall that
absorbs the energy of
incoming waves
(makes water calmer
for back reef zone)
• REEF FLAT:
– Shoreward of the reef
crest is the reef flat, a
shallow, relatively flat
expanse of limestone,
sand, and coral
fragments that may
become exposed at
high tide.
– The number of corals
decreases toward the
shore.
• Barrier reefs and
atolls have a final
zone, the lagoon
area.
LAGOON
• a shallow body of water
separated from a larger body
of water by barrier islands or
reefs.
• Lagoons are commonly
divided into coastal lagoons
and atoll lagoons.
• They have also been identified
as occurring on mixed-sand
and gravel coastlines.
• Lagoons are common coastal
features around the world.
Reef Flat and Lagoon Areas
AKA “Back Reef”
• Contains shallow water
habitats for reef species
• Vital role in food web
• Experiences large
temperature and salinity
changes, reduced water
circulation, and
sediment accumulation
• Main Habitats here:
• Patch reefs
• Sand plains
• Seagrass meadows
• Mangrove forests
Types of Reefs &
Importance and Human Impacts
of/to Reefs
Importance of Reefs• Coral reefs provide a buffer, protecting our coasts
from waves, storms, and floods.
• Corals form barriers to protect the shoreline from
waves and storms.
• The coral reef structure buffers shorelines against
waves, storms, and floods, helping to prevent loss
of life, property damage, and erosion.
– Provide protective barrier around islands and
coasts
– Slows down strong currents and waves before it
hits the shore
– Prevent erosion
Importance of Reefs• Create more living biomass than any other marine ecosystem
• provide a habitat, spawning and nursery grounds for
economically important fish species;
• provide jobs and income to local economies from fishing,
recreation, and tourism
• Support more species than any other marine environment
• Possibilities in medicines and science
– induce and ease labor; treat cancer, arthritis, asthma, ulcers,
human bacterial infections, heart disease, viruses, and other
diseases; as well as sources of nutritional supplements,
enzymes, and cosmetics
• Control carbon dioxide levels in ocean water
– The coral polyp turns carbon dioxide in the water into a
limestone shell
Types of Reefs• The basic Coral Reef classification scheme was first
proposed by Charles Darwin
• There are three main types of reefs:
Fringing
Barrier
Atolls• There are two other
reef types:
Patch reefs
Bank reefs
Fringing Reefs
• Occur adjacent to the land,
with little or no separation
from the shore
• They develop through
upward growth of reef-
forming corals on an area of
continental shelf.
• May have a completely
shallow lagoon in some
areas, or no lagoon at all
• Most common reef in the
Greater Carribbean and Red
Sea
• Also surround many South Pacific and
Indian Ocean Islands
• Most susceptible to coastal development,
agriculture, pollution, and other human
activities resulting in sedimentation and
freshwater runoff
Barrier Reefs
• Broader and Separated from land
by a lagoon that can be miles wide
and at least a dozen yards deep
• Usually parallel the shore
• Parts of the reef structure often
protrude above sea level as low-
lying coral islands.
– These develop as wave action deposits
coral fragments broken off from the reef
itself
• Largest reefs develop on the edges
of continental shelves (called “shelf
barrier reefs”
– Great barrier reef, Belize barrier reef
Atolls• Large, ring-shaped reefs,
surrounding a central
lagoon
• found well away from
large landmasses, such
as in the South Pacific
• Usually circular or
horseshoe-shaped
• parts of atolls may
protrude above the
surface forming coral
islands as well.
• Most common in the
Indo-Pacific region
(over 300)
• Rare in Caribbean
(only 10-15)
– Southern Mexico and
Belize
• Can exceed 100
miles in diameter
• Central lagoons can
be several thousand
square miles
ANATOMY OF A REEF
Patch Reefs• Small reefs found within
the lagoons of other reefs
• Usually small, isolated outcrops of coral surrounded by sand and / or seagrasses
• Provide refuge and food for may species of animals and fishes
• patch reefs appear golden brown surrounded by a white halo and seagrass meadows.
Bank Reefs
• Reef structures with no obvious link to a
coastline
• Offshore bank reefs occur seaward of the
patch reefs. Bank reefs are larger than the
patch reefs and are generally linear or semi-
circular in outline.
• Most of the snorkeling and scuba diving takes
place on these reefs
Evolution of the Three Main Reef Types
• As first proposed by Charles Darwin:
• Darwin proposed the three main reef
types are simply different stages in
the geological ‘evolution” of Pacific
oceanic islands.
Darwin’s Theory
• Fringing reefs began to
grow near the shorelines of
new islands when
conditions for growth were
ideal
• As the island began
to gradually subside
into the sea, the coral
was able to grow at
the same rate, and
remained in place at
the sea surface, but
farther from shore.
• It was now a barrier
reef
• Eventually, the island
disappeared below
the sea surface,
leaving only the ring
of coral surrounding it
• It was now an atoll
• Darwin’s theory of “reef evolution” was
verified for the Indo-Pacific reefs in the
early 1950’s
– After analyses of deep core drilling at Bikini
and Eniwetok Atolls
– We now know, however, that in some cases,
the three types can be formed by different
processes as well
Coral Reef Threats
FYI….Did you know…• Coral reefs occupy only 2% of the oceans’ area, but are home to ¼
of all known marine species
• We have already lost 27% of the world's coral reefs. If present rates
of destruction are allowed to continue, 60% of the world's coral reefs
will be destroyed over the next 30 years
• Occupying less than one quarter of 1% of the marine environment,
coral reefs are home to more than 25% of all known marine fish
species
• 58% of the world's coral reefs are potentially threatened by human
activity
• Coral reefs are found in 109 countries; significant reef degradation
has occurred in 93
• More than 80% of the world's shallow reefs are severely over-fished
• Properly managed coral reefs can yield an average of 15 tons of fish and other seafood per square kilometer each year
Human Impacts on Reefs• Coastal and ocean pollution
– Oil slicks, pesticides, chemicals, heavy metals, garbage, etc.
• Poisons coral polyps
– Fertilizer and untreated sewage encourages algae growth
• High concentrations of algae can cover the coral and block sunlight if not kept under control by herbivores
Massive oil slick as seen from satellite photos
Human Impacts on Reefs
• Uncontrolled development of
coasts
– Deforestation
– Dredging and coastal development
• Hotels
• Homes
• harbors
Soil run-off - Hawaii
Runoff from a pipe in
the Virgin Islands,
directly near a reef
Human Impacts on Reefs
• Recreation
– Boat anchors crush
corals and gouge the
reef
– Diving tourism
• Divers and snorklers
sit, stand on, or
handle corals
Human Impacts on Reefs• Collection of corals and organisms
– International seashell and aquarium trades have put
a strain on coral reef ecosystems
– Upsets the balance of the ecosystem
• Market for coral skeletons, shells, sponges and
reef animals for decorations, jewelry, sculptures
• Tropical fish trade
• Coral skeletons are are sold as “live rock”
–Popular in aquariums because of the living
bacteria and algae that acts as a natural
biological filter
Human Impacts on Reefs
• Uncontrolled mining for building materials
Human Impacts on Reefs
• Destructive fishing practices
– Overharvesting of species
can lead to the species’
demise
– Fishing with dynamite,
cyanide, or bleach
– Careless handling of nets,
lines, and lobster traps
can lead to reef damage
– Boating / anchors also
leads to reef damage
• Between 1986 – 1991, ½ of
the coral reefs in the
Philippines were destroyed
by this
Coca-Cola bottle with slightly
burned fuse found around the
Capone Islands, Phillipines
Human Impacts on Reefs• Natural disturbances:
– Hurricanes and tropical storms can strip corals from
miles of reef habitat
Human Impact on Reefs
• Increases in atmospheric carbon dioxide
increases the acidity of the ocean
• Higher ocean acidity makes it harder for
reefs to construct their calcium carbonate
skeletons
The Ocean is a Carbon Sink
What does this mean?
-The Ocean absorbs Carbon Dioxide
Atmospheric
CO2Oceanic
CO2
pHOcean
acidification
Temperature
Coral
Bleaching
What are the effects of too much CO2?
1. Ocean Acidification
2. Coral Bleaching
What is Ocean Acidification?
What is Ocean Acidification?
Normal Conditions
• The Ocean is naturally Basic (pH ~8)
• Calcium Carbonate (CaCO3) present in the water and available for organisms to use for their shells and skeletons
What is Ocean Acidification?
• A decrease in Ocean pH means that there are more H+ ions will react with the Carbonate Ions to form Bicarbonate INSTEAD of Calcium Carbonate
Atmospheric
CO2Oceanic
CO2
pHOcean
acidification
What do you observe?
Ocean Acidification Decrease in Calcium Carbonate
• It DOES NOT mean that the ocean is so acidic that it is dissolving the shells of bivalves and skeleton of corals…yet.
• It DOES mean that there is not enough Calcium Carbonate for these shelled organisms to build their structures
What is Coral Bleaching?
• An increase in CO2 (a greenhouse gas) causes an increase in temperature
• The increase in temperature is an environmental stressor for the Coral
• Other environmental Stressors: pH change and pollution
Atmospheric
CO2Oceanic
CO2
Temperature
Coral
Bleaching
What do you observe?
What is Coral Bleaching?
• As Corals are stressed, they will start to expel and/or actively digest their zooxanthellae
• If the stress is intense, they Corals will expel all their zooxanthellae leading to the bleached look
Effects of Coral Bleaching
• The corals can survive a bleaching episode
• They are animals so they can still eat food to live
BUT
• They are more vulnerable to diseases, infections, and mortality
• Zooxanthellae can be resorbed but will not survive long outside of the coral
Natural Threat: Crown of Thorn
Natural Threat: Crown of Thorns
• When balanced, the Crown of Thorns play an important role of consuming the fast growing coral; therefore, regulating the population and enabling slow growing corals to grow
• Cyclical outbreaks are natural but they have been happening more often than previously
-possibly linked with the warmer waters because the sea star spawn during warmer seasons
Case Studies
• Human Impacts on Coral Reefs
• Crown of Thorns Impact
Coral Bleaching
• Occurs when corals become stressed
– They expel the zooxanthellae living in them
• They lose their color and become whitened
• Can be caused with warmer surface waters (maybe even by 1-2 degrees)
– May have a link to global warming
• Pollution can also be a cause
• Full recovery takes decades
CORAL BLEACHING:
• From 1876-1979 only three bleaching
events were recorded
• whereas 60 are on record from 1980
until 1993
• in 2002 more than 400 events were
recorded
Bleaching can be seen in areas of the Great Barrier Reef
Coral Poisoning
• Very destructive
fishing practice
• A diver sprays
sodium cyanide to
catch a fish
• The poison kills all
corals in the area
Crown of
Thorns Starfish
Coral Reef Diversity
• Healthy reefs can house thousands of species
– Fish
– Invertebrates
– Sponges
– Soft corals
• Every part of a reef is used by some animal
• Mutualism –relationship between two different species where they both benefit
Organisms of a Coral Reef
Corals
Leafy Sea Dragon and Weedy Sea Dragon
Clownfish
Blue Tangs
Parrot Fish
-Eat Coral
with their
strong beaks
-They cannot
digest Coral, so
they pass the
crushed Coral
makes the nice
white sand
Class Cephalopoda (Phylum Mollusca)
• “Head-Foot”
• Intelligent (largest centralized brain of all the invertebrates)
• Soft Bodied
• Sophisticated Eyes (but Colorblind) Visual Predator
• Tentacles with suction cups
• Contain Chromatophorees (color changing cells)
• Contain Iridophores (reflective cells)
• Beak
Cuttlefish
Octopus
Squid
Moray Eels
Gobie fishMandarin fish