Corals are animals in the phylum Cnidaria that live in colonies. They require warm, tropical waters with sufficient light, salinity, and wave action to build reef structures through calcium carbonate deposition. Reefs support high biodiversity and include zones from the reef crest at the surface down to the drop off. Corals reproduce both sexually through spawning and asexually by budding or fragmentation.

1. BICD 2005
An Introduction to Coral ReefsAn Introduction to Coral Reefs
Bay Islands College of Diving, UtilaBay Islands College of Diving, Utila

2. BICD 2005
ContentsContents
• Animal or Plant?Animal or Plant?
• What is a coral?What is a coral?
• Location and limitationsLocation and limitations
• ReproductionReproduction
–– Sexual and AsexualSexual and Asexual
• Reef ClassificationReef Classification
• Components of the ReefComponents of the Reef
EcosystemEcosystem
• Reef ZonationReef Zonation
• Main Groups of CoralMain Groups of Coral
• SummarySummary

3. BICD 2005
Animal or Plant?Animal or Plant?
• In 1753, J. A. de Peysonell proved corals were animals rather thanIn 1753, J. A. de Peysonell proved corals were animals rather than
plants.plants.
• All corals are classified under theAll corals are classified under the PhylumPhylum CnidariaCnidaria..
• Other members of group: hydroids, jellyfish and anemones.Other members of group: hydroids, jellyfish and anemones.
• All Cnidaria have stinging cells calledAll Cnidaria have stinging cells called nematocystsnematocysts. They are. They are
located on their tentacles and are used for:located on their tentacles and are used for:
– Capturing preyCapturing prey
– DefenceDefence
• Usually the stings from these corals cause no harm to divers withUsually the stings from these corals cause no harm to divers with
the exception of fire corals which can cause a small irritation.the exception of fire corals which can cause a small irritation.

4. BICD 2005
What is a coral?What is a coral?
• ANATOMY:ANATOMY:
– A cup-shaped body, with aA cup-shaped body, with a
single, central opening that issingle, central opening that is
surrounded by tentacles.surrounded by tentacles.
– The opening acts as a mouthThe opening acts as a mouth
as well as an anus.as well as an anus.
• DIFFERENT APPEARANCES:DIFFERENT APPEARANCES:
– PolypsPolyps: solitary or colonial.: solitary or colonial.
– Unattached, free swimmingUnattached, free swimming
medusamedusa or jellyfish.or jellyfish.

5. BICD 2005
What is a coral?What is a coral?
• There are 2 main types of coral:There are 2 main types of coral:
– Reef building (Reef building (hermatypichermatypic ))
– Non-reef building (Non-reef building (ahermatypicahermatypic ))
• Reef builders have massive skeletons and are the majority of theReef builders have massive skeletons and are the majority of the
basic framework of the reef.basic framework of the reef.
• The coral polyps act as building blocks, and coralline algae acts likeThe coral polyps act as building blocks, and coralline algae acts like
cement which holds the whole structure together.cement which holds the whole structure together.

6. BICD 2005
Location and limitationsLocation and limitations
• Found throughout the world in tropical waters where:Found throughout the world in tropical waters where:
• Water temperatureWater temperature needs to be above 18.5needs to be above 18.5°°C (approx 70-85C (approx 70-85°°C).C).
• There the water is subject toThere the water is subject to movementmovement ..
• Corals can only live within theCorals can only live within the euphotic zoneeuphotic zone (0-90m).(0-90m).
• Water clarityWater clarity – allows beams to light to reach the single celled algae– allows beams to light to reach the single celled algae
calledcalled zooxanthellaezooxanthellae which live within the tissues of the coral polyp.which live within the tissues of the coral polyp.
– Symbiosis:Symbiosis:
– Algae provides oxygen and glucose.Algae provides oxygen and glucose.
– Coral provides carbon dioxide, and shelter.Coral provides carbon dioxide, and shelter.

7. BICD 2005
Location and limitationsLocation and limitations
• Hermatypic corals gain over 80% of this energetic intake from thisHermatypic corals gain over 80% of this energetic intake from this
relationship with the algaerelationship with the algae
• Coral growth even in pristine conditions is usually less than 1 inchCoral growth even in pristine conditions is usually less than 1 inch
per year for most speciesper year for most species
• Other requirements: sufficient salinity, wave action and a firm baseOther requirements: sufficient salinity, wave action and a firm base
for attachmentfor attachment
• Different species vary in their resistance to each of these factors, soDifferent species vary in their resistance to each of these factors, so
a zonation pattern will resulta zonation pattern will result
• These conditions are required to keep the rate of deposition (newThese conditions are required to keep the rate of deposition (new
growth) greater than of the erosion and dissolutiongrowth) greater than of the erosion and dissolution

8. BICD 2005
Reproduction - SexualReproduction - Sexual
• Definition: genetically new individuals formed from the combinationDefinition: genetically new individuals formed from the combination
of male and female genes produced by different parental coloniesof male and female genes produced by different parental colonies
((genetic recombinationgenetic recombination ).).
• Coral species have:Coral species have:
– Separate male and female colonies, or;Separate male and female colonies, or;
– Colonies can be hermaphroditic.Colonies can be hermaphroditic.
• Fertilized eggs - inside a colony or outside in open water.Fertilized eggs - inside a colony or outside in open water.
• Spawning techniquesSpawning techniques
– BroodersBrooders
– Broadcast SpawnersBroadcast Spawners
• Develop intoDevelop into planula larvaeplanula larvae – disperse - settle on hard substrate– disperse - settle on hard substrate
in clear shallow water and begin producing a tiny calcium skeleton.in clear shallow water and begin producing a tiny calcium skeleton.

9. BICD 2005
Reproduction - AsexualReproduction - Asexual
• Definition - the development of genetically identical clones without the unionDefinition - the development of genetically identical clones without the union
of male and female gametes.of male and female gametes.
• Advantage is that the new colony is more likely to succeed thanAdvantage is that the new colony is more likely to succeed than
Planular LarvaePlanular Larvae
• Disadvantage is that the new colony is cloned and thereforeDisadvantage is that the new colony is cloned and therefore
susceptible to the same diseases as the parent colonysusceptible to the same diseases as the parent colony
• Two main ways:Two main ways:
– BuddingBudding (Extratentacular budding)(Extratentacular budding)
• The polyps bud off a from the side creating a new polypThe polyps bud off a from the side creating a new polyp
– FissionFission (Intratentacular budding)(Intratentacular budding)
• Polyps split into half through the tentacles creating the newPolyps split into half through the tentacles creating the new
polyppolyp
• New colonies can also form byNew colonies can also form by fragmentationfragmentation
– Broken pieces of a colony fall off and reattach themselves to theBroken pieces of a colony fall off and reattach themselves to the

10. BICD 2005
Reef ClassificationReef Classification
a)a) Fringing Reef (youngest)Fringing Reef (youngest)
b)b) Barrier Reef – e.g.Barrier Reef – e.g. The Mesoamerican Barrier ReefThe Mesoamerican Barrier Reef
c)c) Atoll (oldest)Atoll (oldest)

11. BICD 2005
Components of the ReefComponents of the Reef
EcosystemEcosystem
• MangrovesMangroves -- stands of vegetation with astands of vegetation with a
terrestrial ancestry.terrestrial ancestry.
• Grow in sandy and muddy waters around theGrow in sandy and muddy waters around the
coasts, areas which are generally saline andcoasts, areas which are generally saline and
anoxic.anoxic.
• In the Caribbean, mangroves form aIn the Caribbean, mangroves form a vital partvital part
of the ecosystem, linked with the lagoon andof the ecosystem, linked with the lagoon and
reef habitats.reef habitats.
• Mangroves actively uptake and utilise nutrients,Mangroves actively uptake and utilise nutrients,
therefore act as recyclers mobilising nutrients.therefore act as recyclers mobilising nutrients.• Mangroves actively uptake and utilise nutrients, act as recyclers mobilising nutrients.Mangroves actively uptake and utilise nutrients, act as recyclers mobilising nutrients.
• Grow in areas low in oxygen and actively increase levels through photosynthesis.Grow in areas low in oxygen and actively increase levels through photosynthesis.
• Provide a number of habitats for a variety of organisms to live and feedProvide a number of habitats for a variety of organisms to live and feed
• Particularly important as a nursery ground.Particularly important as a nursery ground.

12. BICD 2005
Components of theComponents of the
Reef EcosystemReef Ecosystem
Lagoons-Lagoons-
• Lagoons are one of the most important and extensive habitats of coastal waters, theyLagoons are one of the most important and extensive habitats of coastal waters, they
occur in protected areas and are primarily covered with seagrass beds on sandy, silty oroccur in protected areas and are primarily covered with seagrass beds on sandy, silty or
rubble substratum.rubble substratum.
• Seagrass beds, large proportion of primary production,Seagrass beds, large proportion of primary production, physically causes sediment tophysically causes sediment to
settle out of the water column.settle out of the water column.
• Provides food for herbivores and indirectly carnivores up the food chain.Provides food for herbivores and indirectly carnivores up the food chain.
• Lagoons offer a soft sandy substrate and the surface of seagrass blades as differentLagoons offer a soft sandy substrate and the surface of seagrass blades as different
habitats for many species to exploit.habitats for many species to exploit.
• Animals live in/on the sandy/muddy bottom (Animals live in/on the sandy/muddy bottom (benthic formsbenthic forms),),
• On plants (On plants (epiphytic formsepiphytic forms),),
• In water surrounding plants (In water surrounding plants (epibenthic or pelagic formsepibenthic or pelagic forms ).).
• As lagoons are sheltered by the reef their waters are relatively calm, encouraging fragileAs lagoons are sheltered by the reef their waters are relatively calm, encouraging fragile
species or ones preferring calm conditions. (e.g. Sea turtles, molluscs, urchins andspecies or ones preferring calm conditions. (e.g. Sea turtles, molluscs, urchins and

13. BICD 2005
Components of the ReefComponents of the Reef
EcosystemEcosystem
Coral ReefsCoral Reefs
• Biogenic limestone reefs which are geologicBiogenic limestone reefs which are geologic
structures built over time by living organisms.structures built over time by living organisms.
• They bring high productivity to areas whichThey bring high productivity to areas which
otherwise would be relatively unproductive.otherwise would be relatively unproductive.
• High species diversity is also an importantHigh species diversity is also an important
defining feature of coral reefs.defining feature of coral reefs. There are anThere are an
amazing array of habitats, food, shelter, livingamazing array of habitats, food, shelter, living
space and substrate for a huge number ofspace and substrate for a huge number of
species.species.
•
• Coral reefs are considered as an ecologicallyCoral reefs are considered as an ecologically
stable environment. This fact has resulted instable environment. This fact has resulted in
evolutionary specialisation.evolutionary specialisation.

14. BICD 2005
Components of the ReefComponents of the Reef
EcosystemEcosystem

15. BICD 2005
Reef ZonationReef Zonation
• Physical and biologicalPhysical and biological
features of the zones arefeatures of the zones are
controlled by a range ofcontrolled by a range of
factors, wave action, andfactors, wave action, and
photic levels.photic levels.
• Back ReefBack Reef - consists of patch- consists of patch
reefs, rubble areas and areefs, rubble areas and a
carbonate platform.carbonate platform.
• Relatively low diversity asRelatively low diversity as
suspended particles deposit.suspended particles deposit.
• Species which exist there areSpecies which exist there are
more resilient tomore resilient to
sedimentation. But require asedimentation. But require a
lot of light.lot of light.

16. BICD 2005
Reef ZonationReef Zonation
• Reef CrestReef Crest -- Top of the reefTop of the reef
system.system.
• Reef can break the water’s surfaceReef can break the water’s surface
at low tide.at low tide.
• Greatest physical stress, poundedGreatest physical stress, pounded
by incoming waves, species strongby incoming waves, species strong
to dissipate wave action.to dissipate wave action.
• Species grow fast and regrow ifSpecies grow fast and regrow if
they are broken away from theirthey are broken away from their
primary structure.primary structure.
• Commonly a lot of coralline algaeCommonly a lot of coralline algae
which holds the reef together, firewhich holds the reef together, fire
coral and colonial zoanthids.coral and colonial zoanthids.

17. BICD 2005
Reef ZonationReef Zonation
• ForereefForereef - Major reef zone in- Major reef zone in
Caribbean waters.Caribbean waters.
• Shallow, but high in energy whereShallow, but high in energy where
oceanic waters meet the reef.oceanic waters meet the reef.
• Reef slopes downward at an angleReef slopes downward at an angle
less than 45less than 45°° and eventually theand eventually the
physical force of waves is reduced.physical force of waves is reduced.
• Species diversity reaches aSpecies diversity reaches a
maximum around 20m wheremaximum around 20m where
corals find the optimum locationcorals find the optimum location
which balances low wave actionwhich balances low wave action
and relatively high light levels.and relatively high light levels.

18. BICD 2005
Reef ZonationReef Zonation
• DropDrop--offoff - Forereef becomes- Forereef becomes
a steeper slope or wall ata steeper slope or wall at
greater than 45greater than 45°° where itwhere it
continues to the depths of thecontinues to the depths of the
ocean.ocean.
• Corals become restricted byCorals become restricted by
light, so numbers are reduced.light, so numbers are reduced.
• Morphology is also adapted toMorphology is also adapted to
present a larger surface areapresent a larger surface area
to increase the ability toto increase the ability to
absorb lower levels of light.absorb lower levels of light.
• Corals can also have a moreCorals can also have a more
fragile structure due to thefragile structure due to the
severely reduced wave action.severely reduced wave action.

19. BICD 2005
Main Groups of CoralMain Groups of Coral
• There are 4 main groups of coral:There are 4 main groups of coral:
• Class: Hydrozoa (hydrozoans) – “Fire Corals”Class: Hydrozoa (hydrozoans) – “Fire Corals”
• Class: Anthozoa – Subclass: Octocorallia (octocorals) –Class: Anthozoa – Subclass: Octocorallia (octocorals) –
“Soft Corals”“Soft Corals”
• Class: Anthozoa – Subclass: Hexacorallia (hexacorals) –Class: Anthozoa – Subclass: Hexacorallia (hexacorals) –
“Stony/Hard Corals”“Stony/Hard Corals”
• Class: Anthozoa – Subclass: Ceriantipatharia – Order:Class: Anthozoa – Subclass: Ceriantipatharia – Order:
Antipatharia (antipatharians) – “Black Corals”Antipatharia (antipatharians) – “Black Corals”

20. BICD 2005
SummarySummary
• Animal or Plant?Animal or Plant?
• What is a coral?What is a coral?
• Location and limitationsLocation and limitations
• ReproductionReproduction
– Sexual and AsexualSexual and Asexual
• Reef ClassificationReef Classification
• Components of the ReefComponents of the Reef
EcosystemEcosystem
• Reef ZonationReef Zonation
• Main Groups of CoralMain Groups of Coral