CoralsCorals

Landlords of the ReefsLandlords of the Reefs

What is a coral?

Phylum CnidariaPhylum Cnidaria Cl. AnthozoaCl. Anthozoa

Order Gorgonacea Order Gorgonacea (soft corals, (soft corals, gorgonians)gorgonians)

Order Scleractinia Order Scleractinia (hard/stony reef (hard/stony reef builders)builders)

What should you know What should you know about corals?about corals?

They are animalsThey are animals Plants live inside of Plants live inside of

themthem Two kindsTwo kinds

Soft coralsSoft corals Hard corals (These Hard corals (These

build reefs!)build reefs!) They are made of They are made of

tiny polyps tiny polyps (which look (which look like upside-down like upside-down jellyfish)jellyfish)

What’s a Polyp?What’s a Polyp?

Tentacles release Tentacles release stinging cells when stinging cells when something brushes something brushes by themby them

Polyps make their Polyps make their own limestone cup to own limestone cup to hide in during the hide in during the dayday

At night, polyps At night, polyps come out to catch come out to catch plankton floating by.plankton floating by.

““Nerve Net”Nerve Net”

Zoo-what!?! Zoo-what!?! Algae, Coral Polyps’ Algae, Coral Polyps’

TenantsTenants Inside polyps live Inside polyps live zooxanthellaezooxanthellae, ,

which are algae.which are algae. ZooxanthellaeZooxanthellae give corals their color. give corals their color. Since algae are plants, they use Since algae are plants, they use

sunlight and COsunlight and CO22 to make food to make food (photosynthesis).(photosynthesis).

Symbiosis:Symbiosis:So Happy TogetherSo Happy Together

Two organisms living together and Two organisms living together and helping each other is called helping each other is called symbiosissymbiosis.. Zooxanthellae make oxygen, remove the Zooxanthellae make oxygen, remove the

polyp’s wastes, and make food for the polyp’s wastes, and make food for the polyp from photosynthesis.polyp from photosynthesis.

Coral polyps protect the zooxanthellae, Coral polyps protect the zooxanthellae, release COrelease CO22, and provide it with , and provide it with necessary nutrients from their own waste.necessary nutrients from their own waste.

Hard Corals - Hard Corals - ScleractiniansScleractinians

The Reef BuildersThe Reef Builders Polyps build hard Polyps build hard

limestone (CaCOlimestone (CaCO33) ) cups around their cups around their basesbases

The cups cement The cups cement together to make a together to make a coral colonycoral colony

Reefs are made of Reefs are made of hundreds of hard coral hundreds of hard coral colonies next to and colonies next to and on top of each otheron top of each other

Hermatypic – reef Hermatypic – reef buildersbuilders

Coral ColoniesCoral Colonies Corallite = CaCO3

structure around polyp

Gastrovascular cavities of polyps connected by tube

Colony Morphology Colony Morphology ArrangementArrangement

FeedingFeeding

Suspension feeders Feed on zooplankton, small organisms on reef Use cnidocytes to stun prey Most are nocturnal (during day the polyps are

retracted into corallites Mesenterial filaments – extruded by gut, absorb

digested organic matter in sediments Bacteria absorb DOM, polyps feed on bacteria Up to 90% nutritional needs - zooxanthellae

Reproduction

Asexually budding fragmentation

Sexually some are hermaphroditic (have both testes

& ovaries) broadcast spawners – release gametes into

sea few are brooders – sperm boradcast, eggs

retained & fertilized internally, planula larvae released

Life Cycle of a Broadcaster

Coral Spawning Pacific reefs –

synchronous, brief annual event

Caribbean – nonsynchronous, long periods

Reef FormationReef Formation

Constructive & Destructive phases Destructive = bioerosion

usually initiated by boring organisms, continued by storms/heavy surges damaging weakened areas

Constructive accumulation of sediments, pieces of

broken corals, new planula larvae settle on newly exposed substrate surfaces

Reef Structure

Types of ReefsTypes of Reefs

4 types of reefs

1.1.Fringing ReefsFringing Reefs

2.2.Barrier ReefsBarrier Reefs

3.3.AtollsAtolls

4.4.Patch ReefsPatch Reefs

Fringing ReefsFringing Reefs

borders shores of borders shores of tropical tropical islands/continental islands/continental massesmasses

Common in S. Pacific Common in S. Pacific & some parts of & some parts of CaribbeanCaribbean

Barrier ReefsBarrier Reefs

furthest offshorefurthest offshore form when land masses form when land masses

sink & fringe reef sink & fringe reef separates from shoreseparates from shore

assoc. with lagoons or assoc. with lagoons or deep channelsdeep channels

common in Caribbean common in Caribbean and Indo-Pacificand Indo-Pacific

Great Barrier Reef, Austr.2100 km

AtollsAtolls

elliptical; central elliptical; central lagoon; in deep lagoon; in deep seasseas

< 1km to > 130 km < 1km to > 130 km diameterdiameter

form as volcanic form as volcanic islands sinkislands sink

Darwin's Volcano

Patch ReefsPatch Reefs

small, numeroussmall, numerous found in lagoons of found in lagoons of

atolls or barrier reefsatolls or barrier reefs can be created by can be created by

heavy grazers like sea heavy grazers like sea urchinsurchins

Reef Types – recap!Reef Types – recap!

Typical Reef ZonesTypical Reef ZonesReef zonesReef zones

Fig. 15-13b: view from above, spur & groove formations

Where do we find coral Where do we find coral reefs?reefs?

Distribution Distribution determined by:determined by: Temp.Temp. LightLight Sediment Sediment

accumulationaccumulation SalinitySalinity Wave actionWave action Duration of air Duration of air

exposureexposure

DistributionDistribution

Most are tropical (annual temps. Most are tropical (annual temps. 2323⁰⁰C-25C-25⁰⁰C)C)

Most < 60 ft. deep (25 m or less)Most < 60 ft. deep (25 m or less) Moderate wave actionModerate wave action Saline areas (less freshwater Saline areas (less freshwater

runoff/input)runoff/input)

Pacific ReefsPacific Reefs Atlantic Atlantic Reefs Reefs

olderolder growth seldom growth seldom

exceeds 60 mexceeds 60 m > % coverage> % coverage greater diversity greater diversity

of organismsof organisms more extensive more extensive

algal ridgesalgal ridges mostly diurnalmostly diurnal sexual reprod.sexual reprod.

growth extends growth extends beyond 100 mbeyond 100 m

deeper buttress zonesdeeper buttress zones often dom. By often dom. By

MilliporaMillipora(fire coral)(fire coral) > biomass of sponges> biomass of sponges mostly nocturnalmostly nocturnal fragmentationfragmentation

Reef EcologyReef Ecology

Source of NutrientsSource of Nutrients req. abund. Nreq. abund. N22 and P and P possibly from runoff, upwelling, flow possibly from runoff, upwelling, flow

rates, recycling, Nrates, recycling, N22 fixation by bacteria, fixation by bacteria, fecal matterfecal matter

PhotosynthesisPhotosynthesis Zooxanthellae, algae, phytoplankton, Zooxanthellae, algae, phytoplankton,

sea grassessea grasses Turf algae & zooxanthellae fix the most Turf algae & zooxanthellae fix the most

CC

Ecology cont’dEcology cont’d

ProductivityProductivity High as result of production and High as result of production and

efficient use of nutrientsefficient use of nutrients 1 of the most productive ecosystems1 of the most productive ecosystems Exactly how productive is not really Exactly how productive is not really

known!known!

Coral Reef CommunityCoral Reef Community

Complex & biologically diverseComplex & biologically diverse Light, space & other resources are Light, space & other resources are

limited therefore there is much limited therefore there is much competitioncompetition

Slow growing corals use mesenterial Slow growing corals use mesenterial filaments to kill competitor polypsfilaments to kill competitor polyps Faster growing corals respond w/ Faster growing corals respond w/

sweeper tentaclessweeper tentacles

Slow growers – more aggressiveSlow growers – more aggressive Some take advantages of different Some take advantages of different

locationslocations More massive corals – more shade tolerant More massive corals – more shade tolerant

– deeper– deeper Faster growing, branching – dominate Faster growing, branching – dominate

upper, shallow reefupper, shallow reef Corals in shallow water rely on grazing Corals in shallow water rely on grazing

animals to help control algal growthanimals to help control algal growth

CompetitionCompetition

Among reef fishesAmong reef fishes > diversity than other marine habitats> diversity than other marine habitats 3D structure of reef = microhabitats 3D structure of reef = microhabitats

for fish (& others)for fish (& others) Competitive Exclusion PrincipleCompetitive Exclusion Principle

Time of day, size of prey, position of Time of day, size of prey, position of water column, etc. provide unique nicheswater column, etc. provide unique niches

Natural mortality (incl. predation) controls Natural mortality (incl. predation) controls population sizespopulation sizes

Chance determines larval settlementChance determines larval settlement

Effects of GrazingEffects of Grazing

Urchins & fishes prevent algal Urchins & fishes prevent algal overgrowthovergrowth

Diadema Diadema (long spined urchin) is a (long spined urchin) is a keystone predatorkeystone predator

Effect of PredationEffect of Predation

Some predators prey on coral Some predators prey on coral competitors giving some inferior competitors giving some inferior corals advantagecorals advantage

Some feed directly on polyps & limit Some feed directly on polyps & limit their growththeir growth corallivorescorallivores Parrot fish, surgeon fishParrot fish, surgeon fish add sediment to reef (do not digest the add sediment to reef (do not digest the

coral skeletons)coral skeletons)

Symbiotic RelationshipsSymbiotic Relationships

help organisms exploit niches, help organisms exploit niches, survivesurvive

Mutualism – zooxanthellaeMutualism – zooxanthellae Cleaning stationsCleaning stations

Inverts & small fish clean parasites Inverts & small fish clean parasites of larger animalsof larger animals

OthersOthers clownfish & anemonesclownfish & anemones hermit crabs & snail shellshermit crabs & snail shells

Evolutionary AdaptationsEvolutionary Adaptations

Adaptive BehaviorsAdaptive Behaviors Nocturnal feedersNocturnal feeders Eviscerate internal Eviscerate internal

organsorgans

Produce toxic mucusProduce toxic mucus Hide @ nightHide @ night

Sea Cucumber Sea Cucmber eviscerating

Structural Adaptations – feedingStructural Adaptations – feeding Cnidocytes (cnidarians)Cnidocytes (cnidarians) AppendagesAppendages

like radioles (hairlike; on Christmas tree like radioles (hairlike; on Christmas tree worms, filter)worms, filter)

““feathers” on feather duster worms for feathers” on feather duster worms for suspension feeding Feather Duster wormsuspension feeding Feather Duster worm

““forelimbs” of Mantis Shrimp Mantis shrimp forelimbs” of Mantis Shrimp Mantis shrimp punchpunch

Cirri of Crinoids (feather stars)Cirri of Crinoids (feather stars) Radula – molluscsRadula – molluscs Cephalopods – suckers, mantle (jet Cephalopods – suckers, mantle (jet

propulsion), eye sight, modified radula or propulsion), eye sight, modified radula or beakbeak

Protective Body CoveringProtective Body Covering CaCOCaCO33 deposits in tissues (algae, deposits in tissues (algae,

corals, sponges) or in shells corals, sponges) or in shells (molluscs)(molluscs)

Hardened outer cover & spines (test Hardened outer cover & spines (test & spines of sea urchins)& spines of sea urchins)

Bony skin (trunkfish)Bony skin (trunkfish)

Role of ColorRole of Color CrypticCryptic AposematicAposematic DisruptiveDisruptive Defend territoryDefend territory Mating Mating

rituals/attract rituals/attract matesmates

ThreatsThreats HumanHuman

Destructive fishing practicesDestructive fishing practices OverfishingOverfishing Dynamite Dynamite CyanideCyanide

Coastal DevelopmentCoastal Development Human-induced Climate ChangeHuman-induced Climate Change

Coral BleachingCoral Bleaching Coral Diseases - bacterialCoral Diseases - bacterial

Other ThreatsOther Threats

PollutionPollution Mining coralMining coral Collecting coral for commercial Collecting coral for commercial

trade (trinkets)trade (trinkets) Boat anchorsBoat anchors

Coral BleachingCoral Bleaching

Corals expel zooxanthellae due to:Corals expel zooxanthellae due to: Inc. temps.Inc. temps. Excessive radiationExcessive radiation Aerial exposureAerial exposure SedimentationSedimentation Bacterial infectionBacterial infection

Inc. greatly since 1980Inc. greatly since 1980