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Corals and Coral Reefs

Nancy Knowlton

National Museumof Natural History

Part 1: Past, Present and Future

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Reefs have come and gone through time

Many organisms build reefs

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Today corals build enormous structures

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Complex three-dimensional habitats

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Reefs are home to millions of species

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So what is a coral? Polyp Zooxanthellae

Skeleton

Animal + Vegetable + Mineral

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Corals also capture food

Tentacles have nematocysts

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Some corals dont have zooxanthellae

These corals grow more slowlyThey only build reefs in the deep sea

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Corals grow by budding and adding skeleton

Usually < 1 cm per year

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Corals also reproduce sexually

Egg-sperm bundles being released

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Fertilized eggs -> planula larva -> coral recruit

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Why do we care about coral reefs?

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Monetary Value of Coral Reefs

Food, Tourism, BiodiversityShoreline Protection

(non-extractive uses often dominate)

Globally - 29.8 billion US$ per year Indonesia - 1.6 billion US$ per yearHawaii 364 million US$ per year

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Coral reef crisis local & global

NutrientsToxics

SedimentsInvasives CO2

AnythingBig

In Out

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GLOBAL LOSSES OF CORAL REEFS

Discovery Bay, Jamaica - 1975

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GLOBAL LOSSES OF CORAL REEFS

Caribbean: 80% declinein 30 years

Pacific reefs not far behind

Not just Jamaica

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Riegl and Luke 1998

Direct Destruction Dynamite and Cyanide Fishing

Effects of Blasting, Red SeaControl reefs: 43-65% coral cover Blasted reefs: 2-15% coral cover

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Sedimentation smothers corals

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Lionfish invasion

Voracious predator of baby reef fish

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Predator Plagues: Crown of thorns starfish

Photo: John Ogden

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Photo: Enric Sala

Why? Loss of Predators and Excess Nutrients

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Coral-algal competion

Coral-coral competitionNutrients and over-fishing also favor seaweeds

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Urchin die-off

Lessios et al. 1984

X

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More disease in a warmer nutrient-rich ocean

White-banddisease

Black-banddisease

Often no known pathogen Could be due to stress or

bacterial overgrowth

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1988

1998

Catastrophic Mortality

Black band

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1971

1988

1971

1988

Catastrophic Mortality

White band -> EPA listing

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Coral Bleaching

Caused by stressExtreme temperature, light, salinity

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Breakdown in symbiosis between coral and algae

Tissues become transparentCan see skeleton through tissue

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Massive mortality if severe

During 1998 El Nio in Indian Ocean80% bleached, 20% died

Photo: Ove Hoegh-Guldberg

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Bleaching threshold 1o C?

Rising temperatures -> more bleaching

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Ocean Acidification

The other CO2 problem

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Some corals cant grow skeleton in acidic water

Skeleton needed to make a reef

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Skeletons provide essential 3-D habitatInvertebrate diversity

inverts

Photo: Wolcott Henry 2011

20ferti

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0

10

20

0 100 200 300

Time from first spawning colony

Averagef

0

20

40

60

80

100

0 1 2 3 4 5 6 7

Number of spawning corals/diver

P

eakfertilization

pote

ntial

R2 =

0.88

B

Even surviving corals need mates

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Lewis 2002

Dead reefs turn into sand

1950

1991

18.5%loss

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So what can we do to reverse decline

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California Condor Approach

Individual protection of species notrealistic for most species

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Hurricane Allen 1980Category 5 Storm

Need to Build Resilience

150 years

150 years

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Marine Protected Areas -> MoreResilient ReefsGold Standard

Great Barrier Reef,Australia

More than 33%in no-take zones

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Four mega-protected areas in US waters

Australia

Hawaii

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Many peopleFew fish

Little coral

Kingman (US)pop. 0

Palmyra (US) pop. ~10

Tabuaeran (KR)pop. ~ 2000 Kirimati (KR)pop. ~ 6000

Few peopleMany fish Much coral

Gradient in human impacts

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Bottom cover

Increasing protection

*

*

Striking ecological changes with protection

Photos: Enric Sala

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Bacteria

Viruses

Othermicrobes

Fewer Pathogens

Increasing protection

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Increased Resilience

Increasing Protection

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Local and global action needed

Short /Local Scale: Control fishing pressureImprove water quality

Not Rocket Science

Longer Term/Global Scale:Reduce CO2 emissionsPrevent extinctions

Is Rocket Science

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~Thank you~

Photo: Ove Hoegh Guldberg

Grand challenge: ensuring that people andreefs coexist