coral reefs— health and hazards dr. maia mcguire university of florida/sea grant photo by mike...
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Coral Reefs—health and
hazards
Dr. Maia McGuireUniversity of
Florida/Sea GrantPhoto by Mike White, FKNMS
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What is a Coral?Animal, vegetable or mineral?
It’s an animal which may live with a plant and makes a mineral-based skeleton.
Illustration by Geoff Kelley in JEN Veron (2000) Corals of the World, AIMS, Townsville
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Coral structureIndividual animals are called
polypsSeveral polyps make up a
colonyCorals are closely related to
jellyfish and sea anemones—they all contain stinging cells called nematocysts.
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Coral reefs
Reef-building corals require clear, warm waterShallow areasMost reefs are between 26° N and S
latitudeThere are corals found off Alaska
and other cold waters, but they grow very slowly and do not form reefs
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Symbiosis
Many hard and soft corals (and some jellyfish and sea anemones) contain a symbiotic single-celled brown dinoflagellate (algae) called zooxanthellae
This is a mutualistic symbiosisBleaching occurs when corals lose
their zooxanthellae
E.C. Peters
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Coral Bleaching
Response to stressTemperatureUVOxygen DarknessSedimentation
Who initiates bleaching?
Can corals recover?
J. Hoggesteger
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Patterns of bleaching
Geographically, often begins in the Caribbean and spreads northwards
Physically, there are often bleached patches on the sides of large coral heads (especially Montastraeas)
Seasonal—usually in summer
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ENSO
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Zooxanthellae “clades”
Three groups of zooxanthellae have been identifiedEach group has different
environmental tolerances and is found in different locations on the coral head
Photo by Scott R. Santos, SUNY Buffalo
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Where do zooxanthellae go?
“Free” zooxanthellae are rarely found in plankton samplesMay become benthic, sessileMay go into dormant stage
Presumably free zooxanthellae do exist
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Coral reproduction
Asexual reproduction (usually in branching corals; often storm-related)
Sexual reproductionHermaphroditic or gonochoristicSelf- or cross-fertilizationInternal or external fertilizationBrooders or broadcast spawners
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Richard Fitzpatrick
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Bette Willis in J.E.N. Veron (1987) Corals of Australia
and the Indo-Pacific. Hawaii University Press
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BroodersEggs develop into larvae
internally and may be brooded for several weeks
Larvae are released, often at night, often in response to the lunar cycle
Brooders may have up to 12 reproductive cycles per year R. Hays Cummins
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Coral larvae (planulae)
Swim using tiny hairs (cilia)May already contain
zooxanthellaeSwim for days to weeks
before they settle and metamorphose
Settlement may be in response to chemical cues and may be gregarious
Bob Richmond
NOAA
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Status of coral reefs
Globally, coral reefs are generally in decline
Increasing human population (especially in coastal areas) increases the impacts on coral reefs
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Human impacts on coral reefs
OverfishingSedimentationNutrient
enrichmentChemicals/oilPhysical damage
(anchors, fishing, groundings)
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Overfishing
Changes trophic structure
Many large predators are no longer present
Grazing fish species are being collected as food fish
May allow algal overgrowth of corals
NOAA
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Nutrient enrichment
Nutrients are elements needed for growth
If there are not enough of certain types of nutrients, they are said to be limiting nutrients
Most common limiting nutrients in the marine environment are N and P
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NitrogenAvailable in water as
nitrate, nitrite, ammonium or organic nitrogen (e.g. urea, plant or animal tissues)
PhosphorusAvailable in water as dissolved inorganic phosphate or organic phosphorus (dissolved or particulate)
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How does nutrient enrichment occur?
Septic tanks/sewageLeaksPumping into the
oceanFertilizer runoff
AgriculturalHomeownersGolf courses
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Effects of increasing nutrients
Cause increase in plant (algae) growthMacroalgaeMicroalgae
(phytoplankton)
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HAB’s/Red tides
Blooms of “harmful algae”PfisteriaCause human health
problemsCause fish killsMay be killing dolphins,
manateesFMRI
Mote Marine Lab
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Cause decrease in coral growthDirect chemical
interference with skeleton formation
Result of overshading by algae
Effects of increased nutrients on corals
Jennifer M. Smith
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The nutrient-calcification mystery
If zooxanthellae help corals calcify, then why do enriched corals, which contain more zooxanthellae, calcify less?Zooxanthellae are N-limited“Excess” photosynthate is given to
coralIf zooxanthellae grow, there is less
photosynthate to give to the corals
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But….There are more zooxanthellae per cm² of
coral, so the animal receives the same amount of carbon…
=Is the type of carbon compound different
in enriched and control corals?
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Chemicals/oil
Non point-source pollution– 51% of the oil entering the oceans is
from runoff– 5% is from big spills– 19% is from routine maintenance– 2% is from offshore drilling– 13% is from burning fuels (e.g. car
exhaust)– 10% is from natural seeps
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Physical damage
Fishing techniques in the South Pacific include dynamiting or poisoning reefs to collect aquarium fish for export
Boat anchors and boat/ship groundings cause damage that can take thousands of years to re-grow
Thomas Heeger, Philippines
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Natural impacts
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Marine debris
Suffocation riskBalloons/bags
Entanglement/entrapmentFishing line/ropesOld netsAbandoned traps/pots
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What can you do?
Reduce, reuse, recycleMotor oilFishing line
Read and follow instructions on chemicals, including fertilizers
Fix automotive leaks
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What does the future hold?
The answer is up to you…
1988
1998
USGS
USGS