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Coral Reefs—health and hazards. Dr. Maia McGuire University of Florida/Sea Grant. Photo by Mike White, FKNMS. What is a Coral?. Animal, vegetable or mineral?. It’s an animal which may live with a plant and makes a mineral-based skeleton.

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coral reefs health and hazards

Coral Reefs—health and hazards

Dr. Maia McGuire

University of Florida/Sea Grant

Photo by Mike White, FKNMS

what is a coral
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

coral structure
Coral structure
  • Individual animals are called polyps
  • Several polyps make up a colony
  • Corals are closely related to jellyfish and sea anemones—they all contain stinging cells called nematocysts.
coral reefs
Coral reefs
  • Reef-building corals require clear, warm water
    • Shallow areas
    • Most reefs are between 26° N and S latitude
  • There are corals found off Alaska and other cold waters, but they grow very slowly and do not form reefs

E.C. Peters

  • 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 symbiosis
  • Bleaching occurs when corals lose their zooxanthellae
coral bleaching
Coral Bleaching
  • Response to stress
    • Temperature
    • UV
    • Oxygen
    • Darkness
    • Sedimentation
  • Who initiates bleaching?
  • Can corals recover?

J. Hoggesteger

patterns of bleaching
Patterns of bleaching
  • Seasonal—usually in summer
  • Geographically, often begins in the Caribbean and spreads northwards
  • Physically, there are often bleached patches on the sides of large coral heads (especially Montastraeas)
zooxanthellae clades
Zooxanthellae “clades”
  • Three groups of zooxanthellae have been identified
    • Each group has different environmental tolerances and is found in different locations on the coral head

Photo by Scott R. Santos, SUNY Buffalo

where do zooxanthellae go
Where do zooxanthellae go?
  • “Free” zooxanthellae are rarely found in plankton samples
    • May become benthic, sessile
    • May go into dormant stage
  • Presumably free zooxanthellae do exist
coral reproduction
Coral reproduction
  • Asexual reproduction (usually in branching corals; often storm-related)
  • Sexual reproduction
    • Hermaphroditic or gonochoristic
    • Self- or cross-fertilization
    • Internal or external fertilization
    • Brooders or broadcast spawners

Bette Willis in J.E.N. Veron (1987) Corals of Australia and the Indo-Pacific. Hawaii University Press

  • Eggs 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

coral larvae planulae
Coral larvae (planulae)
  • Swim using tiny hairs (cilia)
  • May already contain zooxanthellae
  • Swim for days to weeks before they settle and metamorphose
  • Settlement may be in response to chemical cues and may be gregarious

Bob Richmond


status of coral reefs
Status of coral reefs
  • Globally, coral reefs are generally in decline
  • Increasing human population (especially in coastal areas) increases the impacts on coral reefs
human impacts on coral reefs
Human impacts on coral reefs
  • Overfishing
  • Sedimentation
  • Nutrient enrichment
  • Chemicals/oil
  • Physical damage (anchors, fishing, groundings)
  • 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


nutrient enrichment
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
  • Available in water as nitrate, nitrite, ammonium or organic nitrogen (e.g. urea, plant or animal tissues)


  • Available in water as dissolved inorganic phosphate or organic phosphorus (dissolved or particulate)
how does nutrient enrichment occur
How does nutrient enrichment occur?
  • Septic tanks/sewage
    • Leaks
    • Pumping into the ocean
  • Fertilizer runoff
    • Agricultural
    • Homeowners
    • Golf courses
effects of increasing nutrients
Effects of increasing nutrients
  • Cause increase in plant (algae) growth
    • Macroalgae
    • Microalgae (phytoplankton)
hab s red tides
HAB’s/Red tides
  • Blooms of “harmful algae”
    • Pfisteria
    • Cause human health problems
    • Cause fish kills
    • May be killing dolphins, manatees

Mote MarineLab



Effects of increased nutrients on corals

  • Cause decrease in coral growth
    • Direct chemical interference with skeleton formation
    • Result of overshading by algae

Jennifer M. Smith

the nutrient calcification mystery
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 coral
    • If zooxanthellae grow, there is less photosynthate to give to the corals
  • 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?
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
physical damage
Physical damage

Thomas Heeger, Philippines

  • 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
marine debris
Marine debris
  • Suffocation risk
    • Balloons/bags
  • Entanglement/entrapment
    • Fishing line/ropes
    • Old nets
    • Abandoned traps/pots
what can you do
What can you do?
  • Reduce, reuse, recycle
    • Motor oil
    • Fishing line
  • Read and follow instructions on chemicals, including fertilizers
  • Fix automotive leaks
what does the future hold
What does the future hold?

The answer is up to you…