Coral Reefs—health and

hazards

Dr. Maia McGuireUniversity of

Florida/Sea GrantPhoto 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.

Illustration by Geoff Kelley in JEN Veron (2000) Corals of the World, AIMS, Townsville

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.

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

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

Coral Bleaching

Response to stressTemperatureUVOxygen DarknessSedimentation

Who initiates bleaching?

Can corals recover?

J. Hoggesteger

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

ENSO

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

Where do zooxanthellae go?

“Free” zooxanthellae are rarely found in plankton samplesMay become benthic, sessileMay go into dormant stage

Presumably free zooxanthellae do exist

Coral reproduction

Asexual reproduction (usually in branching corals; often storm-related)

Sexual reproductionHermaphroditic or gonochoristicSelf- or cross-fertilizationInternal or external fertilizationBrooders or broadcast spawners

Richard Fitzpatrick

Bette Willis in J.E.N. Veron (1987) Corals of Australia

and the Indo-Pacific. Hawaii University Press

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

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

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

OverfishingSedimentationNutrient

enrichmentChemicals/oilPhysical damage

(anchors, fishing, groundings)

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

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

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)

How does nutrient enrichment occur?

Septic tanks/sewageLeaksPumping into the

oceanFertilizer runoff

AgriculturalHomeownersGolf courses

Effects of increasing nutrients

Cause increase in plant (algae) growthMacroalgaeMicroalgae

(phytoplankton)

HAB’s/Red tides

Blooms of “harmful algae”PfisteriaCause human health

problemsCause fish killsMay be killing dolphins,

manateesFMRI

Mote Marine Lab

Cause decrease in coral growthDirect chemical

interference with skeleton formation

Result of overshading by algae

Effects of increased nutrients on corals

Jennifer M. Smith

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

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?

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

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

Natural impacts

Marine debris

Suffocation riskBalloons/bags

Entanglement/entrapmentFishing line/ropesOld netsAbandoned traps/pots

What can you do?

Reduce, reuse, recycleMotor oilFishing line

Read and follow instructions on chemicals, including fertilizers

Fix automotive leaks

What does the future hold?

The answer is up to you…

1988

1998

USGS

USGS