Transcript Coral Reefs - University of Florida

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.
Illustration by Geoff Kelley in
JEN Veron (2000) Corals of
the World, AIMS, Townsville
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
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
Symbiosis
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
Response to stress
Temperature
UV
Oxygen
Darkness
Sedimentation
Who initiates bleaching?
Can corals recover?
J. Hoggesteger
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)
ENSO
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?
“Free” zooxanthellae are rarely
found in plankton samples
May become benthic, sessile
May go into dormant stage
Presumably free zooxanthellae do
exist
Coral reproduction
Asexual reproduction
(usually in branching
corals; often stormrelated)
Sexual reproduction
Hermaphroditic or gonochoristic
Self- or cross-fertilization
Internal or external fertilization
Brooders or broadcast spawners
Richard Fitzpatrick
Bette Willis in J.E.N. Veron
(1987) Corals of Australia
and the Indo-Pacific.
Hawaii University Press
Brooders
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)
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
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
Overfishing
Sedimentation
Nutrient enrichment
Chemicals/oil
Physical 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
Nitrogen
Available in water as
nitrate, nitrite,
ammonium or organic
nitrogen (e.g. urea,
plant or animal tissues)
Phosphorus
Available in water as
dissolved inorganic
phosphate or organic
phosphorus (dissolved
or particulate)
How does nutrient
enrichment occur?
Septic tanks/sewage
Leaks
Pumping into the ocean
Fertilizer runoff
Agricultural
Homeowners
Golf courses
Effects of increasing
nutrients
Cause increase in
plant (algae)
growth
Macroalgae
Microalgae
(phytoplankton)
HAB’s/Red tides
Blooms of “harmful algae”
Pfisteria
Cause human health
problems
Cause fish kills
May be killing dolphins,
manatees
Mote Marine Lab
FMRI
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
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
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
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
Natural impacts
Marine debris
Suffocation risk
Balloons/bags
Entanglement/entrapment
Fishing line/ropes
Old nets
Abandoned traps/pots
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?
The answer is up to you…
1988
USGS
1998
USGS