Coral Reefs
What is coral?
 It’s a living organism!
 It is an invertebrate
 Cnidaria!!
Sun Coral Polyps
Where Can You Find Coral Reefs?
 Coral is found all over the
world:
 Tropical
 Temperate
 Only tropical corals build reefs
Coral reefs around the world
Coral Builds Reefs?
 The animal portion of the reef
is called a polyp
 The polyp absorbs calcium
carbonate out of the water
 The calcium carbonate is used
to build the reef
Coral are Cnidarians
 Soft bodied
 Carnivorous
 Stinging tentacles arranged in
a circle around their mouth
 Radial symmetry
Cnidarians
 Usually two life stages:
 Polyp
 Medusa
Anatomy of Coral
 The coral polyps build a
calcium carbonate cup called a
corallite to live in
 Coral has stinging cells called
nematocysts
Stinging Cells
 Nematocysts help coral
catch food
 They also help protect the
coral
 When the cell is
stimulated, it releases a
sharp barb
 The barb will fire and
catch the food and bring it
back towards the mouth
Coral and Zooxanthella (algae)
 Symbiotic relationship
 Zooxanthella is an algae that lives in the skin of coral
 Coral provides protection
 Zooxanthella provides food and color!
Coral is Picky
 Very specific habitats:
 Temperature: 73-75F
 Depth: Less than 80 ft to 230 feet
 Salinity: Normal salt levels (35ppt)
 Light: Zooxanthellae need light to survive
 Sedimentation: Being covered with silt
interferes with photosynthesis
 Desiccation: being exposed to air. The
corals will die if exposed too long
Key Concepts
 Coral reefs are primarily found in tropical clear
water, usually at depths of 60 meters or less.
 The three major types of coral reefs are fringing
reefs, barrier reefs, and atolls.
 Both physical and biological factors determine
the distribution of organisms on a reef.
© 2006 Thomson-Brooks Cole
Key Concepts
 Stony corals are responsible for the large
colonial masses that make up the bulk of a coral
reef.
 Reef-forming corals rely on symbiotic
dinoflagellates called “zooxanthellae” to supply
nutrients and to produce an environment
suitable for formation of the coral skeleton.
 Coral reefs are constantly forming and breaking
down.
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Key Concepts
 The most important primary producers on coral
reefs are symbiotic zooxanthellae and turf
algae.
 Coral reefs are oases of high productivity in
nutrient-poor tropical seas.
© 2006 Thomson-Brooks Cole
World of Coral Reefs
 Coral reefs are highly productive, but occur in
nutrient-poor waters
 This is made possible by the symbiotic
relationship between coral animals and
zooxanthellae
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Coral Animals
 Coral nutrition
 symbiotic zooxanthellae
 supply 90% of nutritional needs of stony coral
 coral polyp provides a suitable habitat and nutrients,
absorbed directly through the animal’s tissues
 zooxanthellae remove CO2 and produce O2
 need of zooxanthellae for sunlight limits the depths
to which stony corals can grow
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Coral Animals
 Coral nutrition (continued)
 corals as predators
 small animals paralyzed by the nematocysts are
passed into the digestive cavity
© 2006 Thomson-Brooks Cole
Coral Animals
 Coral nutrition (continued)
 other sources of nutrition
 corals can feed off bacteria living in their tissues,
which feed on dissolved organic matter directly from
the water
© 2006 Thomson-Brooks Cole
Coral Reef Types
 Fringing reefs border islands or continental
landmasses
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Coral Reef Types
 Barrier reefs are similar to fringing reefs but
separated from the landmass and fringing reef
by lagoons or deepwater channels
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Coral Reef Types
 Atolls, usually elliptical, arise out of deep water
and have a centrally-located lagoon
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Reef Structure
 Reef front or forereef—portion of the reef that
rises from the lower depths of the ocean to a
level just at or just below the surface of the
water, on the seaward side
© 2006 Thomson-Brooks Cole
Reef Structure
 Reef crest—the highest point on the reef and
the part that receives the full impact of wave
energy
 Reef flat or back reef—portion behind the reef
crest
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Coral Reef Distribution
 Major factors influencing distribution:
 temperature – corals do best at 23-25o C
 light availability – photosynthetic zooxanthellae




need light
sediment accumulation – can reduce light and clog
feeding structures
salinity
wave action – moderate wave action brings in
oxygenated seawater, removes sediment that
could smother coral polyps
duration of air exposure – can be deadly
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Coral Reef Ecology
 Coral provides:
 foundation for reef food webs
 shelter for resident organisms
 Reefs form a complex 3-dimensional habitat for
many beautiful and strange creatures
© 2006 Thomson-Brooks Cole
Coral Reef Community
 Sponges and cnidarians
 sessile organisms, though anemones can move if
necessary
 filter feed; anemones also paralyze and consume
small fishes and crustaceans
 Annelids
 sessile filter feeders include featherduster and
Christmas tree worms
 fireworms are mobile predators
 palolo worms burrow through and weaken coral
and usually deposit feed
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Coral Reef Community
 Crustaceans
 shrimps, crabs and lobsters
 vary from parasites to active hunters
 Molluscs
 gastropods eat algae from coral surfaces
 giant clams are filter feeders, but also host
symbiotic zooxanthellae
 octopus and squid are active predators
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Coral Reef Community
 Echinoderms
 feather stars, sea urchins, brittle stars, sea stars,
and sea cucumbers
 filter feed, scavenge, or eat sediment
 Reef fishes
 most prominent and diverse inhabitant
 diverse food sources, including detritus, algae,
sponges, coral, invertebrates, other fish
© 2006 Thomson-Brooks Cole
Species Interactions on Coral
Reefs
 Competition among corals
 fast-growing, branching corals grow over slower-
growing, encrusting or massive corals and deny
them light
 slower-growing corals extend stinging filaments
from their digestive cavity to kill faster-growing
corals
 fast-growing corals can also sting and kill using
long sweeper tentacles with powerful nematocysts
© 2006 Thomson-Brooks Cole
Species Interactions on Coral
Reefs
 Competition among corals (continued)
 slower-growing corals are more tolerant of shade,
and can grow at greater depths
 as a result…
 fast-growing, branching corals on many reefs
dominate upper, shallower portions
 larger, slower-growing corals dominate deeper
portions
© 2006 Thomson-Brooks Cole
Species Interactions on Coral
Reefs
 Competition between corals and other reef
organisms
 sponges, soft corals and algae can overgrow stony
corals and smother them
 algae outcompete corals at shallow depths unless
grazers control the algae growth
© 2006 Thomson-Brooks Cole
Species Interactions on Coral
Reefs
 Effect of grazing
 grazing of larger, fleshier seaweeds permits
competitively inferior filamentous forms or
coralline algae to persist
 herbivory decreases with depth
 damselfish form territories where they exclude
grazers and permit abundant algal growth
 provides habitat for small invertebrates
 overgrows corals; fast-growing, branching corals are
most successful near damselfish
© 2006 Thomson-Brooks Cole
Coral Reef Ecology
 Coral reefs - marine habitats with greatest
diversity/abundance of fishes
 Seems to defy competitive exclusion principle,
which suggests that no 2 species can occupy the
same niche
 60-70% of reef fishes are general carnivores
 about 15% are coral algae grazers or omnivorous
© 2006 Thomson-Brooks Cole
Threats to Coral Reefs
 Effect of physical changes on the health of coral
reefs
 hurricanes and typhoons topple and remove coral
formations
 El Niño Southern Oscillation (ENSO)
 changes winds, ocean currents, temperatures, rainfall
and atmospheric pressure over large areas of tropical
and subtropical areas
 can cause massive storms
© 2006 Thomson-Brooks Cole
Threats to Coral Reefs
 Coral bleaching
 a phenomenon by which corals expel their
symbiotic zooxanthellae
 most often associated with warming of the ocean
water by or global warming
 if the stress is not too severe, corals may regain
zooxanthellae and recover
 if the stress is prolonged, corals may fail to regain
zooxanthellae and die
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Threats to Coral Reefs
 Human impact on coral reefs
 overfishing may occur
 human-sewage bacteria cause white pox
 nutrient-rich runoff (eutrophication) increases
algal growth, which covers and smothers corals
 e.g. Kane’ohe Bay in Hawaii
© 2006 Thomson-Brooks Cole
Evolutionary Adaptations
of Reef Dwellers
 Role of color in reef organisms
 color for concealment and protection
 countershading
 disruptive coloration
 camouflage (bright colors in reef environment)
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Evolutionary Adaptations
of Reef Dwellers
 Role of color in reef organisms
 other types of camouflage
 body shape
 warning coloration
 other roles of color
 defending territories
 mating rituals
© 2006 Thomson-Brooks Cole
Evolutionary Adaptations
of Reef Dwellers
 Symbiotic relationships on coral reefs
 cleaning symbioses
 cleaner wrasses, gobies, etc. feed on parasites of
larger fishes
 cleaning organisms set up a cleaning station
 Other symbiotic relationships




clownfishes and anemones
conchfish and the queen conch
gobies and snapping shrimp
crustaceans and anemones
© 2006 Thomson-Brooks Cole
Coral Reefs
http://tools.coralreef.org/content/
objects/view.acs?object_id=545
http://ourworld.compuserve.com/homepages/
mccarty_and_peters/coral/C-intro.htm
Importance of Coral
Reefs
 0.2% of world’s oceans
 Habitat for 1/3 of marine fishes
 Habitat for tens of thousands of
other animals
 The rainforests of the oceans
Importance of Coral
Reefs
 PROTECTION TO COASTLINES
 ECONOMIC RESOURCES
 BIODIVERSITY
 NATURAL BEAUTY
Importance of Coral
Reefs
 PROTECTION TO COASTLINES
 absorb energy of ocean waves
 reduce erosion of shoreline
 storm damage
 flooding
Importance of Coral
Reefs
 ECONOMIC RESOURCES
 Fisheries for food
 Fisheries for jobs
 Tourism
 Building materials
 Aquarium trade
Importance of Coral
Reefs
 BIODIVERSITY
 The rainforests of the sea
 Genetic diversity
 Pharmaceuticals
Importance of Coral
Reefs
 NATURAL BEAUTY
http://sustainableseas.noaa.gov/missions/
florida2/background/coralspawning.html
$375 billion in environmental goods and services
Reefs at Risk 1998 (http://www.wri.org/powerpoints/reefswww/sld011.htm
Caribbean reef values
(annual net benefits in 2000)
 Fisheries: $310 million
 Dive tourism: $2.1 billion
 Shoreline protection: $0.7-2.2
billion
Total: $4.1-4.6 billion
REEFS WORLDWIDE ARE
THREATENED
• 11% of reefs have been lost
• 16% of reefs severely damaged
• ~60% of studied reefs threatened by
human activities
• No pristine reefs left
CARIBBEAN REEFS DECLINING
• 1970s: ~50% coral cover
• Present: ~10% coral cover
• =80% reduction in coral cover over
last 30 years
Gardner et al. 2003 Science 301: 958-960
Threats to coral and
coral reefs:
1) Natural
2) Anthropogenic
– of human origin
Natural disturbances that affect
corals and coral reefs?
• Hurricanes
• Tsunamis
• Volcanoes
• Earthquakes
• Predators & competitors
• Bleaching
• Pathogens
Hurricanes
 Physical damage
•Smothering
•Freshwater poisoning
http://www.nhc.noaa.gov/
1989hugo.html
•Destruction of other ecosystems upon
which coral reefs depend
Tsunamis
 Physical damage
•Erosion
•Possible disruption of
reproduction and recruitment
Volcanoes
 Depends upon
where volcano
occurs
•Heat
•smothering and
sedimentation
http://volcano.und.nodak.edu/vwdocs/
current_volcs/montserrat/montserrat.html
Earthquakes
 Little direct impact
•Indirect impacts
-triggers tsunamis
-coastal landslides
Predators
 crown of thorns starfish
 snails
 parrotfish
 butterflyfish
http://www.aims.gov.au/pages/reflib/
cot-starfish/pages/cot-q07.html
http://www.sanctuaries.nos.noaa.gov/pgallery/pgflower/living/fg_living.html
Competitors
 algae
http://catbert.er.usgs.gov/african_dust/algae.html
 Loss of zooxanthellae
 causes
 higher than usual
ocean temperature
 sharp changes in
salinity
 heavy UV light
exposure
http://ourworld.compuserve.com/homepages/
mccarty_and_peters/coral/Bleach.htm
http://orbit-net.nesdis.noaa.gov/orad/coral_bleaching_index.html
Pathogens
 Diseases on the rise
 new pathogens (8+)
 land pathogens
(Aspergillus)
 occurring at all depths
 More susceptible when
stressed
http://ourworld.compuserve.com/
homepages/mccarty_and_peters/
coral/Bbd.htm
Anthropogenic
threats to coral reefs:
•Overfishing
•Development
•Mining and dredging
•Recreation
Overfishing
 Ecological imbalance
http://www.photolib.noaa.gov/r
eef/reef2570.htm
http://tools.coralreef.org/content/objects/view.acs?object_id=545
Overfishing
 Ecological imbalance
http://catbert.er.usgs.gov/african_dust/events.html
Overfishing
• Destructive fishing practices
http://oceanworld.tamu.edu/stud
ents/coral/coral5.htm
http://www.wri.org/indictrs/rrcyanid.htm
Development
 Sediment  smothering
 Freshwater input
 Pollutants & nutrients
(sewage, pesticides, fertilizer, heavy metals,
pathogens)
Development
http://www.wcmc.org.uk/marine/data/co
ral_mangrove/coral.danger.html
http://ourworld.compuserve.com/homepages/
mccarty_and_peters/coral/c-intro.htm
Development
http://www.sanctuaries.nos.noaa.gov/scied/science/habitat/influences.html
Mining for construction
materials and dredging
 Destruction of reef structure
 stirs up sediment
Recreation
Anchors, boats, flippers,
hands, feet
•Kill animal tissue
•Skeleton breakage
http://www.sanctuaries.nos.noaa.gov/scied/science/
habitat/influences.html
Global climate change
 Reduced reef building
 Increase in frequency and intensity
of hurricanes
 Increases in bleaching
 Increased in disease