1. Nature’s Gardens: Coral Reefs
- Building a Reef: Symbiosis
- Types of Reefs
- Life on a Reef
- Coral Reefs and the Future
Reading
4th Ed: Ch 16 Sec 5, 15, 21-22 Ch 15 Sec 5, Ch 12 Sec 22-24
5th Ed: Ch 16 Sec 5, 15, 21, Ch 15 Sec 5, Ch 12 Sec 21-23
Graphic: Coral reef, courtesy of NOAA.
2. Cnidaria - Carnivorous Stinging Animals
Jellyfish, anemones, corals
- Simple digestive system
- Stinging cells (cnidoblasts) shoot upward from tentacles penetrate, entangle
or disable prey
-Two forms medusa (jellyfish) and polyp (anemones)
Graphics: Left: Anemone. Collection of Dr. J.P.McVey, NOAA Photo Library.
Right:Garrison, Fig. 15.4, 4th Ed., pg 380, 5th Ed., pg 358.
3. So What is a Coral Reef?
- Largest animal-built structures on Earth (Great Barrier Reef = 2500 km long)
- Composed of coral animal skeletons, which accumulate, gradually forming a reef
- Reefs grow slowly (1 cm/yr) and are sensitive to changes in sea level and
temperature
Graphics: (top) Coral polyps, (middle) colonial coral, (bottom) coral skeleton,
all from the collection of Dr.J.P.McVey, courtesy of NOAA.
4. Coral Biology
Many species of coral have symbiotic algae (zooxanthellae)
Coral reefs are located where the needs of both the coral animals and their
symbiotic algae are met
Coral animals - feed using tentacles
Algae - photosynthesizers that require strong sunlight
Graphic: Garrison, Fig. 15.6, 4th Ed., pg 382, 5th Ed., pg 360.
5. Coral Reefs and Environmental Conditions
Reefs require:
- abundant light
- warm water temperature
- typical ocean salinity
- sediment-free water
- high oxygen
Graphic: Maldives atolls, images and photographs courtesy Bruce Hatcher and
Abdulla Naseer, Dalhousie University, provided by NOAA.
6. Types of Coral Reefs
Fringing reef
- forms around the margin of land where rainfall runoff is low
Barrier reef
- separated from land by a lagoon
- can form around islands or off continents
Atoll
- ring-shaped island of coral enclosing a shallow lagoon
Graphics: Courtesy of NOAA, See Garrison, Fig. 12.27a-c, 4th Ed., pg 307, 5th
Ed., pg 293.
7. Where are Coral Reefs Found?
Reefs are found in clear, shallow tropical waters with moderate wave action
Graphics: (top) Great Barrier Reef, Australia, Image provided by the SeaWiFS
Project, NASA/GSFC and Orbimage, (bottom) Global distribution of coral reefs,
courtesy of NOAA.
8. Coral Reefs are Complex Communities
Coral reefs are diverse marine communities
- sustained by invertebrates
- home to many vertebrates
- intense competition for food and space
Coral reefs are 0.17% of Earth's surface area but home to 4-5% of all species
Graphics: (too) Coral reef, photo courtesy of NOAA, (bottom) Gulf of Aqaba, Red
Sea, Al Momamy, photographer, courtesy of NOAA.
9. Coral Reef Communities
Coral reefs are "oases" within the "biological desert" of the tropical oceans
Coral animals- about half of reef biomass
Coralline algae (plants) -form crusts that "cement" the reef together
Most other animal groups inhabit reefs forming a complex food web
Graphic: Garrison, 4th Ed., Fig. 16.12, pg 426, 5th Ed., Fig. 16.6, pg 396.
10. Biodiversity on a Coral Reef
Coral reefs are:
- sustained by invertebrates
- home to many vertebrates
- intense competition for food, light and space
Coral reefs are 0.17% of Earth's surface area but home to 4-5% of all species
Graphics: (too) Coral reef, photo courtesy of NOAA, (bottom) Gulf of Aqaba, Red
Sea, Al Momamy, photographer, courtesy of NOAA.
11. Competition on a Reef – Survival of the Fittest
Fast-growing coral can overgrow slower-growing species, restricting access to
light and food
Long sweeper tentacles can inject venom into adjacent competing coral colonies
Dispersal of toxic water-borne chemicals can deter neighbors
Graphics: (top) Red Sea, M. Al Momany, photographer, courtesy of NOAA, (bottom)
elkhorn and clubtip finger corals, Florida Keys National Marine Sanctuary,
courtesy of NOAA.
12. Self-Defense on the Reef
- Toxic venoms and distasteful substances are common among coral, fish and other
animals on the reef
- Bright colors serve as warnings to other species – many poisonous species are
brightly colored
- Camouflage and confusing coloration helps some species hide from predators
Graphic: Brightly colored coral and fish on a North Carolina reef, C. Liipfert,
photographer, courtesy of NOAA/NURP and Univ. N.Carolina at Wilmington.
13. The Value of Coral Reefs
- Billions of dollars for the U.S. economy through tourism, fisheries, and
recreation
- Natural storm barriers help protect coastal areas
- Home to 1 million+ species
- “Medicine cabinets” of the 21st century (treatments for heart disease,
arthritis, cancer and HIV)
Graphics: (top) Diver enjoying a reef slope, courtesy of NOAA, (bottom) A
deepwater reef community that was the focus of a recent expedition in search of
new pharmaceuticals from the sea, photo courtesy of NOAA.
Info from U.S. Coral Reef Task Force, NOAA,
http://www.coralreef.noaa.gov/outreach/protect/welcome.html
14. Threats
Under current pressures, 60% of coral reefs could die by 2050
Natural threats:
- hurricanes, storms
- changes in climate
- disease
- predators
Human threats:
- poor fishing practices (e.g., cyanide and "blast" fishing)
- pollution
- overexploitation (for recreation and commerce)
Graphic: (top) Development in coastal Florida, A.Lack, photographer, courtesy of
NOAA National Marine Sanctuaries. (bottom) Coral afflicted with fast-spreading
yellow-band disease. The left-hand picture was taken several weeks before the
right-hand picture, A.Bruckner, photographer, courtesy of NOAA.
15. Coral Bleaching
Some species of coral expel their zooxanthellae when stressed = coral bleaching
- Many cases of coral bleaching have been attributed to higher than normal ocean
temperatures (e.g., El Nino)
- Under current climate trends, there is concern among scientists for the
long-term health of coral reefs
Graphic: Bleached coral, Florida Keys, S.Miller, photographer, courtesy of OAR/NURP
and Univ. Univ.N.Carolina at Wilmington.
16. Maintaining Healthy Reefs for the Future
Research and monitoring programs
- learn more about how reef systems “work” and their potential vulnerabilities
- determine which reefs are most at risk and why
Educational programs
- targeted at both tourists and local populations
Graphics: (top) Landsat satellite images of reefs are used to map and monitor
reefs, French Frigate Shoals, Hawaii, courtesy of NOAA, (bottom) a healthy reef,
photo courtesy of NOAA.
17. Preview of Next Lecture
Life in Extreme Environments
Reading:
4th Ed: Ch 16 Sec 18, Ch 4 Sec 14, Ch 14 Sec 2
5th Ed: Ch 16 Sec 19, Ch 4 Sec 14, Ch 13 Sec 4
Graphic: Submersible exploring a brine pool. Penn. State Univ.