© 2007 W.W. Norton & Company, Inc.

Intro. to Ocean Sciences, 2nd Ed.

Coral ReefsMost coral polyps live in large coloniesHard calcium carbonate structuresCoral reefs limited to

– Warm (18o < Temp. < 30o) seawater– Sunlight (for symbiotic algae)– Strong waves or currents– Clear seawater– Normal salinity– Hard substrate

Reef-Building Corals

© 2007 W.W. Norton & Company, Inc.Intro. to Ocean Sciences, 2nd Ed.

Reef-Building Corals

Symbiosis of Coral and Algae

Corals are anthozoans and are related to anemones

Coral reefs made of algae, mollusks, foraminifers as well as corals

Hermatypic coral mutualistic relationship with algae– Algae provide food– Corals provide nutrients

http://www.coris.noaa.gov/about/what_are/what_are.html

Coral Polyp

Get a portion of their nutrition from algae living in their tissues

Includes corals, foraminifers, sponges, and mollusks

Coral reefs contain up to 3 times as much algal biomass as animal biomass

Staghorn coral sponge

Mixotrophs

Reef Formation

http://www.coris.noaa.gov/about/what_are/what_are.html

Coral Reef Zonation Different types of corals at different depths

– Sunlight and Wave Action

•No sunlight at depth•Algae can’t live so NO CORALS

•Delicate corals at base of euphotic zone•Little wave energy

Big, beefy, branching corals in shallow water BUTTRESS ZONE Can withstand wave impact

Importance of Coral Reefs

Largest structures created by living organisms– Great Barrier Reef, Australia, more than 2000 km

(1250 m) long

Great diversity of species- Analogy to tropical rain forests

Important tourist locales

Fisheries

Reefs protect shorelines

Crown-of-Thorns Starfish and Reefs

Sea star eats coral polyps

Outbreaks (greatly increased numbers) decimate reefs

Humans and Coral Reefs

Activities such as fishing, tourist collecting, sediment influx due to shore development harm coral reefs

Sewage discharge and agricultural fertilizers increase nutrients in reef waters– Hermatypic corals thrive at low nutrient levels– Phytoplankton overwhelm at high nutrient

levels– Bioerosion of coral reef by algae-eating

organisms

Corals release their algae and die

May be due to very warm water temperatures

El Nino event killed 70% of corals in Pacific coast of Central America

Figure from http://www.nsf.gov/od/lpa/forum/colwell/rc01aibs/sld021.htm

Coral Bleaching

East Flower Gardens

WestFlowerGardens

Flower GardensFlower GardensNational Marine SanctuaryNational Marine Sanctuary

Coral Reefs in theGulf of Mexico

West Flower Gardens Bank Flyover Animation

http://walrus.wr.usgs.gov/pacmaps/wf-fly.html

Fly-by of the shaded-relief bathymetry of West Flower Garden Bank National Marine Sanctuary, Gulf of Mexico. The movie flies by a modern living reef platform, the top of which is at about 15 m water depth. The upper white contour line is 30-m water depth and the lower contour line is 42-m water depth. The top of the platform is approximately 1 km long and 275 m wide. The flight approaches from the west toward the north side of the reef platform.