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

Coral Reefs  Most coral polyps live in large colonies  Hard calcium carbonate structures  Coral reefs limited to –Warm (18 o < Temp. < 30 o ) 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, 2 nd 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 at_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

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 Coral Bleaching

East Flower Gardens West Flower Gardens Flower Gardens National Marine Sanctuary Coral Reefs in the Gulf of Mexico

West Flower Gardens Bank Flyover Animation 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.