Bio 125 - Ch 30 Coral Reefs

Coral Reefs

hermatypic corals

reef builders, contain zooxanthellae, tropical in distribution: warm, shallow water.

ahermatypic corals

not reef builders, may not contain zooxanthellae, can be found in cold, deep water.

How do corals get food/nutrition?

Coral zooxanthellae produce organic matter through photosynthesis. Corals can also feed using mesenterial filaments.

mesenterial filaments

Extensions of the gut wall on corals. Secrete digestive enzymes.

zooxanthellae

symbiotic photosynthetic dinoflagellates that produce organic matter through photosynthesis and help in the deposition of the calcium carbonate skeleton.

conditions for coral growth

hard substrate for settlement, optimal light for zooxanthellae, narrow temperature range, narrow salinity range, low sediment load in water, low pollution levels.

How corals reproduce

corals reproduce both sexually and asexually. Asexual reproduction allows for the growth of a colony of polyps. Sexual reproduction results in the release of planktonic planula larvae for dispersal into new locations.

coral bleaching

results from coral stress, an expulsion of zooxanthellae from the coral polyp. Zooxanthellae gives corals their distinctive colors.

Where do corals live and what do they require?

corals live in warm, shallow salty waters with a narrow temperature range, optimal light.

Coral growth forms

branching, encrusting, foliose, columnar, massive, plating

3 major types of coral reefs

fringing reefs, barrier reefs, atolls

fringing reefs

A reef that forms around a land mass. Develops as narrow strips along the shore.

barrier reefs

A coral reef parallel to the shore but is separated by a channel of water. Develops farther from shore. Ex: Great Barrier Reef, Australia, Belize off Central America.

Keys or Cays

Enough sediment may accrue to form small islands on the reef.

atolls

A ring-shaped circular coral reef, consisting of a coral rim that encircles a lagoon.

How atolls form

Begins developing when a volcanic island is formed, a hypothesis first presented by Charles Darwin. Coral begins as a fringing reef around the newly formed island which eventually disappears below the water surface, leaving only the outer band of coral surrounding a lagoon. The fringing reef becomes an atoll.

competition on reefs for space

corals may feed directly or sting one another if they come in contact. May produce toxic or foul-tasting chemicals. Other animals compete for limited resources by feeding in slightly different ways and/or times of the day by reproducing at different times of the year.

Impact of grazers on reefs

Important in structuring coral reef communities. Grazers (fishes, sea urchins) keep seaweeds from taking over coral surfaces.