• Domain

• Kingdom

• Phylum

• Class

Coral ClassificationEukarya

Animalia

Cnidaria

Anthozoa (Anemones and Corals)

Coral ReefsOCN 201 Biology Lecture 12

• Octocorals (8 tentacles, almost always colonial) - Gorgonians, Soft corals, etc.

• Zoantharia (More tentacles, solitary or colonial) - Anemones, stony corals (reef building), black coral, etc.

Coral Types

Octocorals Zoantharia

Gorgonia Soft CoralBlack Coral

Stony Corals

Reef-Building Coral Polyp

Have symbiotic zooxanthellae (photosynthetic dinoflagellates)

Calyx (or cup)

Hermatypic: Reef-builders secrete Calcium Carbonate Skeleton

Zooxanthellae

• Coral Nutrition - Coral ingests small fish, zooplankton (protein/nitrogen) - Zooxanthellae photosynthesize (carbohydrate)

• Growth - Zooxanthellae assists in calcification - Calcification 10 x faster with zooxanthellae

Symbionts enter coral cells by Endocytosis

http://en.wikipedia.org/wiki/Endocytosis

Coral BleachingIf temperatures too warm, corals lose (or eject) the zooxanthellae

http://en.wikipedia.org/wiki/Coral_bleaching

• Polyp secretes calcium carbonate underneath

• Occasionally will lift up and create a new floor (basal plate), leaving a trapped space

• Carbonate deposition varies with temperature

Growth

• Age (# bands)

• Growth rate (band width)

X-ray of coral section

• Reproduction is frequently by synchronized broadcast fertilization (release of eggs and sperm into water)

• Fertilized eggs develop into larvae

• Many settle quickly, but can stay in plankton for 60 days or more - dispersal by currents

• Settlement is controlled by chemical cues

• Settled larvae develops into polyp and forms colony

Reproduction

• Reefs are the foundation of incredibly complex communities

• The reef provides structure that shelters diverse creatures and primary productivity that provides food

Coral Reef Habitat

• Found in tropical, nutrient-poor areas

• Where water temperature does not go below 18°C

• Higher diversity at western side of the ocean basins

Coral Reef Distribution

Coral ReefsAnnual Temp. Range <3°C

Distribution and Diversity of Stony Corals

Evolution of Island Reefs

Text

Time

Fringing

Eventually Atoll Drowns

Barrier Atoll

The Darwin Point

• Volcanic Islands ride the Pacific Plate northward into cooler waters

• Growth rate declines until it can no longer keep up with subsidence

• Critical Point (Darwin Point) is at 29° North: Atoll drowns

The Darwin Point

Empe

ror

Seam

ount

Cha

inMidway Atoll

Hawaiian Ridge

Hawaii

Darwin Point