B. Polyps grow in groups called colonies

1. each succeeding generation builds its home upon the foundation of skeletons left by the last

2. colonies attach to other colonies

C. Growth factors: depth of water, amount of light, water movement, temperature and water clarity affect the way in which a coral colony

grows; corals are naturally long-lived but are intolerant of changes

1. corals require a water temperature of 22̊C (72̊F) or more so they

are only found in the tropics

2. reef-building corals are limited to growing no deeper than 50m (164') as they need sunlight

a. they need sunlight because within the living tissue of the polyp are tiny plant cells called zooxanthellae

b. causes tissue to look brownish

D. Zooxanthellae fix sugar (photosynthesis) and corals use it for nutrition

(up to 90% of energy used by coral comes from algae); deeper forms of

coral intake more plankton.

1. zooxanthellae receive nutrients and a place to live from the coral

2. so corals are a composite organism - part animal and part plant

E. Life history of coral polyps

1. Food: regularly feed on small creatures floating by, captured bysticky stinging tentacles.

a. feeding usually occurs at night as tentacles would be bittenoff by fish during the day; tentacles are withdrawn into the protection of a hard skeleton formed by the polyp (limestone).

b. digested food can go to their neighbors (which are clones) and is transported by cili