1. Introduction to Coral Reef Ecosystems

2. Reef Development Coralline algae – precipitate calcium carbonate
Sponges – secrete silica
Dominant species = Framework Builders because they provide the matrix for the growing reef

3. Reef Development
Scleractinia (“hard-rayed”) corals – start reefs – form the base
Colonial corals:
large numbers of individual coral
polyps that are interconnected by
living tissue and calcium carbonate
skeletons
Hermatypic corals – contribute most to reef growth the more zooxanthellae the higher the calcification rates (ahermatypic corals do not build reefs)

4. Scleractinia corals come in two forms: Massive mound shaped often irregular grow slowly (1 cm/year) Branching tree-branch or elkhorn shapes grow rapidly (10 cm/year) spread rapidly across reef fragments can start new colonies

5. Mutualism in corals
Mutualism – both species benefit Zooxanthellae – photosynthetic single-celled algae Coral polyp – microscopic animal in the Cnidaria family

6. Mutualism in corals
Benefit to zooxanthellae protection nutrition from coral excretion Benefit to coral polyp get energy in form of carbohydrates Corals still need to eat to get other nutrients and minerals such as nitrogen and calcium but the zooxanthellae provide the base energy to keep them healthy and alive

7. Limits to reef growth – abiotic factors
Temperature
Lowest temp = 64
Optimal range = 73 – 84
Highest tolerance observed for short time in one specie = 104
Light
Active reef building stops below 25 m – 50 m depending on species
Turbidity
Sedimentation
Salinity
32 – 42 ppt

8. Limits to reef growth - Bioerosion
Vertebrates scrape corals
Parrot fish
Surgeon fish
Invertebrates bore into coral
Urchins enlarge crevices
Sponges use chemical attack

9. Depth zonation in reefs
Different corals occur at different depths because…
Wave and current strength
Light
Suspended sediments
*Competition for resources leads to one dominant species in each habitat

10. Depth zonation