Introduction to Coral Reef Ecosystems
Reef Development
• Coralline algae – precipitate calcium carbonate
• Sponges – secrete silica
• Dominant species = Framework Builders because they provide the
matrix for the growing reef
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)
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
Mutualism in corals
Mutualism – both species benefit
Zooxanthellae – photosynthetic single-celled
algae
Coral polyp – microscopic animal in the
Cnidaria family
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
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
Limits to reef growth - Bioerosion
• Vertebrates scrape corals
• Parrot fish
• Surgeon fish
• Invertebrates bore into coral
• Urchins enlarge crevices
• Sponges use chemical attack
Depth zonation in reefs
Different corals occur at different depths because…
1. Wave and current strength
2. Light
3. Suspended sediments
*Competition for resources leads to one dominant species in each
habitat
Depth zonation