Download Powerpoint

Class 38
CORAL REEF COMMUNITIES
•Description
•Coral ecology and symbiosis
•Threats
•Diverse and productive
•Thousands of invertebrate and vertebrate
species
•“Rainforests” of the marine world
Coral Reef
Coral animal -- dominant reef-builder
•Related to Jellyfish and Sea Anenomes
•Colonies; individual polyps with tentacles
-predators and filter feeders.
Coral animal -- dominant reef-builder
Individuals secrete supporting "cup" of CaCO3
(grow up to 10 cm per year!)
•Variety of growth forms -massive, columnar, branching, etc.
Environmental requirements of
growing coral reefs:
T: >18˚C…..23-25˚ is best
--> mostly low latitude, < 30˚ N or S
Environmental requirements of
growing coral reefs:
T: >18˚C…..23-25˚ is best
--> mostly low latitude, < 30˚ N or S
Salinitycannot be low (e.g., near rivers)
Depth: Photic zone only, cannot grow deeper
than 50-150 m
Clear water (little suspended sediment,
phytoplankton)
Coral Nutrition
Symbiotic algae provide much food
Tentacles capture additional food
Symbiotic zooxanthellae in corals
Zooxanthellae are dinoflagellates (photosynthesis)
... give corals color (pink, purple, green)
... corals grow only in photic zone
Symbiosis:
Zooxanthellae get from corals:
•constant, protected environment
•source of CO2 and nutrients (P, N)
Zooxanthellae give to corals:
•Food (sugars; they are not eaten)
•O2
Types of coral reefs:
Fringing reef -- borders shoreline
Barrier reef -- further offshore, lagoon in between
Atolls -- ring-shaped
Coral reefs
in trouble
1.Natural predators
(e.g., crown of
thorns star fish)
Coral reefs in trouble
2. Human activities (nutrients, fishing,
recreation)
Cyanide
Fishing
Coral reefs and nutrients
•
•
Coral ecosystems well suited for low nutrient
levels (P and N)
Nutrients can come from sewage and fertilizer
Coral reefs and nutrients
•
•
•
•
Coral ecosystems well suited for low nutrient
levels (P and N)
Nutrients can come from sewage and fertilizer
Increased nutrient levels allow other species to
dominate (e.g., phytoplankton)
Ecosystem changes, slow-growing corals can’t
compete, or are attacked by disease
Coral reefs in trouble
3. Coral bleaching: zooxanthellae expelled
• Most common in unusually warm waters: >32˚C
• 2 degrees above normal maximum causes it
• Result of global warming?
Blue=low threat, yellow= med., red= high