DescriptionDescription Coral ecology and symbiosisCoral ecology and symbiosis ThreatsThreats Class...

•DescriptionDescription•Coral ecology and symbiosisCoral ecology and symbiosis•ThreatsThreats

Class 38 Class 38

CORAL REEF COMMUNITIESCORAL REEF COMMUNITIES

•Diverse and productiveDiverse and productive•Thousands of invertebrate and vertebrate Thousands of invertebrate and vertebrate speciesspecies•““Rainforests” of the marine worldRainforests” of the marine world

Coral Reef

•Related to Jellyfish and Sea AnenomesRelated to Jellyfish and Sea Anenomes•Colonies; individual polyps with tentacles Colonies; individual polyps with tentacles

-predators and filter feeders.-predators and filter feeders.

Coral animal -- dominant reef-builderCoral animal -- dominant reef-builder

Individuals secrete supporting "cup" of CaCOIndividuals secrete supporting "cup" of CaCO33

(grow up to 10 cm per year!)(grow up to 10 cm per year!)•Variety of growth forms -- Variety of growth forms --

massive, columnar, branching, etc.massive, columnar, branching, etc.

Coral animal -- dominant reef-builderCoral animal -- dominant reef-builder

T: >18˚C…..23-25˚ is best T: >18˚C…..23-25˚ is best

--> mostly low latitude, < 30˚ N or S--> mostly low latitude, < 30˚ N or S

Environmental requirements ofEnvironmental requirements of growing coral reefs:growing coral reefs:

T: >18˚C…..23-25˚ is best T: >18˚C…..23-25˚ is best

--> mostly low latitude, < 30˚ N or S--> mostly low latitude, < 30˚ N or S

Salinitycannot be low (e.g., near rivers)Salinitycannot be low (e.g., near rivers)

Depth: Photic zone only, cannot grow deeper Depth: Photic zone only, cannot grow deeper than 50-150 mthan 50-150 m

Clear water (little suspended sediment, Clear water (little suspended sediment, phytoplankton)phytoplankton)

Environmental requirements ofEnvironmental requirements of growing coral reefs:growing coral reefs:

Symbiotic algae provide much foodSymbiotic algae provide much food

Tentacles capture additional foodTentacles capture additional food

Coral NutritionCoral Nutrition

Zooxanthellae are Zooxanthellae are dinoflagellatesdinoflagellates (photosynthesis) (photosynthesis)

... give corals color (pink, purple, green)... give corals color (pink, purple, green)

... corals grow only in photic zone... corals grow only in photic zone

Symbiosis:Symbiosis:

Zooxanthellae get from corals:Zooxanthellae get from corals:•constant, protected environmentconstant, protected environment

•source of COsource of CO22 and nutrients (P, N) and nutrients (P, N)

Zooxanthellae give to corals:Zooxanthellae give to corals:•Food (sugars; they are not eaten)Food (sugars; they are not eaten)

•OO22

Symbiotic zooxanthellae in coralsSymbiotic zooxanthellae in corals

Types of coral reefs:

Fringing reef -- borders shoreline

Barrier reef -- further offshore, lagoon in between

Atolls -- ring-shaped

1.Natural predators (e.g., crown of thorns star fish)

Coral reefs in trouble

2. Human activities (nutrients, fishing, recreation)

Coral reefs in trouble

Cyanide Fishing

• 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 and nutrients

3. Coral bleaching: zooxanthellae expelled• Most common in unusually warm waters: >32˚C• 2 degrees above normal maximum causes it• Result of global warming?

Coral reefs in trouble

Blue=low threat, yellow= med., red= high