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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