3-7 Coral Reefs

3-7 Coral Reefs - Coral and Coral Reefs • Chapter 9,...

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Unformatted text preview: Coral and Coral Reefs • Chapter 9, pages 407-453 • Topic 23 CORALS AND CORAL REEF COMMUNITIES • Dominant subtidal tropical habitat • High topographic complexity and biodiversity • Complex communities with strong competitive, symbiotic and mutualistic relationships, complex predator-prey interactions and chemical defenses What is a reef? • Massive deposit of CaCO 3 (limestone) produced by a thin veneer of algae, coral and other inverts • Largest “bio-construction” project on Earth • Marine equivalent to tropical rainforests – Similar in color, beauty and biodiversity Importance to humans • Reefs create harbors and protect mangroves and seagrass beds • Significant fisheries • Aesthetic appeal and tourism • Biodiversity high and chemical ecology complex – potentially important pharmaceutical and consumer products await discovery Hermatypic or Scleractinian 1. Reef-building (stony) corals have symbiotic dinoflagellates called zooxanthellae – Algae impart a light brown color – Abundances of 10 6 algal cells/cm 2 of coral – Line gastrodermis layer 1. Living polyp secretes a massive limestone skeleton Figure 9.5 Hermatypic or Scleractinian • Tropical in distribution – Limited to about 25 o N and S – Exception along the west coasts of South America and Africa • Calcification limited to warm seas Figure 9.1 Where do corals thrive? • Reef-building corals grow best in warm, shallow, clear blue and nutrient-poor waters of the Indo- Pacific and Caribbean Figure 9.4 Important factors for hermatypic coral • Corals limited to seas > 20 o C isotherm – optimal 23-25 o C • High light intensity necessary for photosynthesis – Compensation depth at 15-20% of surface light Coral ecology: • Water depth limited to 50-70 m with the majority < 25 m – Coral species diversity decreases with increasing water depth • Grow fastest at 35‰ but tolerate higher salinity better than lower – Persian Gulf often exceeds 40‰ but corals don’t thrive near large river mouths Coral ecology: • Wave energy – Too much can topple coral heads – But coral reefs resist turbulence and thrive under moderate to high energy regimes Coral ecology: • Sedimentation - corals smothered/clogged by sedimentation or harmed by reduced light – mucus production plentiful and may remove sedimented material • Air exposure - limited ability to withstand air exposure – most corals are subtidal and even spring low tides cause mortality Coral and zooxanthellae biology: • Phylum Cnidaria, class Anthozoa – Polyp stage only (no medusa) • Non-reef building corals (ahermatypic or soft corals) are found worldwide, but are mostly solitary – Deep water soft corals are more prominent than thought • Most hermatypic/scleractinian corals are colonial – polyps occupy small cups (corallites) set in a massive skeleton of limestone – coral heads grow by adding new polyps • A series of sclerosepta rise from the base and are important taxonomic features in coral Coral growth...
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This note was uploaded on 09/13/2010 for the course BIOL 4262 taught by Professor Stickle during the Spring '10 term at LSU.

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3-7 Coral Reefs - Coral and Coral Reefs • Chapter 9,...

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