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Explore the Vibrant World of Coral Reefs

Dive into the fascinating realm of coral reef communities. Discover the types of coral reefs, their ecological importance, and the intricate relationships within these vibrant ecosystems.

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Explore the Vibrant World of Coral Reefs

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  1. Coral Reef Communities Chapter 15

  2. Key Concepts • Coral reefs are primarily found in tropical clear water, usually at depths of 60 meters or less. • The three major types of coral reefs are fringing reefs, barrier reefs, and atolls. • Both physical and biological factors determine the distribution of organisms on a reef.

  3. Key Concepts • Stony corals are responsible for the large colonial masses that make up the bulk of a coral reef. • Reef-forming corals rely on symbiotic dinoflagellates called “zooxanthellae” to supply nutrients and to produce an environment suitable for formation of the coral skeleton. • Coral reefs are constantly forming and breaking down.

  4. Key Concepts • The most important primary producers on coral reefs are symbiotic zooxanthellae and turf algae. • Coral reefs are oases of high productivity in nutrient-poor tropical seas. Nutrients are stored in reef biomass and efficiently recycled.

  5. Key Concepts • Inhabitants of coral reefs display many adaptations that help them to avoid predation or to be more efficient predators. • Coral reefs are huge, interactive complexes full of intricate interdependencies.

  6. World of Coral Reefs • Coral reefs are highly productive, but occur in nutrient-poor waters • This is made possible by the symbiotic relationship between coral animals and zooxanthellae • These symbionts + algae form the basis of the community; other reef animals depend on these organisms

  7. Coral Animals • Stony (true) corals deposit massive amounts of CaCO3 that compose most of the structure of coral reefs • Hermatypic—coral species that produce reefs, found in shallow, tropical waters

  8. Coral Animals • Ahermatypic—corals that do not build reefs, which can grow in deeper water from the tropics to polar seas • most do not harbor zooxanthellae

  9. Coral Animals • Coral colonies • large colonies of small coral polyps, each of which secretes a corallite • a planula larva settles and attaches • a polyp develops, and reproduces by budding to form a growing colony • polyps’ gastrovascular cavities remain interconnected • a thin, usually colorful epidermis overlies the colony surface

  10. Coral Animals • Sexual reproduction in coral • mostly broadcast spawners—release both sperm and eggs into the surrounding seawater • some are brooders—broadcast sperm, but retain eggs in the gastrovascular cavity • spawning is usually synchronous among Pacific reef species, but nonsynchronous among Caribbean species

  11. Coral Animals • Reproduction by fragmentation • some branching corals are fragile and tend to break during storms • if they survive the storm, fragments can attach and grow into new colonies • fragmentation is a common form of asexual reproduction for branching corals

  12. Coral Animals • Coral nutrition • symbiotic zooxanthellae • supply 90% of nutritional needs of stony coral • zooxanthella provide glucose, glycerol and amino acids • coral polyp provides a suitable habitat and nutrients, absorbed directly through the animal’s tissues • zooxanthellae remove CO2 and produce O2 • need of zooxanthellae for sunlight limits depths to which stony corals can grow

  13. Coral Animals • Coral nutrition (continued) • corals as predators • small animals paralyzed by the nematocysts are passed into the digestive cavity

  14. Coral Animals • Coral nutrition (continued) • other sources of nutrition • corals can feed off bacteria living in their tissues, which feed on dissolved organic matter directly from the water • mesenteric filaments (coiled tubes attached to the gut wall) can be extruded from the mouth to digest and absorb food outside the body

  15. Reef Formation • Involves both constructive and destructive phases • Bioerosion—the destructive phase of reef formation • boring clams or sponges attack exposed surfaces on the undersides of large corals • the coral stand weakens, then topples in a storm or ocean surge • debris smothers boring organisms, cracks are filled with CaCO2 sediments, and coralline algae cement it together

  16. Coral Reef Types • Fringing reefs border islands or continental landmasses

  17. Coral Reef Types • Barrier reefs are similar to fringing reefs but separated from the landmass and fringing reef by lagoons or deepwater channels

  18. Coral Reef Types • Atolls, usually elliptical, arise out of deep water and have a centrally-located lagoon

  19. Coral Reef Types • In addition, patch reefs can occur within lagoons associated with atolls and barrier reefs • Darwin’s theory of atoll formation: • corals colonize shallow areas around newly-formed volcanic islands to form a fringing reef • the island sinks and erodes, and a barrier reef is formed about the island • the island sinks completely, leaving an atoll

  20. Reef Structure • Reef front or forereef—portion of the reef that rises from the lower depths of the ocean to a level just at or just below the surface of the water, on the seaward side • drop-off—a steep reef-front that forms a vertical wall • spur-and-groove formation or buttress zone—finger-like projections of the reef front that protrude seaward; disperses wave energy and helps prevent damage

  21. Reef Structure • Reef crest—the highest point on the reef and the part that receives the full impact of wave energy • where wave impact is very strong, it may consist of an algal ridge of encrusting coralline algae, lacking other organisms, and penetrated by surge channels—grooves of the buttress zone • Reef flat or back reef—portion behind the reef crest

  22. Coral Reef Distribution • Major factors influencing distribution: • temperature – corals do best at 23-25o C • light availability – photosynthetic zooxanthellae need light • sediment accumulation – can reduce light and clog feeding structures • salinity • wave action – moderate wave action brings in oxygenated seawater, removes sediment that could smother coral polyps • duration of air exposure – can be deadly

  23. Comparison of Atlantic and Indo-Pacific Reefs • Pacific reefs are older and have a greater depth of reef carbonates • Buttress zone is deeper on Atlantic reefs and coral growth may extend to 100 m down • Pacific coral growth rarely exceeds 60 m • Algal ridges more common in the Pacific because of wind and waves

  24. Comparison of Atlantic and Indo-Pacific Reefs • Hydrozoan Millipora complanata (fire coral) is dominant on Atlantic reefs • Similar species never dominate in the Pacific • Gorgonians more abundant in the Atlantic • Soft corals (subclass Alcyonaria) more abundant in the Pacific • Atlantic corals nocturnal; Pacific corals diurnal

  25. Comparison of Atlantic and Indo-Pacific Reefs • Atlantic corals often reproduce by fragmentation; Pacific corals by sexual reproduction • Coral diversity is far greater in the Indo-Pacific than the Atlantic • Greater sponge biomass in the Atlantic • Pacific has giant clams and sea stars that prey on corals

  26. Caribbean reef

  27. Pacific reef

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