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Coral Reefs

Coral Reefs

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Coral Reefs

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  1. Coral Reefs Ms. Springstroh Source of information:

  2. Structure (again) • Almost all corals are colonial organisms • Composed of hundreds of thousands of individual polyps • Polyps are animals • Polyps in a colony are connected by a thin sheet of tissue (cells aggregated together) • Polyps are sessile

  3. From polyps to reefs • Reefs form when polyps secrete calcium carbonate skeletons • Limestone • CaCO3

  4. Calcium carbonate skeleton secreted by the lower portion of the polyp • Produces a cup-like structure called a calyx, which the polyp sits in • Bottom of cup is called a basal plate • Every so often, a coral polyp will lift itself up off its basal plate and secrete a new calyx • More CaCO3 • This is how a coral reef grows

  5. Calyx • When corals are stressed, they retract into their calyx so that no part of the polyp is exposed above its skeleton • Polyps also may extend out of their calyx, especially when they feed

  6. How Corals Form: Coral Life Cycle • Free-swimming coral larva, called a planula, attaches to rocks or other substrates near shallow areas, such as by islands or the edges of continents • Planulametamorphoses(transforms) into a polyp • Polyps divided over and over to form reefs

  7. Coral Reproduction • Corals may utilize asexual or sexual reproduction • Asexual reproduction: reproduction that does not require gametes (sex cells) • A new polyp– a clone of its parent– “buds” off from the parent and begins a new colony itself • Sexual reproduction: some corals release gametes (sperm and egg cells) into the water • Egg and sperm combine to form planulae

  8. Coral Reproduction

  9. In some reefs, the all the coral species release their sperm and egg at the same time • Called broadcast spawning • Influenced by temperature, length of day, lunar cues, time of sunset • Planulae swim toward the light • Become part of the waters at the surface of the ocean • Current transports planulae • Planulae eventually swim back toward bottom of ocean • Will settle there if conditions are favorable  metamorphose  build a colony

  10. The “Z” word that nobody can pronounce • Zooxanthellae are photosynthetic algae which live in corals’ tissues • Have a mutualistic symbiotic relationship with corals • Symbiosis: close relationship between two organisms of different species • Mutualism: a symbiotic relationship in which both species benefit (symbolized by + / + )

  11. Corals provide zooxanthellae with a protected environment in which to live, and with the materials needed for photosynthesis • Zooxanthellae help the coral eliminate waste, provide the coral with oxygen and glucose, & help the coral secrete its skeleton • If the coral has enough glucose/ “energy”, it can secrete a calcium carbonate skeleton and grow! • This energy comes from the ‘waste’ molecules produced by the zooxanthellaeduring photosynthesis. • Both of these contribute to the “recycling of nutrients” • This mutualistic symbiotic relationship is VERY VALUABLE because tropical waters are nutrient-poor!

  12. Lab: Building a Coral Skelton • Lime (calcium and oxygen) is dissolved in sea water • Corals have carbon and oxygen in their cells • Combines with calcium and oxygen from the water • Produces CaCO3

  13. Chalk = contains calcium • Clear liquid from chalk + vinegar (C2H4O2) mixture = dissolved lime = “sea water” • Baking soda = sodium bicarbonate, NaHCO3 = coral’s cells • Adding baking soda + water to dissolved calcium (chalk + vinegar mixture)  CaCO3

  14. Lab Directions: Day 1 • Pour 250mL of vinegar into a beaker. • Break chalk into small pieces. Put into beaker. • Label beaker. • Let stand overnight.

  15. Day 2 • Pour off some clear liquid from chalk mixture into cup labeled “dissolved limestone”. Rinse your beaker. • Obtain 240mL of tap water in beaker. Add 3-4 tablespoons baking soda; stir, then let stand for 15 minutes. • Pour off some clear liquid from baking soda beaker into another cup labeled “dissolved baking soda”. Rinse your beaker. • Pour “dissolved baking soda” into “dissolved limestone” beaker. Observe what happens.

  16. Lab notes • Mixing of the “dissolved limestone” and the “dissolved baking soda” represents a coral polyp extracting calcium from sea water, combining it with carbon dioxide, and producing CaCO3. • Chalk = contains calcium • Clear liquid from chalk + vinegar (C2H4O2) mixture = dissolved lime = “sea water” • Baking soda = sodium bicarbonate, NaHCO3 = coral’s cells • Adding baking soda + water to dissolved calcium (chalk + vinegar mixture)  CaCO3 • Source:

  17. Lab • Write a paragraph (using at least four complete sentences) about how a coral builds its skeleton. Try to use as many examples from this lab as possible. • Things to think about and include: • What does the white precipitate represent? • What does the “dissolved limestone” represent? • What does the “dissolved baking soda” represent? • What does mixing the “dissolved limestone” and “dissolved baking soda” represent?

  18. Lab Results • White precipitate= calcium carbonate • How does it form? • Coral polyp extracts calcium from sea water (vinegar + chalk mixture, aka dissolved limestone) & combines it with carbon dioxide

  19. Types of Coral Reefs • Corals can build 3 types of reefs: • Fringing: grows very close to or on shore • Barrier: also grows close to shore but has a lagoon separating it from the shore • Atoll: a ring of coral that surrounds a lagoon, often grows on a submerged mountain or volcano


  21. Midway Atoll

  22. Coral Bleaching • Zooxanthellae provide coral with greenish-brown color • When under stress, corals expel their zooxanthellae • Coral therefore loses its color and one of its foods sources • Result: coral polyps will die • Leave behind white calcium carbonate skeleton



  25. Coral Reef Food Chains • Food chains show how living things get their nutrients, and how these nutrients are passed from one organism to another • Producers produce their own nutrients, via photosynthesis • Consumers eat other organisms to obtain nutrients • 3 kinds of consumers: • Herbivores: eat only plants • Carnivores: eat only animals • Omnivores: eat both plants and animals

  26. A trophic level is the position in a food chain an organism occupies • The first trophic level is made up of producers. These producers are called primary producers. • Use photosynthesis to create nutrients such as sugars • Examples within a coral reef: seaweed, zooxanthellae

  27. The next trophic level is made of primary consumers– organisms which consume the primary producers, OR the ‘waste’ products given off by the primary consumers • Examples within a coral reef: corals, sponges • Secondary consumers prey on primary consumers • Examples within a coral reef: grouper, turtles, crown-of-thorns sea star

  28. Crown of thorns sea star • Feeds on corals by pushing its stomach out through its mouth • Covers coral colony with its stomach • Digests coral tissue

  29. Tertiary consumers prey on secondary consumers • Examples within a coral reef: gray reef shark (also considered a top predator: has no natural enemies)

  30. Food chains are inefficient! • Only about 10% of the energy at one trophic level on a food chain is passed onto the next level. • The remaining 90% of energy will be used by the organism at the lower trophic level to do its normal activities, such as movement & respiration, OR will be lost during the energy transfer.