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Coral Reefs—health and hazards

Coral Reefs—health and hazards

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Coral Reefs—health and hazards

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  1. Coral Reefs—health and hazards Dr. Maia McGuire University of Florida/Sea Grant Photo by Mike White, FKNMS

  2. What is a Coral? Animal, vegetable or mineral? It’s an animal which may live with a plant and makes a mineral-based skeleton. Illustration by Geoff Kelley in JEN Veron (2000) Corals of the World, AIMS, Townsville

  3. Coral structure • Individual animals are called polyps • Several polyps make up a colony • Corals are closely related to jellyfish and sea anemones—they all contain stinging cells called nematocysts.

  4. Coral reefs • Reef-building corals require clear, warm water • Shallow areas • Most reefs are between 26° N and S latitude • There are corals found off Alaska and other cold waters, but they grow very slowly and do not form reefs

  5. Symbiosis E.C. Peters • Many hard and soft corals (and some jellyfish and sea anemones) contain a symbiotic single-celled brown dinoflagellate (algae) called zooxanthellae • This is a mutualistic symbiosis • Bleaching occurs when corals lose their zooxanthellae

  6. Coral Bleaching • Response to stress • Temperature • UV • Oxygen • Darkness • Sedimentation • Who initiates bleaching? • Can corals recover? J. Hoggesteger

  7. Patterns of bleaching • Seasonal—usually in summer • Geographically, often begins in the Caribbean and spreads northwards • Physically, there are often bleached patches on the sides of large coral heads (especially Montastraeas)

  8. ENSO

  9. Zooxanthellae “clades” • Three groups of zooxanthellae have been identified • Each group has different environmental tolerances and is found in different locations on the coral head Photo by Scott R. Santos, SUNY Buffalo

  10. Where do zooxanthellae go? • “Free” zooxanthellae are rarely found in plankton samples • May become benthic, sessile • May go into dormant stage • Presumably free zooxanthellae do exist

  11. Coral reproduction • Asexual reproduction (usually in branching corals; often storm-related) • Sexual reproduction • Hermaphroditic or gonochoristic • Self- or cross-fertilization • Internal or external fertilization • Brooders or broadcast spawners

  12. Richard Fitzpatrick

  13. Bette Willis in J.E.N. Veron (1987) Corals of Australia and the Indo-Pacific. Hawaii University Press

  14. Brooders • Eggs develop into larvae internally and may be brooded for several weeks • Larvae are released, often at night, often in response to the lunar cycle • Brooders may have up to 12 reproductive cycles per year R. Hays Cummins

  15. Coral larvae (planulae) • Swim using tiny hairs (cilia) • May already contain zooxanthellae • Swim for days to weeks before they settle and metamorphose • Settlement may be in response to chemical cues and may be gregarious Bob Richmond NOAA

  16. Status of coral reefs • Globally, coral reefs are generally in decline • Increasing human population (especially in coastal areas) increases the impacts on coral reefs

  17. Human impacts on coral reefs • Overfishing • Sedimentation • Nutrient enrichment • Chemicals/oil • Physical damage (anchors, fishing, groundings)

  18. Overfishing • Changes trophic structure • Many large predators are no longer present • Grazing fish species are being collected as food fish • May allow algal overgrowth of corals NOAA

  19. Nutrient enrichment • Nutrients are elements needed for growth • If there are not enough of certain types of nutrients, they are said to be limiting nutrients • Most common limiting nutrients in the marine environment are N and P

  20. Nitrogen • Available in water as nitrate, nitrite, ammonium or organic nitrogen (e.g. urea, plant or animal tissues) Phosphorus • Available in water as dissolved inorganic phosphate or organic phosphorus (dissolved or particulate)

  21. How does nutrient enrichment occur? • Septic tanks/sewage • Leaks • Pumping into the ocean • Fertilizer runoff • Agricultural • Homeowners • Golf courses

  22. Effects of increasing nutrients • Cause increase in plant (algae) growth • Macroalgae • Microalgae (phytoplankton)

  23. HAB’s/Red tides • Blooms of “harmful algae” • Pfisteria • Cause human health problems • Cause fish kills • May be killing dolphins, manatees Mote MarineLab FMRI

  24. Effects of increased nutrients on corals • Cause decrease in coral growth • Direct chemical interference with skeleton formation • Result of overshading by algae Jennifer M. Smith

  25. The nutrient-calcification mystery • If zooxanthellae help corals calcify, then why do enriched corals, which contain more zooxanthellae, calcify less? • Zooxanthellae are N-limited • “Excess” photosynthate is given to coral • If zooxanthellae grow, there is less photosynthate to give to the corals

  26. But…. • There are more zooxanthellae per cm² of coral, so the animal receives the same amount of carbon… = • Is the type of carbon compound different in enriched and control corals?

  27. Chemicals/oil • Non point-source pollution • 51% of the oil entering the oceans is from runoff • 5% is from big spills • 19% is from routine maintenance • 2% is from offshore drilling • 13% is from burning fuels (e.g. car exhaust) • 10% is from natural seeps

  28. Physical damage Thomas Heeger, Philippines • Fishing techniques in the South Pacific include dynamiting or poisoning reefs to collect aquarium fish for export • Boat anchors and boat/ship groundings cause damage that can take thousands of years to re-grow

  29. Natural impacts

  30. Marine debris • Suffocation risk • Balloons/bags • Entanglement/entrapment • Fishing line/ropes • Old nets • Abandoned traps/pots

  31. What can you do? • Reduce, reuse, recycle • Motor oil • Fishing line • Read and follow instructions on chemicals, including fertilizers • Fix automotive leaks

  32. What does the future hold? The answer is up to you… 1988 USGS 1998 USGS