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What is a coral?A “coral”is actually a “coral colony”Rocky limestone base,Surface is coveredby thousands of tiny coral animals, called“polyps”.Polyps are filled with microscopic algae
What should you know about corals? They are animals Plants live inside of them Two kinds Soft corals Hard corals (These build reefs!) They are made of tiny polyps (which look like upside- down jellyfish)
Hard Corals :-The Reef Builders Polyps build hard limestone cups around their bases. The cups cement together to make a coral Colony. Reefs are made of hundreds of hard coral colonies next to and on top of each other.
Anatomy of acoral polyp.- Each polyp looks like a tiny sea anemone- Ring of stinging tentacles around a central mouth- Rests in a “cup” on the surface of the colony
What’s a Polyp? Tentacles release stingingcells when somethingbrushes by them. Polyps make their ownlimestone cup to hide induring the day. At night, polyps come out tocatch plankton floating by.
Like a seaWhat do corals eat? anemone, the polyp can capture small prey (mostly zooplankton) with its tentacles & Also get nutrition from a Symbiotic relationship with zooxanthellae.….
What are zooxanthellae? -Algae that live in the coral polyp’s surface layer -Algae get nutrients and a safe place to grow -Corals get oxygen and help with waste removal -Corals also get most of their food from the algae.
Symbiosis: So Happy TogetherTwo organisms living together and helping each otheris called symbiosis.Zooxanthellae make oxygen, remove thepolyp’s wastes, and make food for the polypfrom photosynthesis.Coral polyps protect the zooxanthellae, releaseCO2, and provide it with necessary nutrientsfrom their own waste.
What is coral bleaching? Healthy Bleached coral coralCoral bleaching is caused by stressPoll question: what might be stressful for acoral? We’ll get back to the answer later….
What turns the coral white?As a stress response, corals expel thesymbiotic zooxanthellae from their tissuesThe coral tissue is clear, so you see thewhite limestone skeleton underneath.
What can stress a coral?High light or UV levelsCold temperaturesLow salinity and high turbidity from coastalrunoff events or heavy rainExposure to air during very low tidesMajor: high water temperatures
Thermal stressCorals live close to their thermal maximum limitIf water gets 1 or 2°C higher than the summer average,corals get stressed and bleachNOAA satellites measure global ocean temperature andthermal stress.
How warm is warm?How hot do you think the ocean has to getbefore corals start to bleach?
Can corals recover?Yes, if the stress doesn’t last toolong Some corals can eat morezooplankton to help survive thelack of zooxanthellae.Somespecies are more resistant tobleaching, and more able torecover
Can corals recover?Corals may eventuallyregain color by repopulatingtheir zooxanthellaeAlgae may come from thewater columnOr they may come fromreproduction of the few cellsthat remain in the coralCorals can begin to recoverafter a few weeks
Does bleaching kill corals? Yes, if the stress is severe Some of the polyps in a colony might die If the bleaching is really severe, whole colonies might die Bleaching in Puerto Rico killed an 800- year-old star coral colony in 2005
What else can stress do to corals?Question: what is something that happens topeople when they are highly stressed?Gain weight Get sick Turn orangeAnswer: More likely to get sick
Bleaching and coral disease Coral diseases are found around the world. High temperatures and bleaching can leave corals more vulnerable to disease. Can quickly kill part or all of the coral colony.
Bleaching and bioerosion We have seen that bleaching can kill part or all of a coral colony. Areas of dead coral are more vulnerable to bioerosion (when animals wear away the coral reef’s limestone structure.)
Hurricanes & coral bleaching 2005: Most named storms Most hurricanes Most damage in USThe same warm water that causes corals tobleach can also lead to strong hurricanes.
Hurricanes can cause directphysical damage to coral reefsHowever, the storms also cools thewaterHurricane Katrina led to lessbleaching in the Florida Keys, 2005
Hurricanes: a mixed blessing Sombrero Reef , FL DHW (degC week) SST (degC) Dennis 9 July Katrina 26 Aug Rita Wilma 21 Sept 24 OctEach passing hurricane in 2005 cooled thewater in the Florida Keys.
Can we protect corals from bleaching? Shade reefs. Cool reefs. Improve water quality. Reduce other stress. Reduce overfishing.