When Coral Turns White

Science · Ocean Life · ages 12-13

Name ______________________ Date ____________

What happens to coral's color when it bleaches?
- It turns bright red
- It turns white
- It grows extra tentacles
What do the tiny algae living inside coral polyps do for them?
- Give them sugar from photosynthesis
- Attack predators to defend the coral
- Change the direction of ocean currents
Ocean water is becoming more acidic partly because it absorbs extra carbon dioxide from the air.
Circle one: True False
About what percent of all marine species depend on coral reefs for habitat at some point in their lives? Type the number.
Answer: ______________
A reef has sat in unusually warm water for weeks. What is most likely happening to the coral?
- It's absorbing even more algae than usual
- It's growing a thicker, stronger skeleton
- It's pushing its algae out and starving
Why does lower ocean pH make it harder for corals to build their skeletons?
- Acid dissolves the calcium carbonate corals need
- Acidic water blocks sunlight from reaching the coral
- Acidic water kills coral polyps instantly on contact
Marine biologists grow heat-tolerant coral in nurseries and transplant it onto damaged reefs. Why isn't this enough on its own to save reefs worldwide?
- It removes carbon dioxide directly from the atmosphere
- It makes the surrounding ocean water warmer
- It reaches only a few reefs, not the warming ocean
A classmate says, 'Bleached coral is dead coral, it can never turn healthy again.' What's wrong with that idea?
- Bleaching only happens to coral that was already dead
- Bleached coral is alive and can recover if water cools
- Bleaching means the coral has grown too much algae, not too little

Answer key

For grown-ups. Fold this page away before handing over the rest.

When Coral Turns White W1-mt_EXO1bJ3G_v-s1

It turns white · The coral expels its colorful algae, so the clear tissue shows the white skeleton underneath.
Give them sugar from photosynthesis · The algae, called zooxanthellae, photosynthesize and share the sugar they make with the coral.
True · CO2 dissolves into seawater and forms carbonic acid, which lowers the pH.
25 · Roughly a quarter of marine species use reefs for shelter, feeding, or breeding at some point.
It's pushing its algae out and starving · Heat stress makes the coral push out its algae, cutting off its main food source.
Acid dissolves the calcium carbonate corals need · More acidic water makes calcium carbonate harder to form and easier to dissolve away.
It reaches only a few reefs, not the warming ocean · Nurseries help individual reefs, but they can't yet keep pace with heat and acidification across every ocean.
Bleached coral is alive and can recover if water cools · Bleaching is a stress response, not death. Coral can regain its algae and recover if conditions improve in time.