A coral polyp houses zooxanthellae in its tissues. The algae receive shelter, while the coral receives sugars. What ecological relationship is this?

During daylight, zooxanthellae photosynthesize inside coral tissues. What do they provide that helps fuel the coral animal?

What does a coral polyp provide to its zooxanthellae besides a place to live?

Reef-building corals usually grow best in clear, shallow tropical water. Why does this environment favor their symbiosis?

A coral releases ammonium produced during metabolism, and its zooxanthellae absorb it. How does this exchange help the symbiosis?

Zooxanthellae provide energy that helps coral polyps grow. Over many generations, what process builds the hard framework of a coral reef?

After several weeks of unusually warm seawater, a living coral colony turns white. What has most likely happened?

Why does a bleached coral often appear white even though the coral animal may still be alive?

A marine heat wave raises water temperature above a coral's normal range. What change inside the coral most directly leads to bleaching?

Heavy rain sends freshwater across a shallow reef, sharply lowering salinity. If corals bleach afterward, what is the most likely cause?

A long-lasting sediment plume makes reef water cloudy. What is the first effect on the coral-algae partnership?

Water temperatures return to normal soon after a bleaching event. Which outcome gives the coral its best chance to recover?

Why do repeated marine heat waves generally cause more reef mortality than one short heat event?

Clearing hillsides near a tropical coast increases sediment runoff after storms. How does this runoff harm a fringing reef?

Fertilizer runoff enters a lagoon containing a coral reef. What damage is most likely after nutrient concentrations remain high?

As atmospheric carbon dioxide dissolves into seawater, ocean pH decreases. How does this threaten reef-building corals?

A recreational boat repeatedly drops anchor on a shallow reef. What is the most direct damage caused by this activity?

Fishers use explosives on a reef to catch stunned fish. Why can this practice damage the reef for many years?

A fishery removes many parrotfish from a reef. What ecological change is most likely?

Untreated sewage enters water near a coral reef. Besides adding nutrients, what threat can sewage introduce?

A reef disappears from a stretch of tropical coastline. What change is most likely during strong storms?

A coastal community catches reef fish for food and income. If reef habitat declines, what effect is most likely on that fishery?

A town depends on visitors who snorkel and dive on nearby reefs. What ecosystem service is directly reduced when the reefs are badly degraded?

Why do biomedical researchers study some reef organisms?

Juvenile fish shelter on a reef before moving into nearby waters where they are caught. If the reef is lost, what can happen beyond the reef itself?