Read the following passage carefully and answer the following questions.

The largest coral reef in the world, the Great Barrier Reef, is home to at least 400 individual species of coral and thousands of different species of fish, mollusks, sea snakes, sea turtles, whales, dolphins, birds, and more. As with the other coral reefs of the world, this incredible ecological hotspot is under threat. A heatwave in 2016 caused a large percentage of the corals in the Great Barrier Reef to undergo severe bleaching and death.