system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What happens on a global ecological level if the Great Barrier Reef is entirely bleached and dies?
gpt
The Great Barrier Reef is a zone which indicates a relative diversity of life on Earth, like Rainforests. The more diverse life is on the planet, the better, as we humans like to harvest things. Imagine if rubber trees didn't exist? Or if the fungi that made up immune suppressants didn't exist? Diversity is really good and when one of these places loses its diversity, we see that most other places are losing diversity too. Furthermore, an estimated 375 billion dollars are generated from food and tourism related to reefs, with about 500 million people dependent on their survival. Animals that depend on these corals for food go too. Entire food chains are disrupted. Imagine no more snapper, grouper, clams, or oysters! Fish rely on corals for protection from larger predators. 

About 70% of Earth's oxygen comes from the ocean, from the smallest organisms to the largest kelp forests. Losing life in the ocean directly impacts our world's ability to sustain life. If the reefs, which are some of the most fragile ecosystems start to die, then it's an early warning sign that things are going to get worse.