Recently, scientists have discovered some "dead zones" in the ocean, where there is hardly any oxygen in the seawater that living things depend on to survive. Now, "dead zones" are gradually expanding in the world's oceans like a chronic disease spreading throughout the body, and have become a global issue.
Robert J. Diaz of the Virginia Institute of Marine Science said: "We must realize that hypoxia is not a local problem, but a global issue which has caused serious consequences for ecosystems. Meanwhile, this problem is getting more and more severe, and has even started to affect the marine resources that we humans use."