why can't animals from the abyssal zone cannot survive in upper ocean zone

This phenomenon could transform the seas as much as global warming or ocean acidification will, rearranging where and what creatures eat and altering which species live or die.

Globally, these low-oxygen areas have expanded by more than 1.7 million square miles (4.5 million square kilometers) in the past 50 years. Included are vast portions of the eastern Pacific, almost all of the Bay of Bengal, and an area of the Atlantic off West Africa as broad as the United States. Already naturally low in oxygen, these regions keep growing, spreading horizontally and vertically. These are not coastal dead zones, like the one that sprawls across the Gulf of Mexico, but great swaths of deep water that can reach thousands of miles offshore.

Yet, “with all the ballyhoo about ocean issues, this one hasn’t gotten much attention.” “Two hundred meters down, there is a freight train of low-oxygen water barreling toward the surface,” says William Gilly, a marine biologist with Stanford University’s Hopkins Marine Station, in Pacific Grove, California.

Why can't animals from the abyssal zone cannot survive in upper ocean zone