Relentlessly rising human demand for deep-sea resources - fish, gas and oil, rare materials - is posing such a risk that international cooperation is needed if aquatic ecosystems are to be saved, US scientists warn.

The doubling of the world's population over the past five decades is putting great strain on the deep-sea ecosystems, which cover more than half of Earth, they told an annual science congress in Chicago on Sunday.

The ecosystems are now threatened by the same kind of mass industrialization common on land during the 20th century, according to researchers gathered at the American Association for the Advancement of Science meeting.

"At the same time, human society has undergone tremendous changes and we rarely, if ever, think about these affecting our ocean, let alone the deep ocean," said Lisa Levin, who heads the Center for Marine Biodiversity and Conservation at the Scripps Institution of Oceanography in California.

"As we exhaust many coastal stocks, commercial fishers have turned toward deeper waters," she said.

The quadrupling of energy demands over the past 50 years have led companies to search for oil and gas in the deep seas, defined as waters more than 1,000 meters (3,300 feet) deep.

"Oil and gas exploration now routinely targets seabeds in more than a thousand meters of water depth," said Levin.

Today there are some 2,000 platforms drilling on deep sea ocean floors, "bringing with it the potential for environmental disaster of the sort we saw with the Deepawater Horizon," Levin said, referring to a massive 2010 BP oil spill in the Gulf of Mexico.

At the same time, the demand for hard-to-find rare earth elements needed for portable electronics and batteries for hybrid vehicles is pushing mining companies to scour the ocean floors.

Also in demand: minerals such as nickel, cobalt, manganese and copper.

"Vast tracts of deep seabed are now being leased in order to mine nodules, crusts, sulfides, and phosphates rich in elements demanded by our advanced economy," said Levin.

Deep sea mining is not something out of science fiction, said Cindy Lee Van Dover, director of the Duke University Marine Laboratory.

"Those deposits exist and cover national and international waters," and with major advances in deep sea robotics "we have access to the deep sea like never before."

Even though the process of building a deep sea mine is unknown "because we have not done it," mining companies know that the potential value of the mineral reserves on the ocean floor "is a very good one."

Extraction from the deep sea is a tradeoff, said Lindwood Pendleton, an economist with Duke University's Nicholas Institute for Environmental Policy Solutions.

"Is the value of what we're extracting greater than the damage?" he asked. "Are there ways to extract that might be more economically costly but have lower ecological impact? How can we repair the considerable damage that has already been done to the sea floor through trawling, pollution, and other practices?"

"These questions need to be answered "before industrial activity gets ahead of scientific understanding," he warned.

Human knowledge of the deep sea ecosystem however has not kept pace with the growth of human activities affecting the deep seas, Levin said.

Levin called for "international cooperation and an entity that can develop and oversee deep-ocean stewardship."