Voyager: Some animals live deep in the ocean at great depths and pressure. How do you study them? Won't they die when you remove them from their native environment?

When deep-sea organisms are brought to the surface, they encounter several serious problems. If they have any gas space in their body, such as a swim bladder, the gas will expand due to the pressure difference between the deep sea and the surface and will kill the animal. Organisms that live deep in the ocean also have changes in their physiology, such as different cell membranes or different enzymes, that can make it impossible for them to survive at surface atmospheric pressures. You also need to keep them in water at the same temperature as where they came from, which can be as cold as 0°C.

There are several ways to observe and experiment with live deep-sea animals. One way is to bring the experiments to where the animals live naturally. For example, it is possible to deploy a trap that attracts and collects a certain kind of animal, such as shrimp. A scientist can then measure the oxygen consumption of this organism using oxygen electrodes and a recording device that has been deployed with the trap. After the measurements are done, the trap can be released from its weight and returned to the surface. The shrimp remains in the deep sea.

Another possibility for experimentation is to collect animals at depth with a submarine, such as Alvin, bring them to the surface, and quickly re-pressurize them in high-pressure aquaria. Seawater is pumped into these aquaria using hydraulic pumps and released again through valves that are used to adjust the pressure within the tanks. Many animals survive extended periods of time under these artificial conditions. Experiments can then be done with detectors and sensors that have been placed inside the pressure aquaria. Re-pressurization only works, however, if animals survive the short period of time between collection, return to the surface at normal atmospheric pressure, and transfer into the aquaria. Many deep-sea animals survive this period of a few minutes as long as the scientist keeps them cold while being brought to the surface.

The survival time of deep-sea animals depends on what they are. Many live only hours, while some invertebrates such as shrimp can live for months.

-- Horst Felbeck, professor of marine biology, Marine Biology Research Division