Many biologists, given the choice, would prefer to study living organisms in their natural environment rather than in the laboratory. The limits of resourfes and technology, however, often forbid such luxury. The challenge for marine biology, as Boston University Marine Program (BUMP) director Rudi Strickler sees it, is to bring to the depths of the oceans the tools now restricted to the laboratory.
Dissatisfied with the scientist's ability to photograph underwater microscopic organisms in the field, Strickler turned his attention to building an underwater micro-imaging "satellite" to provide visual records of deep-sea organic activity. "This was truly a Woods Hole area collaboration," Strickler says, noting the contributions of his own MBL/BUMP lab, Robert Knudson of the MBL's Instrument Development Laboratory, and technicians from the neighboring Woods Hole Oceanographic Institution (WHOI).
In the perpetual darkness of the depths, standard video equipment provides high resolution for large areas only, as the 1986 video images of the Titanic illustrated. In Strickler's system, however, a tiny infrared laser diode generates a beam of light that is enlarged by a special lens to illuminate an area about the diameter of a baseball.
The beam is aimed at an ordinary compact video camera in a modified arrangement known as a Schlieren optical path. A black spot on the camera lens stops laser light from reaching the image plane. "However, if you put something into the beam," Strickler explains, "the light from that object will be deflected and will pass through the lens, forming an image."
The Schlieren system was developed more than 100 years ago, but Strickler has made significant changes with modern optical equipment, including a new filtering method to control the light source. He has also incorporated laser diodes into the system. The result is a camera that is able to resolve organisms as small as five microns in diameter.
The entire device, small enough to fit in a suitcase, can be mounted on a manned submersible like Alvin, the vehicle that visited the Titanic two summers ago. But to fully realize the instrument's potential, it should be sent down with its own maneuvering system as an underwater reconnaissance satellite. Because the laser diode uses little energy, it is powered by several AA cell and can operate for as long as 24 hours.
Since infrared light does not disturb marine organisms, Strickler's camera will be remarkably unobtrusive. "When they go down in a manned submersible, they disrupt the whole place," he says. "But I will go down the sneaky way."
The new system also avoids the problem researchers face in bringing samples of water containing the organisms to the surface. Such a trip can take more than a hour, and some speciments run a high risk of being eaten on the way up, while others arrive at the top with unnatural gut contents.
With the satellite in position, molluscs, zooplankton and other microscopic marine animals become living photographic subjects, Some of the most promising areas targeted for research are the recently-discovered thermal vents, which are rich with ocean life. Of particular interest to Skrickler is the feeding pattern of tiny crustaceans known as copepods.
Another MBL scientist, Arthur Humes, has described the copepods similar to those Strickler is now filming. Humes, who was BUMP director from 1971-81, has identified 29 new species of copepods taken since the late 1970s from the five vents located in the Pacific and two on the Mid-Atlantic ridge. No one knows how the copepods have travelled from vent to vent. "We don't know much at all about their behavior," says Humes.
"We know nothing about these marine animals in their home," says Strickler. "So we decided to go have a look."
The micro-imaging system, known affectionately as the "Critter Cam," was installed and tested in August. Even before the results were in, however, Strickler was receiving inquiries about his design from the Harbor Branch Oceanographic Institution in Florida.
Work is continuing on refining the prototype. One of the last technical hurdles involves the limited volumn of water illuminated. "If you get an animal in the field of vision, how do you keep it there, and how long can it be observed?" he asks.
Strickler came to the MBL and BUMP in December 1986. He had previously been a research professor in marine biology at the University of Southern California, and a principal researcher at the Australian Institute of Marine Science.