James Childress studies one of the world’s most inaccessible species. The objects of his research—tube worms—live along rifts in the ocean floor, feeding on dissolved minerals that well up from Earth’s interior. The worms he studies—Riftia pachyptila—grow to several feet long and have red gill-like plumes engorged with hemoglobin. The worms use their plumes to collect hydrogen sulfide, nitrate, and other nutrients to feed the symbiotic bacteria in their guts that break down these compounds for them. To reach the worms, Childress, an ecological physiologist at the University of California at Santa Barbara, makes grueling eight-hour, 2.5-mile descents in the submersible craft Alvin to the East Pacific Rise, a submarine mountain range west of Mexico and South America.
In the next few years Childress may be able to forgo some of these arduous voyages. Along with one of his graduate students, he has managed to re-create the tube worms’ habitat in the laboratory, the first time anyone has managed to keep the animals alive for more than a few days away from the ocean. Childress and his grad student Peter Girguis collected tube worms from the East Pacific Rise last fall using Alvin’s robotic arms. Back on the research ship, they put the worms into pressurized cylindrical aquariums designed by Childress. The aquariums consist of an acrylic cylinder encased in a second, snug-fitting stainless-steel cylinder. Together the chambers are three and a half feet long and seven and a half inches wide. The pressure inside is a worm-comfortable 3,000 pounds per square inch. Holes in the outer steel cylinder allow the researchers to peek at the worms.
During the six-week cruise the researchers selected 29 worms to bring to their lab in Santa Barbara. We set aside those that were the right size—about half an ounce and eight to ten inches long—so that we could fit a fair number in the pressure vessel, says Childress.
At the end of the cruise the researchers moved the worms from the cylinders into a lighter steel chamber for delivery to the lab. When the worms arrived at the lab, Childress and Girguis put them back into the pressurized nested cylinders. A system of pumps continually flushed new seawater—warmed to about 70 degrees—into the cylinders. Girguis also rigged up filters to adjust the concentrations of hydrogen sulfide, nitrate, oxygen, and carbon dioxide in the cylinders to match the worms’ natural environment.
The worms seemed to thrive. I was positive that we really understood what they needed to stay alive, Childress says. Then disaster struck: the entire colony died on a single day in early February. Childress and Girguis aren’t sure why the worms died, but as with other natural disasters in California, they blame El Niño. They suspect that an El Niño–related storm that hit the central California coast washed something toxic into their seawater supply. Our seawater intake is about half a mile offshore, but it’s downstream from the outflow of a major slough that drains a large part of the local area, Childress says. Mud carried by the slough entered the intake, so we had a huge amount of sediment coming through our seawater system. You could see it clogging the filters. I suspect that something else—something toxic to the worms—came through as well.
Normally at sea, the worms come out of the tubes if they are killed by low pressure. But if you put in something that is noxious to the plume, they will pull down in the tube and die down in there. And that is what we saw, which suggests that there was something in the water that they could not handle.
This fall Childress and Girguis are scheduled for another cruise to the East Pacific Rise, where they plan to gather more worms. Childress already has some ideas about how to avoid contamination from storms. We have a couple of 500-gallon tanks in the lab, and I think we’ll recirculate the water through them if the weather gets bad. I think we will be more successful next time. We know now what the problems are.