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Summer 1994 |
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Page 5 |
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Inside |
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Discoveries From the Deep |
pg. 5 |
by Shelly Foster Nixon
Even from 1500 feet below the ocean, the video images being sent back to the ship from the small unmanned submersible made it clear the creature was not thrilled with the attention. Its normally dark and quiet world was being invaded by glaring lights and whirring motors. Though without eyes for seeing or ears for hearing, it definitely responded to the presence of the stranger. Dr. Bruce Robison, marine biologist with the Monterey Bay Aquarium Research Institute (MBARI) watched from his vantage point at the water's surface, aboard the ship the Pt. Lobos. He studied the animal as it writhed and reached and swirled. The hundred-odd finger-like stomachs along the creature's six foot length touched quizzically around. The delicate bubble float at one end of the animal sometimes expanded, sometimes shrank, but never stopped twisting.
This is the world of the Siphonophores, denizens of the deep. Until recently, only 67 species of this complex group of gelatinous creatures had been identified. With the exception of a few species that live near the surface, very little is known about how they live. Only one member of the group is familiar to most people &emdash; the surface-floating Portuguese-man-of-war. For the deeper dwelling creatures, their delicate, gelatinous bodies make them extremely difficult to collect. The large, rough trawling nets used to sample the sea in the past turned these animals into goo, leaving little to decipher.
"Nobody knows beans about these animals," says Robison referring to the new found animal, "the absence of information is appalling." The siphonophore he found floating 1500 feet below the ocean surface was the first ever found living in the eastern Pacific, and never before had someone managed to capture its behavior in the wild on over an hour's length of film. Robison, impressed with the uniqueness of the animal, wanted more information. He wanted to know how it survived in the wide open ocean, how it reproduced, how it captured food. He wanted to know how it was all put together, and the only way to do that was to capture it and study it in the laboratory. Robison first began his travels into the siphonophore's world because he wanted to understand food chains in the broad open ocean. What he found were jelly-like animals of all shapes and sizes, the most prolific of which looked like long thin ropes, dragging their gossamer nets of tentacles behind them--the siphonophores.
Strung together like beads on a necklace, these animals are basically gelatinous tubes with a series of stomachs attached. Each stomach has its own fishing line tentacle, spiked with a barb or a toxin.
For all its functioning as one whole unit, the siphonophore is actually a well orchestrated chorus-line of individuals, some taking on the form of a fishing stomach, while others evolve into swimming bells or breeding organs. The fact that siphonophores in some species can get as long as 120 feet and still function virtually as one animal continues to amaze biologists. Capturing this smaller animal would allow Robison and other biologists to better understand other species of siphonophores as well.
Robison and Ventana's pilot Jim MacFarlane watched the siphonophore closely. It was clear this species lacked the fluttering swimming bells some of the other siphonophores use for propulsion. It had only a small translucent float for buoyancy. Robison was interested to see how it managed to maneuver. The results were impressive. The delicate siphonophore raised its lower, more mature, stomachs and then plunged them down through the water. By using the weight of the more mature stomachs and recoiling the upper, lighter portions into the sinking lower half, the siphonophore seemed to be able to make itself quickly sink. But the submersible moved faster than the animal. Gently MacFarlane eased the large acrylic jar called a detritus sampler around the siphonophore, pushed the trigger to remotely slide the door closed, and the animal was captured.
For two months the siphonophore floated in the quiet dark bubbling tank in Robison's lab. Periodically Robison and MBARI research associate Kim Reisenbichler, would turn on a light in the siphonophore's tank. The iridescent gold and opaque white of the animal had an almost ethereal quality. Over time, stomach by stomach, the animal began casting off pieces of itself. The remaining stomachs continued to cast out web-thin tentacles that coiled and recoiled in a dance all their own. Still, try as the biologists would, the animal would not eat.
Not knowing if this is the animal's natural life cycle or a reaction to the new environment, Robison and Reisenbichler watched closely to learn as much as possible. As the stomachs fell away, the animal revealed golden clumps of eggs growing along the main stem. The biologists watched as these egg clusters are released like tiny golden balloons into the surrounding water.
"This animal has taught us a lot about how siphonophores are put together," says Reisenbichler, "but there are still a lot of questions to be answered." The hope is that with more answers humans will begin to better understand the complex relationships of deep-sea food chains and our own influence on its delicate balance.
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