Graduate Student Finds Some Jellyfish Can Swim
By Scott Brinckerhoff
ncient and abundant, jellyfish are familiar to humans who splash
in salt water the world over. But few people know them as well, or with such affection, as UConn graduate student Sean Colin.
Colin established himself as a jellyfish expert when he and a colleague, Jack Costello, who teaches at Providence College, published a research paper that challenged a long-held belief about one of the planet's oldest animals.
Colin and Costello discovered that not all jellyfish use jet propulsion to move through the water as squid do. Some "row" - for lack of a better term. "Jellies are extremely graceful swimmers, and actually are some of the first metazoan multi-cellular animals to have evolved an ability to swim," Colin says.
In their experiments, described in detail in the February issue of The Journal of Experimental Biology, the authors videotaped jellyfish they gathered from Puget Sound, Wa. The article was illustrated with Colin's drawings.
By adding particles to the water and slowing down the video, they were able to observe and measure such phenomena as vortices and wakes surrounding the jellies as they moved through the water.
The two scientists' observations led to the unmistakable conclusion that some flat-shaped jellyfish use their body edges to gently row through the water, and that this method of locomotion affects their hunting strategy.
Colin found that the rowing jellyfish cruise through the water in search of prey to immobilize with their tentacles, while the jet-propelled jellies lie in wait for targets of opportunity, relocating only from time to time.
Although the discovery that some jellyfish row may seem modest in terms of impact on humanity, it adds to the body of knowledge about how jellyfish gather food and interact with their environment, one that is shared with mankind. Jellies have been floating around since the Mesozoic era.
"His theory about jellyfish didn't fit with the texts," says Hans Dam, an associate professor of marine sciences at UConn's Avery Point campus and Colin's academic adviser. "He provided new insights about how they forage and capture food."
Graduate students conducting research in marine sciences are often supported by grants. In Colin's case, he had already earned an M.S. in biological oceanography and was pursuing a Ph.D. based on his work with the jellies, when his money ran out. It may have been just as well, as his adviser was in no position to add to Colin's knowledge of medusoids.
"I don't do jellyfish. I can't advise you," Dam told his student at the time. But money was available for another research area, so Colin shifted gears and began studying copepods, tiny marine creatures so numerous they make jellies look like endangered species.
Dam notes that copepods "are more numerous than insects." To jellyfish, they are simply a meal that's pretty much available anywhere.
Just occasionally, however, copepods may be scarce - in the presence of toxic algae such as red tide, for example, a condition that sometimes closes beaches. For his dissertation, Colin is focusing on how copepods react to toxic algae and why some of the 10,000 species, perhaps in support of Darwin's theory of natural selection, have better tolerance than others.
A visitor to Colin's lab first meets the copepods in a large glass container. They are all but invisible. But when an eyedropper's worth is viewed under a microscope, the copepods are revealed as complex animals, highly animated, and magnificent in their detail.
They rocket around their drop of saltwater, moving at a rate of up to 900 body lengths per second and experiencing 8 to 9 Gs, according to Colin. "They're extremely cool animals when it comes to propulsion," he adds.
Referred to as zooplankton, copepods are crustaceans and are related to lobsters. Although only about a millimeter long, copepods are more complex than the jellies that eat them. They have an exoskeleton, jointed legs, antennae, and even a heart and circulatory system, whereas the jellies are mostly gut, mouth, and tentacles.
"These guys are a very important link in the food chain," Colin says. He explains that they feed on phytoplankton, the plant matter that floats in huge masses in seas around the globe. When copepods die, they deplete oxygen in the water and some add a toxin when they die. Tiny though they are, their fate may well be tied to that of all marine creatures - including man.
The 31-year-old Colin grew up in Virginia. Always inquisitive, he discovered scuba diving, boats, and water at an early age and has managed to keep them part of his life. After earning his undergraduate degree at Providence College, he received a master's degree from the State University of New York. He taught high school algebra and life sciences in Massachusetts before entering UConn's program.
Once he completes his current course of study, Colin will likely stay in academia. But that's something to consider in the fall. Right now, he's off to the Adriatic for fresh research.