This is a post by guest blogger Ellen Bulger, written during the cold and long winter of December 2010.
Winsor Locks, CT
In a rarely-seen or photographed event, thousands of hapless jellyfish on their way to spawn were stranded and frozen along the shores of the Connecticut River last week. The gelatinous creatures are not uncommon, but usually go unnoticed because they are a cold water species. But the necessities of reproduction bring them together in great numbers this time of year, as they return to their traditional spawning grounds. A freakish combination of weather conditions allowed lucky and observant onlookers to enjoy this serendipitous spectacle.
“As a rule, we don’t even notice them.” explained Caleb Shoeworthy, whose family have fished these waters for shad for five generations. “The thing is, you just can’t see them in the river. They have no color. You could have half a dozen of them in that bucket and you’d swear there was nothing but water. Even the big ones are pretty much invisible.”
Invisible they may be, but any creatures are hard to ignore when they come drifting in to narrow channels in the hundreds of thousands. In some parts of the world, relatives of these jellyfish have been known to clog cooling intakes of nuclear power plants and have forced some giant cruise ships to change their itinerary. A close relative of the common moon jelly Aurelia aurita, the greater river jelly, A. awlryta spends its adult life in estuaries such as Long Island Sound. The animal, which is easily killed by heat, moves downriver as it matures in the early spring, but swims to deeper cooler water during the warmer months. It is only when the days shorten and water temperatures drop, that they come inshore and start to move upriver.
“The greater river jelly can cause some pretty impressive spectacles” says Dr. Kent Dogwhistle, head of the Department of Tentacular Studies at Miskatonic University in Massachusetts. “But as they are getting their freak on in cold water, not many people are out and about to notice.”
“Aurelia awlryta are very common in the Bay of Fundy,” Dogwhistle said. “But they aren’t equipped to handle the tidal bore very well. And the thwomping great splat of them hitting the rocks at speed is something you never forget once you’ve heard it. It’s one of those great mysteries of nature as to why they are there in the first place. Hardly any of them survive to complete their lifecycle.”
While most jellyfish are marine, freshwater species are not unknown. Greater river jellies are unique in that they are the only jellyfish known to be anadromous. They are born in small freshwater streams, to which they return to mate, lay their eggs, and die. This is especially impressive considering these animals are weak swimmers, moving using contractions of their bell-like bodies in a pumping motion.
“It’s kind of amazing they get anywhere.” Dr. Dogwhistle told this reporter. “They (A. awlryta) wouldn’t seem to move fast enough to even count as pelagic. What they do is hardly more than an agitated sort of drifting. We’d track them, but we’ve yet to design a tag that works. We don’t know how they do it, but as long as there are no dams along the way, they seem to manage to get upstream. They cannot, obviously, make use of a fish ladder.”
And up the Connecticut River they came last week, at least as far as Chicopee. A sudden post-storm drop in water levels left countless jellies high and dry along the shore and even in trees. And if the sight of school of jellyfish stuck to trunks and impaled on stems and branches was not surprising enough, a sudden cold snap froze the stranded creatures solid. It might have been a rum deal for the jellies, but it was a delight and amazement to onlookers along the river, as is evidenced by these photographs from Windsor Locks. The frozen jellyfish looked, exclaimed a tourist from Miami, like Christmas ornaments.
Dr. Dogwhistle assured us that enough of the plucky cnidaria survive to carry on the species, and that they are likely to continue to do so, unless global temperatures continue to rise.
“They’re pollution tolerant, so they are still plentiful, even if no one notices them because they have no commercial value. But they do need the cold. If it does not freeze, we do not see them here. I can only hope that they will continue to thrive and add their beauty to the diversity of these waters.”