Friday, 3 November 2017

Under the sea ice, behold the ancient Arctic jellyfish

October 24, 2017 by Kevin Krajick

The doings of creatures under the Arctic sea ice are many, but they are rarely observed by humans; it's pretty hard to get under the ice to look. In recent years, marine biologist Andy Juhl and his colleagues have gotten around this problem by driving snowmobiles several miles from Point Barrow, Alaska, out onto the adjoining frozen Chukchi Sea, drilling holes in the four-foot-plus thick ice, and poking in a video camera attached to an small underwater vehicle.

Among the things that they have observed: sizable Chrysaora melanaster jellyfish floating by, trailing their foot-long-plus tentacles along the shallow bottom. Their presence came as a surprise: adult jellyfish, or medusae, are generally thought to live only a few months. Scientists had assumed that the species survived winter only in a life stage called polyps–formless masses that cling to rocks and release little baby medusae in the spring. In a scientific paper out this week, Juhl and colleagues say the videos indicate that the creatures in fact last through winter. They could even be several years old–the Methuselahs of medusae.

"One reason we were interested was, first of all, we saw them, and it was kind of weird," said Juhl, a researcher at Columbia University's Lamont-Doherty Earth Observatory. "The whole study is based on videos we made over several years." Also, he says, the rich pollock fishery in the nearby Bering Sea is the engine for "everything fish"–fish sticks, fish paddies and other mystery-meat-type marine fast foods. But in some years, jellyfish numbers in the Bering Sea swell, and fishing nets can get seriously clogged–a problem that may crescendo over several years before dying back again. The study may reveal something about the jellyfish population dynamics that drive these cycles.

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