UAF scientist uses optical instruments to record world’s largest animal movement

FAIRBANKS, Alaska (KTVF) One of the first lessons we learn (and perhaps forget about) in grade-school science classes is about the food chain. In the oceans around Alaska, however, the organisms occupying every rung of the trophic ladder are constantly aware of those below them – and those above them. After all, they’re either thinking about dinner or remembering not to be someone else’s.

The equipment Dr. William Burt used to measure plankton utilizes seawater sucked into the ship as it moves along the water. With this equipment, Burt conducted the first known optic measurement of vertical zooplankton migration. (Dr. William Burt)

In 2019, the University of Alaska Fairbanks’ Dr. William Burt published a paper remarking on an interesting observation he made about a specific animal’s feeding habits while sailing off the coast of Seward in 2016. “Basically, I would wake up in the morning…my data was really messy. It looked like something was wrong,” Burt says at his ground-level office of UAF’s O’Neill building.

Frustrated, Burt decided to stay awake one evening to monitor his equipment and see what was malfunctioning. On this particular expedition, Burt was using optical equipment to measure phytoplankton, or microscopic plants which make up most of the organisms in the water.

As darkness fell, Burt’s measurements spiked. “The signal that I was isolating is normally a signal that you would just throw out as electronic noise,” he explains. However, intuition and experience led him to investigate the matter further. He placed a filter at the end of his instruments and collected samples over the course of an hour. After his expedition was over, he and a colleague observed this sample under a microscope. Sure enough, it was full of migrating zooplankton.

“This pattern was happening night after night…and it sort of occurred to me that this could be a signal of this vertical migration pattern,” says Burt, “Which is something we’ve known about for decades but no one had ever documented using this sort of instrument to measure it.” The use of optical instruments to measure these plankton represents the novel aspect of Burt’s findings.

Zooplankton – unlike phytoplankton -- are not plants, but animals. The reason the word ‘plankton’ is affixed to the names of both creatures is because it simply refers to anything in the water which cannot move under its own propulsion. This is what makes these particular migrating zooplankton unique: although they do not have the strength to move laterally against the current, they can move up and down.

As it gets darker, the upward migration of these plankton is spurred by the lack of their predators’ ability to find them. Baleen whales, arctic cod, and some species of shrimp all feast on these zooplankton using sight as their main sense of locating prey. The darkness provides cover under which these plankton can move upward and feed on surface phytoplankton. When day breaks, the zooplankton migrate back down into the deeper, darker waters.

“The average was 37 minutes before sunset, and they stopped 30 minutes before sunrise. Like clockwork,” Burt says in a press release issued by UAF.

In April 2020, Burt will take an optics system he has built for the university on its research vessel, the R/V Sikuliaq.

“It’s possible that we can go much further with this,” Burt says in the press release, “We’ve only just started.”

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