In November, an unusual swarm of tiny critters caught the attention of a crewmember on a National Oceanic and Atmospheric Administration boat docked in a Lake Michigan channel. He asked Steven Pothoven of NOAA's Great Lakes environmental field station at Muskegon, Mich., what the critters were.
"I could see they weren't fish, so I netted some," the biologist recalls. Under magnification, the half-inch-long animals appeared to be crustaceans known as mysid shrimp. But "they couldn't be the native mysid," Pothoven realized, because those are cold- and deep-water denizens, not shoreline dwellers.