Chapman said the dock float was covered with masses of algae, kelp, barnacles, mussels and other organisms. One square-foot area weighed nine pounds.
"This is a whole, intact, very diverse community that floated across from Japan to here," he said. "That doesn't happen with a log or a thrown-out tire. I've never seen anything like this."
Of particular concern was a small crab that has run wild on the East Coast, but not shown up yet on the West Coast, and a species of algae that has hit Southern California, but not Oregon. The starfish, measuring about three inches across, also appears to be new to U.S. shores.
"It's almost certainly true that most of the things on this have not been introduced to this coast yet," Chapman said. "We're going to see more of these things coming."
Tom Cleveland, a housekeeping supervisor at nearby beachfront condominiums, said people curious to see it have been jamming up traffic at a beach parking lot.
"Everybody and their brother has been here looking at it and checking it out," Cleveland said. "Obviously, we knew things would be coming our way, but I didn't expect anything this size."
Associated Press writers Malcolm Foster in Tokyo and Ryan Nakashima in Los Angeles contributed to this report.
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