When debris from the March 2011 earthquake and tsunami disaster in northeast Japan first wended its over through the Pacific Ocean's currents, concerns about potential radioactive contaminants from the Fukushima No. 1 nuclear plant disaster briefly gripped residents of Hawaii and North America's West Coast.

Fewer paid attention to the living things, such as mussels, barnacles and seaweeds, that clung to the debris, and their capacity to harm marine ecosystems unaccustomed to their presence.

Five years later, debris is still washing up, and scientists have begun to explore whether the invasive species have become established in North America.