A species of shellfish has disappeared along an 18-mile stretch of coast near Japan's devastated Fukushima Daiichi nuclear plant, scientists say.

Researchers from Japan's National Institute for Environmental Studies and National Institute of Radiological Sciences found a species of shellfish known as Thais clavigera was extinct in eight of 10 places within the 12-mile-radius alert zone of the nuclear plant, which was damaged by the March 2011 earthquake and tsunami.

Other shellfish species were found in the alert zone but their numbers had declined and high levels of radioactive materials were detected in them, the researchers said.

Lead researcher Toshihiro Horiguchi said the disappearance of Thais clavigera was likely a result of radiation from the damaged plant.

Researchers ruled out the tsunami as a cause, because the shellfish were found surviving in other areas affected by the disaster, having disappeared only from the immediate vicinity of the Fukushima plant, China's official Xinhua News Agency reported Monday.