Okinawa, Japan – Marine plastic pollution has claimed another victim, this time a swimming crab discovered trapped inside a discarded plastic bottle off the coast of Okinawa. Researchers from Hiroshima University reported the finding in the journal Ecosphere, underscoring the hidden dangers of ocean plastics for smaller marine animals.

During juvenile fish surveys near Sesoko Island in July 2022, researchers Hajime Sato and Yoichi Sakai encountered a floating high-density polyethylene (HDPE) Shaoxing wine bottle. Inside was a live Portunus sanguinolentus crab, far larger than the bottle’s 24 mm opening. The crab measured 40.31 mm long, 88.23 mm wide, and weighed 42.06 g.

Analysis revealed the crab had survived by feeding on juvenile fish, including the rough triggerfish (Canthidermis maculata) and the sergeant major (Abudefduf vaigiensis), as well as algae growing inside the bottle. Barnacle growth on the bottle indicated it had been drifting for about two months. Researchers concluded the crab entered as a juvenile, grew while trapped, and became too large to escape.

“This crab reminds us of Salamander, a short story by Masuji Ibuse, where a creature grows trapped in its burrow, unable to leave,” the authors noted. They warned that discarded plastic bottles can trap crabs and other small marine animals, with similar cases already reported in Japanese waters.

The study was led by Hajime Sato, now a postdoctoral fellow at the Okinawa Institute of Science and Technology, and Professor Yoichi Sakai of Hiroshima University. The late Tetsuo Kuwamura of Chukyo University co-authored the research.