Coastal convergence zones as microplastic hotspots: implications for marine life in the Seto Inland Sea

This study examines microplastic (MP, 1–5 mm) densities in convergence zones in the Seto Inland Sea, comparing them to non-convergence zones. Convergence zones exhibited MP densities 40 to 300 times higher than non-convergence zones, with an extraordinary density of 3.7 ± 6.3 pieces m⁻³, similar to densities in known MP hotspots. Expanded polystyrene was the predominant polymer, varying seasonally and peaking in summer. Juvenile fish associated with driftweed in these zones face potential long-term MP exposure, up to four months. The massive MP accumulation in coastal convergence zones is comparable to accumulation zones in open ocean gyres, with significant implications for coastal marine life. However, these MPs are primarily autochthonous, suggesting potential management through local marine plastic waste initiatives. Our findings highlight the importance of considering small-scale oceanographic features in assessing marine plastic pollution and its ecological risks, emphasizing the need for targeted research on long-term impacts and formation mechanisms of these MP hotspots.

Presentation Preference: Poster

Primary Presenter: Masatoshi Nakakuni, Kagawa University (masatoshi.nakakuni@gmail.com)

Authors:

Miharu Nishida, Kagawa University  (s23g639@kagawa-u.ac.jp)

Ryosuke Nishibata, Kagawa University  (s18a106@stu.kagawa-u.ac.jp)

Koji Kishimoto, Kagawa University  (kishimoto.koji@kagawa-u.ac.jp)

Hitomi Yamaguchi, Kagawa University  (yamaguchi.hitomi@kagawa-u.ac.jp)

Kazuhiko Ichimi, Kagawa University  (ichimi.kazuhiko@kagawa-u.ac.jp)

Masahide Ishizuka, Kagawa University  (ishizuka.masahide@kagawa-u.ac.jp)

Yoshihiro Suenaga, Kagawa University  (suenaga.yoshihiro@kagawa-u.ac.jp)

Kuninao Tada, Kagawa University  (tada.kuninao@kagawa-u.ac.jp)