Location-dependent marine biodegradability of aliphatic polyesters under simulated seawater conditions

• Lab-controlled marine conditions were established using seawater from 12 Japanese sites. • PHBV exhibited consistently high mineralization regardless of the sampling location. • In contrast, PBSA degradation was highly site-dependent, showing mass loss at only one site. • PHBV plastisphere was dominated by Alteromonadaceae, Colwelliaceae , and Oceanospirillaceae . • The variability in PBSA degradability indicates its sensitivity to local microbial communities. Biodegradable plastics can help reduce marine plastic pollution. However, most studies have tested biodegradability at only one site; therefore, distinguishing material effects from seawater conditions is difficult. In this study, we evaluated the location-dependent marine biodegradability of two representative aliphatic polyesters, poly(3-hydroxybutyrate- co -3-hydroxyvalerate) (PHBV) and poly(butylene succinate- co -adipate) (PBSA), under identical laboratory conditions using seawater collected from 12 coastal sites in Japan. Film mass loss, biochemical oxygen demand (BOD) -based mineralization (BOD/theoretical oxygen demand, ThOD), and plastisphere composition were assessed, with polyethylene serving as a non-biodegradable reference. PHBV degraded in all seawater samples, and achieving substantial BOD-based mineralization (52-86%). In contrast, PBSA degraded only in seawater from Isumi, Chiba (CI), Japan, and no measurable mineralization was detected. Amplicon sequencing indicated that PHBV formed a consistent material-specific plastisphere containing members of Alteromonadaceae, Colwelliaceae , and Oceanospirillaceae , independent of the sampling location. PBSA plastispheres varied among sites. Although genera previously linked to polyester degradation (e.g., Pseudomonas, Halopseudomonas, Alcanivorax ) were detected, their involvement in the biofilm community observed at CI remains speculative. Collectively, these findings demonstrate that PHBV biodegradability is robust across locations, whereas PBSA degradation is site-dependent under the same laboratory conditions.