Chitin-rich crab shell by-products modulate the marine lifetime of PHBV films via plastisphere remodeling

• Crab shells modulate the marine biodegradation rate of PHBV films. • The addition of crab shells reduces mass loss and biofilm accumulation on PHBV. • Meta-omics reveal that Crab shells remodel the PHBV plastisphere. • Crab shells suppress early exPhaZ gene expression. • Seafood waste serves as a biological regulator for tuning plastic lifetime. Poly(3-hydroxybutyrate- co -3-hydroxyvalerate) (PHBV) biodegrades in seawater, yet its rapid loss of mechanical integrity limits marine applications. We tested whether crab shells (CrSh)—a chitin- and protein-rich seafood by-product—can modulate plastisphere assembly and thereby slow PHBV degradation. PHBV films were incubated in seawater tanks with CrSh either sandwiched against the film or co-incubated without direct contact. We monitored mass loss, surface morphology and biofilm accumulation, and characterized community structure and gene expression using 16S rRNA amplicon sequencing, metagenomics and metatranscriptomics. CrSh reduced PHBV mass loss and biofilm accumulation; for sandwiched films, mass loss was reduced to <20% of the control at 4 weeks and to 52% at 8 weeks, while biofilm accumulation was 19–61% of the control. Plastisphere communities diverged, with the genera Oceanospirillum and Bowmanella dominating PHBV and Marinobacter prevailing in CrSh treatments. Metatranscriptomics indicated early suppression of putative extracellular PHB depolymerase (exPhaZ) transcripts on PHBV with CrSh, consistent with the delayed surface erosion observed by scanning electron microscopy. Similar inhibition in the non-contact setup suggests CrSh-derived biochemical effects can modulate plastisphere structure, rather than simple physical shielding. Crab shells therefore provide a simple, low-cost and sustainable strategy to tune the service life of PHBV products in marine environments.