Source-resolved PAHs links with microbial diversity and community structure in a multi-stressed coastal system, Saronikos Gulf, Greece (Eastern Mediterranean Sea)

Polycyclic aromatic hydrocarbons (PAHs) are organic pollutants widely abundant in multi-stressed coastal environments worldwide. Herein, seawater (dissolved phase/suspended particles) and sediment samples were collected during a survey on June 2024 across five stations, reflecting multiple anthropogenic stressors, at the heavily impacted Saronikos Gulf, Greece. In the collected samples, 47 PAH homologues were monitored by gas chromatography - mass spectrometry, resolved into source-related profiles by employing the EPA's Positive Matrix Factorization model and examined in relation to bacterial community composition inferred from eDNA metabarcoding sequencing. Our aim was to assess the potential links of PAH sources to microbial diversity and community structure, providing a targeted tool to support coastal monitoring of complex PAHs mixtures in multi-stressed environments. Total PAHs (TPAH₄₇) concentrations ranged between 127 and 462 ng L −1 in the dissolved phase with alkylated 2- and 3-ring compounds dominating, 5.78–10.4 ng L −1 in suspended particles and 860–5450 ng g −1 in sediments, dominated by high-MW 4- to 7-ring compounds. Bacterial community composition based on 16S rRNA gene metabarcoding differed between seawater and sediments. In seawater, community co-varied with physicochemical gradients (temperature, salinity, dissolved oxygen, chlorophyll-a), while PAH source profiles showed weaker associations. In sediments, bacterial assemblages exhibited a stronger statistical association with source-resolved PAH profiles based on the constrained ordination framework. In the dissolved phase the taxa Flavobacterium , Sulfitobacter , and Labedella gwakjiensis , in the suspended particles the genus Algiphilus , and in sediments the species Parahaliea maris were identified as source-associated candidate indicator taxa, highlighting compartment-specific potential bioindicators that require functional validation with -omics tools. • A source-resolved assessment of PAH-microbial linkages in a stressed coastal system • PAH sources/phase associations shape microbial responses more than concentrations. • Sediments show the strongest PAH source-microbial associations. • Phase-specific bacterial taxa identified as PAH source bioindicator candidates • Parahaliea maris identified as a potential PAH bioindicator in sediments