Ports connect cities, economies, and supply chains, but they also create environments where marine ecosystems interact intensely with shipping, wastewater, and coastal development. A new global study has revealed that these pressures leave measurable signatures in the microscopic communities living in port waters.
"Port microorganisms are not only essential contributors to marine nutrient cycling, but also sensitive indicators of environmental change and human influence," said corresponding author Jianhong Shi of Shanghai Maritime University. "By examining ports across multiple continents, we were able to identify shared ecological patterns while also showing how shipping and wastewater may influence microbial diversity and potential pathogen abundance."
The researchers conducted a large-scale synthesis of bacterial communities in port waters from 23 cities in eight countries across five continents. They analyzed 1,045 water samples containing more than 16.5 million high-quality 16S rRNA gene sequences, allowing them to compare microbial diversity, geographic distribution, ecological assembly processes, and possible sources of bacteria.
The results showed a clear distance-decay pattern. In other words, bacterial communities from ports located closer together tended to be more similar, while similarity decreased as geographic distance increased. However, this relationship was weaker in high-capacity ports, suggesting that frequent shipping activity may help transport microorganisms between distant locations, potentially through ballast water or organisms attached to ship surfaces.
Bacterial richness did not follow the familiar pattern often observed in plants and animals, where biodiversity is generally highest in tropical regions. Instead, port-water bacterial richness peaked at mid-latitudes, although latitude explained only a small portion of the overall variation.
Across the global dataset, the researchers identified 12 core bacterial genera, together accounting for nearly one-quarter of the bacterial community. The most abundant was SAR11 subclade IIIa, a widespread marine lineage involved in carbon cycling. Other core groups may contribute to the degradation of organic matter and the cycling of nitrogen and sulfur.
The study also detected 295 distinct potential pathogenic bacterial variants, representing approximately 6% of the analyzed sequences. Their abundance and composition differed substantially among regions, with African port samples showing the highest relative abundance of potential pathogens. Some pathogen-related sequences were geographically restricted. For example, sequences associated with Vibrio parahaemolyticus, a bacterium linked to seafood-borne illness, were detected only in Asian samples.
The authors emphasized that DNA-based identification indicates the presence of sequences associated with potential pathogens, rather than confirming that viable disease-causing organisms were active in every sample.
Source-tracking analysis suggested that air and human-associated sources were major contributors to port-water bacterial communities. Human excretion accounted for an estimated 26.6% of the potential bacterial sources, while air contributed 26.9%.
Wastewater discharge was associated with lower bacterial diversity and greater potential pathogen abundance. Port capacity showed the strongest individual correlation with bacterial community structure and was also positively associated with pathogen abundance. These findings indicate that both land-based pollution and maritime operations can influence port microbiomes.
The researchers found that deterministic ecological processes, including environmental selection by factors such as salinity, temperature, pH, and dissolved oxygen, played a larger role than random processes in shaping global port bacterial communities.
The findings support the use of microbial communities as sensitive indicators of port ecosystem health and highlight the need for stronger wastewater management, pathogen surveillance, and ballast-water controls. The authors also recommend standardized global sampling and more advanced methods, including metagenomics and full-length gene sequencing, to improve future identification of microorganisms and their ecological functions.
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Journal reference: Lv B, Zhang Q, An T, Mei S, Kan G, et al. 2026. A global synthesis of port water microbiome biogeography and anthropogenic associations. Biocontaminant 2: e008 doi: 10.48130/biocontam-0026-0005
https://www.maxapress.com/article/doi/10.48130/biocontam-0026-0005
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Biocontaminant (e-ISSN: 3070-359X) is a multidisciplinary platform dedicated to advancing fundamental and applied research on biological contaminants across diverse environments and systems. The journal serves as an innovative, efficient, and professional forum for global researchers to disseminate findings in this rapidly evolving field.
