The Effects of Microplastic Pollution on Marine Microbial Communities: A Meta-Analysis
2Institute of Environmental Microbiology, National Research Center, Seaforth, Canada
Abstract
Microplastic pollution has emerged as a pervasive environmental threat in marine ecosystems, with potential cascading effects on microbial communities that underpin biogeochemical cycles. This meta-analysis synthesizes data from 47 peer-reviewed studies (published between 2010 and 2023) to quantify the impacts of microplastics on marine microbial diversity, abundance, and function. Using standardized effect sizes (Hedges’ g), we found significant negative effects on bacterial alpha-diversity (g = -0.45, 95% CI: -0.62 to -0.28, p < 0.001) and shifts in community composition towards plastic-degrading taxa. Functional disruptions, including reduced enzymatic activity, were also evident (g = -0.32, 95% CI: -0.51 to -0.13, p = 0.001). Heterogeneity was high (I2 > 80%), driven by polymer type and exposure duration. These findings underscore the need for mitigation strategies to protect microbial ecosystem services.
Keywords: microplastics, marine microbiome, biodiversity, meta-analysis, pollution
Introduction
Microplastics (MPs), defined as plastic particles <5 mm in size, are ubiquitous contaminants in marine environments, originating from the degradation of larger plastics, synthetic fibers, and microbeads (Thompson et al., 2004). Their persistence and bioavailability raise concerns about ecological impacts, particularly on microbial communities that form the base of marine food webs and mediate critical processes such as carbon sequestration and nutrient cycling (Azam et al., 1983).
Prior studies have reported MPs acting as vectors for pollutants and altering microbial colonization, potentially selecting for xenobiotic-degrading bacteria (Zettler et al., 2013). However, results are inconsistent, with some indicating enhanced diversity on plastic surfaces (plastisphere hypothesis; Amaral-Zettler et al., 2020) and others showing suppression. A quantitative synthesis is needed to resolve these discrepancies.
This meta-analysis addresses: (1) Does MP exposure affect microbial diversity and abundance? (2) Are there polymer-specific effects? (3) What moderates these impacts?
Materials and Methods
Literature Search and Selection
We searched Web of Science, Scopus, and PubMed (January 2010–June 2023) using terms: (“microplastic” OR “micro-plastic“) AND (“marine” OR “ocean“) AND (“microbial” OR “bacteri*” OR “microbiome”). Studies were included if they: (i) used controlled MP exposures, (ii) reported microbial metrics (e.g., Shannon index, 16S rRNA OTUs), and (iii) provided sufficient data for effect size calculation. Data were extracted independently by two authors, with discrepancies resolved by consensus (n = 47 studies, 216 effect sizes).
Effect Size Calculation
Hedges’ g was calculated as the standardized mean difference: g = (Xtreatment – Xcontrol) / SDpooled, bias-corrected for small samples (Borenstein et al., 2009). Positive g indicates enhancement by MPs. Multilevel random-effects models accounted for sampling variance and phylogenetic non-independence using metafor package in R (Viechtbauer, 2010).
Moderator Analyses
Categorical moderators (polymer type: PE, PP, PS; exposure time: <30 days, >30 days) and continuous moderators (MP concentration: particles/L) were tested via meta-regression. Publication bias was assessed with funnel plots and Egger’s test.
Results
Overall Effects
MP exposure significantly reduced alpha-diversity (g = -0.45, 95% CI: -0.62, -0.28, p < 0.001; Figure 1). Abundance showed no overall change (g = 0.12, 95% CI: -0.05, 0.29, p = 0.167), but beta-diversity differed markedly (PERMANOVA, pseudo-F = 4.23, p < 0.001).
Figure 1. Forest plot of Hedges’ g for microbial alpha-diversity. Squares represent study effect sizes; size proportional to precision. Diamond shows summary effect.
Moderators
Polystyrene (PS) elicited stronger negative effects (g = -0.68) than polyethylene (PE; g = -0.31; QM = 8.45, p = 0.004; Table 1). Longer exposures amplified declines (beta = -0.02 per day, p = 0.012).
| Moderator | Levels | g (95% CI) | QM | p |
|---|---|---|---|---|
| Polymer Type | PE | -0.31 (-0.52, -0.10) | 8.45 | 0.004 |
| PP | -0.42 (-0.61, -0.23) | |||
| PS | -0.68 (-0.89, -0.47) | |||
| Exposure Time | <30 days | -0.28 (-0.48, -0.08) | 6.78 | 0.009 |
| >30 days | -0.61 (-0.81, -0.41) |
No evidence of publication bias (Egger’s test, z = 0.87, p = 0.385).
Discussion
Our synthesis confirms MPs disrupt marine microbial communities, with strongest effects on diversity from PS, likely due to higher leaching of additives (Rochman et al., 2013). These changes may impair ecosystem functions, such as denitrification, with broader implications for fisheries and carbon cycling.
Limitations include lab-dominated data (89% mesocosms/microcosms), potentially underestimating field variability. Future research should prioritize in situ studies and multi-stressor interactions (e.g., MPs + warming).
In conclusion, MP pollution poses a significant threat to marine microbiomes, necessitating global reduction efforts.
Acknowledgments
Funded by NSF Grant OCE-2032754. We thank reviewers for constructive feedback.
References
