The Effects of Microplastic Pollution on Marine Microbial Communities: A Systematic Review and Meta-Analysis
1Department of Marine Biology, University of Coastal Sciences, Ocean City, OC 12345, USA
2Institute of Environmental Microbiology, National Research Center, Sea Haven, SH 67890, USA
3Center for Ocean Health, International Marine Consortium, Global Waters, GW 45678, International
Abstract
Microplastic pollution has emerged as a pervasive environmental threat in marine ecosystems, with potential cascading effects on microbial communities that underpin oceanic food webs and biogeochemical cycles. This systematic review and 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. We applied PRISMA guidelines for study selection and random-effects models for meta-analytic synthesis. Results indicate a significant negative effect on microbial alpha-diversity (Hedges’ g = -0.62, 95% CI: -0.89 to -0.35, p < 0.001), particularly in bacterioplankton assemblages. Functional disruptions, including reduced nitrogen fixation rates (g = -1.12, 95% CI: -1.68 to -0.56), were also evident. Heterogeneity was high (I2 = 78%), driven by polymer type and exposure duration. These findings underscore the urgency for mitigation strategies and highlight knowledge gaps in polar and deep-sea environments.
Keywords: microplastics, marine microbiome, biodiversity, meta-analysis, ecosystem function
Introduction
Oceans cover over 70% of Earth’s surface and host microbial communities responsible for primary production, carbon sequestration, and nutrient cycling (Falkowski et al., 2008). These microbes form complex biofilms on surfaces, influencing particle dynamics and trophic transfers (Azam and Malfatti, 2007). In recent decades, microplastics—synthetic polymer particles <5 mm—have proliferated in marine environments, originating from primary sources like microbeads and secondary fragmentation of macroplastics (Thompson et al., 2004).
Emerging evidence suggests microplastics act as vectors for microbial colonization, termed the “plastisphere” (Zettler et al., 2013). While some studies report enriched pathogenic taxa on plastics (Kirstein et al., 2016), others document shifts in community structure and reduced metabolic activity (Miao et al., 2019). Discrepancies arise from variability in experimental designs, plastic characteristics (e.g., polyethylene vs. polystyrene), and environmental contexts. To resolve these inconsistencies, we conducted a systematic review and meta-analysis evaluating microplastic effects on microbial diversity, abundance, and function.
Our objectives were threefold: (1) assess impacts on alpha- and beta-diversity; (2) quantify changes in functional genes and processes; and (3) explore moderators such as plastic type, size, and exposure time. This synthesis provides robust evidence for policymakers and researchers addressing plastic pollution under frameworks like the UN Decade of Ocean Science for Sustainable Development.
Materials and Methods
Literature Search and Selection
We searched Web of Science, Scopus, and PubMed using terms: (“microplastic” OR “micro-plastic“) AND (“marine” OR “ocean“) AND (“microbial” OR “bacteri*” OR “microbiome”). No language restrictions were applied; searches spanned January 1, 2010, to December 31, 2023. PRISMA guidelines were followed (Page et al., 2021). Studies were included if they: (i) used controlled exposures or field surveys comparing microplastic-impacted vs. control microbial communities; (ii) reported quantitative metrics (e.g., Shannon index, 16S rRNA gene copies); and (iii) focused on marine environments.
From 1,247 records, 47 studies met criteria after duplicate removal (n=312), title/abstract screening, and full-text review (Figure 1). Risk of bias was assessed via ROBINS-E tool, excluding high-risk studies.
Figure 1. PRISMA flow diagram of study selection process.
Data Extraction and Analysis
Effect sizes were calculated as Hedges’ g (corrected standardized mean difference), with positive values indicating microplastic enrichment. Diversity metrics (Shannon, Simpson), abundance (cell counts, qPCR), and functional rates (e.g., denitrification) were extracted. Meta-analyses used random-effects models in R package metafor (Viechtbauer, 2010). Heterogeneity was quantified via I2 and τ2. Moderator analyses employed meta-regression; publication bias was tested with funnel plots and Egger’s test.
Results
Microbial Diversity
Microplastics significantly reduced alpha-diversity across 32 studies (g = -0.62, 95% CI: -0.89, -0.35, p < 0.001; Figure 2). Beta-diversity shifts were pronounced (PERMANOVA across 18 datasets, pseudo-F = 4.23, p < 0.01), with plastisphere communities dominated by Proteobacteria and reduced Cyanobacteria.
| Metric | k | g (95% CI) | I2 (%) | p |
|---|---|---|---|---|
| Alpha-diversity | 32 | -0.62 (-0.89, -0.35) | 78 | <0.001 |
| Bacterial abundance | 25 | 0.18 (-0.12, 0.48) | 65 | 0.24 |
| Nitrogen fixation | 12 | -1.12 (-1.68, -0.56) | 82 | <0.001 |
| Denitrification | 8 | -0.45 (-0.91, 0.01) | 71 | 0.06 |
Functional Impacts
Nitrogen fixation rates declined markedly (g = -1.12; Table 1), linked to diazotroph suppression (e.g., Richelia spp.). No overall abundance change was detected, though Vibrio spp. proliferated on polyethylene (QM = 6.4, p = 0.04 for polymer moderator).
Figure 2. Forest plot of alpha-diversity effects. Squares: study effect sizes; horizontal lines: CIs; diamond: summary effect.
Funnel plots were asymmetrical (Egger’s test, p = 0.03), but trim-and-fill adjustment minimally altered results (adjusted g = -0.58).
Discussion
Our meta-analysis confirms microplastics perturb marine microbial communities, with strongest effects on diversity and diazotrophy. These align with laboratory assays showing adsorption of quaternary ammonium compounds disrupting membranes (Nolte et al., 2019). Functional losses may amplify eutrophication via altered N-cycling (Seeley et al., 2020).
High heterogeneity reflects real-world variability: polystyrene elicited larger effects than polypropylene (QM = 9.2, p = 0.002), consistent with surface chemistry differences (Hodson et al., 2019). Limitations include underrepresentation of Archaea and viruses, and a bias toward coastal studies.
Future research should prioritize long-term field experiments and omics integration. Mitigation via source reduction and biodegradable alternatives is imperative to safeguard microbial-mediated services.
Conclusion
Microplastics pose a significant threat to marine microbial ecology, with quantifiable declines in diversity and key functions. This synthesis galvanizes action under global plastic treaties.
Acknowledgments
Funded by NSF Grant OCE-2145123. We thank reviewers for insights.
References
