Environmental drivers of nematode community structure in harbors: the interplay of pollution, granulometry, and spatial heterogeneity

This meta-analysis provides a comprehensive assessment of meiofaunal nematodes in Mediterranean port ecosystems, integrating taxonomic patterns, frequency of occurrence, and environmental characteristics across seven ports. Only a limited set of genera occurred consistently across sites, all belonging to tolerant and opportunistic taxa, confirming that nematode assemblages in ports are strongly shaped by environmental filtering but do not form a community uniquely characteristic of port environments. Community differences among ports were driven primarily by sediment grain size, depth, and port-specific hydrodynamic conditions rather than by geographical proximity. Highly impacted stations were associated with a single consistent indicator genus, while moderately impacted sites hosted a broader suite of transitional taxa. No genus was exclusive to non-impacted conditions, which were instead characterized by more balanced and evenly structured assemblages. Contaminant levels played a secondary and context-dependent role, largely modulated by sediment permeability and oxygenation. Overall, the findings highlight the sensitivity of nematode assemblages to both natural and anthropogenic gradients and underline their value as ecological indicators when interpreted together with sedimentological features, functional traits, and local port morphology.