Sediment-associated Irgasan drives functional and taxonomic restructuring of marine nematode communities

Abstract

Sediment-associated contaminants can profoundly alter benthic ecosystem functioning, yet their effects on meiofaunal processes remain poorly resolved. Here, we investigated the impacts of Irgasan (triclosan) enrichment in marine sediments on meiofauna, with a particular focus on functional and taxonomic responses of free-living nematodes from the Bizerte Lagoon (Tunisia). A one-month laboratory microcosm bioassay revealed marked differences between Irgasan-contaminated and uncontaminated sediments. High contamination levels led to significant declines in total meiofauna abundance, including nematodes, copepods, oligochaetes and amphipods, while polychaetes were comparatively unaffected. In parallel, nematode total biomass, taxonomic composition and functional trait structure were strongly altered across all Irgasan-enriched treatments. Multivariate analyses (nMDS and correspondence analysis) demonstrated a clear functional restructuring of nematode communities driven by changes in key biological traits, particularly the feeding strategy, adult body size and amphid morphology. Highly contaminated sediments were dominated by opportunistic and predatory species, whereas uncontaminated sediments supported microvorous and deposit-feeding taxa. These results highlight how sediment-bound Irgasan disrupts the benthic community structure by modifying functional trait distributions, with implications for ecosystem processes mediated by meiofauna in coastal sediments.