Shallow-water hydrothermal vents are naturally fragmented habitats characterized by steep physicochemical gradients and environmental heterogeneity. These systems function as natural laboratories providing unique environments to investigate the processes that regulate community assembly and ecosystem functioning under extreme conditions. Despite the widespread occurrence of hydrothermal activity in the Aeolian Archipelago (southern Tyrrhenian Sea), the ecology of meiofaunal communities inhabiting these environments remains poorly understood.

An investigation was conducted into the abundance, diversity, community composition and functional organization of meiofauna at shallow hydrothermal vents of Vulcano (Porto Levante) and Salina (Pollara Bay), comparing vent-influenced sediments with adjacent non-vent areas. Attention was placed on nematode assemblages, the dominant component of the meiofauna.

Meiofaunal abundance and diversity did not exhibit consistent declines near vent emissions, and diversity indices did not differ significantly among stations. In contrast, community composition varied significantly among sites, stations and sediment layers, suggesting that small-scale environmental heterogeneity strongly influences meiofaunal assemblages. Temperature and pH explained from 43 to 58.1% of the variability in meiofaunal community diversity and composition.

Nematode assemblages inhabiting vent sediments were largely composed of taxa also occurring in surrounding sediments, suggesting that shallow-vent communities are assembled mainly through differential filtering of taxa from the regional species pool rather than through the establishment of vent-endemic specialists. Nevertheless, marked shifts in trophic structure and life-history strategies were observed along the vent gradient, revealing stronger functional than taxonomic responses along the gradient. Particularly, PSU, pH and temperature could explain up to 56.2% of taxonomic diversity, 70.5% of community composition and 90.9% of functional diversity patterns in nematode assemblages.

These findings indicate that shallow hydrothermal vents of the Aeolian Archipelago do not harbour highly specialized meiofaunal assemblages; instead, environmental filtering reorganizes communities primarily at the functional level, generating marked shifts in trophic and life-history strategies despite limited changes in taxonomic diversity.