Ocean acidification (OA), one of the main climate-change-related stressors linked to increasing CO₂ concentration in the atmosphere, is considered an important threat to marine biodiversity and habitats. Studies on CO₂-vents systems, naturally acidified environments that mimic future ocean scenarios, help to explore the sensitivity of species and to understand how benthic communities rearrange their structure and functioning under the pressure of OA. We addressed this problem by studying the benthic invertebrates associated with a habitat-forming brown alga (Cystoseira brachycarpa) in the Bottaro crater vents system off Panarea island (Tyrrhenian Sea, Italy), by sampling along an OA gradient from the proximity of the main venting area (station B3, pH 7.9) to a control zone (B1 station, pH 8.1). Samples were collected in September 2016 and 2018. A total of 184 taxa and 23 different functional traits have been identified, considering feeding habit, motility, size, reproductive and developmental biology, and occurrence of calcareous structures. Invertebrates are distributed according to the distance from the high venting zone and low pH levels and results very consistent between the two investigated years. In the low-pH area (B3), 43% of the species are selected. The functional traits of the fauna mirror this zonation pattern, mainly changing the relative proportion of the number of individuals of the various functional guilds along the OA gradient. Invertebrates inhabiting the low-pH zone are mainly composed of weakly or non-calcified species, with small size, burrower/tubicolous habit, omnivorous or suspension feeders, and with direct development and brooding habit. In the other stations, heavily calcified forms, herbivore and herbivore/detritivore, and with medium (1–5 cm) and large (>5 cm) sizes prevail, showing indirect benthic and planktic development. The taxonomic analysis, coupled with functional aspects, increases our prediction of which traits could be potentially more advantageous for species to adapt to the hypothesized scenarios of OA, and identify present and future winner and/or loser organisms in the future ocean of the Anthropocene.

We assessed the influence of different organic matter (OM) inputs associated with terrigenous/freshwater allochthonous and sewage derive on bioturbation and irrigation potential community indices (BP_c and IP_c) of the soft-bottom macrofauna community. The macrofauna was sampled from two different sedimentary impacted areas, in front of the Po River Delta (northern Adriatic Sea) and sewage discharge diffusion zone (Gulf of Trieste). The highest values of BP_c and IP_c were observed at the northward sampling stations of the prodelta and the stations 25 m distance in front of the main sewage outfall. Species richness showed high values in the prodelta likely due to the OM positive effect from the delta, and it increased with increasing distance from the pipeline due to the effect of OM from the sewage discharge. The bioturbation indices differed due to the presence of surface deposit feeders and the injection depth (from 2 to 5 cm) with limited movement at the station located northwards in the prodelta and 25 m distance in the diffusion zone. We infer that the difference in bioturbation indices was likely due to the effects of grain-size composition and the degree of organic enrichment in both study areas.

The endemic Mediterranean bivalve Pinna nobilis is a typical example of an autogenic ecosystem engineer in sedimentary environments, as it modifies the substrate, creates new complex 3D habitats and concentrates various species, thus increasing local biodiversity. Despite the significant loss of P. nobilis populations due to the epidemic mass mortality that occurred in several regions of the Mediterranean, including the northern Adriatic Sea, the numerous empty shells, still firmly anchored in the sediment, may continue to play the role of basibiont of this species. The persistence of this ecological function was here investigated on dead specimens of P. nobilis through the structural and functional study of the associated epibenthic mollusc community. A large number of mollusc taxa, characteristic of both infralittoral and sublittoral hard and soft bottoms, were identified in thirteen shells collected from four different sites in the Gulf of Trieste. Multivariate analysis revealed a clear separation between sites in terms of taxonomic composition, species abundance and biomass, with differences in expressed functional traits. Overall, considerable taxonomic and functional diversity was found, suggesting that the empty shells continue to provide a suitable habitat for a variety of molluscs that are closely linked to the surrounding environment and fulfil many different ecological functions.

This preliminary study presents an updated checklist of amphipod crustaceans inhabiting Italian seas and provides valuable insights into their diversity, distribution, and ecological traits. By combining existing literature with unpublished data, we were able to record 500 species in Italian waters. The analyses revealed a significant increase in the number of amphipod species documented in the Country, primarily due to intensified research efforts and the introduction of non-native species. This study highlights the importance of ongoing monitoring and research to assess marine biodiversity. Future efforts should prioritize understudied groups, such as planktonic species, and those living in deep-sea marine environments.