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.

Biological invasions are a widespread problem worldwide, as invasive non-indigenous species (NIS) may affect native populations through direct (e. g., predation) or indirect (e.g., competition) trophic interactions, leading to changes in the food web structure. The trophic relationships of the invasive eastern mosquitofish Gambusia holbrooki and the native big-scale sand smelt Atherina boyeri coexisting in three Mediterranean coastal ponds characterized by different trophic statuses (from oligotrophic to hypereutrophic) were assessed in spring through isotopic niche analysis and Bayesian mixing models. The two fish relied on the distinctive trophic pathways in the different ponds, with the evidence of minimal interspecific niche overlap indicating site-specific niche divergence mechanisms. In more detail, under hypereutrophic and mesotrophic conditions, the two species occupied different trophic positions but relying on a single trophic pathway, whereas, under oligotrophic conditions, both occupied a similar trophic position but belonging to distinct trophic pathways. Furthermore, the invaders showed the widest niche breadth while the native species showed a niche compression and displacement in the ponds at a higher trophic status compared to the oligotrophic pond. We argue that this may be the result of an asymmetric competition arising between the two species because of the higher competitive ability of G. holbrooki and may have been further shaped by the trophic status of the ponds, through a conjoint effect of prey availability and habitat complexity. While the high trophic plasticity and adaptability of both species to different environmental features and resource availability may have favored their coexistence through site-specific mechanisms of niche segregation, we provide also empirical evidence of the importance of environmental control in invaded food webs, calling for greater attention to this aspect in future studies.

Biodiversity operates across multiple levels of biological organization, encompassing genes, species, and ecosystems. It plays a crucial role in sustaining ecological resilience and delivering essential services such as food and clean water. Higher biodiversity enhances the ability of ecosystems to withstand and recover from disturbances. Monitoring biodiversity is therefore vital for assessing ecosystem health, identifying imbalances, and preserving these critical services. Within the oceanic ecosystems, Marine Animal Forests (MAFs), structured by key organisms like corals and sponges, serve as biodiversity hotspots and play a vital role in regulating oceanic processes. This paper explores methodologies for studying MAFs across three levels: intra-species diversity, species diversity, and genetic diversity. Intra-species diversity focuses on variation within and between individuals, with an emphasis on phenomena like chimerism and somatic mutations. Species diversity is analyzed using taxonomic, functional, and biotic indices, while genetic diversity is examined through DNA barcoding, species delimitation analyses (SDA), metabarcoding, and microsatellite markers. Although each method provides valuable insights independently, integrating them can significantly enhance the speed and effectiveness of biodiversity assessments. Future efforts should emphasize public engagement through citizen science, ensuring biodiversity monitoring tools become more accessible, affordable, and user-friendly. Additionally, expanding server infrastructure will be key to accelerating bioinformatic workflows. Finally, strengthening global collaborations and increasing awareness of biodiversity and climate change remain essential priorities.