Insights into a patchy meadow of the little Neptune grass Cymodocea nodosa and its epiphytic macroalgal community in the Central Adriatic Sea

Seagrass meadows are recognized as biodiversity hotspots and valuable coastal communities due to the ecosystem services and goods they provide (Orth et al., 2006). In recent years, interest in their monitoring has increased, driven both by their ecological role and by the severe global decline observed over the past decades as a result of human activities (Waycott et al., 2009). For these reasons, restoration efforts are becoming crucial, especially in the face of future environmental challenges (Manca et al., 2024). Cymodocea nodosa is a euryhaline seagrass and a pioneer species able to colonize both degraded and pristine habitats (Orfanidis et al., 2020). Here, we present a monitoring investigation of a discontinuous meadow located in a highly impacted environment, the marina of Torrette (Ancona, Central Adriatic Sea). The preliminary study conducted in 2024 surveyed the meadow approximately monthly from May to October and aimed to assess its environmental status by analysing morphometric parameters (shoot density, leaf length, width, surface, and apex integrity), evaluating its reproductive capability (searching for Llowers and fruits), and describing the macroalgal epiphytic community colonizing the leaves. The epiphytic assemblage of the Torrette marina consisted of 11 macroalgal taxa identiLied by microscopy (3 green algae, 6 red algae, 2 brown algae), mainly showing crustose and Lilamentous morphologies. Overall, results conLirmed the good status of the meadow, and therefore in July 2025, the optimal period for leaf sampling, an additional study within the framework of an INTERREG Italy-Coatia project (BRIGANTINE) was carried out. The BRIGANTINE monitoring campaign involved a destructive sampling approach to collect seagrass biomass and leaves associated macroalgal epiphytic community. Thin encrusting corallines (Hydrolithon and Pneophyllum) and Ceramium cf. deslongchampsii were the most common red algal epiphytes, being recorded during each sampling date, while Cladophora sp. was the most frequent green alga. Data on the macroalgal community were also obtained for the Cymodocea nodosa population of the Grado- Marano Lagoon. Highly similar macroalgal communities were found in the two meadows, where red algae, particularly encrusting corallines, represented the most abundant group. In contrast to Torrette, in the Grado- Marano samples no brown algae were observed, and only one green alga (Cladophora sp.) was recorded. In conclusion, the C. nodosa meadow in Torrette marina hosted a community consisting of ephemeral algae with simple morphology and appeared to rely mainly on clonal propagation. Although the leaves showed signs of damage attributed to temporary boating and mooring activities (as observed during the 2024 preliminary study), these stressors did not appear to threaten the seagrass integrity, nor did the discharges from a nearby restaurant. However, a major potential threat is represented by planned improvement works on nearby road and railway infrastructures, which might eventually lead to the burial of the meadow.