Monitoring the spatio-temporal evolution of fish communities is essential to comprehend their resilience under climate change in coastal-marine ecosystems. This is particularly relevant in transitional ecosystems, where strong environmental fluctuations can lead to pronounced changes over time, making them sentinel environments for detecting and monitoring early signs of climate impacts. The aim of this study was to assess changes in the composition and trophic structure of fish communities inhabiting two sites of a Mediterranean coastal lagoon (Stagnone di Marsala, Italy) subjected to different degree of confinement over a 24-year period.

We used abundance and stable isotope (δ¹³C, δ¹⁵N) data from fish communities collected in 1996-1999 and 2023, to estimate respectively spatio-temporal changes in: (i) community structure; (ii) trophic position (TP) and isotopic niche width as estimated by the Bayesian Standard Ellipse Area.

Preliminary results revealed temporal changes in fish community composition and abundance at both sites, with a decrease in fish density for most resident species, particularly Atherina boyeri. Isotopic data showed that, while community isotopic niche decreased from 1999 to 2023 at both sites, TP partially shifted towards higher values for most species.

Changes observed in the fish communities throughout the considered years suggest high structural and trophic plasticity of the species composing such communities, enabling them to adapt to the strong variability in the environmental conditions and resource availability typical of transitional ecosystems. Further steps will link the observed changes to quantitative descriptors of environmental conditions in the study area, including temperature, salinity and vegetation coverage, to support predictions of fish community trajectories under climate change.