Fine-scale variability of Mediterranean moray (Muraena helena) parasite communities as potential bioindicators of marine ecosystem stability.

Parasites are integral to marine biodiversity, playing key ecological roles and serving as indicators of ecosystem status. Despite their potential to reflect trophic network stability and habitat conditions, parasites often remain underexplored, particularly within broader ecological frameworks. In this study, we investigated the parasite community structure of the Mediterranean moray Muraena helena, a high-trophic-level predator with a strong site fidelity, and assess whether small-scale geographical variations in the Gulf of Naples (central-western Mediterranean) influence parasite assemblages. The parasite community was dominated by crustacean ecto-parasites and trophically transmitted endo-parasitic helminths. Overall, the high parasite diversity and high occurrence of both specialist and parasite species having complex life cycles in all sites might indicate host abundance, trophic network stability, and well-structured ecosystems. Notably, trematodes were more abundant in mainland coastal areas, whereas nematodes were more abundant in insular sites, suggesting variations in intermediate host distribution and local ecological conditions. Multivariate analyses revealed statistically significant differences in parasite community structure between insular and mainland sites, likely driven by environmental factors, host availability, and differential anthropogenic pressures. These findings underscore the potential of parasite assemblages as bioindicators of marine ecosystem health, highlighting the need to integrate parasite community assessments into biodiversity monitoring programs. Moreover, the restricted home range of the Mediterranean moray suggests its suitability as a sentinel species for detecting fine-scale ecological variations, a framework that could be applied to other regions and monitoring objectives over time.