Growth dynamics, feeding preferences and biomass composition of Mnemiopsis leidyi in the Sacca di Goro (Italy)

The invasive ctenophore Mnemiopsis leidyi has recently established recurrent blooms in the Northern Adriatic Sea, yet its ecology in lagoon environments remains poorly documented. This study provides the first integrated assessment of growth, population dynamics, feeding preferences and biomass composition of M. leidyi in the Sacca di Goro (Italy). Sampling carried out at two sites throughout 2021 revealed a strongly seasonal population pattern, characterized by onset in early summer, peak abundances in mid- summer, and collapse in autumn. Growth analyses based on the von Bertalanffy growth function showed similar asymptotic size at both sites but contrasting growth rates between the more confined lagoonal site and the more marine-influenced site, suggesting a key role of hydrodynamics in regulating growth and population turnover. Laboratory feeding experiments demonstrated a significant selective predation by adult M. leidyi on veliger larvae of the Manila clam Ruditapes philippinarum, suggesting a possible mechanistic link between sea walnut blooms and the depletion of natural clam nursery grounds in the Po Delta lagoons. Biochemical analyses revealed a distinctive biomass composition characterized by high ash content and a fatty acid profile dominated by saturated and n-3 polyunsaturated fatty acids.