AUTHOR=D’Ambra Isabella , Saviano Simona , Ambrosio Maria Assunta , Botte Vincenzo , Iudicone Daniele , Mazzocchi Maria Grazia , Merquiol Louise , Cianelli Daniela 

TITLE=Tracking Pelagia noctiluca scyphomedusae by combining modeling and stable isotope approaches

JOURNAL=Frontiers in Marine Science

VOLUME=Volume 12 - 2025

YEAR=2025

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2025.1608726

DOI=10.3389/fmars.2025.1608726

ISSN=2296-7745

ABSTRACT=True jellyfish (Cnidaria, Scyphozoa) often appear in large aggregations along the coasts, where they interfere with human activities (tourism, fisheries, power plants). Therefore, defining their distribution and predicting their outbreaks is crucial for effective coastal management. In this study, we tested the combination of modeling based on the Lagrangian approach and stable isotope (SI) analysis to define the trajectories of the scyphomedusa Pelagia noctiluca in the Gulf of Naples (GoN, western Mediterranean Sea) during 4 outbreaks recorded in March, June, July, and November 2019. SIs were determined in scyphomedusae and their potential planktonic prey collected at the Long Term Research site MareChiara (LTER-MC) during the outbreaks and during the previous three weeks, to account for the turnover rate of medusae. Numerical simulations were performed using a particle tracking model forced by a Regional Ocean Modeling System (ROMS) developed for the GoN. Lagrangian simulations were performed releasing particles 20 days before the outbreaks to align with SI determinations. SI ratios of scyphomedusae indicated offshore foraging, with Lagrangian simulations confirming offshore-to-coastal transport via south Tyrrhenian surface dynamic and southern winds regime. During the outbreak in November, carbon and nitrogen SIs of medusae (-18.7‰ and 1.9‰, respectively) reflected the SIs of plankton typically found in offshore waters. The model corroborated this finding, suggesting a rapid transport of medusae by surface currents driven by intense southerly winds (gusts up to 18.7 m/s). During the other three outbreaks, SI values of medusae (δ13C ranging between -20.1 and -18.5‰, δ15N between 4.6 and 5.9‰) were intermediate between prey found offshore and those in the coastal area. Simulations indicated that surface circulation patterns promoted the permanence of medusae within the coastal area, particularly in summer. Our results suggest that SI ratios of scyphomedusae are intimately dependent on their movements across diverse isoscapes. Therefore, predictive models integrating SI analysis and ocean circulation data could improve early warning systems for jellyfish outbreaks, aiding coastal management.