Biophysical modeling of Posidonia oceanica fruit dispersal in the Mediterranean Sea

Understanding the dispersal dynamics of Posidonia oceanica fruits is essential to assess the resilience and connectivity of Mediterranean seagrass ecosystems. Given the species' clonal growth, floating fruit dispersion represents the critical vector for long-range genetic diversification and population expansion. To characterize these dynamics, a biophysical modeling framework was applied across the Mediterranean Sea, coupling the Ichthyop Lagrangian tracker to high-resolution hydrodynamic fields from the NEMO-based Mediterranean Sea Physics Reanalysis (1/24° resolution). Fruit releases were simulated from 483 mapped meadow polygons over four years (2021-2024) under three buoyancy scenarios (14, 21, and 28 days) to capture biological variability. Results demonstrate that floating duration strongly controls the spatial footprint of dispersal. While short buoyancy (14 days) favors retention within localized hotspots, such as the Gulf of Gabès and the Aegean Sea, extended durations (21-28 days) activate long-distance corridors connecting North African sources to Central and Eastern basins. Network analysis reveals functional heterogeneity among meadows: while most act as localized exporters, a distinct subset emerges as "hub" sources with high export strength and broad sink diversity. Cross-scenario consistency maps identify robust coastal sinks where propagules accumulate regardless of buoyancy duration. Our results demonstrate that Mediterranean connectivity is partitioned between high local retention and strategic long-distance corridors, a structure determined by the interaction of regional currents and fruit floating potential. This study provides a scientific basis for Mediterranean conservation by identifying specific high-value hub meadows that sustain basin-scale gene flow and persistent sink zones where restoration efforts should be prioritized.