Ocean sunfish M. mola in the Mediterranean Sea: Shedding light on an enigmatic species through 14 Years of spatial and environmental assessment.

The ocean sunfish M. mola is frequently sighted in marine waters worldwide, including the Mediterranean Sea, yet information on its distribution and ecology in this region remains limited. This study synthesizes current global knowledge on M. mola and investigates its spatial occurrence in the Mediterranean Sea using long-term visual observations from the Fixed Line Transect Mediterranean Monitoring Network, complemented by environmental DNA (eDNA) samples collected through the Life Conceptu Maris project. A total of 2411 visual surveys conducted between 2009 and 2022 along fixed-line transects across the Western Mediterranean and Adriatic regions yielded 1583 M. mola sightings and were analysed to assess spatiotemporal patterns of occurrence. These analyses were complemented by 447 eDNA samples collected along the same transects (34.7% of which during night hours) between 2019 and 2024, providing complementary information on seasonal patterns and insights into diel activity and foraging ecology. Spatial and inter-annual variability, as well as the influence of environmental drivers (sea surface temperature and chlorophyll-α concentration), were evaluated using spatial and correlation analyses at basin-wide and regional scales. Results revealed a heterogeneous distribution with persistent core areas in the Northwestern Mediterranean Sea and the Strait of Gibraltar, as well as seasonal north-south shifts associated with cooler waters and higher chl-α concentrations. A marked dispersion event during 2015-2017 coincided with elevated SST and reduced chl-α. No significant diel variation was detected by eDNA analyses, although co-occurrence patterns suggested potential nighttime foraging activity. This study highlights the importance of multidisciplinary, long-term monitoring for detecting distribution shifts in poorly known species such as M. mola, providing ecological insights and baseline for future assessments.