The submarine beehives: Insights from the CORSUB Project

Submerged terraces off the Punta Licosa Promontory (Tyrrhenian Sea, Campania, Italy), located at depths of 75 to 100 meters, feature previously unidentified morphological structures. These formations, initially observed during a 2024 survey, display a beehive-like arrangement. A biogenic origin was proposed, but no further investigation was conducted until now. The CORSUB project employs an interdisciplinary and integrated approach, combining geophysical, stratigraphical, sedimentological and palaeontological to explore the formation, evolution, and ecological significance of these submerged morphologies. In December 2024, during the “TREMOR” oceanographic cruise aboard the CNR Italy research vessel Gaia Blu, the CORSUB team collected high-resolution data, including multibeam bathymetry, sub-bottom profiles, and box-corer sediment samples from the study area. Our results restrict our targets at depths between 75 and 85 meters , consisting of clusters of subcircular features with diameters of less than one meter, sunken edges, and gently elevated central portions. Chirp profiles reveal a thin sedimentary layer overlying these structures, underlain by a rocky substrate, likely part of the Cilento Flysch Unit. Box-corer samples show a stratified subseafloor, with coarse detrital sand and gravel at the surface (mostly biogenic in origin) transitioning to muddy-sandy sediment below. Notably, all samples contain dead, centimeter-sized boxwork rhodoliths, at depth of 8 to 20 cm below the seafloor preserved at the top of the box-corer. Only one sample contains live rhodoliths showing clear evidence of ongoing mudding. These preliminary results suggest multiple interpretations. The structures may have a biogenic origin, possibly linked to past rhodolith bed development. Alternatively, they could be related to glacial and post-glacial sea-level changes, potentially forming as erosional features during the Last Glacial Maximum when sea levels were up to 120 meters lower than today. These features may have then provided a substrate for biological colonization as sea levels rose during the deglaciation and into the Holocene. Ongoing geophysical and sedimentological analyses, including absolute dating, will further clarify the nature and evolution of these intriguing submarine features. CORSUB project (n°2022RKHBMB) is funded under the Italian PRIN 2022 program as part of Mission 4 of the Italian Piano Nazionale di Ripresa e Resilienza (PNRR).