In situ growth rates of cold-water corals fouling oceanographic moorings in the Central Mediterranean Sea

Cold-water corals (CWCs) are vital deep-sea ecosystem engineers, yet their growth dynamics remain poorly understood. This study quantifies Desmophyllum dianthus growth in the Southern Adriatic Sea using two unplanned but ideal long-term natural experiments. The first derives from an oceanographic mooring lost at ~ 1200 m depth, allowing a rare four-year in situ assessment via high-resolution ROV footage collected in 2024. The second involves physical specimens from a mooring at ~ 500–600 m in Bari Canyon, recovered after one year. Image-based measurements showed an average linear growth rate of 8.06 ± 0.41 mm yr−1, while physical samples recorded a one-year extension of 6.5 ± 0.6 mm. These in situ growth rates exceed previous records and suggest rapid early growth consistent with asymptotic dynamics. The findings offer crucial benchmarks for natural CWCs growth and support effective conservation and restoration efforts, aligning with goals set by the EU Nature Restoration Law.