Résumé
Anthropogenic land-based disturbances can cascade into the sea, altering coastal ecosystems over long timescales. Mining exemplifies this land-sea connectivity, yet its full environmental footprint is underestimated when marine impacts are overlooked. Here, we investigate long-term coastal changes associated with nickel mining using a paleoecological approach in New Caledonia. A 226-cm sediment core spanning ~1000 years was analysed, combining ancient sedimentary DNA, foraminifera, and geochemistry. Since its onset in 1875, mining has modified sediment run-off and microbial assemblages. The most pronounced changes occurred in the 1960s after the mechanisation of extraction tools, which intensified soil erosion and increased sediment run-off, altering the richness and structure of both microeukaryotic and foraminiferal communities. Although post-1975 regulations mitigated nickel-rich run-off, persistent ecological disturbances remain. These findings highlight how terrestrial disturbances can induce long-term changes in coastal ecosystems, emphasising that land and sea should be studied and managed as a connected continuum.