Séminaire « A tale of two tracks: Immediate, annual, and decadal-scale impacts and recovery of foraminifera from the recent NORI (2022) legacy OMCO (1979) deep-sea mining tests » by Bryan O’Malley

Abstract : The impacts and recovery trajectories of deep-sea ecosystems following mining disturbances remain a critical knowledge gap, particularly concerning the timeframe and extent of organismal recolonization. Benthic foraminifera (BF), including megafaunal-sized xenophyophores, play an ecologically crucial role in abyssal nodule regions. Their contributions to ecosystem function and sensitivity to environmental changes make them valuable bioindicators for assessing the effects of deep-sea mining activities. This study leverages the ecological importance of BF to provide insights into both short-term and long-term ecosystem responses to multiple mining-induced pressures. This study analyzed over 400,000 individuals from the >63 µm size-fraction across two test-mining sites in the Clarion-Clipperton Zone: the 1979 Ocean Minerals Company (OMCO) site, revisited after 40+ years as part of the SMARTEX programme, and the 2022 Nauru Ocean Resources Inc. (NORI) site, sampled immediately (T=0) and one year (T=1) post-test. We evaluated indicators including density, diversity, community composition, stratigraphy, and species-specific responses with sampling regimes covering (1) directly-mined tracks, (2) sites exposed to variable levels of sedimentation, and (3) an unimpacted control area. Results demonstrate that BF and xenophyophores serve as sensitive indicators of impact and recolonization in both directly-mined and sedimented areas, as well as markers of ecological succession after disturbance. Notably, the study revealed a xenophyophore species dominating the bare sediment of the OMCO mining track after 44 years, providing insights into long-term succession of impacted areas. This investigation emphasizes the effectiveness of BF as bioindicators, contributes to the refinement of environmental impact monitoring strategies, informs evidence-based decision-making, and aids in establishing ecologically relevant thresholds as deep-sea mining activities expand in scale.

Place : F117 room, Faculty of Sciences, Angers