Major changes in micro-eukaryotic biodiversity of the abyssal ecosystem of the NE Atlantic: A comparison between 1996 and 2018

Time-separated snapshots of deep-sea regions can provide crucial insights into how fluctuations in environmental changes and food supply shape microbial communities. Here, we compared molecular and environmental data collected in 1996 and 2018 at 4,800-m depth in the northeast (NE) Atlantic Ocean. We report lower values of primary production (-66%) associated with lower concentrations of sedimentary labile organic matter (-12%). Metabarcoding analyses revealed a significant decrease in the Chlorophyta taxa, only partly compensated by the increase in Dinoflagellate taxa, consistent with patterns observed in NE Atlantic Ocean phytoplankton. Benthic prokaryotic assemblages showed a limited response to such changes, whilst micro-eukaryotic assemblages changed significantly even at subdivision level. Overall, data reported here suggest that the Porcupine abyssal plain may undergo significant variations in terms of quantity and quality of biopolymeric carbon and that such changes caused a shift in micro-eukaryotic biodiversity, with potentially relevant effects also on the deep-sea ecosystem functioning.