Biological variability and ecological sensitivity of Arctic deep-sea macrobenthos to environmental change

Global accelerated changes impact deep-sea ecosystems, as particularly the current global warming trend is amplified in the Arctic. Studies on temporal dynamics of the deep-sea benthic fauna and its response to environmental change are scarce, and the long-term observatory HAUSGARTEN is the only one in the Arctic. In the present study, we investigated spatio-temporal variability over a decade (from 2010 to 2021) of macrobenthos from different depths (from 1200 to 5500 m) at HAUSGARTEN by assessing community structure (species composition and diversity), functional composition (functional trait composition and diversity), and linking biological variability to environmental drivers. Our findings provide evidence that a) benthic communities are spatially different along the bathymetric gradient, b) long-term trends of benthic communities were subtle, but response of species and functional metrics to the warm water anomaly in 2015-2017 reveal high sensitivity to episodic climate forcing, c) depth and food availability were the primary drivers of macrobenthic spatial and temporal variability and d) communities of deeper habitats (>4000 m) have a low and temporally more variable functional richness, diversity and redundancy in contrast to shallower bathyal communities. Our study indicates that deep-sea macrobenthos, particularly that deeper than 4000 m, might be more sensitive to species loss and regime shifts in the future, as the fauna strongly depends on the prevailing food conditions modulated by atlantification or marine heat waves, and have a lower capacity than shallower bathyal communities to maintain ecological functioning against environmental changes.