Trophic connections between Calanus spp. and deep-sea benthos in the Fram Strait, Arctic Ocean

Copepods of the genus Calanus are central to the ecological and biogeochemical functioning of polar pelagic ecosystems. They graze on seasonal phytoplankton blooms, collectively releasing large quantities of fast-sinking faecal pellets as they convert ingested food into carbon-rich lipid reserves. Towards the end of summer, they migrate down to bathyal and abyssal depths and overwinter by subsisting on their lipid reserves until the following spring. This ontogenetic vertical migration, the so-called ‘seasonal lipid pump’ (SLP), actively transports enormous quantities of organic matter and surface-derived carbon into the deep ocean. Quantification of the SLP’s contribution to the global carbon cycle has attracted major interest, yet little is known about trophic connections between Calanus spp. and deep-sea benthic ecosystems. We address this knowledge gap by undertaking lipid biomarker analysis and determining δ15N signatures of Calanus spp. and selected benthic taxa collected from 1255–5414 m in the Fram Strait, Arctic Ocean. Calanus spp. lipid profiles were dominated by C20:1 and C22:1 fatty acids and alcohols. Substantial quantities of these biomarkers were present in the lipids of all the benthic taxa examined: mean relative abundances ranged from 11.18 mol% in holothurians (trophic level = 1.73) to 29.27 mol% in mysids (trophic level = 2.85). These results suggest an important trophic connection between Calanus spp. and deep-sea benthic Arctic ecosystems. We discuss the likely routes through which individual taxa obtain these biomarkers and highlight the potential significance of this trophic link as a pathway for the transferral of organic matter into the deep-sea.