Changing krill and salp fecal pellet carbon production in West Antarctica

Abstract Ocean carbon export modulates Earth’s rapidly changing climate1,2. Zooplankton play a key role in export through the production and sinking of fecal pellets3,4, yet climate-driven shifts in zooplankton abundance and species composition strongly alters this export pathway5,6. As one of the fastest warming places on Earth, the West Antarctic Peninsula is experiencing changes in marine ecosystem structure as zooplankton species dominance is shifting from the keystone Antarctic krill (Euphausia superba)7–9 to gelatinous salps (Salpa thompsoni), with major implications for carbon export10,11. This study sought to determine if changes in Antarctic zooplankton composition affected carbon export by using an unprecedented 28-year zooplankton time series with 11 years of zooplankton fecal pellet production experiments. Here we show spatial, interannual, and multi-decadal patterns in krill- and salp-mediated fecal pellet production. We found previously undocumented ~5-year oscillations in krill fecal pellet production that is related to krill abundance, body size, and environmental conditions, and which alternated with peaks in salp fecal pellet production. Habitat preferences further drive significant differences, as krill favor colder, higher sea ice, southern Peninsula conditions and salps warmer, lower sea ice, northern conditions12,13. This interannual and spatial partitioning is consistent with ongoing climate warming expanding salp-favorable habitats and altering carbon export. Our results emphasize how rapid WAP warming10,11 will alter zooplankton-mediated fecal pellet carbon production and export in this productive yet vulnerable polar ecosystem.