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<p>The pelagic tunicate <i>Salpa thompsoni</i> is a widespread cold-water metazoan and a major grazer of phyto- and microzooplankton in the Southern Ocean. Long-term time series and spatiotemporal models predict that salps will expand their distribution towards higher latitudes over the next decades with ramifications for pelagic food webs, including higher trophic level predators. Salps are potentially less nutritious and energy-rich than co-occurring euphausiids. This, however, may differ seasonally. To address this, we utilised published and unpublished body composition data, i.e., organic content (ash-free dry weight as percent of dry weight, DW), carbon content (carbon weight as percent of DW), and proximate biochemical composition (carbohydrate, lipid, and protein weight as percent of DW), collected over forty-one years (1980–2020) across the Southern Ocean. Energy content values were calculated using published conversion factors and corrected for residual water with a conversion factor of 12.9%. Salp energy contents based on organic content were systematically higher than on carbon and proximate composition. We found higher weight-specific energy content values in summer than in autumn and winter, even when correcting for size. Salp energy content did not vary between blastozooids and oozooids, but showed a significant negative relation with size in blastozooids, while there was no significant effect of size in oozooids. Our results indicate that salp energy values are comparable to those of Antarctic krill (when considering dry weight units). Salps may become an attractive prey for higher trophic predators during Austral winter and in krill-void seasons in an increasingly warmer Southern Ocean pelagic ecosystem.</p>

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Seasonal variability of the energy content of Salpa thompsoni, a key metazoan in Southern Ocean food webs

  • 期刊论文

  • 发表日期：

    2025年2月19日

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  • Florian Lüskow,
  • Corinna D. Dubischar,
  • Christoph Plum,
  • Leonid K. Pshenichnov,
  • Evgeny A. Pakhomov

摘要

The pelagic tunicate Salpa thompsoni is a widespread cold-water metazoan and a major grazer of phyto- and microzooplankton in the Southern Ocean. Long-term time series and spatiotemporal models predict that salps will expand their distribution towards higher latitudes over the next decades with ramifications for pelagic food webs, including higher trophic level predators. Salps are potentially less nutritious and energy-rich than co-occurring euphausiids. This, however, may differ seasonally. To address this, we utilised published and unpublished body composition data, i.e., organic content (ash-free dry weight as percent of dry weight, DW), carbon content (carbon weight as percent of DW), and proximate biochemical composition (carbohydrate, lipid, and protein weight as percent of DW), collected over forty-one years (1980–2020) across the Southern Ocean. Energy content values were calculated using published conversion factors and corrected for residual water with a conversion factor of 12.9%. Salp energy contents based on organic content were systematically higher than on carbon and proximate composition. We found higher weight-specific energy content values in summer than in autumn and winter, even when correcting for size. Salp energy content did not vary between blastozooids and oozooids, but showed a significant negative relation with size in blastozooids, while there was no significant effect of size in oozooids. Our results indicate that salp energy values are comparable to those of Antarctic krill (when considering dry weight units). Salps may become an attractive prey for higher trophic predators during Austral winter and in krill-void seasons in an increasingly warmer Southern Ocean pelagic ecosystem.