Standard Presentation Australian Marine Sciences Association Annual Meeting 2023

Self-organisation of zooplankton communities produces similar food chain lengths throughout the ocean (#205)

Jason D Everett 1 2 3 , Ryan F Heneghan 4 , Julia L Blanchard 5 , Iain M Suthers 3 , Evgeny A Pakhomov 6 , Patrick Sykes 1 , David S Schoeman 7 , Mark E Baird 8 , OPC Consortium 1 , Anthony J Richardson 1 2
  1. The University of Queensland, Brisbane, QLD, Australia
  2. Commonwealth Scientific and Industrial Research Organization (CSIRO), Environment, Brisbane, QLD, Australia
  3. Centre for Marine Science and Innovation (CMSI), The University of New South Wales, Sydney, NSW, Australia
  4. School of Mathematical Sciences, Queensland University of Technology, Brisbane, QLD, Australia
  5. Institute of Marine and Antarctic Studies, University of Tasmania, Hobart, TAS, Australia
  6. Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, BC, Australia
  7. School of Science, Technology and Engineering, University of the Sunshine Coast, Maroochydore, QLD, Australia
  8. Commonwealth Scientific and Industrial Research Organization (CSIRO), Environment, Hobart, TAS, Australia

For over 50 years, the conceptualisation of low-nutrient oligotrophic systems having longer food chains and thus lower energy transfer to fish than their high-nutrient eutrophic counterparts has achieved the status of an ecological paradigm. However, recent global assessments indicate global fish biomass could be much higher than previously thought, suggesting that our traditional understanding of food-webs may need to be revisited. Here, we challenge the paradigm by exploring the role of zooplankton in food-webs across the world’s oceans. Using observed zooplankton size-spectra, and output from a size-spectrum model that resolves nine zooplankton groups, we conclude that food-chains in oligotrophic and eutrophic systems have similar lengths. We offer a compelling hypothesis to explain this emergent pattern: self-organisation of zooplankton groups across the global productivity gradient regulates food-chain length. We find that in oligotrophic systems the increased carnivory and longer food-chains are offset by relatively large gelatinous filter feeders eating the dominant small phytoplankton, resulting in shorter-than-expected food chains, but decreasing food quality for fish. Our findings highlight the pivotal role zooplankton play in regulating energy transfer. Better resolution of zooplankton in models will increase our ability to estimate global fish biomass and provide more-robust forecasts of nutrient and carbon cycling.