Self-organisation of zooplankton communities produces similar food chain lengths throughout the ocean

Abstract

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 counterparts1 has achieved the status of an ecological paradigm. However, recent global assessments indicate global fish biomass could be much higher than previously thought2–4, suggesting that our traditional understanding of food webs may need to be revisited. Here, we challenge the classical 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 (low-nutrient) and eutrophic (high-nutrient) 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 groups, their feeding relationships and carbon content in models will increase our ability to estimate current global fish biomass 5, project future fish biomass under climate change6–8, and provide more-robust forecasts of nutrient9 and carbon cycling10.

Seasonal Changes in the Size Distribution of Copepods Is Affected by Coastal Upwelling

“…Our data simultaneously evaluated the relative importance of sea surface temperature and Chl-a concentration in regulating seasonal changes in copepod abundance in different size classes. The results show the effects of zooplankton size classes throughout upwelling cycles (bottom-up and top-down) on trophic links [2] and the cascading effect described on the Brazilian coast of upwelling [3]. Nevertheless, these links are species-specific and size-dependent [16].…”

“…Zooplankton is traditionally described as a trophic link between primary producers and secondary consumers at higher trophic levels [1][2][3]. They are composed of small animals and heterotrophic protists ranging from microns up to centimeters but rarely reaching meters [4][5][6].…”

Filter‐feeding gelatinous macrozooplankton response to climate change and implications for benthic food supply and global carbon cycle

“…Associated with a climate change-induced decrease in NPP, marine ecosystem models project a decrease in the average body size of phytoplankton (Peter & Sommer, 2013) and zooplankton, as low-productive environments favor smaller body sized organisms (Armengol et al, 2019). As recently suggested by Heneghan et al (2023) using a model representing nine zooplankton groups, including salps and larvaceans, FFGM could replace other macrozooplankton organisms (e.g., krill and large copepods; Everett et al, 2022) due to their high clearance rate (Acuña et al, 2011), their access to prey up to five orders of magnitude smaller than themselves (Sutherland et al, 2010;Sutherland & Thompson, 2022), and their ability to exploit low-chlorophyll environments (Clerc, Bopp, Benedetti, et al, 2023;Luo et al, 2022;Sutherland & Thompson, 2022). Climate change has the potential to alter the composition of zooplankton and consequently their role in marine biogeochemical cycles (Chelsky et al, 2015;McKinley et al, 2017;Steinberg & Landry, 2017) and in the regulation of upper trophic levels (UTLs; Dupont et al, 2022;Heneghan et al, 2023).…”

Key link between iron and the size structure of three main mesoplanktonic groups (Crustaceans, Rhizarians, and colonial N2-fixers) in the Global Ocean

“…In marine ecosystems, numerous plankton communities were shown to self-assemble on a global scale according to their functional traits. For example, families of copepods ( 28 ), and other broad groups of zooplankton ( 29 ), typically present distinct biogeography primarily driven by their diet (e.g. carnivore versus omnivore versus filter-feeders).…”