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7 pages, 2 figures, 3 tables, supplementary material https://doi.org/10.1016/j.pocean.2020.102369.-- We agree to make the data necessary to reproducing our results available and R codes for analysis on Mendeley Data http://dx.doi.org/10.17632/sh683s8mwf.1, Manipulative laboratory studies provide strong evidence that phytoplankton primary production (PP), stoichiometry, and taxonomic composition affect marine copepod production (CP), which is the biomass-dominant zooplankton group. However, field observations investigating the simultaneous effects of prey stoichiometric quality, PP, and phytoplankton and copepod taxonomic composition on CP remain relatively rare. Here, we examined how in situ CP is affected by carbon:nitrogen:phosphorus (C:N:P) molar ratios of prey, PP, and phytoplankton and copepod composition in the East China Sea (ECS) and Dongsha Atoll in the South China Sea. Field estimates of CP were measured directly as the product of in situ instantaneous growth rate estimates by artificial cohort method and copepod biomass. We found that CP was low when prey C:N and C:P ratios were high, but the variation of CP was large when prey C:N and C:P ratios were low. CP did not, however, show a strong positive relationship with PP. Multivariate regression indicates that prey C:N ratio explains most of the variation of CP, followed by phytoplankton and copepod compositions, while PP exerts a weak influence on CP. Our findings suggest that copepod community production is affected by prey stoichiometry, with further modification by copepod and phytoplankton compositions in the ECS. However, the total variance explained by those key factors is less than 50%, indicating that marine copepod growth and biomass production are influenced by complex interactions in nature, This work was supported by the National Center for Theoretical Sciences, Foundation for the Advancement of Outstanding Scholarship, and the Ministry of Science and Technology, Taiwan, With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

Body size exerts multiple effects on plankton food-web interactions. However, the influence of size structure on trophic transfer remains poorly quantified in the field. Here, we examine how the size diversity of prey (nano-microplankton) and predators (mesozooplankton) influence trophic transfer efficiency (using biomass ratio as a proxy) in natural marine ecosystems. Our results support previous studies on single trophic levels: transfer efficiency decreases with increasing prey size diversity and is enhanced with greater predator size diversity. We further show that communities with low nano-microplankton size diversity and high mesozooplankton size diversity tend to occur in warmer environments with low nutrient concentrations, thus promoting trophic transfer to higher trophic levels in those conditions. Moreover, we reveal an interactive effect of predator and prey size diversities: the positive effect of predator size diversity becomes influential when prey size diversity is high. Mechanistically, the negative effect of prey size diversity on trophic transfer may be explained by unicellular size-based metabolic constraints as well as trade-offs between growth and predation avoidance with size, whereas increasing predator size diversity may enhance diet niche partitioning and thus promote trophic transfer. These findings provide insights into size-based theories of ecosystem functioning, with implications for ecosystem predictive models.

Background: Trophic structure and trophic transfer efficiency are among the most fundamental characteristics of an ecosystem. They characterize the transfer of nutrient and energy and are crucial in estimating the yield of harvestable biomass. In this study, we investigated the regulation of trophic structure (phytoplankton, zooplankton, and larval fish abundance) and biomass ratio of zooplankton to phytoplankton (as an indicator of transfer efficiency) in the East China Sea, one of the largest marginal seas in the world and an important fishing ground. Results:Theresults showed that when sea surface temperature was below 25°C, temperature co-acted with resource availability (zooplankton for larval fish and phytoplankton for zooplankton) in determining the trophic structure. When sea surface temperature was above 25°C, resource availability dominated the regulation of trophic structure. Biomass ratio of zooplankton to phytoplankton decreased with increasing phosphate concentration. Conclusions: Our study suggested that the trophic structure of the East China Sea might be controlled by bottom-up processes, and this control is mediated by temperature.