Prey stoichiometry and phytoplankton and zooplankton composition influence the production of marine crustacean zooplankton

Abstract

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.