Prey stoichiometry, primary production, and plankton composition influence production of marine zooplankton

Abstract

Manipulative laboratory studies provide strong evidence that phytoplankton stoichiometry and taxonomic composition, in addition to phytoplankton carbon (C) biomass and primary production (PP), affects zooplankton biomass production (ZP). However, field observations investigating the simultaneous effects of prey stoichiometric quality, PP, and community composition on ZP remain relatively scarce. Here, we examined how in situ ZP is affected by carbon:nitrogen:phosphorus (C:N:P) molar ratios of prey, PP, and plankton composition in the East China Sea. To obtain field estimates of ZP, we measured zooplankton biomass using net samples and in situ growth rates using artificial cohort incubation experiments. Our focus was on copepods as they are biomass-dominant in mesozooplankton community. We found that ZP was low when prey C:N and C:P ratios were high (i.e. prey carbon exceeds the need of zooplankton consumers), but the variation of ZP was large when prey C:Nand C:P ratios were low. ZP did show a weak positive relationship with PP; however, removing high PP condition (PP > 100 mg C m-3 d-1) renders the association non-significant. Multivariate regression also indicates that prey C:N ratio explains most of the variation of ZP, followed by prey and zooplankton compositions, while PP exerts a weak influence on ZP. Our findings suggest that ZP is affected by prey stoichiometry, with further modification by consumer and prey compositions in marine food webs. However, the total explained variance by those key factors is less than 50 %, indicating that marine zooplankton biomass production is influenced by complex factors in nature