Organic matter partitioning and stoichiometry in response to rising water temperature and copepod grazing

Rising ocean temperature is expected to change the balance between production degradation of organic matter due to different temperature sensitivities of auto- and heterotrophic . Copepods are the most prominent zooplankton group, and elevated temperature their growth and grazing rates. So far, it is unknown to what extent copepods affect partitioning and stoichiometry of organic matter in a warmer surface ocean. We therefore a mesocosm experiment with 3 copepod densities and 2 temperature scenarios to effects on the pools of dissolved and particulate organic matter and their C:N:P ratios. we show that particulate organic C (POC) concentrations decreased with increasing copepod . This effect was more pronounced at elevated temperature, yielding a decrease in POC to particulate nitrogen ratio (POC:PN) from 26 to 13 and in the POC:particulate organic (POP) ratio from 567 to 257, from low to high copepod density. Dissolved organic carbon (DOC) accumulation was positively affected by temperature. However, increasing copepod decreased the accumulation of DOC at elevated temperature. Copepod grazing and enhanced the recycling of N and P, thereby increasing the availability of these nutrients autotrophs. In concert with temperature-induced shifts in the phytoplankton community composition size, changes in copepod abundance may therefore have contributed to altering the composition of seston. Our findings suggest combined effects of zooplankton grazing temperature on the composition and recycling of organic matter that should be taken into when simulating biogeochemical cycles in a future ocean.