Award: OCE-1829378

The daily vertical migration (DMV) of zooplankton and fish across hundreds of meters between shallow and deep waters is a predominant pattern in pelagic ecosystems. Through their physiological activity, migratory animals move nutrients and energy (an estimated 15 to 40 % of the total global organic export) from the surface directly to depth where it feeds the midwater food chain and sequesters nutrients away from atmospheric mixing. The overall objective of this project was to improve the ability of scientists to understand and predict zooplankton contributions to the movement of carbon and nitrogen in the ocean by detailing daily changes in physiological processes of these organisms. This collaborative project focused on the abundant subtropical copepod Pleuromamma xiphias. P. xiphias were sampled offshore from Bermuda every 4-7 hours over a 3-day period as they migrated through the water column. Measurements were made of rates of oxygen consumption, ammonium excretion, fecal pellet production, gene expression profiles (RNA-seq) and proteome composition. Fecal pellet production rates were highest in copepods that had been feeding at the surface for several hours. Fecal pellet production was also consistently observed in animals collected from deep water in morning, demonstrating active transport of nutrients from the surface. Surprisingly, and in contradiction to previous studies, a daily rhythm in oxygen consumption rate was not detected. This suggests that within the region sampled, any daily signal is small relative to variation in feeding activity or exposure to environmental stress. Glutamate dehydrogenase and citrate synthase were highest in animals collected from surface waters at night, and electron transport system activity was highest in animals collected from deep water during afternoon. These results show that copepod metabolic potential varies over a daily cycle which should be accounted for in future predictions of active flux. A new piece of equipment (thermally-insulated cod end) was designed that allows sampling of animals from deep water without exposing them to temperature stress during collection. Broader Impacts of the work included providing laboratory and sea-going field experiences to two undergraduates. Results have been presented at national meetings, including presentations by both undergraduate researchers, archived in public databases and published in the peer-reviewed literature. Outreach has been through an online lesson plan, a blog, and a scheduled Twitter "ReadAlong" (scheduled for November 2021). Last Modified: 11/09/2021 Submitted by: Ann Tarrant