Award: OCE-1829318

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 migratory organisms. This collaborative project focused on the abundant subtropical copepod Pleuromamma xiphias. Copepods 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. Analysis of enzyme activity levels demonstrated peaks in activity for energy production and ammonium excretion over diel cycles. This is important as sometimes these enzymes are used to estimate active flux activity without regard to the time of sampling. Patterns of gene expression and protein composition also showed diel changes that are indicative of digestion, variation in energy metabolism, and reproductive effort. To integrate these observations into seasonal estimates of copepod size and depth of migration, we have created a new computer code that allows for an improved understanding of the movement of carbon and nitrogen by this model species. Synthesizing all of these results, we demonstrate the sensitivity of global models to the various physiological changes that migrators undergo on daily and seasonal cycles and suggest that feeding state is an important variable to consider in future models. Broader Impacts of the work included providing laboratory and sea-going field experiences for students in a 7-person 3-week course of and more intensive participation by 7 high school, undergraduate, and graduate students/interns as well as one high-school teacher. Results have been presented at national meetings, including presentations by undergraduate researchers, archived in public databases and published in the peer-reviewed literature. Public outreach has been through an online lesson plan, articles in local magazines, a blog, and Twitter. Last Modified: 11/29/2021 Submitted by: Amy E Maas