Funded Research

Zooplankton-Mediated Export Pathways: Quantifying Fecal Pellet Export and Active Transport by Diel and Ontogenetic Vertical Migration in the North Pacific and Atlantic Oceans

Steinberg, Deborah: William & Mary - VIMS (Project Lead)

NRA: 2016 NASA: Ocean Biology and Biogeochemistry   

This proposal responds to the Amendment A.3. OBB call for the EXPORTS field campaign. Using satellite remote sensing data to predict export and fate of net primary production (NPP) in a given region and time requires an understanding of the drivers and characteristics of plankton community structure. The EXPORTS Science Plan characterizes 5 pathways for the export of NPP from the surface ocean into the interior, two of which are mediated by mesozooplankton: production and sinking of fecal pellets, and active transport by vertical migration. We propose to address EXPORTS science questions SQ1 (1a and 1b) and SQ2 (2a,b,d) by conducting field-based, process studies of mesozooplankton-mediated export in the NE Pacific and N Atlantic Oceans. The guiding hypothesis is that changes in phytoplankton community structure and NPP affect zooplankton abundance, biomass, size, and taxonomic structure, all of which controls and scales to export in a quantifiable and predictable way. Satellite observables and data products, including euphotic zone phytoplankton biomass and functional type, particle size spectrum, light attenuation, and temperature will be used to predict zooplankton community structure, and in turn zooplankton-mediated export, significantly advancing our ability to predict export and fate of NPP. The first research objective is to quantify production and export of fecal pellets and other zooplankton by-products (e.g., mucous feeding webs, molts, carcasses). Fecal pellet (FP) production rates in the surface ocean are hypothesized to positively scale with temperature, NPP, and zooplankton size. FP flux as a component of the total sinking particulate organic carbon (POC) flux varies considerably across regions and seasons, and reprocessing of sinking material is evidenced by changes in types of zooplankton fecal pellets with depth. Our approach is to collect representative, abundant live zooplankton from different size classes (including migrators) via day/night net sampling in the epipelagic zone for use in fecal pellet production experiments. FP production rates will be scaled up to community rates using abundance quantified from the same tows using a ZooScan optical imaging system. Production of FPs in surface waters will be compared to export of FPs at different depths as measured by sediment traps–to examine export efficiency of pellets or other zooplankton by-products, and to mesopelagic zooplankton community structure. The second research objective is to quantify active transport of carbon from the euphotic zone by both diel and ontogenetic (seasonal) vertical migrations. Diel vertically migrating zooplankton feed in the surface waters at night and metabolize this ingested POC in the mesopelagic zone during the day. In the subarctic N. Pacific and N. Atlantic oceans, active transport by seasonal migrants (e.g., Neocalanus and Calanus, respectively) as they develop through their life cycles is an additional export. Our approach is to characterize zooplankton biomass and community structure with depth-stratified day/night net sampling through the epi- and mesopelagic zones using a MOCNESS (multiple opening-closing net) and an Underwater Vision Profiler, UVP, camera system. The latter will characterize delicate gelatinous zooplankton and enable sampling of thin layers. Onboard incubation experiments measuring metabolism (respiration, excretion, and FP production) of migrating taxa from different size classes, combined with size-temperature algorithms of metabolism will be used to quantify export by migrators. These will also be compared with electron transport system measurements to determine depth-stratified metabolic carbon demand. Synergies with other potential components of the field campaign (e.g., grazing, sediment trap particle flux, acoustics to characterize zooplankton mesoscale variability) will mutually benefit EXPORTS .