Phytoplankton productivity and microzooplankton grazing within planktonic thin layers in the northern Gulf of Mexico

Plankton thin layers (PTLs) serve as trophic hot spots and have significant impacts on regional aquatic food webs. While much of the physical and biological dynamics associated with PTL formation, persistence, and dissipation have been examined, less is known about the variability in phytoplankton-productivity and microzooplankton-grazing rates. Thus, our overarching research objectives were to describe the trophic interactions between single-celled autrotrophic and heterotrophic eukaryotes (protists) within PTLs in the Mississippi Bight (MB). Specific objectives were to describe phytoplankton photosynthetic potential using photosynthesis-irradiance (P-E) parameters, quantify protist-grazing rates, and identify microplankton (20-200 µm) species and their particle characteristics (e.g. biovolume) using imaging flow cytometry (FlowCAM®). Although PTLs are ephemeral features, they may account for a considerable fraction of total water column primary production and contain a significant fraction of water-column integrated autotrophic biomass. The research presented here will fill information gaps in PTL dynamics, and will serve to calibrate regional ecological models that are key to our visualization of energy flows within this ecosystem.