In Situ Analysis of Appendicularian Distribution in Relation to Planktonic Biomass and Community Composition

Information regarding the abundance and distribution of gelatinous zooplankton (e.g., medusae, ctenophores, and pelagic tunicates) in the water column is scarce despite the relative importance of this community in the pelagic food web and the biological pump. Appendicularians are one group of pelagic tunicates that are abundant globally and significant in ocean food webs, through their frequent building and discarding of mucous feeding apparatuses that gather prey across a large size range and contribute to the vertical carbon flux. Using an In-Situ Ichthyoplankton Imaging System (ISIIS), satellite data, and a suite of experiments to characterize the water column, this study examined the distribution and abundance of these organisms in their natural environment as a function of phyto- and zoo- plankton community composition. The zooplankton community, including appendicularians, was enumerated using ISIIS data collected across the inner, middle, and outer Delaware continental shelf. Phytoplankton biomass and communities in these locations were characterized by pigments. Preliminary results suggest appendicularians and other gelatinous zooplankton aggregate more offshore (~400-600 ind m^-3 offshore versus <200 ind m^-3 inshore), and crustaceous zooplankton (eg, copepods) tend to have higher abundances inshore (~30-50 ind m^-3 inshore versus 10-20 ind m^-3 offshore). This study demonstrates the trophic role of appendicularians in their community and allows for improved estimates of POC fluxes in the ocean. Applications of similar advanced technologies can be used to develop a fundamental understanding of the ecology of appendicularians and other (understudied) pelagic tunicates.