Appendicularians and marine snow in situ vertical distribution in Argentinean Patagonia

Detailed in situ vertical and temporal distribution of appendicularians, marine snow, fecal pellets, nano- and microplankton were recorded simultaneously with environmental data in the San Jorge Gulf, Argentinean Patagonia (45°–47°S). Data were taken at a fixed station over 36 h in February 2014 with an autonomous Video Plankton Recorder and a FlowCAM®. The water column was thermally stratified with a pycnocline at ~ 40 m. Appendicularians dominated in the upper 65 m with a condensed pattern above the pycnocline at high chlorophyll a concentrations, matching the subsurface chlorophyll maximum layer at ~ 20 m. Our results suggest the absence of vertical migration of appendicularians. Marine snow, strongly correlated with appendicularians, showed high concentrations above the pycnocline, whereas fecal pellets from krill were distributed throughout the water column. Discarded houses of appendicularians or their mucus fragments were the main components of marine snow aggregates, with phytoplankton, detritus and krill pellets also contributing. Nanoplankton dominated over microplankton, with vertical distribution patterns that might depend on local grazing pressure and advective processes. Our study, the first one in the region using underwater imagery, emphasizes the leading contribution of appendicularians to marine snow aggregates in the San Jorge Gulf and their potential implications in the bentho-pelagic coupling.