Presenter: Alexis Anne Bahl (University of British Columbia)

Description:
Salp grazing on picoplankton to microzooplankton can structure food webs during plankton blooms as well as serve as a conduit for export of particulate organic carbon to depth. Salp fecal pellets and sinking carcasses (passive transport) are known to contribute disproportionally to the total vertical carbon flux out of the mixed layer. In addition, diel vertical migrations (DVMs, active transport) are documented for many salp species. However, recent studies suggest salp DVM is size-specific, which remains unresolved and undetermined against environmental change. We hypothesize species size-specificity in DVM has important implications for active carbon transport. Utilizing samples collected during research cruises in three regions, we aim to describe inter- and intraspecific differences in DVM patterns of four geographically widespread salp species: Salpa aspera (NE Pacific, Aug/Sep 2018), S. thompsoni and S. fusiformis (Chatham Rise, Oct/Nov 2018), and Soestia zonaria (NE Atlantic, May 2021). All salps were collected, enumerated (approximately 2000 salps total), and analyzed for size and life cycle (aggregate vs. solitary) and development stages. In addition, we aim to explore environmental variables collected from accompanied CTD casts as potential drivers affecting these migrations. Depth-stratified sampling using MOC-1 tows within the top 1000 m (day-night pairs) allows for a direct comparison of species’ depth distribution and DVM patterns. All biological parameters show strong differences in vertical distribution patterns between paired day and night tows for the investigated species and migration distance varies with salp species and size, confirming previous findings. Our findings are compared against previous DVM estimates and we discuss a few hypotheses related to visual predator avoidance, prey preference, and size- and stage-specific behavior as well as consider the implications for vertical carbon fluxes in these different regions of the world ocean.