Gelatinous zooplankton are important grazers in mesopelagic food webs, although their diet and trophic impacts are unclear. One group, salps (Tunicata), are efficient filter feeders with extensive vertical migration behaviors that transport carbon through the mesopelagic zone. Metabarcoding allows accurate detection of a broad taxonomic range of consumed prey and is thus providing new insights into trophic pathways and dynamics of pelagic food webs. We report results on the prey diversity of Salpa aspera from a field expedition of the Ocean Twilight Zone project in the NW Atlantic Ocean. Diet composition was determined with DNA metabarcoding analysis of the gut contents of Salpa aspera. Salps (solitary and aggregate forms) for this study were collected in vertically-stratified tows (0 – 200, 200 – 400, 400 – 600, 600 – 1000 m) of a 10-m² MOCNESS in the NW Atlantic Slope Water during March 2020. DNA was extracted from salp gut contents and sequenced for V4 and V9 hypervariable regions of the 18S rRNA gene. Taxonomic assignments of V4 and V9 sequences were resolved and classified using custom scripts and reference databases. Multivariate statistical analysis was used to compare prey composition for salps collected from 4 depth strata at 5 stations. When combined with diel vertical distribution patterns from in situ shadowgraph imaging, results of the metabarcoding analysis of the salp diet were used to summarize the trophic relationships of S. aspera, infer sources of productivity, evaluate the impacts of salp forms (aggregate or solitary) and vertical migration on particle and energy transfer in the mesopelagic ecosystem.

Primary Presenter: Paola Batta Lona, University of Connecticut (paola.batta_lona@uconn.edu)

Authors:

Heidi Sosik, Woods Hole Oceanographic Institution  (hsosik@whoi.edu)

Peter Wiebe, Woods Hole Oceanographic Institution  (pwiebe@whoi.edu)

Ann Bucklin, University of Connecticut  (ann.bucklin@uconn.edu)