Role of Salps in Mesopelagic Food Webs: Metabarcoding Analysis of Trophic Interactions and Diet Diversity

Salps are among the most important and efficient primary consumers in the mesopelagic zone (200m-1,000m). In the NW Atlantic Ocean, these deep sea ecosystems are impacted by seasonal and interannual variation, causing changes in biodiversity and biomass of the pelagic assemblage, and potentially altering the dynamics of the mesopelagic food web. High Throughput DNA sequencing (metabarcoding) analysis of salp gut contents allows accurate detection of prey across a broad taxonomic range. Salps were collected by mid water-trawl during cruises of the NOAA R/V Bigelow in the NW Atlantic Slope Water in Summer 2018 and Spring 2019. Selected salp specimens were removed from samples immediately upon collection and flash-frozen in liquid nitrogen. Salps were partially thawed for dissection of gut contents and tissue for molecular species identification. Salpa aspera, Salpa fusiformis, and Iasis zonaria were paired by species and life stage for metabarcoding analysis of gut contents. Extracted DNA was sequenced for the V4 and V9 hypervariable regions of 18S rDNA using an Illumina MiSeq. Sequences and Operational Taxonomic Units (OTUs) were resolved and classified using custom scripts and reference databases. Multivariate statistical approaches were used to compare prey composition among different species between collections. DNA metabarcoding analysis revealed differences between salp species in the taxonomic composition of consumed prey, and is providing new insights into particle and energy transfer in mesopelagic food webs.