Characterizing the Diets of Siphonophores (Cnidaria:Hydrozoa) in the Offshore Central California Current Ecosystem using DNA Metabarcoding

Siphonophores are abundant and diverse predators in the Offshore Central California Current (OCCC) ecosystem. Due to limited access to the deep midwater environment, little is known about the diets of most deep-dwelling species. Early work on the diets of epipelagic siphonophore species relied on visual gut content inspection, which can rarely detect and identify soft-bodied prey which does not leave recognizable parts behind. For deep-sea species, Remotely Operated Vehicle (ROV) observations are unable to identify small prey items (such as copepods, ostracods, and larval fish) through video recordings. Recently, the application of DNA metabarcoding in other marine predators has revealed the importance of prey taxa that were overlooked by visual methods. Moreover, metabarcoding can detect prey that was ingested hours before specimen collection from traces of DNA released during digestion and thus is better suited for the study of deep-sea species with long intervals between prey captures. In this study, we perform DNA metabarcoding of the gut contents of 27 siphonophore species across the water column and characterize their diets. We collected siphonophore specimens using blue water dives and ROV dives in OCCC waters. We extracted DNA from the feeding bodies, then amplified and sequenced six barcode markers along the 18S gene. OTUs are being assigned to prey taxa using a local zooplankton database of 18S amplicons. We expect this method to detect both small prey and gelatinous prey underrepresented by other methods. Our results may reveal hidden links between mesozooplankton and higher trophic levels in the midwater food-web. This study will improve our understanding of the role of siphonophores in the open ocean, and the importance of their local species diversity in the OCCC for nutrient flow and ecosystem functioning.