Resolving Pyrosome Prey Consumption Through Gut Content Analysis

Pyrosomes are colonial, columnar-shaped pelagic tunicates that filter feed on small planktonic organisms and marine microbes. These tunicates provide a unique pathway for energy transfer in marine food webs, lowering the number of trophic steps required to transfer energy from microbial organisms to mesozooplankton. Yet, little research has investigated the prey preferences and selectivity of pyrosome grazing. Given the recent occurrence of pyrosome blooms in the Northeast Pacific Ocean, there is renewed interest in their prey consumption and the implications for plankton community composition. In this study, we coupled light and electron microscopy techniques to better understand prey consumption by Pyrosoma atlanticum. We analyzed 32 pyrosome guts during the winter and summer of 2018 in the Northern California Current. Preliminary results show the consumption of picocyanobacteria, centric and pennate diatoms, and some thecate dinoflagellates by the pyrosomes. Prey size ranged from 1µm-50µm in diameter. These results corroborate and expand on complementary findings using flow cytometry and sequencing techniques (see accompanying poster: Sweeney et al.). Feeding on diverse prey items may allow pyrosomes to succeed under a range of environmental conditions and, once present, they may facilitate new linkages between marine organisms. Minimizing energy lost through trophic transfer may ultimately increase carbon availability to predators and deep-sea communities during sinking events.