Gut analyses are an important tool in determining dietary preferences for a wide variety of marine organisms. Whilst there are limitations to microscopy-based approaches to gut content analysis, Scanning Electron Microscopy (SEM) allows identification from small fragments or incomplete cells. During the South-East Australian Marine Ecosystem Survey (SEA-MES) voyage in July 2023 Thetys vagina was a notable component of the trawl composition. This large salp feeds by filtering and trapping particles across a wide range of sizes. We analysed the gut contents of T. vagina using SEM and found more than 60 phyto- and microzooplankton taxa, including foraminifera, silicoflagellates, tintinnids, radioalaria, diatoms, dinoflagellates and coccolithophorids.
Taxa with hard components like diatom frustules, dinoflagellate theca, silicoflagellates skeletons, foram tests and tintinnid lorica were often well preserved and complete, while calcifying taxa like coccolithophores were often identified from individual liths separated from the coccospheres. Occasionally larger copepods up to 1mm were observed. Delicate scale-bearing taxa like prasinophytes and chrysophytes were inferred from individual dislodged scales.
We present a summary of the taxa identified in the guts as part of understanding the ecology of salps, their place in the food web and the trophic implications for the South-East Australian Marine Ecosystem Surveys.