Gut contents and isotopic profiles of Salpa fusiformis and Thalia democratica

Little is known about the diet of planktonic tunicates such as salps, which can comprise around 80% of zooplankton abundance under bloom conditions. The gut contents of solitary and aggregate phases of the salps Thalia democratica and Salpa fusiformis were analysed with scanning electron microscopy (SEM), high-performance liquid chromatography (HPLC) and stable isotope analyses (SIA) to describe their diets under field conditions. The gut contents contained representatives of diatoms, dinoflagellates, haptophyte flagellates (Order Prymnesiales and Coccolithophorales), prasinophytes (Order Chlorodendrales) and, in a few instances, copepods (Crustacea). SEM confirmed the presence of many species of phytoplankton in the salp guts and was broadly supported by HPLC and SIA. The dominant peaks in the HPLC chromatograms corresponded to fucoxanthin, alloxanthin, chlorophyll b and β-carotene, indicating the ingestion of diatoms, cryptophytes and green algae. Solitary stages of both S. fusiformis and T. democratica fed on items that were not common in the phytoplankton samples, namely coccolithophores and copepods, respectively.