Although the oceanic widespread pelagic tunicate Soestia zonaria has been studied for more than a century, little ecological information exists. Soestia primarily occurs in tropical to warm-temperate regions. Soestia specimens were collected in 2008 and 2021 during two research expeditions (EXPORTS cruise to the Northeast Atlantic and TAN0806 over the Chatham Rise, New Zealand) using MOCNESS-1 net and large midwater trawl with maximum sampling depths of 1000 m. In total, 140 Soestia specimens (oral-atrial length: 7–54 mm) were analysed for biomass parameters (wet weight, dry weight, ash-free dry weight, water content, organic content) and stoichiometry (carbon and nitrogen content, carbon-to-nitrogen ratio).

This study was additionally supported by two PhD projects (International Doctoral Fellowship & University of British Columbia's Graduate Four-Year Fellowship), the Ministry of Business, Innovation and Employment (MBIE) under NIWA's Strategic Science Investement Fund Coasts and Oceans and the Royal Society of New Zealand Marsden Fund.---Instruments used for: Freeze-drying: Edwards Modulyo Freeze Dryer (Oakville, Ontario, CA) Ashing: muffle furnace (SYBRON Thermolyne) Weighing: analytical balances (Mettler Toledo XP205, Sartorius BP 211 D), both used for all samples CN analysis: CN vario MICRO cube