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 between 2015 and 2021 during three research expeditions (EXPORTS cruise to the Northeast Atlantic and TAN1516 and TAN1810 over the Chatham Rise, New Zealand) using MOCNESS-1 net and large midwater trawl with maximum sampling depths of 1000 m. More than 530 Soestia specimens (oral-atrial length: 4–68 mm) were analysed for their vertical distribution, i.e., weighted mean depths (WMD) during the day and night, and migration distance.

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.