The composition and abundance of the major zooplankton taxon tunicates were analyzed in a multi-year study and correlated with environmental parameters in the area around the hydrothermal vent field of Kueishantao (Turtle Island) in Taiwan. This provided the first study about tunicates above hydrothermal vents worldwide. We chose seven different stations for sample collection. Sampling was carried out in September of 2009, 2014, and 2015 (autumn) and June 2015 (summer). A total of ten tunicate species were identified belonging to the classes Appendicularia and Thaliacea during the above periods throughout the area. Considering the limited diversity of these organisms worldwide (40 species are identified in each class), we affirm that Kueishantao, a shallow water hydrothermal vent field, with 10 species provided an unexpected biodiversity hot spot for pelagic tunicates. The sampling of the organisms in the surface waters provided higher abundances compared to oblique tows. Comparing results from three autumn seasons we found that temperature values correlated with changes in tunicate abundances. We discovered strong seasonal changes in pelagic tunicate abundances over the entire survey period, with the highest abundances observed during autumn.