Basin-scale distribution of salps and doliolids in the transition region of the North Pacific Ocean in summer: Drivers of bloom occurrence and effect on the pelagic ecosystem

•The large-scale distribution of thaliacean blooms in the North Pacific transition region was investigated in early summer.•The significant drivers on bloom formation were salinity, pico-sized chlorophyll a, phosphate, silicate, and seawater density.•The most dominant species, Thalia democratica thrived in the area south of the subarctic boundary with the influence of the HNLC water mass from the subarctic region.•Doliolids generally occur in area where regeneration production prevails, indicating that they are important components of the microbial food web.