Biology and distribution of salps in the subarctic Northeast Pacific

Historical samples collected from 1985 to 2020 in coastal and open ocean regions of the Northeast Pacific were utilised to explore salp assemblage composition, morphometrics, and ontogeny of dominant species, as well as spatial, seasonal, and interannual distribution patterns at subarctic latitudes. Species richness was low, however, three of the seven observed species ( Cyclosalpa bakeri, Salpa aspera , and S. fusiformis ) were dominant and widely distributed in oceanic waters. Salpa maxima and Ihlea punctata were sporadically encountered, while Thalia democratica and Thetys vagina were observed exclusively during the 2014–2016 heatwave. Of the regions sampled, salps occurred at the shelf break and offshore, only occasionally on the shelf and never in inner waterways. Although salps were encountered year-round, salps were most prevalent between late spring and autumn. Over the 35 years, no clear up- or downward trend in the percentage of presence was detected due to high and perhaps cyclic variability. For some species, abundance was significantly affected by season, year, bottom depth, and Multivariate El Niño/Southern Oscillation Index. There is an urgent need for detailed research to realistically incorporate pelagic thaliaceans in North Pacific ecosystem models. The present study lays the foundation for future research on salps at high northern latitudes, utilising a unique and rich sample collection.