Salp biology (Salpa thompsoni) at the Chatham Rise, New Zealand

The abundant pelagic tunicate Salpa thompsoni is a major grazer in the Southern Ocean. We report the length-frequency distribution, maturity stage composition, growth, and size-specific diel vertical abundance patterns at one of the northernmost habitats of S. thompsoni (Chatham Rise, east of New Zealand, ~ 44°S 178°E). By observing the in situ growth of distinct size cohorts using integrative krill net tows (upper 200 m, 2 mm mesh size, 3.2 m² mouth opening) and ex situ on-board experiments, relative growth was estimated for small blastozooids to be between 8.8–11.7% d−1 at ambient temperatures of 11 °C. Integrative Bongo tows in the upper 200 m (202 µm mesh size, 0.4 m² mouth opening) showed that S. thompsoni not only have daytime-dependent vertical abundance patterns, but also that these are size-specific, with medium-sized blastozooids and large oozooids contributing most to the elevated values during the night.