Sample collection
Salpa fusiformis were collected in March 2023 aboard the R/V Atlantic Explorer (AE2306) during the monthly Bermuda Atlantic Time Series (BATS) cruise (31°50'N, 64°10'W). From 2023-03-19 to 2023-03-26, nighttime tows were conducted using a 1 meter circular Reeve net with 150 µm mesh, a 20 L cod end, and a miniSTAR-ODDI pressure and depth sensor deployed to 200 m depth. Conductivity, Temperature, Density, and Dissolved Oxygen (CTD-DO) casts were conducted at the same location following BATS protocols.
Only pristine salps, actively swimming, filtering, transparent, and free of abrasions, were used. Individuals were held for 12 hours to acclimate and confirm viability before experiments.
Oxygen consumption
Measurements followed Trueblood (2019), using Firesting optodes (PyroScience GmbH, Aachen, Germany), 50 mL gas-tight syringes with 0.2 µm filtered seawater at 21°C (sea surface temperature) or 14°C (temperature at 200 m). Routine metabolic rate (RMR) was used, as spontaneous activity could not be controlled for salps in the respirometer. Background respiration, determined using blank syringes with the same filtered seawater, was subtracted from RMR.
Critical oxygen partial pressure measurement
Critical partial pressure (Pcrit) was calculated using the calc_alpha and the calc_pcrit() function in the “respirometry” package in R (Birk, 2024) based on metabolic rate (R) as a function of PO2 (Seibel et al., 2021).
All salps were placed in cryo-vials and stored at -80ºC at sea. Samples were thawed; wet and dry weights were measured on shore. After obtaining wet mass, individuals were dried for 72 hrs at 60 ºC and then weighed.
