Dataset: Krill physiology - Experimental conditions

Krill for both experiments were collected from surface waters (upper 50 m) at approximately 48.01, -122.29 using a 60-cm diameter Bongo frame equipped with black 335-μm mesh nets and non-filtering cod ends towed for <10 min. The contents of each cod end were immediately diluted in coolers of seawater and sorted to remove healthy euphausiids. For the pH experiment krill were collected on 23 July 2017 between 23:00-00:30, stored in 1-4 L containers at a concentration of 5 ind L-1, sealed with all air removed to eliminate splashing, and transported in coolers to the University of Washington Friday Harbor Laboratories (FHL) where they were sorted for healthy female E. pacifica (obvious ovary) and put in in experimental chambers between 06:00-08:00 on 24 July 2017. For the DO experiment krill were collected on 20 Sept 2017 between 20:00 and 21:15, krill were transported in coolers to the NOAA Mukilteo Research Station within an hour, sorted for healthy female E. pacifica (obvious ovary), and immediately put in experimental chambers. Krill were kept chilled (10-14 °C) at all times and were gently transferred using broad spoons to prevent damage. During experiments krill were fed Shellfish Diet 1800 (Reed Mariculture) twice per day and newly hatched Artemia salina (San Francisco Bay Brand) nauplii once per day. All physiological measurements were taken after 10 days of acclimation; individuals were flash frozen in liquid nitrogen after oxygen consumption was measured.

Experimental acclimation to pH was conducted at the FHL Ocean Acidification Environmental Laboratory, using a flow-through system with pH controlled by CO2 bubbling. Target pH levels were 8.0, 7.5, and 7.2: three flow-through systems were used, one per pH treatment. Within each system, conditioned seawater was delivered to eight flow-through boxes that each contained two 500-mL mesh-sided experimental chambers with one individual krill per chamber, for a total of 16 individuals per system. Experimental systems were kept covered in black plastic to reduce light. Temperature was set to 12 °C and oxygen was maintained at ambient levels through bubbling, but not monitored.

Acclimation of krill to different oxygen levels in the laboratory was done at the NOAA Mukilteo Research Station in flow-through experimental systems with independent temperature, pH, and oxygen control. Target dissolved oxygen levels were 3, 5, and 9 mg DO L-1: nine systems were used, three per DO treatment, with krill held individually in a mix of both 250- and 500-mL flow-through containers within the experimental systems. Temperature was maintained at 12 °C and pH at ~7.82; temperature, pH, and dissolved oxygen were monitored continuously.