Dataset: AE1910 Organismal Physiology
Deployment: AE1910

Methods detailed in Tarrant, A. M., N. McNamara-Bordewick, L. Blanco‐Bercial, A. Miccoli, and A. E. Maas. in review. Oceanic Copepods Fine-Tune Their Metabolism During Diel Vertical Migration.

Briefly, Pleuromamma xiphias were collected offshore from the Bermuda Institute of Ocean Sciences (BIOS) during a cruise aboard the R/V Atlantic Explorer from May 20-22, 2019. Net tows were conducted at 12 time points, spaced 4-7 hours apart to target mid-day, early night, mid-night and morning. Nighttime tows (early- and mid-night) were conducted using a 1-m² Reeve net deployed to 200 m depth, with 150 µm mesh size, 20 L cod end, and a miniSTAR-ODDI pressure and depth sensor. Daytime tows (morning and afternoon) were conducted using a 1-m² MOCNESS with 150 µm mesh size and a custom thermally-insulated closing cod with one closing net sampling from 400-600 m. Because the cruise coincided with Tropical Storm Andrea, it was necessary to relocate the ship twice to avoid high winds and continue sampling. The latitude, longitude, date and time (local) for each tow details this relocation. After each tow, copepods were examined under a Leica M205 C stereo microscope to identify adult P. xiphias and determine their gender. Copepods were used immediately for respirometry and excretion measurements.

Water for physiological experiments was obtained daily from 200 m using the rosette on the CTD. It was gravity filtered past a 0.2 µm Supor filter in a Georig 142 mm filter holder and equilibrated to 20°C in an upright incubator. At each time point, up to six copepods were transferred into individual respiration chambers that consisted of 50 mL glass syringes containing an optically sensitive oxygen sensor (OXFOIL: PyroScience, Aachen Germany) and 30 mL of 0.2 µm filtered seawater. Oxygen concentration in each chamber was then measured non-invasively and continuously (every 60 seconds) for approximately 3 hours using two FireSting optical oxygen meters (PyroScience, Aachen Germany). At the end of the experiment, the chambers were visually inspected to ensure that the copepods were still swimming. A 15-mL subsample of water was filtered at a 30º upward angle (to avoid damaging copepods or fecal pellets) through 0.7 µm GFF filters into 15-mL conical vials that had been pre-treated with OPA working reagent (21 mM sodium tetraborate, 0.063 mM sodium sulfite, 50 mL L¹ o-phthalaldehyde in ethanol). This filtered water was refrigerated (4°C) for less than 24 h and then run for ammonium measurements at sea. Ammonium was measured using the OPA (o-phthalaldehyde) method (Holmes et al. 1999). The copepod and any fecal pellets from each chamber were rinsed into a petri dish. Any fecal pellets were counted and photographed under a stereomicroscope. Copepods were rinsed once in DI water and frozen at -80ºC. Frozen copepods were subsequently weighed on a Mettler-Toledo XPR microbalance, dried, and reweighed.