Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

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.

BCO-DMO Processing:
- converted latitude and longitude from degrees and decimal minutes to decimal degrees;
- added ISO8601 date/time field.

NSF Award Abstract:
The daily vertical migration (DMV) of zooplankton and fish across hundreds of meters between shallow and deep waters is a predominant pattern in pelagic ecosystems. This migration has consequences for biogeochemical cycling as it moves a substantial portion of fixed carbon and nitrogen (an estimated 15 to 40 % of the total global organic export) from the surface directly to depth where it feeds the midwater food chain and sequesters nutrients away from atmospheric mixing. Estimates and predictions of these fluxes are, however, poorly understood at present. New observations have shown that one source of uncertainty is due to the assumption that metabolic rates and processes do not vary over the course of the day, except based on changes in temperature and oxygen availability. Rates are, however, also driven by differences in feeding, swimming behavior, and underlying circadian cycles. The objective of this project is to improve the ability of scientists to understand and predict zooplankton contributions to the movement of carbon and nitrogen in the ocean by detailing daily changes in physiological processes of these organisms. By producing a set of respiration and excretion measurements over a daily time series, paired with simultaneously collected gene and protein expression patterns for an abundant vertically migratory species, the investigators will provide unprecedented and predictive insight into how changes in the environment affect the contribution of zooplankton to biogeochemical fluxes. The sampling design of the project will advance discovery and understanding by providing hands-on training opportunities to at least two undergraduate researchers. The project will broaden dissemination of the research via development of an educational module, focusing on rhythms in the ocean. The module will initially be piloted with the Bermuda Institute of Ocean Sciences (BIOS) summer camp students and then disseminated through the BIOS Explorer program, the Teacher Resources Page on the BIOS website, and published in a peer-reviewed educational journal.

This project will characterize the metabolic consequences of daily physiological rhythms and DVM for a model zooplankton species, the abundant subtropical copepod Pleuromamma xiphias. Flux processes (oxygen consumption, carbon dioxide production, production of ammonium and fecal pellet production) will be interrogated using directed experiments testing the effects of temperature, feeding and circadian cycle. Circadian cycling will further be examined using transcriptomic and proteomic profiling. These experiments will be related to field samples taken at 6-h intervals over the course of the diel migration using an integrated suite of molecular and organismal metrics. Combined organismal, transcriptomic and proteomic profiles will provide an understanding of which metabolic pathways and associated flux products vary in relation to particular environmental variables (food, light cycle, temperature). Diel variation in metabolic rates will also be assessed across seasons and species using other important migratory groups (pteropod, euphausiid, and another copepod). The metabolic data will then be contextualized with abundance estimates from archived depth-stratified tows to allow scaling to community-level patterns and will be used to improve calculations of zooplankton contribution to particulate organic carbon, nitrogen and respiratory active flux. The results of this study will both improve our flux estimates and provide predictive insight into how various environmental variables influence the underlying physiological pathways generating carbon and nitrogen flux.

Cruise reports are available from the completed cruises:
SD031019
AE1910
AE1918