Table of Contents

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

Data from two Antarctic krill (Euphausia superba) 24-hour feeding experiments under ambient temperature and pCO2, ambient temperature and elevated pCO2, and elevated temperature and pCO2.

We conducted perturbation experiments to determine potential changes in feeding rates of Euphausia superba (32-41 mm) due to decreased pH and elevated temperature. Target pH was reached in the experiments via CO2 bubbling of seawater flowing through gas equilibration columns. The two feeding experiments differed in acclimation time.  Krill in experiment 1 (Exp 1) and experiment 2 (Exp 2) were acclimated to treatment conditions for 48 hours and 21 days, respectively.

Sampling and analytical procedures: 

Capture and husbandry: Antarctic krill (Euphausia superba) were captured during the austral summer of 2013/2014. Krill were collected by net tow (2 m diameter, 1000 m mesh, non-filtering cod end) off the R/V Laurence M. Gould near the Western Antarctic Peninsula and transported directly to the Palmer Station biological laboratory. One to two thousand krill were housed in one 4'w x 3'h circular holding tank and two 5’ x 2’ x 1’ rectangular tanks provided with aeration and flow-through seawater. Water was non-filtered and individuals were able to feed on plankton ad libitum throughout the season.

Experimental treatments: Three experimental treatments were targeted in this study: (1) ambient temperature and ambient pCO2/pH (400ppm/8.10), (2) ambient temperature and elevated pCO2 (800ppm)/reduced pH (7.7), and (3) elevated temperature (3 degrees C) and elevated pCO2 (800ppm)/reduced pH (7.7). Two replicate feeding experiments were conducted: Experiment 1 and 2. Temperature treatments were obtained using two separate recirculating systems. Two 800 L cylindrical polycarbonate carboys were attached to temperature controlled chillers (Delta Star) and inline pumps. The carboys were filled with non-filtered seawater acquired from the Palmer Station intake line, placed in a flow-through water bath, and maintained at 0 degrees C. Another 800 L carboy was set up without a chiller and placed in an environmental chamber set at bated for about 24 hours before sacrificed for sampling the end points. The samples collected in the bottles at T0 and Tfinal include: pH, total alkalinity, and fluorometric chlorophyll a. 

The systems were replaced with new water daily and allowed to acclimate to temperature for a minimum of 24 hours before the start of a trial or water change. High CO2 conditions were obtained using a peristaltic pump to inject straight CO2 into the propeller of a pump submerged in seawater. Treated water was then gently siphoned with minimal disturbance into treatment bottles. 

For each of the three treatments, 14, 4 L wide-mouth polycarbonate bottles were filled with the appropriate equilibrated seawater. Two bottles per treatment served as T0 controls (no krill added) and were sacrificed for an initial suite of samples. Two bottles served as Tfinal (24 h) controls, and one juvenile krill was added to each of the remaining 10 bottles per treatment (Tfinal treatments). The Tfinal bottles were capped to maintain target pCO2/pH, incubated in the appropriate location to maintain desired temperature (water bath for ambient, 0 degrees C; 3 degrees C environmental chamber for elevated temperature), and incubated for about 24 hours before sacrificed for sampling the end points. The samples collected in the bottles at T0 and Tfinal include: pH, total alkalinity, and fluorometric chlorophyll a.

Analyses:  pH was determined spectrophotometrically using the indicator dye thymol blue (Dickson et al. 2007; Zhang and Byrne 1996). Total alkalinity was determined on 100 ml subsamples with an open-cell, potentiometric titration of seawater (Metrohm 888 Titrando) with 0.1 M HCl following the potential of a pH electrode (Dickson et al. 2007). Tiamo software (version 2.3) was used to process the alkalinity data. Measurements of pH and TA were quality controlled using certified reference materials (CRMs) obtained from Andrew Dickson at UCSD Scripps Institute of Oceanography. An aliquot of seawater from each incubation bottle was also filtered onto a GF/F filter, which was wrapped in foil and frozen for fluorometric chlorophyll a  analysis (Parsons et al. 1984). Salinity was measured with a bench top conductivity meter (YSI 3100) calibrated daily with a conductivity standard (50,000 uS/cm; Ricca Chemical Company).

BCO-DMO Processing Notes:
- data submitted in Excel file "2014_AntarcticKrill_GrowthExperiment.xlsx" sheet "Sheet1" extracted to csv
- removed carbonate table to server separately
- added conventional header with dataset name, PI name, version date
- modified parameter names to conform with BCO-DMO naming conventions
- converted dates to ISO format (yyyy-mm-dd)
- replaced ND with nd for 'no data'

NSF Award Abstract:
Climate change projections for this century suggest that the Southern Ocean will be the first region to be affected by seawater chemistry changes associated with enhanced carbon dioxide (CO2). Additionally, regions of the Southern Ocean are warming faster than any other locations on the planet. Ocean acidification and warming may act synergistically to impair the performance of different organisms by simultaneously increasing metabolic needs and reducing oxygen transport. However, no studies have measured krill acid-base regulation, metabolism, growth, or reproduction in the context of ocean acidification or synergistic ?greenhouse? conditions of elevated CO2 and temperature. In the present project, the investigators will conduct both short and prolonged exposure experiments at Palmer Station, Antarctica to determine the responses of Euphausia superba to elevated CO2 and temperature. The investigators will test hypotheses related to acid-base compensation and acclimation of various life stages of krill to elevated CO2 and temperature. Furthermore, they will determine these impacts on feeding, respiration, metabolism, growth, and reproduction.

The Antarctic krill, Euphausia superba, is a key species in Antarctic food webs as they are a primary food source for many of the top predators in the Southern Ocean including baleen whales, seals, penguins, and other sea birds. This project will determine the responses of Antarctic krill exposed to elevated CO2 and temperature and whether or not krill have the capacity to fully compensate under future ocean conditions. The proposed field effort will be complemented by an extensive broader impact effort focused on bringing marine science to both rural and urban high school students in the Midwest (Kansas). The core educational objectives of this proposal are to 1) instruct students about potential careers in marine science, 2) engage students and promote their interest in the scientific process, critical thinking, and applications of science, mathematics, and technology, and 3) and increase student and teacher awareness and understanding of the oceans and global climate change, with special focus on the Western Antarctic Peninsula region. Finally, this project will engage undergraduate and graduate students in the production, analysis, presentation and publication of datasets.