Table of Contents

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

Antarctic krill (Euphausia superba) growth data collected during an experiment where krill were allowed to molt once in ambient conditions then placed in individual bottles maintained at one of six target treatments: 1) Ambient temperature (0 degrees C) and ambient pH (8.00); 2) Ambient temperature (0 degrees C) and pH = 7.50; 3) Ambient temperature (0 degrees C) and pH = 7.10; 4) Elevated temperature (3 degrees C) and ambient pH (8.00); 5) Elevated temperature (3 degrees C) and pH = 7.50; 6) Elevated temperature (3  degrees C) and pH = 7.10. The bottles were incubated until the either the krill molted a second time or the experiment ended (after 26 days).

Sampling and analytical procedures:

Capture and husbandry: Antarctic krill (Euphausia superba) were captured during the austral summer of 2014/2015. 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: Six experimental treatments were targeted in this study: 1) Ambient temperature (0 degrees C) and ambient pH (8.00); 2) Ambient temperature (0 degrees C) and pH = 7.50; 3) Ambient temperature (0 degrees C) and pH = 7.10; 4) Elevated temperature (3 degrees C) and ambient pH (8.00); 5) Elevated temperature (3 degrees C) and pH = 7.50; 6) Elevated temperature (3  degrees C) and pH = 7.10. Temperature treatments were obtained using two separate recirculating systems. Three 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. Three other 800 L carboys were set up without a chiller and placed in an environmental chamber at 3 degrees C. 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.

Krill were picked and placed in individual 4 L wide-mouth polycarbonate bottles with airtight lids (n = 26 per experimental treatment). Bottles were filled with ambient seawater. Bottles were immediately closed and placed in environmental chambers at ambient temperature (0 degrees C). Every 24-48 hours, 80% of the water was siphoned out of each bottle and replaced with new ambient seawater to minimize excretory and respiratory effect. Bottles were checked for molts twice per day. If a molt was observed, the molt was removed for processing (measured for krill uropod and total length), and the krill was placed in another individual 4 L wide-mouth polycarbonate bottle containing one of the six pre-acclimated treatment waters as described above to begin the second phase of the experiment. The bottle was then immediately closed and placed in environmental chambers at either 0 or 3 degrees C. This process was repeated for all the krill after each molted for the first time, enabling the experiment to continue with a total of 26 krill per treatment. Water changes every 24-48 hours with either ambient seawater (for krill awaiting first molt) or with pre-acclimated treatment water (for krill awaiting second molt) and twice daily checks for molts continued for the duration of the experiment. If a second molt was observed, that bottle was pulled from the experiment and the molt and live krill processed. The experiment ended on March 7 due to the end of the Palmer Station field season, and a majority of the krill did not molt a second time. However, the remaining krill were processed for uropod and total length and wet weight.

Analyses: Upon the first molting event for each krill, the molt was gently removed from the bottle. The molt was measured for uropod and total length (mm) with digital calipers (Fowler). 

Once a krill molted a second time, both the krill and molt were gently removed from the bottle. Both the molt and krill were measured for uropod and total length (mm) with digital calipers (Fowler), and the krill wet weight (mg) was measured. At the end of the experiment, the remaining krill that did not molt a second time were processed for uropod and total length (mm) and wet weight (mg). 

pH was measured in each experimental bottle at the start of the experiment. Salinity, pH, and total alkalinity were measured during water changes. The water changes occurred every 24-48 hours, but we were unable to collect salinity, pH, and total alkalinity samples at every water change due to time constraints. Salinity was measured with a bench top conductivity meter (YSI 3100) calibrated daily with a conductivity standard (50,000 uS/cm; Ricca Chemical Company). 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

BCO-DMO Processing Notes:
- data submitted in Excel file "2015_AntarcticKrill_GrowthExperiment_1.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.