DOI: 10.5061/dryad.hhmgqnkdx
title: Lipid content and stable isotopes of zooplankton during five winters around the northern Antarctic Peninsula

description: The Southern Ocean zooplankton community is diverse, yet most species are
 understudied, especially with respect to their overwinter feeding
 ecologies. This dataset describes body condition and trophic biomarker
 data (lipid content and stable isotopes of carbon and nitrogen) from 19
 zooplankton species collected over five consecutive winters (August and
 September 2012 – 2016) around the northern Antarctic Peninsula. To
 complement these data and provide context for interpretation, we report
 environmental data (percent sea-ice cover, sea-ice type, water
 temperature, salinity, and integrated chlorophyll-a (to 100 m)) as well as
 species abundance data at each sampling location. For most species, these
 are the first winter measurements or time series of body condition,
 trophic position, and abundance in relation to environmental variables
 around the northern Antarctic Peninsula. 
description: The U.S. Antarctic Marine Living Resources (AMLR) Program
 conducted five winter surveys (August - September 2012 - 2016) around the
 northern Antarctic Peninsula and South Shetland Islands. A description of
 the survey area and environmental and zooplankton sampling methods can be
 found in Walsh et al. (2020). Briefly, we surveyed a grid of 110
 historical fixed stations around the South Shetland, Elephant, and
 Joinville Islands. We conducted a Conductivity-Temperature-Depth (CTD)
 cast and an Isaacs-Kidd Midwater Trawl at each station. Upper mixed layer
 (UML) depth was defined according to Mitchell and Holm-Hansen (1991). UML
 temperature and salinities were defined to be means over the depth range
 of the UML. Water samples from CTD casts were processed for chlorophyll-a
 (integrated to 100 m, mg chl-a m<sup>-2</sup>) according to
 Holm-Hansen et al. (1965) and Holm-Hansen and Riemann (1978). We defined
 daylight conditions according to three categories. Day (D) was defined as
 one hour after local sunrise to one hour before local sunset; night (N)
 was defined as one hour after sunset to one hour before sunrise; and
 Twilight (T) was defined as one hour before and after sunrise and sunset.
 Sea-ice percent cover and type were classified according to a modification
 of the standardized visual approach from the Scientific Committee on
 Antarctic Research Antarctic Sea Ice Processes and Climate Program
 (ASPeCT) (Worby and Allison 1999). We extracted lipid
 from zooplankton according to a modified approach from Folch et al. (1957)
 as described by Budge et al. (2006). We analyzed lipid-free zooplankton
 for stable isotopes at the University of California Davis Stable Isotope
 Facility (https://stableisotopefacility.ucdavis.edu/ ). We also analyzed a subset of whole-animal zooplankton to address the issue of skewed nitrogen stable isotope values resulting from lipid extraction. References: Budge, S.M., Iverson, S.J. & Koopman, H.N. Studying trophic ecology in marine ecosystems using fatty acids: A primer on analysis and interpretation. <i>Mar. Mammal Sci. </i><b>22</b>, 759-801 (2006). Folch, J., Lees, M. & Sloane Stanley, G. A simple method for the isolation and purification of total lipides from animal tissues. <i>J. Biol. Chem. </i><b>226</b>, 497-509 (1957). Holm-Hansen, O., Lorenzen, C.J., Holmes, R.W. & Strickland, J.D.H. Fluorometric determination of chlorophyll. <i>J. Cons. perm. int. Explor. Mer. </i><b>30</b>, 3-15 (1965). Holm-Hansen, O. & Riemann, B. Chlorophyll a determination: improvements in methodology. <i>Oikos </i><b>30</b>, 438-447 (1978). Mitchell, B.G. & Holm-Hansen, O. Observations and modeling of the Antarctic phytoplankton crop in relation to mixing depth. <i>Deep-Sea Res. </i><b>38</b>, 981-1007 (1991). Walsh, J., Reiss, C.S. & Watters, G.M. Flexibility in Antarctic krill <i>Euphausia superba </i>decouples diet and recruitment from overwinter sea-ice conditions in the northern Antarctic Peninsula. <i>Mar. Ecol. Prog. Ser. </i><b>642</b>, 1-19 (2020). Worby, A. & Allison, I. A technique for making ship-based observations of Antarctic sea ice thickness and characteristics. Part I: observational technique and results. Research Report No. 14. Antarctic Cooperative Research Center, Hobart, Tasmania (1999).
description: For samples from pooled stations (denoted as “POOLED” in the
 station column), we estimated tow depth and environmental variables by
 calculating the mean of each variable for the sampling area and year.
 Reported abundance for pooled stations is the mean abundance for a given
 species within the sampling area and year. To estimate sea-ice type, we
 assigned a number to each ice type (0 = none, 1 = slush, 2 = thin, 3 =
 first, 4 = multi), calculated the mean for the area and year, and rounded
 the result to the nearest whole number. Station coordinates and daylight
 conditions are not reported for samples from pooled stations (denoted as
 “NA”). In 2012, percent sea-ice cover and sea-ice type
 were not determined. Sampling stations were characterized as “ice” (100 %)
 or “no ice” (0 %). Where sea-ice conditions were not reported,
 "NR" appears in the dataset. For most species
 in 2012 and for small species in other years, the number of individuals
 analyzed for lipids and stable isotopes were not recorded (denoted as
 "NR" in the dataset). In a few cases, lipid was
 undetectable in samples. These are denoted “ND” (for none detected) in the
 dataset. Stable isotope values are reported for these samples.
 In some cases, especially
 for gelatinous species, the calculated percent mass loss when wet samples
 were dried exceeded 100 %. In these cases, only percent lipid of wet mass
 is reported in the dataset. For one sample in 2012
 (2012TM02), we were unable to obtain stable isotope values. Stable
 isotopes are reported as “NR” for this sample, but lipid data for this
 sample are reported. Lipid data are not reported for
 whole-animal (“WAN”) samples, since lipid was not extracted from these
 samples.