Research ArticleECOLOGY

Northern cod species face spawning habitat losses if global warming exceeds 1.5°C

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Science Advances  28 Nov 2018:
Vol. 4, no. 11, eaas8821
DOI: 10.1126/sciadv.aas8821
  • Fig. 1 Distribution patterns of Atlantic cod and Polar cod in the Seas of Norden.

    (A) Atlantic cod; (B) Polar cod. Populations of both species reproduce during winter and spring (Atlantic cod: March to May; Polar cod: December to March) at species-specific locations (i.e., spawning habitats, blue-shaded areas) with characteristic temperature and sea-ice conditions (Atlantic cod: 3° to 7°C, open water; Polar cod: −1° to 2°C, closed sea-ice cover). Green arrows indicate egg and larval dispersal driven by prevailing surface currents. During summer, the feeding grounds (green-shaded areas) of both species partly overlap, for example, around Svalbard, which marks the northernmost distribution limit of Atlantic cod. Red symbols denote the origin of animals (spawning adults) used in this study. Distribution maps were redrawn after (4, 13, 33). NEW, Northeast Water Polynya; FJL, Franz-Joseph-Land; NZ, Novaya Zemlya.

  • Fig. 2 Effects of elevated Pco2 on temperature-dependent oxygen consumption rates (MO2) and growth of Atlantic cod embryos and Polar cod embryos (right).

    (A and B) MO2 was measured in eyed-stage embryos (image). Symbols are means (±SEM depicted as bars, n = 6 or 4). Performance curves (lines) are based on n = 28 data points. Dark and light shadings indicate 90 and 95% Bayesian credible confidence intervals, respectively. (C and D) Larval yolk-free body area at hatch was assessed as an indicator of somatic growth and resource (yolk) utilization. Box plots overlaid with individual values show the 25th, 50th, and 75th percentile; whiskers mark 95% confidence intervals. (D) Sufficient sample sizes were not available at 6°C because most individuals died or hatched malformed. (E and F) Offsets between regression lines (with 95% confidence intervals) indicate CO2-related differences in size-weight relationships of newly hatched larvae (image). Individuals were pooled across temperature treatments (E: 0° to 12°C, F: 0° to 3°C). (A to F) Significant main effects of temperature, Pco2, or their interaction (T * Pco2) are indicated by black ★, whereas orange ★ denote significant CO2 effects within temperature treatments (Tukey post hoc test, n = 6 or 4 per treatment). See table S1 for details on statistical tests. N.a., not available.

  • Fig. 3 Effects of elevated Pco2 on temperature-dependent egg survival in Atlantic cod and Polar cod.

    (A) Atlantic cod; (B) Polar cod. Symbols represent means (±SEM depicted as bars, n = 6). Thermal performance curves (TPCs, lines) of each species are based on n = 36 data points. Dark and light shadings indicate 90 and 95% Bayesian credible confidence intervals, respectively. TPCs were extrapolated into subzero temperatures by incorporating freezing tolerance thresholds from the literature (Materials and Methods). Significant main effects of temperature, Pco2, or their interaction (T * Pco2) are indicated by black ★, whereas orange ★ denote significant CO2 effects within temperature treatments (Tukey post hoc test, n = 6 or 4 per treatment). See table S1 for details on statistical tests.

  • Fig. 4 Current (baseline) spawning habitat suitability for Atlantic cod and Polar cod in the Seas of Norden.

    (A) Atlantic cod; (B) Polar cod. Spawning habitat suitability is expressed as PES (%PES, color coded) by combining experimental survival data (Fig. 3) with WOA13 temperature fields (1° × 1°, upper 50 m of shelf seas) for the baseline period 1984–2005. Values are averaged over spawning seasons (Atlantic cod: March to May; Polar cod: December to March) and referenced against locations where spawning has been documented [yellow dashed areas (13, 33)]. The spatial extent of thermally suitable spawning habitat (PES > 90%) is typically larger than the “realized spawning habitat” because other limiting factors are not considered. Dotted magenta lines indicate the respective seasonal sea-ice edge positions (defined as areas with ice concentrations > 70%; note that sea-ice edge various slightly between species due to varying species-specific spawning seasons).

  • Fig. 5 Change in thermally suitable spawning habitat of Atlantic cod (left) and Polar cod (right) in the Seas of Norden under RCPs.

    (A to C) RCP8.5: Unabated OWA. (D to F) RCP4.5: Intermediate warming (no acidification considered). (G to I) RCP2.6: Less than 2°C global warming (no acidification considered). Maps show the shift in PES between the baseline period (1985–2004; spawning season of Atlantic cod: March to May; spawning season of Polar cod: December to March; see Fig. 3) and the median of CMIP5 multimodel-based projections (seasonal sea surface temperature, 0 to 50 m; see Materials and Methods) for this century’s end (2081–2100). Black shading indicates areas (cells, 1° × 1°) with high uncertainty (that is, the shift in PES within that cell is smaller than the CMIP5 ensemble spread; see Materials and Methods). Dotted magenta lines represent the sea-ice edge positions of the respective species-specific spawning season (defined as areas with ice concentrations > 70%). (C, F, and I) For each map, values (change in PES) of individual cells are summarized by kernel density estimations, with the width corresponding to the relative occurrence of values. Box plots show the 25th, 50th, and 75th percentile; the ends of the whiskers mark the 95% intervals.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/11/eaas8821/DC1

    Fig. S1 Thermal niches of adult Atlantic cod and Polar cod.

    Fig. S2 Treatment effects on larval morphometrics at hatch.

    Fig. S3. Water quality measurements.

    Fig. S4. Effects of temperature and Pco2 on daily mortality rates of Atlantic cod and Polar cod.

    Fig. S5. Effects of temperature and Pco2 on embryonic development of Atlantic cod and Polar cod.

    Fig. S6. Spawning habitat maps for Atlantic cod and Polar cod are based on experimental egg survival data and climate projections under different emission scenarios.

    Table S1. Summary table for statistical analyses conducted on data presented in Figs. 2 and 3 of the main text and in figs. S1 and S5.

    Table S2. Length and weight of female and male Atlantic cod and Polar cod used for strip spawning and artificial fertilization.

    Table S3. Mean egg diameter and fertilization success of egg batches (±SD, n = 3) produced by different females (n = 6).

    Table S4. List of CMIP5 models that met the requirements for this study (for details, see the “Spawning habitat maps” section in the main text).

    References (4855)

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1 Thermal niches of adult Atlantic cod and Polar cod.
    • Fig. S2 Treatment effects on larval morphometrics at hatch.
    • Fig. S3. Water quality measurements.
    • Fig. S4. Effects of temperature and PCO2 on daily mortality rates of Atlantic cod and Polar cod.
    • Fig. S5. Effects of temperature and PCO2 on embryonic development of Atlantic cod and Polar cod.
    • Fig. S6. Spawning habitat maps for Atlantic cod and Polar cod are based on experimental egg survival data and climate projections under different emission scenarios.
    • Table S1. Summary table for statistical analyses conducted on data presented in Figs. 2 and 3 of the main text and in figs. S1 and S5.
    • Table S2. Length and weight of female and male Atlantic cod and Polar cod used for strip spawning and artificial fertilization.
    • Table S3. Mean egg diameter and fertilization success of egg batches (±SD, n = 3) produced by different females (n = 6).
    • Table S4. List of CMIP5 models that met the requirements for this study (for details, see the “Spawning habitat maps” section in the main text).
    • References (4855)

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