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Climate change tightens a metabolic constraint on marine habitats

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Science  05 Jun 2015:
Vol. 348, Issue 6239, pp. 1132-1135
DOI: 10.1126/science.aaa1605
  • Fig. 1 Hypoxia tolerance versus inverse temperature.

    Laboratory data were compiled from published literature (see the supplementary materials) for 16 species in which hypoxic thresholds (PO2crit) were experimentally determined at three or more different temperatures. Of these species, 11 showed statistically significant relationships to temperature. Hypoxic thresholds are measured as the O2 level below which the rate of metabolism cannot be maintained or an increase in mortality is observed. The parameters of the metabolic index are obtained from the slope (Eo) and intercept (Ao) of the linear regressions (table S1) (10).

  • Fig. 2 Global relative distribution of metabolic index.

    The metabolic index is computed from climatological temperature and O2 and normalized to depict large-scale patterns but not absolute values. Variation across latitude (top) is shown for the depth-averaged metabolic index of the upper ocean (0 to 200 m), divided by the mean value throughout the tropics (15°S to 15°N, 0 to 200 m). The metabolic index increases by >10-fold from the tropics to high latitudes due to the tendency for warm waters to have low O2. Variation with depth (bottom) is computed as the relative difference between the average value in the upper 100 m and the average from 100 to 200 m. Negative values correspond to a decrease in Φ with depth. Vertical variations of Φ are reduced by the compensating decreases in both temperature and O2 with depth but can be strongly negative in the presence of sharp OMZs. Both maps are computed with Eo = 0.7 eV, but the patterns depend only slightly on this parameter.

  • Fig. 3 Distribution of the metabolic index (Φ) in the Atlantic Ocean for all four species in Fig. 1 with documented marine population distributions.

    (A) Atlantic cod, (B) Atlantic rock crab, (C) sharpsnout seabream, and (D) common eelpout. For each species, Φ is averaged over its observed depth range (cod, 0 to 400 m; eelpout, 0 to 40 m; seabream, 0 to 60 m) except for rock crab, where values have been averaged over longitude in bottom grid cells along the North American margin. The minimum value found within the species distribution (Φcrit) is contoured (black lines; values in table S3). For rock crabs, the contour of Φ includes both monthly maximum (winter) and minimum (summer) values above 100 m; below 100 m, it is cumulatively averaged downward along the slope at each latitude, to approximate the effect of seasonal movement of these crabs up and down the continental shelf. Occurrence data for each species are plotted (blue dots, interpolated to climate grid) for all species except crabs, whose latitudinal range of seasonal and year-round (annual) habitat in shelf and slope waters is indicated by gray arrows (see the supplementary materials).

  • Fig. 4 Change in metabolic index and associated habitat compression from 1971–2000 to 2071–2100.

    (A) Global fractional change in Φ averaged over the upper 200 m, as projected by multiple Earth system model simulations under an 8.5 W/m2 greenhouse gas emissions scenario (Representative Concentration Pathway 8.5), averaged across species. White areas indicate an increase in metabolic index, in all cases attributable to an increase in subsurface O2. The individual contributions of changes in temperature and O2 are shown in fig. S6. (B to E) Projected loss of metabolic habitat (denoted ΔH) for species with calibrated metabolic index values. Metabolic habitat is defined as any grid cell with Φ > Φcrit on a monthly basis. For cod (B), seabream (D), and eelpout (E), habitat changes are mapped as the percentage of change in annual mean thickness of the habitable water column between 1971–2000 and 2171–2100. For Atlantic rock crab (C), the background color map shows relative changes in Φ (%), and contours indicate the migration of Φcrit. For all species, the relative change is an average over all months, so that the loss of habitat includes both vertical compression and a shortening of the habitable season.

Supplementary Materials

  • Climate change tightens a metabolic constraint on marine habitats

    Curtis Deutsch, Aaron Ferrel, Brad Seibel, Hans-Otto Pörtner, Raymond B. Huey

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods
    • Supplementary Text
    • Figs. S1 to S6
    • Tables S1 to S5
    • References

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