Impact of deoxygenation and warming on global marine species in the 21st century
Abstract. Ocean temperature and dissolved oxygen shape marine habitats in interplay with species’ physiological characteristics. Therefore, the observed and projected warming and deoxygenation in the 21st century of the world’s oceans may strongly affect species’ habitats. Here, we implement an extended version of the Aerobic Growth Index (AGI), which quantifies whether a viable population of a species can be sustained in a particular location. We assess the impact of projected deoxygenation and warming on the contemporary habitat of 47 representative marine species covering the epipelagic, mesopelagic/bathypelagic, and demersal realms. AGI is calculated for these species for the historical period and into the 21st century using bias-corrected environmental data from six comprehensive Earth System Models. While habitat viability decreases nearly everywhere with global warming, impact of this decrease is strongly species-dependent. Most species lose less than 5 % of their contemporary habitat volume over the 21st century even at 3 °C of global warming relative to preindustrial, although some individual species are projected to incur losses 2–3 times greater than that. We find that the contemporary spatiotemporal variability of O2 and temperature (and hence AGI) provides a quantifiable measure of a species’ vulnerability to change. Species’ vulnerability is the most important indicator for large (>5 %) potential habitat losses – not relative or absolute changes in habitat viability (i.e., AGIrel or ΔAGI), temperature or O2. Loss of contemporary habitat is for most epipelagic species driven by warming of ocean water and is therefore expanded with increased levels of global warming. In the mesopelagic/bathypelagic and demersal realms habitat loss is also affected by pO2 decrease for some species. Our analysis is constrained by the uncertainties involved in species-specific critical thresholds, which we quantify, by data limitations on 3D species distributions as well as by high uncertainty in model O2 projections in equatorial regions. Focus on these topics in future research will strengthen our confidence in assessing climate-change driven losses of contemporary habitat across the global oceans.
Anne L. Morée et al.
Anne L. Morée et al.
Anne L. Morée et al.
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I find this research using AGI to evaluate the effect of long-term warming and deoxygenation on contemporary habitat useful. It uses the AGI an index that represents the o2 supply to demand ratio for maintenance activity. It is handy as it requires few data somewhat easily accessible. The authors show how this index can be used to assess species vulnerability to environmental changes using only species-specific biogeographic data of 47 species. An interesting point, is that the authors show that tendencies and mean changes alone (warming, deoxygenation and mean changes in AGI) do not suffice to predict species vulnerability within their present habitat, but rather the quantity of habitat volume close to AGIcrit as show by the CDF of the AGIs. They also show the high inter-species variability in terms habitat preferences and critical thresholds greatly influence the changes in viable habitat. Indeed the mean changes do not reflect species-specific changes in habitat viability. It is also very interesting to present the results by degrees of global warming.
A few improvements could be made to facilitate the reading of the results (see specific comments):
Questions regarding the AGI need to be discussed.
In general, a more systematic presentation of results is need to ease the reading and further support the demonstration. In particular, a more systematic presentation of the figure (to facilitate the reading, so the reader doesn’t have to go back and forth in the main text. Also more consistency when choosing the warming level, scenario, etc. when presenting the figure in the main text. If you start presenting results for the levels of warming (Fig. 3 and 4) , please do so for the rest of the manuscript. Even with figures in the supplemental.
Line 17-20: not clear, please rephrase.
Methods and data
Line 139 : which data ? O2, T, salinity ?
Line 156 : please detail a bit more. You mean global mean SST reached by 2100 ?
Line 174 : « habitat viability » suggests you refer to where AGI>AGIcrit, but you refer to AGIrel. It can be confusing. AGIrel would indicate « potential viable habitat » ?
Also, « AGIrel reduction » is incorrect. AGI is either negative or positive reflecting a decrease or increase in AGI between t0 and t1. Please rephrase.
Line 180-191 : A figure to show this would be better.
Line 201 : «A relative reduction in habitat viability […] we expect a reduction in habitat viability ». Please rephrase. See comment above (line 174) relative to « habitat viability ».
Line 207 : Please detail somewhere how the contribution of po2 and T to AGI and AGIrel is calculated.
Line 209 – 216 : Not clear what the difference is between the calculation method of the contribution of po2 and T is between line 208-210 and 212-216. For instance, « the AGIrel due to T is -xx % for the epipelagic» (line 209) and « an average 87 % of AGIrel is driven by… warming » (line 212). What is the difference be the two ? please detail calculation.
Figure 2 : please provide the same map as Fig. 2 (and C2) for 1.5 °C and 3°C to be consistent with the remainder of the paper.
Fig C3 caption : « AGIcrit as the minimum in-habitat AGI value, the 5th percentile, the 10th percentile, the 15th percentile and the 20 th percentile ». Word missing ?
Line 242-246 : in the text, changes in viable habitat are expressed in terms of habitat loss, but in the referenced figure (Fig. 3) changes in viable habitat are expressed in terms of remaining habitat. Please be consistent.
Line 256: please define “absolute loss”.
Figure 3 : not clear how the different models/scenarios are represented or used for the calculation of changes in viability.
Fig. 5 : for which degree of warming ? Scenario ? Period of AGI ? Please precise in the figure caption. Also C4 is presented for a 3°C global warming. For the purpose of the demonstration, I understand that the chosen level is not determining, but consistency between figs within the same result section would be better to support the demonstration. Also distribution of AGI +/.
Line 316: “The correspondent linear equation taken across all depth realms is 𝑣𝑜𝑙𝑢𝑚𝑒 𝑙𝑜𝑠𝑠 (%) = 7.31 ∗ vulnerability − 0.10.” not useful.
Line 322: ΔAGI is AGI(t1) – AGI(t0) ? please define.
Fig 6 : please provide same for 1.5 and 3 °C. Also, why only SSP5-8.5 ?
Line 336-337 : any hypothesis regarding those two species ?
Line 43 : ref Bopp et al. 2013 is about CMIP5
Line 139 : please specify « all data »
Line 201 : « reduction in AGIrel », see comment above.
Line 204: « AGIrel reduction » see comment above.
Line 229 : « decrease in AGIrel », see comment above. See also line 231, 239
Line 240 : habitat volume is where AGI>AGIcrit ? Please precise.
Line 291-296 : Please precise which period of the AGI is used for the PDF.
Line 302 : Only → only
Line 303 : In → An
Line 306 : indicates → remove s