Research Article

Thermal bottlenecks in the life cycle define climate vulnerability of fish

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Science  03 Jul 2020:
Vol. 369, Issue 6499, pp. 65-70
DOI: 10.1126/science.aaz3658

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Some cope better than others

Increasingly, research is revealing how organisms may, or may not, adapt to a changing climate. Understanding the limitations placed by a species's physiology can help to determine whether it has an immediate potential to deal with rapid change. Many studies have looked at physiological tolerance to climate change in fishes, with results indicating a range of responses. Dahlke et al. conducted a meta-analysis to explore how life stage may influence a species's ability to tolerate temperature change (see the Perspective by Sunday). They found that embryos and breeding adult fishes are much more susceptible to temperature change than those in other life stages and that this factor must therefore be considered in evaluations of susceptibility.

Science, this issue p. 65; see also p. 35

Abstract

Species’ vulnerability to climate change depends on the most temperature-sensitive life stages, but for major animal groups such as fish, life cycle bottlenecks are often not clearly defined. We used observational, experimental, and phylogenetic data to assess stage-specific thermal tolerance metrics for 694 marine and freshwater fish species from all climate zones. Our analysis shows that spawning adults and embryos consistently have narrower tolerance ranges than larvae and nonreproductive adults and are most vulnerable to climate warming. The sequence of stage-specific thermal tolerance corresponds with the oxygen-limitation hypothesis, suggesting a mechanistic link between ontogenetic changes in cardiorespiratory (aerobic) capacity and tolerance to temperature extremes. A logarithmic inverse correlation between the temperature dependence of physiological rates (development and oxygen consumption) and thermal tolerance range is proposed to reflect a fundamental, energetic trade-off in thermal adaptation. Scenario-based climate projections considering the most critical life stages (spawners and embryos) clearly identify the temperature requirements for reproduction as a critical bottleneck in the life cycle of fish. By 2100, depending on the Shared Socioeconomic Pathway (SSP) scenario followed, the percentages of species potentially affected by water temperatures exceeding their tolerance limit for reproduction range from ~10% (SSP 1–1.9) to ~60% (SSP 5–8.5). Efforts to meet ambitious climate targets (SSP 1–1.9) could therefore benefit many fish species and people who depend on healthy fish stocks.

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