Fish are far more vulnerable to global warming than previously thought


Spawning fish and embryos are far more vulnerable to Earth’s warming waters than fish in other life stages, according to a new study, which uniquely relates fish physiological tolerance to temperature across the lifecycles of nearly 700 fish species.

The results reveal a critical bottleneck in the lifecycle of fish and suggest that many ecologically and economically important fish species are threatened by climate warming more than studies based on adult fish thermal tolerance alone have shown.

Understanding an organism’s physiological limits to temperature changes can provide a window into how some species will likely respond to Earth’s changing climate. However, thermal tolerances often vary throughout an organism’s life.

Thus, the vulnerability of a species to climate change hinges on its most temperature-sensitive life stages. But due to a lack of experimental data, large-scale climate risk assessments often simplify or fail to account for the effects of these thermal bottlenecks across the entire lifecycle of many major animal groups, including fish.

Whether our current climate mitigation targets are sufficient enough to sustain healthy fish populations remains poorly understood. Flemming Dahlke and colleagues compiled published observational and experimental data to assess the life stage-specific thermal tolerances for 694 marine and freshwater fish from waters worldwide.

Their large-scale meta-analysis found that spawning adults and embryos were much more susceptible to temperature changes than other life stages across fish species.

Dahlke et al.’s findings suggest that, with unchecked warming, a significant proportion of the fish species they evaluated will not be able to exist in the current geographic range of their most vulnerable life stages within a century – a finding that stands in stark contrast when compared to the relatively low percentage of species estimated using only the thermal tolerance of adults.

“The minute thermal safety margins of spawning fish and embryos in the tropics suggest that there are limited fish species on Earth that can tolerate warmer or less oxygenated habitats.

Intensified efforts to stabilize global warming are warranted more than ever,” writes Jennifer Sunday in a related Perspective.

Source: AAAS

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