Featured image: Mean annual temperature reported for terrestrial and marine land cover. (Source: permission from Malin Pinsky; available from the GitHub repository archived at Zenodo DIO:10.5281/zenodo.2576197)
Reference: Pinsky, M., Eikeset, A., Mccauley, D., Payne, J., & Sunday, J. (2019). Greater vulnerability to warming of marine versus terrestrial ectotherms. Nature, 569 (7754), 108-111. DOI: http://dx.doi.org/10.1038/s41586-019-1132-4
A new study by Pinsky et al. (2019) has found that our current climate crisis is causing a greater “hit” to marine species than terrestrial species.
History repeats itself
Our planet is currently in its sixth mass extinction- a massive and accelerated die out of species. This extinction event has been brought about by multiple factors such as habitat destruction, overexploitation, pollution, invasion by non-native species and ultimately, climate change.
Earth has undergone five major extinctions prior to this one, including the greatest loss to life, the Permian-Triassic mass extinction around 252 million years ago, when 95% of marine and 70% of terrestrial vertebrate species went extinct. What is striking about the Permian-Triassic mass extinction and our current extinction event is that it seems marine species are “hit” harder than terrestrial species.
A new study by Pinsky et al. (2019) has found that our current climate crisis is causing a greater “hit” to marine species than terrestrial species. The only difference between the Permian-Triassic extinction and the one now is that we, humans, are here. We can do something about this climate crisis and that first step begins the determination of where to place conservation efforts.
Critical research efforts
Scientists have debated which habitats and regions of the globe are likely to be most affected by human-caused climate change. This knowledge is critical for guiding conservation and management.
A study by Pinsky et al. (2019) is the first to comprehensively compare marine and terrestrial species’ sensitivity to climate warming. The authors found that marine species have a smaller thermal safety margin—a metric for comparing warming tolerance—which is driving more frequent population extirpation in the ocean. Pinsky and co-authors found that extirpations (i.e., local extinctions) at the warm edges of species’ ranges were twice as common in the ocean (56%) as on land (27%).
To get at this conclusion the international team of researchers searched through previously published literature to assemble data on the highest temperatures that 88 marine and 299 terrestrial species can tolerate. The species included in the study are all ectotherms, cold-blooded species whose body temperatures are dependent on their surroundings. Next, the researchers used various computer modeling approaches to estimate the body temperatures reached by each species during the hottest hours of the year. The authors considered animals’ ability to escape from the heat in underground burrows, patches of shade, or deeper water. With this information, the authors calculate the thermal safety margin as the difference between the acute upper thermal limit of a species and the extreme hot hourly body temperature of the species in the coolest microhabitat that is available.
The researchers found that marine species have narrower thermal safety margins than terrestrial species – on average, the thermal safety margin for a marine ectotherm is about 80% as wide as that of a terrestrial one (see Figure 1). On land, thermal safety margins are narrowest around the edges of the tropics. In the oceans, thermal safety margins are narrowest around the equator. Marine species are more likely to live near their upper thermal limit than land-based species in part because terrestrial species have more access to thermal refugia such as shade or underground dens. For marine species it isn’t that simple to find shade, it does get colder the deeper you go but not all marine life is equipped to dive.
What does this mean for future species?
Conservation resources are scarce, and it is always difficult to decide where to put resources to help the most vulnerable species. Research findings by Pinsky and co-authors suggest that new conservation efforts will be needed if the oceans are going to continue to support marine life, human wellbeing, nutrition, and economic activity. My previous article (here) reinforces the need for protected areas to consider the dynamic nature of species movement, especially with climate warming altering species’ thermal safety margins. Intact land environments, with trees for shade and accessible water for evaporative cooling, will be crucial for the persistence of terrestrial species in a warming world. Greater dispersal and colonization abilities in the ocean may help some marine species to avoid global extinction, but only if habitat is available for colonization.