Temperature, metabolic rates, and the future of your lineage

We all know that during spring, when the light and temperature start to rise, life blooms everywhere. The increase in temperature during this season activates most organisms, especially ectotherms, also known as cold-blooded animals. In these animals, the relationship between metabolism and temperature is direct, usually following an exponential function. Examples of ectotherms are fish, reptiles, insects, and, of course, zooplankton. In endotherms, such as mammals and birds, the relationship is more complex and dependent on multiple factors.

For an ectotherm, as the temperature increases, metabolic processes speed up. To quantify the effect of temperature on different metabolic rates, scientists usually use the Q10 coefficient (which has nothing to do with the coenzyme of the same name). The Q10 of a process is defined as the increase it undergoes when the temperature increases by ten degrees Celsius. Thus, a Q10 of 2 means that the speed of a metabolic process doubles when the temperature rises by 10°C. Obviously, not all rates respond equally to temperature, and sudden increases can lead to imbalances in different functions. Usually, however, if the increase is gradual and not too exaggerated, with sufficient time, the different physiological rates will balance out. This process is called thermal acclimation. When this response to temperature includes changes in the genome and is transmitted from generation to generation, we speak of thermal adaptation.

Before equilibrium is reached, however, the organism undergoes a series of uncouplings in its metabolic processes that can lead to a decrease in its survival capacity and even death. Therefore, when we talk about an organism’s resistance to temperature, we usually define its thermal window. These values ​​are defined for each species adapted to its environment. If the same species inhabits both tropical and cold zones, it is usual for the values ​​of individuals in tropical zones to be displaced to the right (toward higher values ​​at higher temperatures). Some species that have a very wide range of thermal amplitude, while others are restricted to a very narrow range of temperatures. In plankton, we have everything. Keep in mind that there is plankton in both polar and tropical regions, or hydrothermal vents. We even find plankton in tide pools that can fluctuate by tens of degrees Celsius in 24 hours. No matter how harsh the living conditions are, there will always be a species that finds its niche and survives.

Although species are usually adapted to the thermal conditions in which they live, they have some plasticity and can end up invading new habitats, and over time, colonizing and adapting completely to them. However, in nature, competition is fierce, and if the adaptive process is slow, there is always the possibility that another, already adapted, species will take its place. An example of this is the migration that many planktonic species are undergoing towards the north, to follow temperatures closer to those they were accustomed to. Thus, Calanus helgolandicus is replacing Calanus finmarchicus in the North Atlantic (which has led to a gradual collapse in cod fisheries), and Calanus hyperboreus (native to the Arctic Ocean) is increasingly found farther north. The problem is, as always, at the extremes. Species from very cold regions will inevitably disappear if the temperature continues to rise. Species from very warm climates will have to face extreme situations and, if they cannot adjust their metabolism in time, they may end up disappearing as well. One concerning issue in this regard is the heatwaves, which are becoming more and more frequent and can put many organisms in serious difficulties in just a few days.

So, what does the future hold? Concerning plankton, I am sure we will experience changes in the coming years. In fact, we are already observing some, as we mentioned earlier. Some authors point to a massive dominance of jellyfish and other gelatinous plankton in most oceans. Others predict a significant decrease in algae production, with its consequences for the entire food web. It is also important to consider that organisms from warmer climates are usually smaller than those from colder climates. This results in changes in the structure of food webs and, ultimately, the entire marine ecosystem. A few degrees of average water temperature can stop upwelling of cold nutrient-rich waters, change currents (affecting the climate of the entire planet), and cause massive migrations in marine organisms (well, those that can escape, which are not all). Practically, all scenarios point to a reduction in fish populations.

It is true, however, that if we do the work and stop CO2 emissions as much as possible, we will not see results until maybe 50 or 60 years from now. Moreover, without significant changes in our current lifestyle, it is impossible to talk about a sufficient reduction in emissions. Consequently, when results on the ecosystems begin to be seen, many species will have likely been lost along the way, and the sea we know will be quite different. Then, should we do something?


It is clear that the conservation of the ecosystem has never been a strong incentive for any government, probably because of a lack of education and awareness of the importance of nature. Nature is not just what you see in the small forests you enjoy on weekends, or the four little fishes you see on the beach. Nature is more complex than we think and is interconnected within the entire planet. If one link fails, others may collapse. Life will go on, even if the temperature rises by 10°C, but under conditions that may not be favorable for us, humans, and for many other species as important as us. We believe we are above other species because we are “smart”. Intelligence is, however, something defined and measured by human standards. Who is smarter, an architect that designs a 10-floor house or an ant that can build a huge anthill, proportionally more complex and larger than the previous house? Actually, ants have been on Earth near 100 million years, whereas we, humans, are here for only 200-300 thousand years. 

Coming back to climate change, the sad reality is that if effective action is taken in the end, it will not be to conserve nature, but because hunger, desperation, and the collapse of entire human populations will force extreme measures. Which politician will sacrifice today’s electoral votes by taking restrictive and annoying measures that may not have visible repercussions until he or she is dead? Unfortunately, very few, if any. However, it is crucial that we all understand that doing everything possible to conserve nature today is the only solution to ensure the survival of our children and grandchildren. If you don’t consider relevant taking energy-saving measures, reducing emissions, etc. for four species that you have been told may disappear, do it for your descendants. Think that they cannot do anything right now, but they will inherit our legacy. Or perhaps the best thing would be to do nothing and wait for us to be caught in a wave of mass extinction? It is up to you.

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