Global warming and plankton

Today, it is undeniable that the earth is warming at a faster rate than it should due to merely natural causes. From the anthropogenic point of view, that is to say purely human, one might think that nothing happens if the temperature rises a couple of degrees. We could even believe that global warming is positive, because it will not be so cold in winter, and in summer a little more heat is not noticed if you are under the air conditioning. Well, nothing could be further away from the truth. The consequences of a rise in average temperature, even if small, can be catastrophic for our current lifestyle. Extreme droughts, heat waves, more frequent and violent stormy episodes, torrential rains, sea-level rise, changes in species distribution, mass deaths of some animals or plants (remember that plants cannot escape), etc. 

Is there a solution? The short answer is no; however, what we can do is to slow down the temperature rise. In the Paris agreement, signed in 2016 by most United Nations countries (unfortunately some of the most contaminating countries refused to sign), the subscribers to the agreement promised to reduce emissions by a certain percentage of CO2, one of the usual suspects among others of global warming. This gesture was intended to dampen the rise in temperature on the planet. It seems, sadly, that only a few countries are doing what was promised and that the temperature continues to rise. Think that only during the first wave of the SARS-Cov2 pandemic in 2020, when the economy, transport, and industry were reduced to unprecedented levels for two months, was the annual emission reduction required in the Paris agreement. We must therefore prepare for the worst. 

It is important to understand, however, that the climate of the earth cannot be understood without the ocean and the other way around. Water stores heat much better than the soil, and releases it more slowly, which generates daily sea breezes, among other climatic phenomena. Temperature gradients between polar regions and the equator are the engine of a planetary water circulation that transports heat (energy) and nutrients around the planet (ocean circulation). This transport, however, may be affected by variations in temperature and atmospheric circulation. For example, the periodic thawing of the Arctic plate in the spring causes the resulting cold water to sink near the east coast of Greenland generating a displacement of water masses that generates the Gulf Stream and helps move the entire global oceanic circulation (the conveyor belt). In the unlikely event that an increase in global temperature significantly reduces the surface area of ​​the northern polar plaque, cold water resulting from thawing in the spring may not be enough to activate the Gulf Stream. The climatic consequences of such a phenomenon are very difficult to predict. We may not get to the extremes of the movie “The day after tomorrow” where the United States freezes in hours, but that there would be major weather changes is quite certain. 

Schematics of the effects of el Niño in the Peruvian upwelling

Climate change could also affect the periodicity and intensity of upwellings, and have important consequences for the world’s major fisheries and overall productivity for the entire marine ecosystem. Warming of the oceans can lead to variations in the direction and intensity of currents and affect the distribution of marine species. As we said in the post “The rhythms of plankton“, phenomena such as El Niño depend directly on climatic conditions and control the outflow of nutrients, and therefore fisheries, from the west coast of South America. At more local scales, the invasion of new species (a process sometimes aided by the transport of organisms in the ballast water of ships or by the exchange of species in aquaculture), the increase in the frequency and amplitude of harmful algal blooms (also related to other anthropogenic impacts), or the expansion of anoxic zones in the seas and oceans are a small sample of the changes that await us in the immediate future. Not all is lost, though. The species have some plasticity and adapt to changes in temperature, especially if they are gradual. In fact, in the laboratory, it has been shown that both algae and copepods (and I suppose also protozoa), after a period (long, about a year) of genetic adaptation to higher temperatures, end up regulating their metabolic rates and offsetting the effects of temperature. If, for example, we expose an alga to a temperature 5 degrees Celsius above the temperature it normally lives, its respiration rate will exceed its photosynthesis rate. This is because respiration is more sensitive to thermal changes than photosynthesis. In science, the rate at which a process, or metabolic rate, responds to temperature is called Q10 (not to be confounded with coenzyme Q10). Each metabolic activity of each species is associated with a Q10, which is defined as the increase in that rate as the temperature rises by 10ºC. Thus, the Q10 of respiration is higher than that of photosynthesis. However, after many generations in the new temperature conditions, the two rates are returning to their original balance. Then you will ask me why we care so much? The problem is that during this adaptation process, which can last for months and even years, the species in question is in metabolic imbalance and it is not competitive with other better-adapted species. A clear example is a displacement of the copepod Calanus finmarchicus (cold-water) by the Calanus helgolandicus (warmer water) in the North Sea. The first species is very prolific and nutritious, and thanks to it all the cod fishery in the area is maintained. It seems that C. helgolandicusdoes not reproduce so fast and that it is not enough to sustain cod populations, so the collapse of these important fisheries may be a reality soon. The question also reminds regarding the fate of species adapted to high Arctic conditions, such as polar bears and also some copepods, e.g., Calanus hyperboreus.

Calanus hyperboreus, a high Arctic copepod that may disappear after global warming

We also find a similar case in the Mediterranean. Whether it is because of the change of species in plankton or its poorer nutritional quality due to the temperature, it is being seen that there are fewer and fewer sardines and anchovies in the Mediterranean and that these have less nutritious fats. Especially the sardine is quite endangered on our shores (NW Mediterranean). Obviously, to this process we must add the impact of overfishing, making it increasingly difficult for this species to recover if we do nothing to prevent its collapse. 

We find our last example in the tropics, where the inhabiting species are already at the limit of their thermal capacities. Will the animals and plants of these ecosystems survive a temperature rise like the one expected at the end of the century? It’s hard to predict, but surely many will be lost in the way. 

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