Temperature increases faster than fish can adapt

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Tiistai 29.12.2020 klo 16:28 - Mikko Nikinmaa


A temperature increase will affect fish populations everywhere. Depending on the species, the depth of the aquatic body and its accessibility the effects can be drastic – the most extreme outcome being  the total disappearance of the fish from the habitat. Because of this, the research on temperature biology of fish has become an important field of study in climate change research. The importance of fish studies is strengthened, as they can be an primary source of animal protein in food.

Fish can be either stenothermal or eurythermal. The definitions indicate the phenotypic plasticity of species with regard to temperature. Stenothermal species tolerate only small temperature changes, whereas eurythermal species can live in wide temperature range. It should be noted that most of the preferred fisheries species have narrow genotypic temperature tolerance. If they live in environments with different temperatures, their genotypes are different, each still having narrow temperature tolerance so that the cold-temperature genotype would not be able to tolerate the temperatures that the warm-temperature genotype lives in and vise versa. Although a temperature increase may actually increase the amount of fish flesh produced per unit time, the species accounting for the increased productivity are not preferred catch or food.

The roles of phenotypic plasticity and the speed of heritable genetic adaptation to temperature changes has been surprisingly little studied. 

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Further, it is almost completely unknown, if the temperature tolerance is affected by environmental contaminants. One important recent study with zebrafish (Morgan et al. PNAS 2020: https://www.pnas.org/cgi/doi/10.1073/pnas.2011419117) suggests that the genetic adaptation to increased temperature is not fast enough to keep pace with the temperature increase that is currently occurring. It also appears that the plasticity of tolerated temperatures decreases, when the population adapts to increased maximal temperature.

So, this is bad news throughout. The fish that we like to eat are stenothermal. The eurythermal species could substitute for them, but even they have problems in genetic adaptation. Furthermore, it seems that tolerance to reduced temperature evolves faster than that to increased temperature. All of these points make the case for markedly slowing down and stopping the current temperature increase stronger. If we want to eat fish, climate change must be stopped.

 

Avainsanat: climate change, fisheries, phenotypic plasticity, genetic adaptation


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