An underexplored source of climate change information: scientific studies on temperature effects in animals between 1970 and 1990

Keskiviikko 5.6.2024 klo 20.01 - Mikko Nikinmaa

The major problems of climate change and eutrophication caused to aquatic environments are caused by increased temperature and reduction of oxygen in water. Both problems have started getting public attention from 2000 onwards. However, scientists were interested in these questions already in 1960’s and 1970’s, generating a lot of information that could be, and to some extent has been, used in order to understand which aspects of animal life can be adjusted in climate change scenarios.

I am proud to say that I started working on temperature and hypoxia acclimation among the pioneers. For example, my thesis RESPIRATORY ADJUSTMENTS OF RAINBOW TROUT (Salmo gairdneri RICHARDSON) TO CHANGES IN ENVIRONMENTAL TEMPERATURE AND OXYGEN AVAILABILITY was published in 1981, long before such work became fashionable.  Being among the dinosaurs one unfortunately notices that much of the information from 40-50 years ago is not known to many of today’s researchers, leading to unnecessary waste of resources and occasional inventing the wheel again.

Both temperature increase and decreased oxygen levels cause mainly respiratory problems, as with increasing temperature the oxygen consumption of poikilotherms such as fish increases. At high temperatures the efficiency of circulatory system (including heart function) cannot increase adequately to allow for required oxygen consumption. Increased temperature as such also causes a reduction in the dissolved oxygen level, causing the likelihood of hypoxic or even anoxic waters to increase. With reduced oxygen levels, gill function, properties of oxygen-transporting haemoglobin and tissue oxygen consumption become decisive for tolerance. Fishes, which comprise about a half of all vertebrate species, have invaded all aquatic environments from the cold arctic waters to tropical anoxic ponds. Because of this, it is not likely that temperature increase or hypoxia would result in completely fishless aquatic environments in today’s temperate or cold latitudes in the long run. However, individual species may disappear completely, and often the species unable to adapt are today’s commercially important species like cod and salmonids. Furthermore, it takes time for new species to immigrate to areas, where earlier fish species have disappeared, leaving the areas virtually fishless for some time. Surprisingly, tropical areas are in the biggest threat of total fish extinction for two reasons: first, the temperature tolerance of tropical fish is limited: being stenothermal they cannot survive even if temperature increases only a little. Second, no species from an even hotter environment can migrate to the areas left fishless, because such areas do not exist.

It would be useful for today’s researchers to spend more time reading what has been written about the adaptations of fish to changes in temperature and oxygen availability in the past. Also, it would be important to take into account the speed and magnitude of the changes in the natural environment; often the experimental work is carried out in much shorter time scale and much larger environmental changes that are likely to happen in nature. Despite this, the results are usually interpreted as if they gave reliable information of the success of fish in climate change scenarios.