Hot pools and thermal springs are present here and there all over the world and because of their alleged rejuvenating, health-giving, soothing qualities have generated interest amongst human populations since ancient times. The balmy hot water loosens muscles, increases peripheral blood circulation, relaxes the mind and, in combination with dissolved salts and trace minerals, may attack and remove skin parasites.
Although a whole host of heat-loving bacteria and archae-bacteria are now known to make their home in thermal waters, multicellular organisms are much rarer in such environments. Looking at the macrofauna (the animals one can see with the naked eye) we find principally some aquatic beetle and bug species, the larvae of gnats, crane- and other flies and hardy mussel shrimps. A few heat-loving snails, segmented and round worms, as well as slimy green algae have also been reported from water with temperatures of at least plus 40°C.
The champions amongst the fishes are a group of Cyprinodonts, found in sometimes tiny hot water reservoirs and streams of America’s Death Valley. Known popularly as desert pupfish, they are actually killifish that have been reported to be able to tolerate temperatures of up to 44°C, darting in and out of the hottest spots (by the way, what was the temperature again that bathwater for babies was not meant to exceed?). One of the problems of hot water is its lower oxygen content when compared with colder water.
Some insects can overcome this by breathing atmospheric air; others like damselfly larvae possess anal gills or like chironomid larvae haemoglobin as well. Another, and lethal, problem is also heat stupor. Excessive heat affects lipids of the cell membranes, which when leaky can no longer maintain the ionic balance between in and outside of the cell, and heat can inactivate vital enzymes and lead to protein coagulation. That in spite of these hazards a small group of animals have found hot springs and thermal pools nonetheless to be a suitable habitat, may be because of a lack of competition in them or, in the case of the desert pupfish, simply lack of choice.
I remember having read somewhere that in the early 70s of the last century the population of adult Cyprinodon diabolis, a species of pupfish confined to a single tiny Death Valley pool known as Devil’s Hole, amounted to no more than about 50 individuals, but counts from the year 2006 had shown that this population of perhaps the rarest species of fish on Earth had dwindled to just adult 38 fish, still darting around in the shallow, steaming brew that’s been their home for thousands of years before. The question is, how many more years will they be around? A small and economically totally unimportant fish, a survivor. It would be a loss, if this little devil were to join the ever increasing list of extinct species, wouldn’t it?
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2016.
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