I have just studied the difference between fish in warm waters and cold waters. It is clear that the warmer the water is, the more colorful and diverse the fish seems to be, whether because of the actual water temperatures or the plants/coral that can be present in warmer waters. I wonder what differences we will see in fish around the globe if waters start to warm with the trends of global warming.
Hey ryan2238,
That’s an interesting question. Your observation about the correlation between water temperature and fish diversity was very insightful. I fear that if waters become too warm however it will destroy the corals and thus the fish diversity, as you mentioned.
In Colorado we’re starting to see some issues with the water being too warm for the trout in recent years.
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Short answer: it will affect most of them badly. The fish diversity that you mentioned in the tropics is a delicate balance-- if it grows too warm, coral reefs will die in large numbers due to expelling of algae inside the corals that help it to survive. Rainforests would not fare well under too-warm weather either: the Amazon, one of the hotbeds of fish diversity, will collapse if the temperature increases too much. It’s true that as you go towards the tropics, the fish diversity increases, but this is only to a very limited amount and will be very detrimental if it continues warming.
Oxygen gas dissolved in the water is another huge problem. Warmer water contains less dissolved oxygen than cold water (this is one reason trout love cold water). Coldwater fish will see declines in numbers and range as water continues to warm, moving northward if possible and eventually dying out if not.
In Minnesota, tullibee (Coregonus artedi) are a whitefish that form an important link in the food web for many larger species. In this species, oxygen and temperature are both important requirements. They need the deep, cold water for its high oxygen content, and can’t survive too close to the surface in the lethally warm water. However, the deep water they need can also run out of oxygen if the lake doesn’t mix very well. As surface waters warm even further due to climate change, the tullibee are squeezed between warmer surface waters and oxygen-depleted deep waters. The DNR is currently trying to figure out which lakes will be refuges for tullibee under climate change: https://www.dnr.state.mn.us/mcvmagazine/issues/2016/may-jun/refuge-lakes.html
There will be some fish species, many of them invasive, that will do quite well under climate change. Rarer species, especially those with strict temperature and oxygen requirements, will likely not survive, or will be forced further northward in range. Range shifting will likely affect ocean fishes the most; many freshwater fishes, living in restricted areas such as lakes, will have nowhere to go. Endemic species that only live in a specific area, and/or endangered species that are already decreasing in population, will struggle the worst.
Additionally, the fisheries scientist Daniel Pauly has found that climate change will likely cause fish to shrink in size due to oxygen constraints: https://onlinelibrary.wiley.com/doi/full/10.1111/gcb.13831
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The other factor, for freshwater fish, is the food supply. If the water becomes too warm, or even stagnant (drought conditions), aquatic, or semi-aquatic insect species will not lay their eggs. This will affect small fish who feed on semi-aquatic larva and larger fish who feed on adult insects that fly near the surface.
https://www.tu.org/magazine/conservation/how-are-aquatic-insects-coping-with-climate-change/
Relevant for those choosing to reply: https://forum.inaturalist.org/t/school-homework-questions-on-the-forum/34848/44
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Interesting,
was this is salt water or fresh water. @dinofish99 comments on this about colder water containing more oxygen.
This is a consideration in Himalayan Rivers and their damming, silting and eventually also getting warmer.
This is one of the best answers I have seen on the forums - well written and with is clearly a lot of thought and experience.
Thank you
ram
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