Why is Temperature Important?

Water temperature is important to plants and animals that live in the water in two ways: by affecting the temperature of the creature itself, and by its affect on the water chemistry.

Let's think first about the direct effect of temperature on creatures. Animals and plants are like machines or motors. Just like a car has to warm up before it performs optimally, your body has to be a certain temperature for it to perform optimally. The difference between your human body and the body of most creatures living in water is that your can make your own heat and cool yourself down. A fish cannot regulate its temperature like a human can.

How does temperature affect a creature's biology? Well, heat speeds up molecules. When molecules are moving faster, things happen faster, like the burning of oxygen by muscles and the consumption of food molecules by cells. This means that when a creature is warmer, it can move faster. But only to a certain degree. Just like when you get a fever you are sick and don't feel well, if any creature gets too warm, it also becomes sick. Water temperatures do not have to boil to kill a creature living in it. In the same way, it doesn't have to freeze solid to kill a creature living in it.

Why is it that water creatures generally don't have the ability to make their own heat and most land creatures do have this ability? Well, water temperatures typically don't change quickly. Air temperatures do - just think about the difference between the air temperature outside at night and it the early afternoon. If you had a preferred temperature range of even 10 degrees, you would have to travel a long distance north and south on a daily basis to stay in an area that had your preferred temperature. For example, if you preferred a temperature of 50 degrees (like an Atlantic Salmon does), you would have to be in a place with a temperature of 50 degrees in the day, and a place with the same temperature at night. This would mean that, in January, you would have to live in Norfolk, Virginia during the day and 750 miles south in Orlando, Florida at night!

Experiments

Do you think the same variations occur in water in a day? Can you design an experiment that would help you to answer this question?

So what about the affect of temperature on water chemistry? The primary way that temperature affects water chemistry is through its effect on how much oxygen can dissolve in water. The colder the water is, the more oxygen can dissolve into it.

Why is Water Temperature Important? | What is Dissolved Oxygen (DO)? | What is pH?

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