
Originally Posted by
PhDemon
Not a biologist but as a chemist my thoughts are:
It is probably due to either 1) oxygen production rate -- the algae produce oxygen quicker than it can dissolve and so it saturates the water locally around the leaf and so any further oxygen cannot dissolve near the plant, in this scenario you get visible bubbles which will disappear as they move away from the plant into oxygen poor areas where the O2 can dissolve or 2) the water already being saturated with oxygen so none of the produced oxygen dissolves in the water and stays in bubbles of gas, in this scenario the O2 bubbles would stick around until they reached the surface and release the O2 to the surroundings.
If the water is not saturated with O2 or the O2 production rate is low the O2 will dissolve as soon as it comes out of the plant and you will see no bubbles (this is usually the case I'm guessing which is why you don't "normally" see bubbles).