What is the means of locomotion for spirogyra?
To my knowledge, Spirogyra simple floats to the surface probably due to the oxygen it produces during photosynthesis. There are not motile stages of this alga. Another genus, Mougeotia, can rotate its single, flat chloroplast to get maximum exposure to the sun or turn it on edge to reduce exposure. Here is a link describing Spirogyra: http://www.microscopy-uk.org.