|MadSci Network: Cell Biology|
I am not an aquatic botanist, but I suspect that if you we're transfer a saltwater plant such as kelp or algae, these organisms will be very unhappy. The reason for this is because these plant have lived and evolved in saltwater for millions of years adapting their structure and internal cellular processes to a life bathed in salt. When a saltwater plant is moved into freshwater, the plant is not used to these conditions and may not be equipped to trnsport the low amounts of salts in the water which are essential for the plant cells to live. The other huge probelem is that the "osmotic pressure" in the two water conditions is very different and these plants have developed a system of dealing with one of these conditions. Since saltwater plants are in a salt solution all the time, my guess is that their internal cellular salt concentrations are high compared to freshwater. The freshwater will want to equilibrate with the salt in the plant's cells and rush into the cells, causing them to swell and perhaps burst. This also changes the salt concentration in the plant's cells (bad). This sudden change in internal cellular salt concentration and cell volume in addtion to the plant not being equipped with the cellular machinery to live in freshwater is most likely what contributes to the plant's death. Hope this helps you.
Try the links in the MadSci Library for more information on Cell Biology.