Over the decades local and global ice ages have lowered sea levels. As a result, there is often a decline in marine diversity due to - factors like salinity and temperature of water.
Salinity is the measure of the amount of salt present in any ocean or sea water. High salinity makes it impossible for marine life to survive. Similarly, the temperature of water should be maintained according to every organism's need. Like- Deep sea has a low temperature as compared to shallow sea, due to sunlight. So, deep sea creatures cannot survive in shallow water temperature and shallow water creatures cannot survive in deep sea.