Oceans can be very difficult to live in. It is important to marine organisms to adapt to changes in their environments. They have to deal with salinity, water movement and many more problems.
Salinity or the level of salt in seawater various through out the world. Saltiness of oceans can level from 3% to 4%, or it can increase to40%. Living things in oceans are adapt to maintain the amount of salt in their bodies at a constant level to keep their metabolisms working properly. All kind of fish or sea creatures must learn how to regulate salt that they intake in order to survive. for example, fish eliminate the salt through their gills, seabirds eliminate the salt via the nasal or sneeze out by the birds. Even though a lot of them take great care to maintain the proper balance of water and salt within their bodies, many marines organisms are still affected by changes in the level of salinity.
Some said level salinity affects the whole ecosystem.
Movement of water come in forms of waves, tides and currents. Waves caused by wind acting on the surface of the sea can be very destructive; however, they also cleanse organisms and help to increase oxygen availability.
some organisms are able to resist drying out during low tide that caused from forces of the moon and the sun interacting.
Currents can move food resources and nutrients from the coastline farther out into the ocean. The species in the area might migrate to somewhere else. Different characteristics in the population may help some individuals win the competition to survive and reproduce. They also rely on currents to transport their eggs and larvae.
Many marine invertebrates and plants have the ability to cling on to rocks or other substrates so they are not washed away.