Intertidal organisms must adapt to a variety of conditions that are very threatening to life where land meets sea. The intertidal zone is a very harsh environment for three reasons, the violence of wave action, rapidly changing environmental conditions, and changes in salinity and other water elements.
Tidal zones have rapid changes in oxygen and water levels, light and salinity balances and levels of dissolved nutrients.
Some species, like anemones and algae, ride the tides to new locations where seeds, spores, or larvae are able to establish and start new life. This it more likely that a species can continue in a new location. Other species have strong natural glues, suction cups or root systems that allow them to attach and hold onto rocky surfaces. Some intertidal life forms can adapt to rapidly changing salinity, which allows them to move easily between more or less saline water. Finally, some intertidal species can survive for a time out of the water or can live without constant submersion. Some species can thrive in tiny pools that come and go with the tides.
The Supra Littoral, Mid Littoral, Low Littoral, and Tidal Pool zones each harbor life forms that have adapted to different tidal environments. Rocky zones and zones that go through drastic changes in temperatures present extra challenges.
The Supra Littoral, or highest intertidal zone harbors the biggest threats to intertidal organisms and is the most sparsely populated zone. Rocky Supra Littoral zones are the most hazardous when compared to less rocky zones. Rocky zones go through violent wave action, rapid losses of water and rapid changes in light, temperature and salinity. Hardy organisms like well armored crabs and snails can survive there, Other organisms include lichens like black lichen, plus coralline algae, some small green algae and small, herbivorous snails and limpets. Most of these species have strong glues and ways of attaching or burrowing that allow them to hang on for life.
The Mid Littoral or mid level tidal zone harbors more life, mainly because there are longer periods when the life forms are submerged. Here, the battle for life goes on between mussels and starfish, which attach with glue or burrowing. Mussels would take over the zone if the starfish were not the most voracious predators in the zone. There are also snails, limpets, chitons, barnacles, seaweeds, small anemones and some crabs, each of which is adapted to latching on to the rocks or burrowing under the soil. Again, changes in light, oxygen levels, turbulence and the amount of dissolved nutrients are important factors, so these life forms can thrive under many conditions.
The Low Littoral tidal zone is the most lively, as the submergence time is constant, the dissolved nutrients are at the highest levels, and there is more likely to be bottom soil for burrowing and grazing. Macro algae thrives in this zone. These are algae that are large enough to be visible to the naked eye. Larger anemones, starfish, sponges, flat worms, crabs and mollusks called nudibranchs thrive in this zone.
Tide pools are suitable for the most adaptable species that can tolerate big changes in water depth, salinity, dissolved nutrients, oxygen, light, temperature and all of the other variables that are needed or life. Tidal pools are tiny and ever changing "micro-habitats" harbor Anemones, sea urchins, barnacles, dog whelk (snails), and sculpins that have adapted so that they can tolerate many changing conditions. Most of these species have excellent and multiple abilities to cling to rocks, burrow for safety or swim.