Marine life that lives in a tidepool is continually struggling to survive. One of the main limiting factors when living in a tidepool is having enough water to keep the plant or algae alive. Animals that live part of the time exposed to water must have adaptations that allow them to trap water and keep it until they are submerged again. The water is used for breathing and feeding.
The small cracks frequently found in tide pool areas will trap water and keep it longer. The crack in the rock allows water to collect at a lower place but also has reduced surface area that limits evaporation. This increase in the availability of water allows animals the need more water to survive in these cracks. These cracks essentially allow animals found lower in the tidal zones to live higher in the tidal zones as long as they live in a crack.