Tide pool animals like all animals need three basic elements to survive. Food, water and shelter are the primary factors that will determine where a plant or animal can live. Tide pool animals are animals that live primarily in the ocean that have adapted to live exposed to air during parts of the day. The ocean provides food and water to most all tide pool animals. The more time an animal is exposed to air, the less food and water is available and the harder it is for the animal to thrive.
The limitation of food and water the higher up in the tidal area is the primary reason animals are smaller in higher tidal zones. Plants and animals that live in the upper tide zones have adaptations that allow them to live in these harsh conditions where there is limited time for feeding. Barnacles are a good example of an animal that can thrive where few other animals can live. They have specific adaptations that allow them to manage the limitations related to food, water and protection.
The upper tidal zone or splash zone where these small barnacles live is covered by water only a few hours each day. This means very little ocean borne food is available. Larger animals that require more food simply can’t survive. The small acorn barnacle is only about ¼ inch when adult. This smaller size allows the animal to survive even with this extremely limed food supply.
Another factor that barnacles must manage is desiccation or drying out. Barnacles have a hard outer shell and mouth plates that allows them to close very tightly. They can close tight enough to keep the sea water in for hours at a time.
The barnacle’s hard outer shell also has another function. That is protection from predation. Barnacles live exposed to air more than they are exposed to water. This means that they can be eaten by terrestrial animals or animals that live on land. The hard outer shell is a means to prevent most predation.
It is interesting to note that these smaller barnacles also live in lower parts of the tidal zone. They are frequently found attached to mussels and bare patches of rock. They are such good colonizers that they will attached to any substrate at varying depths.