Periwinkles are small, stocky snails that live high in the inter-tidal region of the California coast. We saw these Periwinkles above the tide pools at La Jolla Cove near San Diego. These snails were very small, perhaps 1/2 inch across.
Periwinkles are algae eaters. These snails scrape microscopic algae from the surface of the rock. In scraping off the algae, the snails sometimes remove tiny bits of the rock. Scientists have estimated that over 100 years Periwinkles may remove as much as two and a half inches of rock.
Periwinkles live high in the inter-tidal region. That is, they usually live out of the water, and may even live above the high-tide mark (that is the spot that marks the highest the tide ever gets). Periwinkles depend on the spray from ocean waves to keep them from getting dehydrated, so these animals must live near the water.
This picture shows four Top Snails in a tide pool near Point Loma in San Diego. Unlike the Periwinkles, these snails live underwater. Top Snails are slightly larger than Periwinkles. These snails were perhaps 1 inch across. There are many different kinds of Top Snails in southern California tide pools.
The small fish in the center of the picture is a Wooly Sculpin.