Periwinkle Littorina planaxis Periwinkles are one organism in the intertidal zone that is able to survive long-term air exposure. In fact, periwinkles cannot withstand prolonged emersion in seawater. They protect themselves by clamping down tightly against the rock, sealing their shell with a glue-like mucus. They are mostly active at night when the humidity is high. As periwinkles glide along rocks, they ìlickî the surface to scrape off microscopic organisms. The main predators of these snails are shorebirds. Habitat/Range: Periwinkles can be found on pilings, docks, bays, and in rocky areas from Alaska to Baja California.