A clingfish's suction cup does double duty. When the tide goes out, a clingfish's pool might be left high and dry. But the cup holds in moisture, so the fish can still breathe. Tucked safely beneath its rock, the clingfish waits until the tide rolls back in again.

Rocky shore creatures are at risk from coastal development and pollution such as oil spills and agricultural runoff. And rocky shores aren't as rugged as they seem. Careless visitors can trample tide pool animals underfoot, and many collect sea stars or other souvenirs to take home, which can leave tide pools barren of life.

• A clingfish can cling so tightly that the rock it's stuck on may be pulled away by strong currents with the fish still attached. 
• Along the shores of the San Juan Islands in Puget Sound, clingfish face danger from land: gopher snakes sometimes enter tide pools to hunt these fish.