Life Between the Tides

SURVIVING THE INTERTIDAL ZONE ALONG CATALINA ISLAND

- Casey Twanow

At first glance, the tumbled rocks at the edge of the ocean cove where I once lived look lifeless-too rugged a place for animals to make their home. But explore these boulders, and you'll meet a fascinating community of creatures that survive in the harsh intertidal zone.

The intertidal zone lies along the ocean's edge. In this unique habitat, the water level changes with the Moon-driven tides. At high tide, seawater covers shoreline that might be several feet, or a few meters, above water at low tide.

Catalina Island's Intertidal Zone

On Catalina Island, 20 miles (32 km) off the coast of Southern California, much of the intertidal habitat is rocky and rough. I worked as a teacher at Catalina Island Marine Institute, an outdoor marine science school that students from fourth grade to twelfth grade visit to learn about the ocean. I loved taking my classes to investigate our constantly changing intertidal zone.

Let's explore this wondrous environment between the tides!

First, listen to the constant rhythm of the intertidal world: a whoosh as blue-green water pours into cracks around the rocks, a gargle as the frothy water is sucked back out.

If we watched one patch of intertidal rock all day, we'd see water swirl over it at high tide, the Sun bake it at low tide, and waves pound on it in between. In California and most places on Earth, there are two high tides and two low tides each lunar day. (A lunar day is the time it takes the Moon to orbit Earth, which is about 24 hours and 50 minutes.)

It's almost low tide now, the perfect time to find intertidal creatures out of the water. Let's go-be careful on the slippery rocks!