Boring Clams and Beaches

November 22, 2009


Photographer: Steve Kluge; Steve’s Web Page
Summary Author: Steve Kluge

Boring clams (Penitella penita) are anything but boring. If you've spent much time picking up rocks along the beaches of southern California you may have wondered how those nearly perfectly round holes are "drilled" into so many of them.  I found the answer last summer while walking along the shore at the University of California, Santa Barbara.  The perfect fit of the clam shells into the holes in the sandstone in the photo at left suggest that the clams may have had something to do with creating those holes.  A closer examination of the shells reveals the sharp ridges visible in the close-up picture on the right.  By persistent grinding and rotation of the cutting edges of their shells against the rock, these rock boring clams create safe homes for themselves -- in solid rock. In doing so, they significantly wear the shoreline rocks, thereby contributing additional sand to the beaches. See also the Earth Science Picture of the Day for September 7, 2009.

Goleta Point UCSB coordinates: 34° 24' 17" N, 119° 50' 39" W