Maybe the clam exhibit isn’t the first tank you’d choose to visit at an aquarium, but is it fair to say clams are boring? Before deciding, travel under water to the rim of the submarine canyon off La Jolla Shores. This marks the precipice of terraced downward-sloping terrain made up of a gooey, peaty-clay material. The slopes’ vertical faces, averaging only a few feet high, are home to a plethora of life, the piddock clam being one of the most populous. These mollusks burrow deeply into the soft substrate, rendering nearly the entire animal invisible to the outside world. The snippet exposed is a pair of smokestacklike siphons. One siphon functions for inhaling and filtering food (microscopic plants), and the other takes care of excreting waste. While several boring clam species make their home in the sandstone wall, my favorite is the wartnecked piddock (Chaceia ovoidea), maybe because of its provocative moniker. The warty one’s siphons are distinctively mahogany and covered with tiny, white bumps. A white, hoselike body winds deeply into the sediment until the body dead-ends in a snow-white bivalve shell. The shell halves are thick and rough, with ridges along the outer sides to aid in boring. Unlike most clam species, the piddock cannot clamp its two shell halves together. Instead, both ends gape open, with the body and external siphons jutting out one end and a short sucker-cup foot sticking out the other end. While the foot clamps down onto the mud, the jagged-edged shell rotates and jiggles to dig the tunnel, an excavation that proceeds nonstop throughout the piddock’s life. It may take a piddock five years to bore three feet into the slope. This last bit of information hints at why a piddock avoids setting up shop too close to its kin. Too many tunnels undermine a hillside, leading to landslides. In fact, piddock clams are the central force in shaping and reshaping the canyon’s slope. On occasion, I’ve come across a landslide in progress, noted when the visibility ahead is obliterated by billowing sand particles. I’m in no danger from the slide but that’s not the case for many of the newly homeless. Mobile species like fish and octopi easily escape the calamity, but sessile marine life like the piddock are now unprotected and vulnerable to predation. Once the dust settles, I fin past chunks of slope strewn below, a reminder that not only has a community been wiped out, but the landscape has been re-contoured. I’ve had to wait months for the sterile slope to become repopulated. From my observations, the turning point arrives on the heels of a dramatic marine life event — like thousands of squid converging on the area to spawn. Such episodes appear to act like a magnet for bringing in all variety of life from points unknown. But unlike the ephemeral stars of the spectacle, which shortly die or otherwise depart, much of the arriving life must remain because not long after, the barren slope transforms into one bustling with life. Revisiting the question of whether the piddock is boring requires a careful answer because, though true, this clam is also charismatic. Consider that while earthquakes and other physical forces have and continue to strongly impact the look of our shoreline, a hidden, biological force, the boring clam, also plays a unique and powerful role in shaping and eroding the coastal scene. I suggest describing the piddock clam as a dichotomy in itself because it is both boring wallflower and influential mover and shaker. Judith Lea Garfield, biologist and underwater photographer, has authored two natural history books about the underwater park off La Jolla Cove and La Jolla Shores. www.judith.garfield.org. Questions, comments or suggestions? E-mail [email protected].
