Nassarius snails will only attack clams (or anything else) if there is dead or dying tissue present. This will most likely happen with an otherwise healthy new clam if the byssal threads are damaged. This is usually caused by a store which doesn't know how to display clams and allowed the byssal foot to become attached and an employee who carelessly yanks the heretofore attached clam out ripping the foot to shreds.
You can prevent scavengers like nassariuses and bristle worms from attacking a new clam by initially placing it in a plastic salad strainer with live rock rubble in the bottom. After the clam heals and attaches to the rubble you can then easily put in your position of choice. You can also take some two-part epoxy and smoosh the clam onto it while the epoxy is still pliable. When the epoxy hardens you'll have yourself a custom protective mold for the clam to sit on.
|