|Barnacles and periwinkles, and probably a crab or two.|
Mud snails are relatively mobile. We have watched them as the tide retreats, just above the water line, hurrying down in pursuit of the disappearing shelter of the waves. They're not fast enough, and after a futile chase of a few minutes, they bury themselves in the sand to wait for conditions to improve. I sometimes follow their trails from exit hole to new retreat; they manage to cover about 10 of my paces, but rarely in a straight line, so they're not too far from home when they stop.
Hermit crabs scuttle about, sometimes covering quite a distance, compared to their size. And I have seen them, caught in the current, rolling, rolling, out with the tide, until they find some strand of eelgrass to grab onto before they get nabbed by a passing fish.
The other day, walking on the bare sand, I picked up every snail shell I saw, and examined it. Every one, every single one, without exception, held a hermit crab. If a hermit borrows the shell from a snail that died and was eaten, then the hermits and snails should be found in the same general location, I reasoned. But I saw no snails where there were hermits.
Maybe the snails had dug themselves into the sand when the tide went out. So when I picked up a hermit in a snail shell, I dug in that area, scooping out the sand and water wrist deep. Each time, I found clams, clams, clams, clams. No snails. Not one.
So the hermits, at least, have travelled some distance from their supply of homes.
All this is well and good; a barnacle or a mussel on a rock is basically set for life; a starfish in a crevice at the mid-tidal zone will still be there next week or month, a snail circles around the bits of beach that feel comfortable.
But what of the poor critters that settle down in a perfect spot, sheltered, climate-controlled, well supplied with food and company, only to find their home uprooted and tossed on some inhospitable shore, exposed to air and light and flies? What of the subtidal residents of bull kelp holdfasts, or the eelgrass root dwellers?
Ma Nature is so unfair!