Not so fast! On the beach, they do tend to separate into zones; there's a wormy patch, with snails on the surface; there's a clean sand patch, with clams underneath and crabs on the surface; there's a snail and hermit area, with worms underground. On our Campbell River beach, there were patches of mostly anemones where the tide pools were full of hermits and snails.
The combinations may be due to water current variations, to the size of the sand grains, to the number of rocks, or the varying salinities and temperatures of any intertidal zone. But personalites may enter into the equation, too.
Hermit crabs get along with each other nicely, even across species lines. They're fine with anemones; they clean up the shells of snails and clams without disturbing their owners. They eat barnacles or worms, but only when they find them already broken. They have no fight with "true" crabs.
Mud snails, periwinkles, and the little Nassas go about their business eating algae and detritus, ignoring anything else. They stay away from anemones, though; the anemones do sting when they're pestered.
But the crabs! A different story altogether. A crab is the top dog on the totem pole, in his own eyes. He'll get along with anything else, as long as it keeps out of his way, gives up its choice tidbits of food, doesn't invade his current hole. Or doesn't look too tasty, like, for example, a newly-molted hermit or a snail small enough to crack like a nut.
|Unfortunate hermit, looking for a shell, with a crab waiting below him. Crab dinner.|
|Patch, recently molted, grown to his full size, ready for action.|