MCGUIRE, B.M.*; WILLIAMS, J.D.; Hofstra University; Hofstra University: Use of partially predated gastropods by the hermit crab Pagurus longicarpus: Who is predating on the snail Littorina littorea?

Although many investigations have focused on the importance of shell resources to hermit crabs, few studies have documented how these shells become available to hermit crabs. Field collections of Pagurus longicarpus from Long Island showed this hermit crab inhabited Littorina littorea shells that exhibited partial predation (i.e., with soft tissue still present but opercula removed). In fact, up to 28% (n= 64) of P. longicarpus inhabited L. littorea shells with soft tissue present in May-October of 2004 and 4.4% (n=158) of hermit crabs in May-August 2005 from sites along the shores of Long Island, NY. Based on these findings, laboratory experiments were set up to determine if P. longicarpus was attacking the snails or inhabiting shells that had been previously attacked by a predator (the most abundant crab at the collection sites was the spider crab Libinia emarginata). To determine the snail predator, P. longicarpus or L. emarginata were placed separately in tanks with live L. littorea at natural densities. Another experiment was conducted to observe the hermit crabs’ use of predated snail shells by removing the opercula of snails and offering the snails to hermit crabs in tanks. L. emarginata was shown to remove the opercula of L. littorea in the laboratory but abandoned the soft tissue, as found in specimens collected in the field. No predation events occurred in the tanks containing P. longicarpus. With the opercula removed, the majority of P. longicarpus switched shells and chose the partially predated shells. These findings are exciting since no studies along the east coast of the U.S. have focused on the use of such shells by P. longicarpus and this behavior may have important impacts on their populations.