Effects of shell and food availability on metamorphosis in the hermit crabs Pagurus hirsutiusculus (Dana) and Pagurus granosimanus (Stimpson)

The effects of shell and food availability on survival and duration of the megalopal stage of the sympatric intertidal hermit crabs Pagurus hirsutiusculus (Dana) and P. granosimanus (Stimpson) were examined. In both species, survival to the first juvenile crab stage in the laboratory was independent of food and shell availability. In P. hirsutiusculus, megalopal duration was also independent of food and shell availability, whereas the presence of a shell shortened the duration of the megalopal stage in P. granosimanus by slightly more than a day. P. granosimanus megalopae look longer to reach competency, but used shells more quickly and consistently, than did P. Hirsutiusculus megalopae. When P. granosimanus megalopae had a shell, the presence of food shortened megalopal duration, whereas when megalopae lacked a shell, food lengthened megalopal duration. This suggests that P. granosimanus megalopae may retain at least a limited ability to feed (although we were unable to directly observe feeding in either species). These observations are consistent with interspecific differences in adult shell-associated behaviors, and suggest that for P. granosimanus shells are more important to early postlarval survival, or more difficult for megalopae to obtain, than for P. hirsutiusculus. However, the delay capabilities of P. granosimanus are relatively trivial compared to other invertebrates, which suggests that pagurid megalopae generally have little trouble locating suitable shells.