Competency, settling behavior, and postsettlement aggregation by porcelain crab megalopae (Anomura : Porcellanidae)

Gregarious settlement by megalopae of the porcelain crabs Petrolisthes cinctipes (Randall) and P. eriomerus Stimpson was investigated to determine possible means of attraction and postsettlement benefits. Megalopae of P. eriomerus were attracted to conspecific adults confined to chambers that prevented tactile or visual contact, suggesting that postlarvae respond to a waterborne cue. There was also clear evidence of an extended period of competency for settlement, since newly molted megalopae of P. cinctipes held with conspecific adults settled within 2–4 days while those without adults delayed settlement for 2–3 wk. Loss of swimming ability at settlement is followed by degeneration of the pleopods and color changes. Following settlement juvenile instars appear to gain protection by continuing to hide between and beneath conspecific adults; this behavior significantly reduced predation in a laboratory experiment.