Gregarious settlement by megalopae of the porcelain crabs Petrolisthes cinctipes (Randall) and P. eriomerus Stimpson

Settlement was studied in two vertically separated populations of the filter-feeding porcelain crabs Petrolisthes cinctipes (Randall) and Petrolisthes eriomerus Stimpson near Bamfield, British Columbia, Canada. Within their respective tidal levels, megalopae of each species settled preferentially in cages containing conspecific adults. In addition, P. cinctipes was induced to settle below its normal tidal level in response to caged adults; similar settlement preference was also found in the laboratory, thus, demonstrating the first example of gregarious settlement among the Decapoda. While not as critical as for sessile organisms, the use of conspecific cues by crabs insures settlement in a suitable location while helping maintain existing zonation patterns, and may enhance postlarval survival through protection imparted by the presence of adult crabs.