Response of the Asian shore crab Hemigrapsus sanguineus to metamorphic cues under natural field conditions

For brachyuran crabs like Hemigrapsus sanguineus, survival past the planktonic life stage requires settlement out of the water column onto appropriate benthic habitat, followed by metamorphosis to the 1st juvenile stage. In the laboratory, H. sanguineus has been shown to respond to cues produced by conspecific adults and to various cues associated with the substratum. The objective of the present investigation was to determine the response of megalopae to cues produced by natural populations of adult H. sanguineus. In this study, laboratory-reared megalopae were deployed in cages at four locations along each of two transects that extended 20m from rocky intertidal habitat that contained a dense population of adult H. sanguineus. One transect extended perpendicular to shore and into open water, while the second extended parallel to shore and adjacent to salt-marsh habitat. The percentage of megalopae undergoing metamorphosis was greatest in the cages that were closest to the adult population and diminished with distance from that population, regardless of transect. Moreover, a comparison of cages at comparable positions on the respective transects showed lower percentage metamorphosis in cages on the marsh transect than on the open-water transect. Our findings are coherent with results of previous laboratory studies and indicate that H. sanguineus megalopae can sense water-soluble metamorphic cues produced by conspecific adults at distances up to a few meters from the source.