Settlement behaviour of the early megalopae of the land hermit crab Coenobita violascens (Decapoda: Coenobitidae) under laboratory conditions: Effects of inshore odours and salinity
The distribution of the land hermit crab Coenobita violascens is restricted to the vicinity of rivers,particularly mangrove estuaries. To infer the recruitment mechanisms of C. violascens, we examined settlement behaviour, such as swimming, walking, shell-inspection, and shell-wearing activities, in 0-day-old to 6-day-old megalopae under different seawater conditions: 1) offshore salinity (34 ppt, control), 2) offshore salinity (34 ppt) with inshore odours (riverine water), and 3) inshore salinity (24 ppt). Salinity was regulated using artificial sweater salts. Coenobita violascens megalopae exhibited nocturnal swimming activity, whereas other activities significantly increased during the daytime period. Inshore odours did not affect the swimming and walking activities, whereas the inshore salinity conditions decreased the swimming activity and enhanced the walking activity, i.e., stimulated the settlement behaviour of megalopae. Shell-related activities were not influenced by any of the seawater types. Our results suggest that megalopae might migrate to the coast using nocturnal flood-tide transport and settle on or near inshore habitats under the reduced salinity conditions that occur as a result of the inflow of groundwater and river water. Further studies are required to elucidate the role of inshore odours in the recruitment of C. violascens megalopae in mangrove estuaries
