Directional swimming behavior by five species of crab postlarvae in response to reef sound.

Abstract

Recent research has shown that pelagic larvae of some coastal fishes and crabs may actively seek out suitable settlement habitat by using extensive swimming abilities and directional sensory cues. Sound has long been suspected as the main potential orientation cue used to guide the long range movements of these larvae. However, experimental evidence for the orientation of larvae to underwater sound has been hard to secure due to the difficulties of conducting field experiments, and controlling sound in experimental aquaria. We report on an effective method for using a binary choice chamber coupled with an artificial source of underwater sound to conduct in situ behavioral experiments on crab postlarvae, at night in coastal waters of Omaha Bay, New Zealand. Postlarvae of five common coastal crabs from around New Zealand were used: Plagusia chabrus (Linnaeus, 1764), Notomithrax ursus (Herbst, 1788), Cyclograpsus lavauxi (H. Milne-Edwards, 1853), Hemigrapsus edwardsii (Helgendrof, 1882), and Pagurus spp. The postlarvae of all five crab species showed an orientation response towards the sound source confirming that the binary choice chamber can be used as a reliable experimental tool for determining directional swimming behavior of postlarvae in response to sound cues. These results also indicate that orientation to a sound cue is widespread among crab species and that this behavior could be of considerable ecological importance in influencing the settlement success of coastal crustaceans.