Crabs on cue for the coast: the use of underwater sound for orientation by pelagic crab stages

Abstract

Several studies have suggested that underwater sound may provide an orientation cue for the pelagic stages of coastal crustacea, such as crabs and lobsters, to find their way from the open ocean to the coast where they can settle. Yet, there has been no field evidence to support this phenomenon and it is unclear whether pelagic crustacean stages even have the ability to orient towards sources of underwater sound, such as that which emanates from reefs. Artificial sources of natural underwater sound were deployed offshore in conjunction with light traps to determine if the larval and post-larval stages of coastal crabs were attracted to coastal reef sound. The results demonstrated that the pelagic stages of crabs respond to underwater sounds and that they may use underwater sound to orient towards the coast. The orientation behaviour was modulated by lunar phase, being evident only during first- and last-quarter moon phases, at the time of neap tides. Active orientation during neap tides may take advantage of these incoming night-time tides for predator avoidance or may permit more effective directed swimming activity than is possible during new and full moon spring tides.