Signaling via water currents in behavioral interactions of snapping shrimp (Alpheus heterochaelis)

The snappping shrimp Alpheus heterochaelis produces a variety of different water currents during intraspecific encounters and interspecific interactions with small sympatric crabs (Eurypanopeus depressus). We studied the mechanisms of current production in tethered shrimp and the use of the different currents in freely behaving animals. The beating of the pleopods results in strong posteriorly directed currents. Although they reach rather far, these currents show no distinctions when directed toward different opponents. Gill currents are produced by movements of the scaphognathites (the exopodites of the second maxillae) and can then be deflected laterally by movements of the exopodites of the first and second maxillipeds. These frequent but slow lateral gill currents are most probably used to enhance chemical odor perception. The fast and focused, anteriorly directed gill currents, however, represent a powerful tool in intraspecific signaling, because they reach the chemo- and mechanosensory antennules of the opponent more often than any other currents and also because they are produced soon after previous contacts between the animals. They may carry chemical information about the social status of their producers since dominant shrimp release more anterior gill currents and more water jets than subordinate animals in intrasexual interactions.