Cues inducing non-sexual conspecific attraction in an invasive shrimp

The aggregation of conspecifics in the invasive shrimp Palaemon macrodactylus could be driven by either patchy environmental conditions or conspecific attraction. This study aimed to determine whether the observed grouped distribution in natural conditions results from gregarious behavior and the type of cue used by shrimp to locate conspecifics. Four experiments were conducted during the non-reproductive season in which a focal shrimp was given the choice between a zone with cues of conspecifics or an empty zone. The cues permitted in each experiment encompassed visual and chemical cues, exclusively visual cues, exclusively chemical cues and a control devoid of any visual or chemical cues. The results indicated that focal shrimps exhibited a preference for conspecific zones when exposed to chemical cues alone or in combination with visual cues. However, visual cues alone were insufficient to induce grouping with their peers. The value of this trait is discussed along with other behavioral characteristics of the species as a possible explanation for its success as an invader.