Early stages of a New Zealand invasion by Charybdis japonica (A. Milne-Edwards, 1861) (Brachyura: Portunidae) from Asia: behavioral interactions with a native crab species.
The Asian paddle crab, Charybdis japonica (A. Milne-Edwards, 1861), is a relatively recent invader (approx. 10 years) to northeastern New Zealand, and its large size and aggressive nature makes it a potentially formidable competitor with native species. The only endemic, similarly sized, New Zealand paddle crab, Ovalipes catharus (White and Doubleday, 1843), overlaps frequently with C. japonica in both habitat and diet. To understand their probable interactions in the field, we performed a series of experimental behavioral trials in a closed laboratory system to determine whether the crabs interact antagonistically over a shared prey resource (Perna canaliculus (Gmelin, 1791) - green-lipped mussel). In interspecific trials, C. japonica frequently displaced both sexes of O. catharus from the prey, while O. catharus usually failed to acquire prey from feeding C. japonica. In addition, male C. japonica dominated both male and female O. catharus in one-on-one competition for food, regardless of which crab possessed the food initially. Overall, male C. japonica behaved aggressively towards O. catharus and conspecifics of equal size when competing for a prey item; O. catharus showed low levels of aggression throughout all trials and increased time spent evading C. japonica as compared to C. japonica's high levels of aggression. Our research highlights the importance of understanding how aggressive behavior may influence establishment success of invading species.