Aggressive interactions and competition for shelter between a recently introduced and an established invasive crayfish: Orconectes immunis vs. O. limosus

Orconectes immunis, a crayfish species from North America, has been recorded first from habitats along the Rhine river (Germany) in the 1990(th). Coincidental with the arrival of O. immunis resident populations of O. limosus, also a non-native crayfish species from North America, declined. We studied in laboratory experiments aggressive interactions and competition for shelter between the two invasive crayfish species as these interactions can result in species replacements. Agonistic behaviour was monitored in heterospecific 1:1 combinations of both species in 20-L aquaria. Orconectes immunis was strongly aggressively dominant over O. limosus when size-matched form I males or females were combined. Even 4mm smaller O. immunis (carapace lenght) were still dominant over larger O. limosus and males of O. limosus were not dominant over similar-sized females of O. immunis. Orconnectes immunis was also highly superior in competition that one of the Rhine catchment may be the inferiority of the former in aggressive contests. Inferiority in aggressive interactions may force O. limosus to leave refuges, making them vulnerable to predators.