Will Astacus leptodactylus displace Astacus astacus and Austropotamobius torrentium in Lake Ageri, Switzerland?

Lake Ägeri hosts three crayfish species: Austropotamobius torrentium, Astacus astacus and Astacus leptodactylus. To study the interspecific competition and a possible scenario of displacement, we monitored the distribution and relative densities of the different species during the years 1996-1999 by SCUBA diving. We examined the association of the species with different types of substrate and investigated the frequency of limb loss and the life history characteristics of the three species.¶A. leptodactylus was found at more sites than A. astacus and A. torrentium. It was also present in much higher densities than the other two species. A. torrentium preferred areas with hard substrate, whereas A. astacus was more often found at sites with soft substrate and reed vegetation. A. leptodactylus was observed on soft and hard substrate. The frequency of limb loss was highest in A. astacus and more frequent at sites with a high density of A. leptodactylus. Limb loss in A. leptodactylus and A. torrentium was more frequent at sites with high self-densities. Females of the two Astacus species carried more eggs than A. torrentium females. The eggs of A. astacus were larger than the eggs of the other two species. Juveniles of A. leptodactylus grew significantly faster in their first year than juveniles of A. astacus and A. torrentium. During the four years of the study A. leptodactylus expanded its range along the southeastern shore of Lake Ägeri. At the northwestern border of its distribution the portion of A. leptodactylus had slightly increased by the end of the study period. In two areas of the lake the population of A. astacus and A. leptodactylus declined between 1997 and 1999.[PUBLICATION ABSTRACT]