Update on the signal crayfish, Pacifastacus leniusculus (Dana, 1852) range expansion in Croatia: a 10-year report

Microbiome of the Successful Freshwater Invader, the Signal Crayfish, and Its Changes along the Invasion Range

“…As the exoskeletal microbiome is determined by the available regional microbial species pool, which also includes microbes of all host individuals in a given environment ( 59 ), we suggest that crayfish density and population structure may significantly affect its composition and lead to the observed high variation in diversity and abundance among all locations and contribute to the observed significant differences from the environmental (sediment) microbiome. In the invasion core populations, only signal crayfish are present in high abundance, while invasion fronts have 7 to 8 times lower signal crayfish abundance than invasion cores and also cooccur with the native congener Pontastacus leptodactylus (Eschscholtz, 1823) ( 30 ). Aggression plays an important role in the dynamics of crayfish populations ( 60 ), and high crayfish abundance has been shown to increase the competition for limited resources and the rate of interaction between individuals ( 61 ).…”

“…We sampled the lower reaches of the Korana River, a 134-km-long karstic river located in continental Croatia that belongs to the Sava River basin, where signal crayfish are spreading both upstream and downstream ( 30 ). The upstream section of the studied area flows through the sparsely populated rural region, while in the downstream section, the river passes through the industrial zone and flows into the Kupa River in the city of Karlovac.…”

“…The ongoing context of range expansion allowed us to sample signal crayfish individuals from two distributional ends: (i) invasion core (longer established population with higher crayfish abundance) and (ii) invasion front (recently established population at the edge of the range with lower crayfish abundance). The crayfish were captured at four sites along the 33 km of the Korana lower watercourse, which were previously ( 30 ) identified as upstream invasion front (UF), upstream invasion core (UC), downstream invasion core (DC), and downstream invasion front (DF) ( Fig. 6 ).…”

“…6 ). Upstream and downstream invasion cores have 7 to 8 times higher relative P. leniusculus abundance than invasion fronts and contain no native crayfish since they were outcompeted from these sites, while at invasion fronts, P. leniusculus cooccurs in interspecific populations with the native P. leptodactylus ( 29 , 30 ).…”

“…Signal crayfish were first recorded in the lower section of the Korana River in 2011 ( 28 ) and have been successfully spreading both upstream and downstream since ( 29 , 30 ). Previous studies have recorded differences in signal crayfish population characteristics along its invasion range in the Korana River, with invasion fronts being male dominated and containing less aggressive individuals in better body and physiological condition ( 31 , 32 ), which may be the result of nonrandom dispersal ( 33 ) and density-dependent effects.…”