The communities of microorganisms in the setae of invasive Chinese mitten crab (Eriocheir sinensis) in the southern Baltic catchment basin

Chinese mitten crabs are one of the largest species of invasive crustaceans in the Baltic Sea catchment basin. Due to their catadromous migration, they can serve as a vector for small organisms, transporting them over distances greater than 500 km. Research on various crab species has shown their notable role in the spread of microorganisms to new aquatic environments. The aim of this study was to determine the diversity and abundance of microorganisms migrating with the Chinese mitten crab on the densely-distributed setae found on their claws. Our analysis also considered the potential differences in the number and genera of microorganisms between male and female Chinese mitten crabs. The study consisted of forty-eight (48) crabs (sex ratio 1:1) fished with a fyke net during their intensive downstream migration in Lake Dabie (which is the southern part of the Oder River estuary) between November 8 and 11 2017. In these Chinese mitten crabs, a rich microbiological flora was found, which can be divided into three basic groups: heterotrophic bacteria, yeasts, and fungi. Microorganism genus biodiversity on claw setae was greater in males than in females, although the total aerobic microbial count (TAMC), total halophile count (THC), and total combined yeasts and molds count (TYMC) showed no statistically significant differences between sexes. Phylogenetic analysis of PCR products and genetic taxonomic analysis of dominating strains in samples from crab claw setae showed the dominance of Bacillus tequilensis bacterium. The presence of these microbiologically antagonistic bacteria, capable of adapting perfectly to different environmental conditions, indicates that the crabs are capable of introducing potentially dangerous microorganisms into new ecosystems.