Impact of biometric parameters and seasonal condition on mercury (Hg) distribution in Harris mud crab (Rhithropanopeus harrisii) body.

Mercury is a potent neurotoxin. The toxicity of Hg depends on the form in which it occurs, which consequently determines its bioavailability to the organism. The processes of distribution and elimination of Hg in organisms from lower trophic levels are still poorly understood. Therefore, in the present study, great point was paid separately to the soft tissues and hard tissues, which may play an important role in the detoxification of the crab's body from neurotoxicant. The study was conducted on the non-native species: Harris mud crab, collected in 2020. Concentrations of total mercury and its forms were carried out using a Direct Mercury Analyzer, DMA-80 (Milestone, Italy). Sex did not determine the Hg concentration of its forms in R. harrisii. Organism size influenced on crab body processes: biodilution of Hg during growth in summer and bioaccumulation of Hg before stagnation in autumn. The distribution of Hg in the crab's soft tissues and walking legs was related to the trophic origin of the mercury, while halide-bound mercury and semilabile forms and HgS were redistributed into the crab's carapace. This protects the soft tissue of crabs against the toxic effect of Hg. Consequently, a smaller load of Hg in the crabs can be introduced to the circulation or biomagnified in the food web in the region where R. harrisii is an important link of the trophic chain.