The effects of microcystin-LR and its location within an environmental pool on rusty crayfish (Faxonius rusticus) behavior and physiology

Anthropogenic factors have negatively impacted the health of freshwater ecosystems by increasing the occurrence of harmful cyanobacterial blooms and their associated toxins. Water column mixing and reworking of substrate by organisms allow for cyanotoxin deposition into sediments and resuspension into the water column. Crayfish rework benthic substrates and are exposed to toxins in both benthic and pelagic phases. Since crayfish are keystone species and ecosystem engineers, understanding the spatial dynamics and effects of aquatic toxins on crayfish is necessary. In this study, crayfish were exposed to low concentrations of microcystin-LR (MC-LR) present in the water column or sediment of a closed system for 108 h. After exposure, crayfish were placed in flow-through mesocosms to monitor foraging and locomotive behaviors and were subsequently dissected to assess membrane integrity of hepatopancreas cells. The presence of EtOH or EtOH/MC-LR in the water column decreased crayfish foraging compared to the control. Crayfish locomotive behaviors increased when the water column was dosed with EtOH or EtOH/MC-LR and when the sediment was dosed with EtOH/MC-LR compared to the control. Non-significant trends suggest that foraging was impaired when MC-LR was present in the water column vs the sediment and that locomotion was enhanced when MC-LR was present in the water column vs the sediment. Additionally, MC-LR present in the water column significantly lowered fluorescein diacetate (FDA) fluorescence per crayfish hepatopancreas cell. A non-significant trend also suggests that the amount of hepatopancreas cells detected was lower when MC-LR was present in the water column vs the sediment. MC-LR was observed to negatively impact crayfish hepatopancreases membrane integrity which could explain the resulting behavioral changes. These findings have implications for crayfish health and for overall ecosystem functioning in environments known for the occurrence of MC-LR.