Disorientation as a marker of neurotrauma in an animal that uses shock waves as weapons

Snapping shrimp (Decapoda: Alpheidae) can create cavitation bubbles by rapidly closing their snapping claws. When these unstable vapor bubbles collapse, they release supersonic high-amplitude pressure waves, known as shock waves. Snapping shrimp regularly use these shock waves as weapons. Shock waves are dangerous to animals because they can cause blast-induced neurotrauma by transferring kinetic energy to neural tissues. Previously, we discovered that helmet-like structures, termed orbital hoods, protect snapping shrimp from blast-induced neurotrauma by damping shock waves. To learn how effectively orbital hoods function, we sought methods for quantifying behavioral changes associated with blast-induced neurotrauma in these animals. In humans, spatial disorientation is a behavioral hallmark of blast-induced neurotrauma. Here, we develop methods for assessing spatial disorientation in snapping shrimp and ask if shrimp, like humans, demonstrate disorientation following exposure to shock waves. To test for spatial disorientation in snapping shrimp, we quantified aspects of shelter-seeking behavior including path tortuosity, fractal dimension, total distance traveled, and speed. We found that shock wave exposure caused snapping shrimp without orbital hoods to travel longer, slower, and more tortuous paths to reach their shelters than it did shrimp with unaltered orbital hoods. By quantifying shelter-seeking behavior in this manner, we show that exposure to shock waves causes spatial disorientation in snapping shrimp without orbital hoods, supporting our hypothesis that orbital hoods mitigate short-term behavioral consequences of blast-induced neurotrauma. Further, we solidify spatial disorientation as a reliable and quantifiable marker of blast-induced neurotrauma in crustaceans.