91.6 Monday, Jan. 6 14:45 Does cavitation limit the speed of mantis shrimp? COX, S.M.*; PATEK, S.N.; University of Massachusetts, Amherst; Duke University firstname.lastname@example.org
With one of the fastest feeding strikes in the animal kingdom, mantis shrimp strike prey with a raptorial appendage that can reach velocities of 30 m/s with accelerations of 1x105 m/s2 in water. Fast movement can lower local pressure causing cavitation bubbles that collapse and emit shockwaves powerful enough to erode holes in metal. Some mantis shrimp generate cavitation while using hammer-shaped appendages to smash hard-shelled prey. Cavitation bubbles form upon impact with their prey and may enhance prey processing. However, cavitation is rarely produced during the extremely fast rotation preceding impact, a time when cavitation bubble collapse would damage the exoskeleton and not provide benefits. Thus, mantis shrimp may have features that reduce cavitation during forward rotation, yet little is known about the conditions for cavitation formation in biological systems. Here we test whether mantis shrimp operate at an upper boundary of speeds that do not produce cavitation. We measured the maximum speeds for 7 individual Odontodactylus scyllarus striking under naturalistic conditions and noted cavitation presence before impact. In addition, O. scyllarus appendages (10 individuals) were attached to a mechanical model of the mantis shrimp strike called 'Ninjabot' and rotated at and above animal strike speeds. When rotated at the same and higher speeds than in natural animal strikes, the appendages cavitated regularly. A stainless steel cylinder of same scale as O. scyllarus appendages rotated with Ninjabot also cavitated above, at and well below mantis shrimp maximum strike speeds. These results suggest that cavitation is difficult to avoid in these conditions and mantis shrimp may indeed be circumventing cavitation through shape and kinematics.