Bubble formation in crabs induced by limb motions after decompression.

In vivo bubble formation was studied in the megalopal stage of the crab Pachygrapsus crassipes. The animals were equilibrated with elevated argon, nitrogen, or helium pressures then rapidly decompressed to atmospheric pressure. Voluntary motions induced bubble nucleation in leg joints after exposures to as low as 2 atm nitrogen (gauge pressure). Delays of several minutes sometimes passed between decompression and bubble formation. Mechanically stimulating the animals to move their legs increased this bubble formation, whereas immobilizing the legs before gas equilibration prevented it, even in animals decompressed from 150 atm nitrogen. We conclude that preformed nuclei are not responsible for bubbles developing in the legs of this animal. Instead, tribonucleation of bubbles apparently occurs as a result of limb motions at relatively low gas supersaturations.