Gas Supersaturation Thresholds for Bubble Formation in and Damage to Sea Urchin Embryos

Eggs and early embryonic stages of the sea urchin Lytechinus pictus were subjected to hyperbaric gas pressures and rapid decompression. All stages showed a remarkable tolerance to gas supersaturations. No damage or internal bubbles were apparent in the eggs after decompression from less than 240 atm nitrogen or 209 atm argon. This indicates (1) a greater resistance to bubble formation than occurs in other invertebrates and vertebrates and (2) a lack of nucleation sites, such as hydrophobic interfaces in contact with the intracellular water. These thresholds decreased gradually to 170 atm and 148 atm, respectively, for 80-h-old plutei. Gas supersaturations above the threshold values often led to formation of internal bubbles, most frequently observed in the eggs. Slow decompression experiments usually had little effect on the organisms, showing that gas supersaturations were the cause of the damage rather than the hydrostatic pressures, the gases per se, or the hyperbaric conditions inherent in the procedures.