Abstract
1. Oxygen uptake (VO2) by sea urchins has been measured and correlated with partial pressures of oxygen in the ambient water (PiO2) and in coelomic fluid (PcfO2). PcfO2 was also analyzed in samples obtained from animals in natural environments using SCUBA-diving technique. In addition, changes in PcfO2 were recorded during prolonged air exposure of the animals.2. The three species investigated, Strongylocentrotus purpuratus, S. franciscanus and S. droebachiensis, showed steady levels of VO2 until PiO2 had dropped to 60-70 mm. Hg. At lower PiO2 the oxygen uptake decreased corresponding to the rate of decline of PiO2.3. Changes in PcfO2 at decreasing PiO2 closely paralleled the changes in VO2, except for a common initial compensatory increase in PcfO2. The data indicate that PcfO2 represents a useful index of the level of VO2.4. PcfO2 in samples obtained from urchins in their natural habitat showed large variations. Means by which the relationship between PcfO2 and VO2 may actively be used by the animals in their energy economy are discussed.5. Air exposure of the urchins while monitoring changes in PcfO2 suggests that external gas exchange in air is not a critical survival factor during tidal exposure.
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