OXYGEN UPTAKE AND RESPONSES TO RESPIRATORY STRESS IN SEA URCHINS

¹ Friday Harbor Laboratories and Department of Zoology University of Washington, Scattle, Washington 98105

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 VO_2, 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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