Reference: Biol. Bull., 143: 657-678. (December, 1972) ADAPTATIONS TO ENVIRONMENTAL OXYGEN LEVELS IN INFAUNAL AND EPIFAUNAL SEA ANEMONES CLAY SASSAMAN 1 AND CHARLOTTE P. MANGUM Department of Biuloi/v. College of }\'illiain and Mary. Williamsburg, l'iri/iiii>i 23185 and Marine Biological Laboratory, Woods Hole, Massachusetts 02543 Numerous investigators have shown correlations between various physiological properties of aquatic organisms and the characteristic levels of oxygen in which the animals are found. Older studies on survival time under low oxygen conditions generally indicate that, within closely related groups, burrowing species are more resistant to oxygen deprivation than epifaunal forms (Packard, 1905). Similarly, animals living in fast-moving streams are less resistant than those living in rela-tively unmixed pond water (Fox, Simmonds and Washbourn, 1935; Bovbjerg, 1952; Walshe, 1948). Walshe (1948) also showed that, among the chironomid larvae, resistance to oxygen lack is better correlated with ecological distribution than with phylogeny. Numerous studies support the very plausible notion that animals from low oxygen environments have a lower rate of oxygen consumption than their counter-parts from high oxygen environments when compared at the same oxygen concen-trations. Examples are two species of Balanns (Prasada Rao and Ganapati, 1968) ; epifaunal and infaunal tropical echinoids (Lewis, 1968) ; oxygen minimum layer mysids (Childress, 1971); stream and pond insect larvae (Fox, Simmonds and Washbourn, 1935), crustaceans (Fox and Simmonds. 1933) and leeches (Mann. 1956) ; and maldanid polychaetes (Mangum, 1963, 1964a). Perhaps the most elusive physiological correlate of environmental oxygen level is the degree to which oxygen consumption rate is maintained constant over a range of ambient oxygen concentrations. It is clear that in many aquatic inverte-brates respiratory regulation within a species is not entirely constant. It varies with temperature (Thomas, 1954; Wiens and Armitage, 1961), weight (Helff, 1928), molt cycle (Thompson and Pritchard, 1969) and previous activity levels (Nimura and Inoue, 1969). Relatively few investigators have examined the metabolic response of aquatic animals to wide ranges of oxygen concentration following periods of oxygen de-privation. Instead, most investigations have characterized the response to anoxia only at oxygen concentrations at or near air saturation. Prosser. Barr, Pine and Lauer (1957) have shown that goldfish respond to chronic exposure to low oxygen conditions by a reduction of standard metabolism and a shift of critical pO 2 to lower oxygen partial pressures, accompanied by increased hemoglobin concentrations and red blood cell counts. After oxygen lack, oxygen consumption rates in the mud snail Xussariiis ohsolctits increase ( Kushins and Mangum, 1971). but the response 1 Present address : Department of Biological Sciences, Stanford University, Stanford, California 94305. 657
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