
EPA Science Advisory Board	Background Information

Document Name	Physiological responses to hypoxia*
Document Author	Burnett, L. E. Stickle, W.B.
Short Description	Pp. 101-114 in Rabalais, N. N. and R. E. Turner (eds.), Coastal Hypoxia: Consequences for Living Resources and Ecosystems. Coastal and Estuarine Studies 58, American Geophysical Union, Washington, D.C.
Category	Subgroup 1: Characterization of the Cause(s) of Hypoxia
Publication Year	2001

Text:

Abstract: Hypoxia can have profound effects on individual organisms. This chapter focuses on the mechanisms different kinds of animal possess to avoid, tolerate, and adapt to low levels of oxygen in water; selected examples illustrate these mechanisms. While some organisms can detect and avoid hypoxic water, avoidance is not always possible, especially in the sense of sessile organisms. When an organism cannot avoid hypoxia, its response may depend on the intensity and duration of the bout of low oxygen. Examples of responses to hypoxia include a depression in feeding as well as a decrease in molting and growth rates. During acute exposures to hypoxia some organisms can maintain aerobic metabolism by making effective use of a respiratory pigment, or increasing ventilation rates, or increasing the flow of blood past the respiratory surfaces or combinations of all three. Responses to chronic hypoxia are different and include the production of greater quantities of respiratory pigment and changing the structure of the pigment to one with an adaptive higher oxygen affinity. Many organisms respond to hypoxia by switching from aerobic to anaerobic metabolism and some simply reduce their overall metabolism. Hypoxia is often accompanied by hypercapnia (an elevation in water CO2), which produces an acidification of the body tissues, including blood, and has physiological implications that can also be profound and separate from the effects of low oxygen. Finally, there is evidence that hypoxia can inhibit immune responses, causing greater mortality than would otherwise occur when organisms are challenged with a pathogen.