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First published online June 16, 2005
Journal of Experimental Biology 208, 2475-2482 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01655
Intragel oxygen promotes hypoxia tolerance of scyphomedusae
1 Laboratory One, The Evergreen State College, Olympia, Washington 98505,
USA
2 Academia Cotopaxi, Casilla 17-01-199, Quito, Ecuador
3 Alfred Wegener Institute for Polar and Marine Research,
Columbusstraße 27568 Bremerhaven, Germany
* Author for correspondence (e-mail: thuesene{at}evergreen.edu)
Accepted 19 April 2005
Populations of jellyfish are known to thrive in many low oxygen
environments, however, the physiological mechanisms that permit these
organisms to live in hypoxia remain unknown. The oxyregulatory abilities of
four species of scyphomedusae were investigated, and it was found that
Aurelia labiata, Phacellophora camtschatica, Cyanea capillata and
Chrysaora quinquecirrha maintain steady oxygen consumption to below
20 hPa oxygen (<10% air saturation). Oxygen content of the mesoglea of
A. labiata was measured using a fibre optic oxygen optode, and oxygen
profiles through the gel are characterised by a gradient that decreases from
just below normoxia at the aboral subsurface to 
85% air saturation near
the subumbrellar musculature. This gradient sustains oxyregulation by
scyphomedusae, and it is demonstrated that A. labiata must be using
intragel oxygen to meet its metabolic needs. Gel can also be used as an oxygen
reservoir when A. labiata moves into hypoxia. Gel oxygen is depleted
after about 2 h in anoxia and recovers to 70% of normal after 2.5 h in
normoxia. Behaviour experiments in the laboratory showed that Aurelia
labiata behaves similarly in normoxia and hypoxia (30% and 18% air
saturation). The acute threshold for provoking behavioural changes in A.
labiata is somewhere near its critical partial pressure, and oxygen
stratification stimulates swimming back and forth across the oxycline.
Intragel oxygen dynamics are recognised as a fundamental component of medusan
physiology.
Key words: critical partial pressure, gel, hypoxia, jellyfish, metabolic rate, oxyregulation, scyphomedusae
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