Rands,-M.L.; Douglas,-A.E.; Loughman,-B.C.; Ratcliffe,-R.G.  
	Avoidance of hypoxia in a cnidarian symbiosis by algal 
	photosynthetic oxygen.  BIOL.-BULL.-MAR.-BIOL.-LAB.-
	WOODS-HOLE. 1992. vol. 182, no. 1, pp. 159-162.

The algal symbionts in a variety of invertebrates are widely 
believed to increase the oxygen tension in the animal tissue 
by producing photosynthetic oxygen. This could be 
advantageous to the animal by maintaining normoxia in anoxic 
waters. Equally, it could be detrimental, through hyperoxia 
and the generation of toxic oxygen radicals, and this may 
contribute to the recurrent incidence of mass bleaching in 
tropical cnidarian symbioses over the last decade. Here, we 
use in vivo  super(31)P nuclear magnetic resonance 
spectroscopy to assess the effect of photosynthetic oxygen 
production by the symbiotic alga Symbiodinium  sp. on the 
energy metabolism of a sea anemone, Anemonia viridis  and, by 
using acidification of the tissues and elevated ADP/ATP 
ratios as linked indices of anaerobiosis, we show 
unequivocally that photosynthetic oxygen can protect an 
invertebrate from hypoxia. Illumination prevents the rapid 
acidification and reduction in ATP that occurs under hypoxic 
conditions in the dark, and we suggest that this effect could 
be partly responsible for algal enhancement of coral 
calcification.