Effect of small variations in salinity on the rates of photosynthesis and respiration of the zooxanthellate coral Stylophora pistillata

This paper deals with the effect of a long term (3 wk) change in salinity (increase or decrease of 2 to 4 psu) on the rates of photosynthesis and respiration of the zooxanthellate coral Stylophora pistillata. Colonies were exposed to 4 levels of salinity (34, 36, 38 and 40 psu, with 38 psu as the control salinity) and results were compared using I-factor ANOVAs. Salinity had a significant effect on the protein concentration. It was 30% higher at 38 psu than at the other salinities. It had also a significant effect on the rates of photosynthesis, respiration and on the P-g:R ratio. Gross maximal photosynthetic rates were 50% lower at 34, 36 and 40 psu than at 38 psu. The P-g:R ratio was always higher at the control salinity. Most of the colonies maintained at 40 psu died, and this was explained by a very low P-g:R ratio (<1). S. pistillata is therefore especially sensitive to small changes in salinity and seems to acclimate more easily to hypo- rather than to hypersaline conditions.