Effects of reduced salinity on the rates of photosynthesis and respiration in the hermatypic corals Porites lutea and Pocillopora damicornis

This paper deals with sublethal salinity stress on reef building corals in the Inner Gulf of Thailand.Maximum photosynthetic and respiratory rates were measured in Porites lutea and Pocillopora damicornis as changes in dissolved oxygen levels per hour and the gross production to respiration ratio (Pg:R) calculated.Pg:R ratios were significantly lowered in both species when exposed to sudden salinity drops from ambient 3OnR> to 20 and 10%, but P lutea was less affected.Photosynthetic rates were lowered in proportion to the salinity reductions in both species, whereas respiration rates were either slightly decreased or unaltered.When calculating the Pg:R ratios on a 24 h basis both species displayed values below 1, even at amblent salin~ty [P.lutea 0 71 k 0.04 and P dan1icornis0.89* 0.02), thus ind~cating that they do not solely depend on internal primary production for their maintenance.In an experiment on the capacity of hctcrotrophic feeding with Arten~ia sahna, P. damicornis showed a clearance rate 4 times higher than P. lutea, indicating that P. darnicornis may be more capable of compensating for a low Pg:R ratio by heterotrophic feeding.