| Summary: | The effects of temperature on two reef building corals <i>Pocilloporadamicornis</i> and <i>P. verrucosa</i> inhabiting the Obhur Creek, a small embayment on thewestern, Red Sea coast of Saudi Arabia, was studied from December 2009 toNovember 2010. The overall annual range of seawater temperature in Obhur Creekwas between 24.5°C and 33°C. Zooxanthellae abundance anddiversity showed seasonal variations: the number of zooxanthellae in <i>P. damicornis</i> was slightly higher than in <i>P. verrucosa</i>, and theabundance of zooxanthellae of both species was low in summer and high duringwinter. The respiration rate of <i>P. verrucosa</i> did not vary between summerand winter, suggesting compensatory acclimation. In contrast, the respiratoryrate in <i>P. damicornis</i> was lower in winter than in summer. During thewinter season the metabolic rate was higher in both species owing to theoptimum seawater temperature (30°C). As a result of the abundance ofzooxanthellae and the optimum seawater temperature, the growth rates of theskeletons of the two coral species were higher in winter and lower in summer.In general, the results showed that <i>P. damicornis</i> is more flexible withrespect to temperature than <i>P. damicornis</i>. The difference inzooxanthellae thermal tolerances at 35°C may be due to the algalgenotypes between the two species, resulting in <i>P. damicornis</i> becomingbleached as the rate of metabolism exceeds the rate of photosynthesis withincreasing temperature.
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