Effects of depth and eutrophication on the zooxanthella cludes of Stylophora pistillata from the Gulf of Eilat (Red Sea)

1. The symbiotic association between corals and zooxanthellae has been a major contributing factor in the success of reef-building corals. 2. The diversity of zooxanthellae harboured in the hermatypic coral Stylophora pistillata in the Gulf of Eilat (Aqaba), northern Red Sea, was investigated on the basis of the length and sequence variation of the 18S small subunit ribosomal DNA. Of several clades found worldwide, only clades A and C were found to be associated with this coral species in the Gulf. 3. No correlation between the pink and brown colour morphs of the coral S. pistillata and the zooxanthella clade was found. Shallow-water colonies (5 m) harbour clade A while deeper-water colonies (17 m) harbour either clade A or C. This coral is a brooding species that associates with different zooxanthellae at different depths. 4. Eutrophication from fish farms did not affect clade identity associated with Stylophora.