en Biology & physiology Biology & physiology پژوهشي Orginal research papers <span style="FONT-FAMILY: "Times New Roman","serif" FONT-SIZE: 12pt mso-fareast-font-family: 'Times New Roman' mso-bidi-language: AR-SA mso-ansi-language: EN-AU mso-fareast-language: EN-AU" lang="EN-AU">Density, mitotic index, Chlorophyll-a content and cell size of symbiotic dinoflagellates of dominant reef-building corals were measured at two different depths in Kish Island and from one depth of Larak Island in the Persian Gulf. The higher densities of symbionts were found in shallow waters of Kish Island. However, ANOVA analyses of the mitotic index yielded mixed results. The cell sizes of symbionts did not significantly differ among depths, except for <i>Porites</i> corals at one site in Kish Island which displayed the larger cells in deeper water. The comparison of symbiont attributes between islands exhibited intraspecific variability. Density of zooxanthellae was only different in <i>Porites</i> and <i>Favia</i> corals between islands. Chlorophyll-a density (cm^-2)was significantly different between islands in all species, with higher values for Kish corals. Chlorophyll a cell^-1 was only significantly different in <i>Porites</i> and <i>Platygyra</i> corals, with higher values for Larak Island. The symbiont cell sizes usually exhibited no variability, except for Porites corals with larger sizes in Kish Island.</span> Density, Mitotic index, Chlorophyll-a, Cell size, Zooxanthellae, Coral reefs, Persian Gulf 475 486 http://jifro.ir/browse.php?a_code=A-10-1-103&slc_lang=en&sid=1 J. Seyfabadi jseyfabadi@gmail.com 10031947532846001521 10031947532846001521 Yes N. Shokri 10031947532846001522 10031947532846001522 No M. R. Fatemi 10031947532846001523 10031947532846001523 No