الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Summary and conclusionCoral reefs are shallow-water ecosystems built principally by reefs as they secrete layers of calcium carbonate beneath their bodies. Calcareous macroalge, foraminifera and bivalves also secrete calcium carbonate and contribute to the construction of reefs. Coral reefs occupy less than 0.1% of the ocean floor yet play multiple important roles throughout the tropics, housing high levels of biological diversity as well as providing key ecosystem goods and services such as habitat for fisheries, coastal protection, and attractive environments for tourism. Red Sea corals are among the world’s greatest natural wonders.
The Red Sea is one of the most important repositories of marine biodiversity in the world. It has an extraordinary range of biological diversity and endemism. The Red Sea is the habitat of over 1,000 invertebrate species, more than 1200 species of fishes, and 200 soft and hard corals.
The collected colonies of Galaxea fascicularis are greenish brown, commonly with tentacles and septa of contrasting colors. Tentacles often have conspicuous white tips. Small colonies are low domes or are irregular. Large colonies are columnar or massive. Corallum are placoid and columnar up to 3 mm high and 6 mm in diameter. Corallites are of mixed sizes, usually polygonal, cylindrical, and less than 10 mm diameter with numerous septa reaching the corallite center.
While the collected colonies of A. humilis were solid, very porous, and branching. These colonies have two colors; brown color with purple branch tips and yellow color with cream branch tips. Individual branches form fat fingers; 10 to 25 mm in diameter and less than 200 mm in length, tapering to large dome-shaped axial corallites. Small branchlets or incipient axial corallites usually occur at the base of main branches. Radial corallites are cup-shaped and have two sizes, the larger are usually in rows and have thick walls and only slightly increase in size down the sides of branches. Axial and radial corallites have a series of vertical rods arranged in concentric rings and horizontal radial and tangential bars. The radial bars form the sclerosepta along with the vertical rods. The tangential bars are synapticulae that connect adjacent sclerosepta to one another. Series of fasciculi form the characteristic scale-like appearance of A. humilis skeleton.
The bioerosion was investigated at least in one branch of some colonies which were harbored by fungi, green algae and cyanobacteria; led to loss of tissues and erosion of rods, bars and fusiform crystals. The surface of Acropora humilis which covered by muco-polysaccharides, its high porosity and its branching form may facilitate the colonization of coral surface by microbiota and boring organisms, eventually causing bioerosion of coral branches.
Corals’ reef-building capability arises from an endosymbiotic relationship with photosynthetic dinoflagellate symbionts (Symbiodinium spp.). The symbionts typically live enclosed within membrane bound ”symbiosomes” in host cells of the gastroderm. The initial infection occurs when host gastrodermal cells lining the gastric cavity phagocytize algal symbionts previously ingested through the host mouth during feeding. The mechanisms of avoiding host digestion remain largely unknown, although some studies suggest that persistence may be due to the failure of phagosomes lysosome fusion. Corals derive photosynthate to fuel much of their metabolic requirements, while symbionts derive inorganic compounds from the host to fuel photosynthesis and symbiont growth. The presence of a photosynthesizing symbiont profoundly influences rates of growth, reproduction, and CaCO3 deposition of scleractinian corals.
Relatively little is known regarding the distribution and diversity of background (low abundance) populations of dinoflagellate endosymbiotic algae (genus Symbiodinium) in corals. This is because the genetic identification methods typically used to distinguish different Symbiodinium are only sensitive enough to detect symbionts that are relatively dominant within the community. Contemporary understanding of the genetic diversity of Symbiodinium recognizes eight phylogenetic clades (A–H), and many genetic variants have been identified within these clades. Reef-building corals most commonly associate with Symbiodinium in clades A–D.
In this work, we focused on the symbiotic relationship between the coral (host) and symbiont (Symbiodinium) from the genetic point of view. In order to understand how corals and their symbionts interacting with each other, we studied the genes that responsible for keeping this relationship in balance like symbiosis- enhanced protein (sym32 gene).
Therefore, the present study was carried out on two species of stony (scleractinian) corals Acropora humilis and Galaxea fascicularis which belonging to two different families (Acroporidae and Oculinidae, respectively), and on their endosymbiontic algae (zooxanthellae) belong to genus Symbiodinium. Also, the study was done on two coral species from different families in order to confirm our results and our understanding about the coral-algae partnership. Zooxanthellae (Symbiodinium spp.) were separated from coral tissues for RNA extraction. Primers were designed for detecting the coding sequence (CDS) of sym32 gene, complementary DNA (cDNA) was done on the coral tissues of A. humilis and G. fascicularis and also on their symbionts. Then purification and sequencing were done, the resulted sequence of G. fascicularis was uploaded at Genbank. After submission the sequence of sym32, GenBank assigned Accession Kx258627 for this sequence and AOG21003.1 for the protein of the same gene. This sequence is now available around the world via internet for everybody who would like to use it in his study and research.
In conclusion, The alignment of the sym32 gene sequences and its translated proteins of zooxanthellae were the same in both of A. humilis and G. fascicularis. This can be indicated that the zooxanthellae of the two Red Sea coral species are originated from the same Symbiodinium clade. Morover, the alignments of the translated sym32 proteins between the coral tissue and zooxanthellae were in the same range in the two species, demonstrating that the coding region which responsible for the gene expression in both samples was similar. This may be implied that sym32 gene expressed itself with the same mode in the two species. Therefore, further studies and researches should be done on other coral species of corals to confirm this finding and to see how this gene expressed itself.