English: Coral (Galaxea fascicularis), Red Sea, Egypt. It's a species of colonial stony coral commonly known as octopus coral, fluorescence grass coral or galaxy coral among various vernacular names. It is a common species on reef slopes in the Red Sea, the Gulf of Aden and in large areas of the Indo-Pacific, and is kept by enthusiasts in reef aquaria. It has been found that the size and proximity of the corallites varies depending on the amount of light incident on the coral, even over different areas of the same colony. In bright positions, small, closely packed corallites maximise the photosynthetic potential of the zooxanthellae. In less well lit positions, there are larger corallites and polyps with longer tentacles with greater food capturing ability. It occurs on coral reef slopes, particularly where the wave action is weak. Its depth range is between 2 metres (6 ft 7 in) and 15 metres (49 ft). Galaxea fascicularis gets its food from two sources. The polyps contain symbiotic photosynthetic microalgae called zooxanthellae which, under good conditions, can obtain almost sufficient energy from sunlight for the coral's needs. It is also heterotrophic; the polyps extend their tentacles and catch and ingest organic particles, sediment, zooplankton, bacteria and even dissolved organic matter. This supplies the rest of the coral's needs. Galaxea fascicularis can reproduce asexually by budding. It also reproduces sexually, with both sperm and eggs being released into the water table in synchronized spawnings for external fertilisation.