Morphological Characterization of Halimeda (Lamouroux) from Different Biotopes on the Red Sea Coral Reefs of Egypt

2 Abstract: The genus Halimeda (Lamouroux) was examined on the basis of collection made from nine locations during 1999-2008 along the Egyptian Red Sea coral reefs with emphasis on the effect of illumination at different biotopes on the morphology of the species. Five species were identified: Halimeda monile (Ellis and Solander) Lamouroux, H. macroloba Decaisne, H. opuntia (L) Lamouroux, H. discoidea Decaisne and H. tuna (Ellis and Solander) Lamouroux. These species are described in detail with original illustrations and an identification key. As for Halimeda monile and H. macroloba showed no marked changes in relation to light conditions; H. opuntia showed marked difference in branching pattern and segment shape; whereas H. discoidea and H. tuna exhibited very similar gross morphology that makes difficulties in distinguishin g some specimens. Nodal structure seems to vary less at different biotopes and, therefore, is more useful in species identification. Southern area of the Egyptian Red Sea coast favored the growth of all species while, only H. opuntia and H. tuna were found in the northern area and this may point out for conservation of the reef communities.