Ten species of the tropical genus, Caulerpa, have been investigated in 29 sites on the Egyptian Red Sea coasts during the period of 1994-1999. These were C. fastigiata Montagne, C. lentillifera J. Agardh. C. mexicana (Sonder) J. Agardh, C. racemosa (Forsskål) J. Agardh, C. peltata Lamouroux, C. scalpelliformis (R. Braun) C. Agardh, C. serrulata (Forsskål) J. Agardh, C. sertularioides (Gmelin) Howe, C. taxifolia (Vahl) C. Agardh, and C. webbiana Montagne. The study describes how their morphology and growth vary along the gradient of habitat conditions. An identification key, original descriptions, illustrations and biogeographical data are also added.
The locality type of the species is the Indian Ocean. C. racemosa and C. serrulata are the most common, while other species were frequent or rare, forming small dense patches where appeared. Six of the identified species were found in the Suez Canal, three of which overrunning the eastern Mediterranean. C. serrulata seems to prefer habitat of open waters, and thus may be excluded from migration through the canal.
The species of Caulerpa prefer growing on sand or mud, dominating several photophilic and sciaphilic biotopes in the infralittoral, frequently inhabiting the littoral zone where the bottom never exposed to air. When found on hard substrates, the species inhabited the area covered by a layer of sand. The length of rhizoids seems to be dependent upon the depth of sand in which the plant anchored. Successful growth of species was observed in nutrient rich bottoms, and sites protected from waves. The variability in species morphology in relation to habitat conditions is evident and reflects differences in light.