X-radographs of vertical sections of Porites colonies (P. lobata and P. columnaris) from coral reefs of the northern Red Sea were examined for their linear growth rate and skeletal density patterns. Results provide the first sclerochronological record of Red Sea corals. Corals sampled from the same area showed marked variations in their linear growth rate. Average growth rates were 7.48 + 1.78 mm yr-' for P. lobata and 5.68 f 1.52 mm yr-' for P. columnaris. High density deposition bands occur

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... ring winter (December to May; low light intensity and seawater temperature), and low density deposition bands during summer (June to November; high light intensity and seawater temperature). A model that relates exogenic factors (e.g. temperature and light) and an endogenic factor (e.g. reproduction) to the density band depositional pattern 1s presented. It is concluded that in the Red Sea water temperature and light intensity are the major factors controlling the identity of band formation in Porites corals, while reproduction is probably of lesser Importance