The deep fore-reef at Enewetak has been examined from the submersible Makali'i. Green algae grow to about -150 m at photon flux densities of approximately 1 μEm-2s-1. Halimeda cover is ≧50% at many sites down to -90 m. Halimeda populations are important within the zone of scleractinian corals down to about -65 m, while a Halimeda zone with low coral cover or lacking corals between -65 m and -150 m probably is an important source of reef carbonate. Halimedas of the deep fore-reef, like those of the lagoon, constitute an important structural component in reef building. Other calcareous green algae such as Tydemania are less important on the deep fore-reef, but growth of coralline red algae continues to over -200m. Halimeda diversity is high down to near the base of the euphotic zone.