The calcareous green alga Halimeda is common in shallow lagoon sites of Enewetak Atoll, and accounts for a high percent of the total reef carbonate budget. It has now been possible to survey outside the atoll for Halimeda, where large populations were found down to 100 m and growth to over 140 m. Halimeda sediments were observed to over 360 m. In a series of vertical and horizontal transects of windward and leeward outer slopes using the submersible Makali'i, two of the three growth strategies, that is rock growers and sprawlers, were observed. Sand growers eventually may be found but cannot be expected to be important in the economy of the reef wall. At least nine species, or ¾ of the rock-associated species known for Enewetak, grow on the outside, and as many as six of these extend to at least 60-m depths. No species has been found yet which is restricted to deep water. Although most of the common species span a wide bathymetric range some may predominate at certain depths. At 90 m Halimeda still provided considerable cover and greatly exceeded the cover by hermatypic corals. Halimeda also grew considerably deeper than the corals. The role of light and temperature in determining the depths to which Halimeda and other algae grow is discussed.

Depth range
50- 140 m

Mesophotic “mentions”
0 x (total of 6315 words)

Classification
* Presents original data
* Focused on 'mesophotic' depth range
* Focused on 'mesophotic coral ecosystem'

Fields
Ecology
Community structure
Connectivity
Oceanography

Focusgroups
Algae (Macro, Turf and Crustose Coralline)

Locations
Micronesia - Marshall Islands

Platforms
Manned Submersible
SCUBA (open-circuit or unspecified)
In-situ instrumentation