116 



COLIN 





Fig. 19 Typical views of seaward reefs off the southwestern islands off Enewetak. Upper left: Rubble area to seaward of the reef 

 flat, depth 5 m. Upper right: Area of isolated coral heads seaward of rubble area. Lower left: Small acroporid corals on the outer 

 reef face, southwestern islands, depth 20 m. These corals are probably less than 10 years old and may represent recruits after 

 major storm damage to the community. Lower right: Outer slope along the southwest islands, depth 20 m. The bottom slopes 

 away at about a 45° angle to great depths. 



often mounds or ridges of talus and carbonate blocks more 

 than 1 m across. 



There was some relief on the rock face at 100 m to 

 about 180 m, often with the surface pitted with shallow 

 depressions less than 50 cm across. There were occasional 

 small caves, seldom penetrating more than 1 m into the 

 reef face. 



Stony corals were observed to grow relatively deep. 

 Below about 60 m only flattened forms were found. Sparse 

 coral communities occurred to at least 90 m depth, with 

 individual colonies occurring to slightly more than 100 m 

 depth. Similarly, attached and living Halimeda colonies 

 were found at more than 120 m (HillisColinvaux, 1986). 

 Green algae were found to almost 150 m and coralline 

 algae to nearly 200 m. 



Some differences in biological zonation were noted 

 between the windward and leeward slopes. The windward 

 areas have more coral at 60 to 90 m depths, larger popu- 



lations and diversity of small reef fishes from 60 to 200 m, 

 and generally more benthic invertebrates. 



In the wide channel area, there seemed to be much 

 down slope transport of sediment, although again the steep 

 slope at 100 to 200 m trapped relatively little sediment on 

 the face. Below about 200 m, huge slopes of Halimeda 

 with seapens growing on them were found (Colin et al., 

 1986). At the eastern edge of the wide channel this uncon- 

 solidated slope was alternating elevated areas of talus and 

 the sand between "pure" sand slopes. 



Lagoon Water Column 



The waters of the lagoon have not received adequate 

 attention. Recent work has examined the circulation of the 

 lagoon (Atkinson et al., 1981), the relationship between 

 reef-produced organic material and lagoon plankton 

 (reviewed in Gerber and Marshall, 1982) and plankton 



