304 



L. HILLIS-COLINVAUX 



-■ TTM - irr - ^ 



Fig. 102a. Grove of H. cylindracea in the lagoon near Enewetak Islet, Enewetak Atoll, 

 at a depth of approximately 1 •5-2-5 m. Young, mature and old thalli are present, 

 with many of the mature and older plants supporting relatively dense epifloral and 

 epifaunal populations. The thalli are also silted. There is a spreading mat of blue- 

 green algae over portions of the sand, and shed segments of Halimeda are 

 visible in the sand. Height range of thalli is c. 11-5-14 cm. 



species were only occasional. On the South Medren pinnacle gigas was 

 the most prominent Halimeda near the surface, that is at about —10 m. 

 The commonest Halimeda species on the three pinnacles in December, 

 both on their more or less horizontal tops and their gently sloping or 

 more often steep sides, was macro-physa. Halim^eda m,acro'physa also 

 grew in widely scattered clumps on rock patches away from the pinnacle 

 base. These deep-water thalli had few segments, however, in this way 

 differing from the more familiar shrubbier plants of the sun-flooded 

 shallows. 



On two of the pinnacles Tydemania expeditionis was draped over 

 considerable areas, in water only 8 m deep. Gilmartin (1966) reported 

 it as prominent at the sites of some of his deepest dives in the lagoon, 

 to about — 63 m. Lush patches of this alga, which generally has been 

 considered a deep-water plant, were also observed at depths of — 3 m 



