ECOLOGY AND TAXONOMY OF Holimeda 



285 



(a) Hard substrates. Proceeding seaward onto the reef from the shore, 

 the first Halimeda species to appear, whether it be a member of the 

 Rhipsahs, Opuntia or Halimeda sections, is determined to a large 

 extent by the substrate available. On the Glory Be reef it is rock, and 

 sprawling over it are large, dense patches of opuntia, sometimes just 

 covered by most low tides, with holdfast filaments developing frequently 

 from between segments where the thallus makes contact with the 

 substrate. When the mapping-transect study was carried out, this 

 species occupied much of the surface of the very shallow inshore rock 

 (regions 2, 4 and 6; Figs 89-91, and Fig. 92) as well as the rock sides of 

 region 2, and rock sides together with coral outcrops of region 5. The 

 total Halimeda cover of the very shallow inshore rocks (region 2), given 

 in Table XXXIII, was the highest encountered in the parts of the reef 



Fig. 92. Clumps oi opuntia providing, at the site shown, about 50-60% thi-ee-dimensional 

 cover on rocks of the inshore reef of Glory Be, in about 1 m of water. The breadth 

 of most of the segments shown is 5-8 mm. 



