The brown algae Dictyota divaricata and the red algae Laurencia papillosa grow 

 in bundles, not epiphytic but intermingled with the leaves of the marine sea- 

 grass. As shown in Figure 1, the values for dissolved oxygen found among the 

 blades of Dictyota divaricata were always extreme, showing that this algae was 

 actually the species responsible for greater daily changes in dissolved oxygen 

 in the surrounding waters, in its microenvironment. 



Found on patches of exposed coralligenous sands were blue-green algae that 

 actually kept the sediment in place, forming crests. The sea-grasses in this 

 area (generally known factor) also retained at the base of their leaves the 

 particles of sediment that move with water currents, thus speeding up the rate 

 of sedimentation. 



On Figure 1 are shown the compilation of the data obtained during 11 days, 

 spread over a period of 24 hours, of the dissolved oxygen present among: 



1. Leaves of natural sea-grasses 



2. Leaves of artificial grasses 



3. Blades of Dictyota divaricata 



4. The water mass 2m above the ground 



The growth on the artificial sea-grass blades was not yet significant enough to 

 show daily variations in the content of dissolved oxygen, and thus its values 

 were the same as the oxygen content present in the water 2m above the grasses. 



2; 6.5 



X - Sea-gra: 



D - Artificial gv^i 



Q - Dictyot 



divai icata 



V 



\ 



\ 



\ 



\ 



^. 



\ 



\ 



"^S" 





\ 



\ 



-^V- 



\ 



x\ 



\ 



\ 



\ •/ 



HOURS OF DAY 



Figure 1. Compilation of data obtained during 11 days. Note: Differ- 

 ences in luminosity and water currents over the 11-day 

 period account for the extremes of the expected curve. 



VI-211 



