306 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1947 



As the tide rises and the surf breaks over the lithothamnium ridge, 

 then surges several inches deep across this flattened part of the reef, 

 great schools of blue-green and dark-red parrot fishes, Scarus, often 

 with their backs exposed in the shallow water, move about on the reef, 

 grazing like a herd of sheep on the algae growing there. Their tooth 

 marks, remaining on the rocks, are easily observed. Wlien the water 

 deepens to a foot, surgeon, needle, trumpet, halfbeaks, damsel, goat- 

 fishes, mullet, and dozens of other kinds appear. The black-tipped 

 shark, Eulamia malanoftera^ with its black-tipped fins sometimes 

 exposed, cruises around on the reef, too. Although they are speedy 

 swimmers, a man with a rubber sling and spear, or with a gun, may 

 capture them without difficulty. 



ISOLATED TIDAL POOLS AND SOLUTION CHANNELS 



Around the shores of certain islands are small tidal pools and solu- 

 tion channels that are eroded in the limestone beach rock. They re- 

 main more or less filled with water at low tide. These depressions are 

 from a few inches to a foot deep, with rounded smooth sides. They 

 vary from a few inches to a few feet in width. Some appear as shal- 

 low pot holes but with the seaward side cut away. On the bottom in 

 favorable places were accumulated coral fragments and occasionally 

 pieces of beach rock. 



During the period of low tide, several kinds of blennies appeared to 

 be trapped in the pools. They remained motionless with their tails 

 curved to one side, then suddenly, when disturbed, would flip through 

 the air from one pool to another over the rocky ledges. Their agility 

 and speed of traveling over "dry land" astounds one on his first visit 

 to a reef. The young of Kuhlia^ mullets, and damsel fishes regularly 

 remain in these shallow pools. The goby Bathygohius is a frequent 

 inhabitant, too. Hiding or trying to hide among the loose beach rocks 

 and in the pools was the black speckled moray eel, Gym/nothorax picta, 

 sometimes curled between black sea cucumbers. As the incoming tide 

 rose and refilled the solution channels and pools, the dark-banded 

 damsel fish, Ahudefduf septemfasciatus^ returned to its favorite habitat 

 along the very edge of the beach rock. 



LITHOTHAMNIUM RIDGE 



The outer margin of an atoll rim on the ocean side usually consists 

 of the slightly raised pink to red-colored lithothamnium ridge con- 

 trasting beautifully with the deep blue ocean beyond. It is dissected 

 by rugged surge channels and deep pools often 20 feet deep directly 

 connected with the ocean. This ridge, creviced and pitted with holes, 

 is about a foot or two higher than the flat part of the reef farther 

 inward and varies in width from 40 to 100 feet. At extremely low 



