DEPARTMENT OF MARINE BIOLOGY. 151 



flats, and it was found that the amount of sand washed off from the 

 reef flat of fringing reefs and destroyed by holothurians is greater than 

 the weight of Hmestone gained due to the growth of corals upon the flat. 



Professor Gary desired to drill through the fringing reef in Pago 

 Pago Harbor in order to obtain a core so that he might determine the 

 relative importance of the Alcyonaria in building up the reef, he hav- 

 ing found that in Florida the Alcyonaria are more important as reef- 

 builders than are the stony corals. Mr. Mills, using the Davis calyx 

 drill, succeeded in drilling through the fringing reef off Utelei village, 

 Pago Pago Harbor, 575 feet from shore, and ran into volcanic rocks un- 

 derlying the coral reef at a depth of 121 feet. The material fragmented 

 so readily, however, that no continuous core could be obtained, but 

 it is believed that this difficulty can be overcome and upon our next 

 return to Samoa another attempt will be made to solve the problem. 



Moreover, we have found places so well protected from dangerous 

 breakers that it will be possible to work in diving-hoods on the pre- 

 cipitous outer faces of the reefs and gain a quantitative knowledge of 

 the conditions of coral growth on the submerged seaweed wall of the 

 reef. The growth-rate of corals at various depths can also be deter- 

 mined, and possibly one may discover the reason for the decided 

 reduction in the number of coral heads at depths greater than 20 

 fathoms. For this purpose also we hope to return to American 

 Samoa as soon as war conditions will permit. 



Many tests were made of the streams and springs of Tutuila and 

 Upolu, Samoa, and of Viti Levu Island, Fiji, and all were either weakly 

 alkaline, neutral, or so slightly acid that even the most acid would 

 give a neutral solution upon being mixed with sea-water in the pro- 

 portion of 8 parts of stream-water to 1 of sea-water. 



It seems well established that the reef flats frmging these volcanic 

 islands of the Pacific can not be dissolved by any hypothetical "acidity" 

 of the usually alkaline surface water which drains outward into the 

 sea. At the same time we must be mindful of the fact that the reason 

 tropical sea-water does not dissolve coral reefs is that it is practically 

 saturated with calcium. The stream-water of Tutuila is, however, 

 only about 1/100 saturated with calcium, and thus when it dilutes 

 the sea-water over the reef flats the mixture may dissolve calcium. 

 Experiments are in progress to determine this effect. 



The only acid streams found were the Tamavua, Lami, and Visari 

 Rivers flowing mto Suva Harbor, Viti Levu Island, Fiji, and these 

 were only 6.6 PH or nearly neutral for the average temperature of 

 25° C. of these streams. It was found that in the dry season the springs 

 and streams of Tutuila are less alkaline than they are in the wet sea- 

 son, when swoUen by the seepage from the surface soil, containing as 

 it does a considerable charge of sea salts derived from the ocean spray. 

 On the other hand, the permanent springs which alone maintained the 



