DEPARTMENT OF MARINE BIOLOGY. 191 



Alfred G. Mayor completed the measuring, weighing, and photo- 

 graphing of all corals which had been under observation at Samoa 

 and Fiji, some of them having been observed since 1917. The corals 

 on the barrier reef off Suva Harbor, Fiji, had made little or no growth, 

 and large areas of the reef had died since August 1918. A clue to the 

 cause of this abnormal death-rate of corals in Fiji may be found in 

 the histoiy of the Samoan reefs in 1920. Thus, from May 15 to 21, 

 there were exceptionally low tides, accompanied by unusual calm 

 and hea\y rains, and thousands of heads of Acropora leptocyathus, 

 which were exposed to the rain and were above the wash of the waves, 

 were killed. Even more destructive was the 37.5 inches of rain which 

 fell at Pago Pago between June 28 and July 1, 1920. The whole inner 

 half of the barrier became covered with densely muddy water, so that 

 one could not see an inch beneath the surface. We found that each 

 cubic yard of this surface-water contained 1 ounce avou'dupois of fine 

 brown mud. This killed thousands of Acropora arcuata, but the 

 A. leptocyathus were not so readily affected. In places near shore 

 many large heads of Porites, which were more than 50 years old, 

 were killed, and possibly some such condition may have largely killed 

 the reefs off Suva, Fiji, ^during 1918-1920. 



It was found that reef corals are not very sensitive to even large 

 quantities of CO2 in the sea-water, for we introduced carbon-dioxide 

 gas into the water until the Ph declined from 8.25 to 5.9 Ph, thus be- 

 coming decidedly acid at 28° C. The introduction of the carbon dioxide 

 displaced some of the oxygen from the sea-water, but it was found 

 by means of Winkler's method that the rate of oxygen consumption 

 by the corals was simply proportional to the concentration of oxygen 

 in the sea-water and no toxic effect due to CO2 could be determined 

 after 2 hours' immersion in the acid sea-water. The concentration of 

 oxygen in sea-water over shallow reef-flats varies greatly. Thus, on 

 the Aua reef, in water about 5 inches deep, impounded for 2 hours by 

 the low tide, the oxygen rose from 4.07 c. c. per liter to 8.44 c. c. per 

 liter, the temperature rising from 26.7° to 27.4° C, and the saUnity 

 changing from 34.7 to 34.79. The corals were uninjured by this change, 

 and the effect was doubtless due to photosynthesis by plants growing 

 over the reef. 



Professor L. R. Caiy continued his observations on the growth-rate 

 of Alcyonaria in Samoa, and he will make a special study of the bio- 

 logical constitu tents of the borings through the Utelei and Aua reefs 

 in order to determine the share taken by niadreporarian and alcyon- 

 arian corals and by limestone-forming plants in building up the reefs. 



Professor RolUn T. Chamberlin made a study of the geologic history 

 of the living and extinct reefs surrounding Tutuila, and we have already 

 quoted from his preliminary report, which he publishes herewith. 



Professor E. Newton Harvey continued his experiments upon the 

 chemical nature of the substances which produce luminescence in 



