598 vaughan: growth-rate of shoal-water corals 



but as the interspaces between the fronds are considerable 



in volume, comparisons with Orbicella annularis must be based 



upon relative increases in weight for a known period. The total 



of the weights* of 5 specimens of Orbicella annularis in 1912 was 



1886 grams; the total increase in weight of the 5 specimens in 



1114 

 2 years was 1114 grams, or 7W^ = 59.1 per cent. The average 



annual increase in height of these specimens was 5.7 mm. 



The total of the weights of 5 specimens of Acropora palmata 

 in 1912 was 745 grams; the total increase in the weight of the 



1727 



same 5 specimens in 2 years was 1727 grams, or = 231.8 



per cent. The average annual increase in height of these speci- 

 mens was 24.4 mm. 



According to weight, the specimens of Acropora palmata have 

 grown 3.91 times as fast as .those of Orbicella annularis; this 

 may be stated in round numbers as 4 times as rapidly, while 

 the increase in height is 4.28 times as rapid. Therefore a reef 

 composed of Acropora palmata might grow upward at the rate 

 of about an inch per year, a growth which would produce a 

 thickness of 150 feet in 150 X 12 = 1800 years, but it is not 

 probable that conditions so favorable have ever been realized 

 in any area for a protracted period. 



These two estimates give a measure of the limits of reef forma- 

 tion under continuously favorable conditions for upward growth. 

 Such corals as Orbicella annularis might form a reef 150 feet 

 thick in between 6500 and 7600 years; while such corals as Acro- 

 pora palmata might form a similar thickness in 1800 years. 



A few references to previous literature will indicate the rate 

 of growth of Pacific and Indian ocean corals. 



H. B. Guppy^ has furnished interesting data on the rate of 

 growth of corals around Keeling Atoll, including in his account 

 the results of some experiments by G. C. Ross. According to 

 Guppy, arborescent Acropores ''grow at the average rate of four 

 to five inches in a year, and will attain their full height in about 



* The weights are of the wet living corals. 

 6 Scottish Geog. Mag., 5: 573-376. 1889. 



