DEPARTMENT OF MARINE BIOLOGY. 



231 



by G. C. Ross. According to Guppy, arborescent acropores "grow at the 

 average rate of 4 to 5 inches in a year, and will attain their full height in about 

 fifteen years." He estimates that branching species of Pontes grow upward 

 at the rate of 1.5 inches per year, while the annual upward growth of massive 

 species of Pontes is from 0.5 to 0.75 inch per year. Montipora, of the facies of 

 M. digitata, is said to have an upward growth of not less than 5 inches per year. 

 J. Stanley Gardiner and F. Wood-Jones have made valuable contributions 

 to the knowledge of the growth-rate of Indo-Pacific corals. Wood-Jones has 

 summarized the data in a privately published paper entitled, "The rate of 

 growth of reef building corals." His observations in Cocos-Keeling Islands 

 corroborate the estimates of Guppy. According to his recomputation of the 

 data supplied by J. Stanley Gardiner, based on a collection of presumably 

 3-year-old corals from Hulule, North Male Atoll, a general average of the 

 upward growth for branching forms is about 44 mm. per year, while that of 

 massive forms is about 29 mm. J. Stanley Gardiner's estimates for the massive 

 forms would be as follows: 



As it is probable that these corals, especially the massive ones, are more than 

 3 years old, I am incHned to the opinion that the estimates for the massive 

 species are too high. Guppy's estimate of the upward growth of massive 

 Pontes, 12.7 to 19.05 mm. per year, seems better founded and falls within the 

 range of a number of the measurements on Pontes astreoides. 



Recent remeasurements by Mayer of some of the corals measured and 

 marked by Saville-Kent at Vivien Point, Thursday Island, Torres Straits, 

 Australia, indicate an annual increase in diameter of 1.9 inches per year. As 

 in massive corals the increase in height is usually one-half to two-thirds that 

 in diameter, the increase in height would probably be between 24 and 32 

 mm. per year, or approaching the figures given by J. Stanley Gardiner and 

 F. Wood-Jones for massive forms. 



The data available for the Pacific corals are not so abundant as those for 

 the Atlantic, nor have the records, with few exceptions, the same degree of 

 precision. However, they are sufficient for some general comparisons. The 

 general gi'owth-rate of branching corals is nearly the same for both regions; but 

 the growth of the massive forms in the Pacific appears to be appreciably 

 more rapid than that of similar forms in the Atlantic. Therefore, it seems 

 probable that in the coral-reef regions of the Pacific and Indian Oceans a reef 

 150 feet thick may form under favorable conditions in less than 6,000 years. 

 According to Gardiner such a reef might form in 1,000 years. 



As the disappearance of the last continental ice sheets is estimated to have 

 been between 10,000 years ago in Scandinavia and Alaska and 40,000 years 

 ago at Niagara, the data presented show that there has been ample time for the 

 development of any known living reef since deglaciation. That recent offshore 

 reefs have been formed either during or immediately subsequent to Recent 

 submergence may be accounted estabhshed. That deglaciation was an im- 

 portant factor in this submergence can scarcely be doubted, but there are other 

 factors which have not yet been evaluated. 



