l8 PAPERS FROM THE DEPARTMENT OF MARINE BIOLOGY. 



rounded patch of living polypites 1 1 inches in diameter near the western side 

 of the dead area. When Saville-Kent measured this coral in June 1890 he 

 found it to be 30 inches in diameter and dome-shaped; thus it has apparently 

 increased 44 inches in diameter in 23.33 years or at the rate of 1.88 inches 

 (48.75 mm.) per annum. 



The large "light brown Porites," ("P. astraoides") shown in figure 1 on 

 page 8 of Saville-Kent's "Great Barrier Reef," and which he states was 19 

 feet wide in 1890, is now 22 feet 9.5 inches wide. Thus it appears to have 

 increased in width by 45.5 inches during the past 23.33 years, or at the rate 

 of 1.95 inches per annum. 



On the other hand, the "gray-green Goniastrea," which Saville-Kent 

 states to have been 8 feet 2 inches wide in 1890, was 8 feet wide according to 

 my measurements on November 9, 1913, and therefore it appears to have 

 grown but little if at all during the past twenty-three years, and in conformity 

 with this conclusion we may observe that the "2-foot channel" described by 

 Saville-Kent, which extended in 1890 between this "gray-green Goniastrea" 

 and the "light brown Porites" has been reduced to a mere cleft not more 

 than an inch or two in width; it thus appears to have been closed solely by 

 the growth of the Porites and not by that of the Goniastrea. 



Saville-Kent speaks of a submerged Porites covered by Pocillopora 10 

 inches in diameter (fig. 2, page 8). The Pocillopora has disappeared, but a 

 submerged Porites apparently occupying the same situation near the Sym- 

 phyllia was 16.5 inches wide in its widest diameter, in November 191 3. 



We are led to conclude that, while some of the large massive reef corals 

 increase in diameter at a rate of nearly 2 inches per annum, others (such as 

 the "gray-green Goniastrea") may, after attaining a certain size, cease 

 growing. Indeed, Vaughan has already observed that this was the case with 

 most if not all of the Florida corals and he also showed that large stocks which 

 had practically ceased to grow or were growing very slowly could be induced 

 to resume a rapid growth-rate by breaking them apart and planting the 

 fragments in concrete. 



The more fragile coral stocks, such as Acropora and Pocillopora, are 

 either short-lived or easily destroyed, for none of those seen and measured 

 by Saville-Kent in 1890 could be found in 1913. 



It is evident that if large massive coral heads (as Porites and Symphyllia) 

 can add nearly an inch to their radius each year, they could fill up a channel 

 at the rate of almost a foot in twelve years, which is fairly close to Gardiner's 

 estimate, based upon a study of the growth-rate of Maldive Island corals, 

 that they might build a reef at the rate of a foot in eleven and a half years, 

 or as Gardiner puts it, 14.5 fathoms in one thousand years. 1 



Although the growth-rate of corals has attracted attention from the 

 earliest times, yet records of carefully made measurements are rare in the 



'Gardiner, J. Stanley, 1903, Fauna and Geography of the Maldive and Laccadive Archipelagoes, vol I, 

 pp. 327-333. 



