vaughan: geowth-rate of shoal-water corals 595 



labyrinthijormis, and Siderastrea siderea. Other corals, the most 

 important of which is Pontes astreoides, with Agaricia and 

 Favia fragum of secondary importance, occur in the area inter- 

 mediate between the prominent heads. In solne areas Acroyora 

 palmata is the dominant species. The massive heads form the 

 strong frame work of the reef, with infilhng by other corals and 

 other organisms. Therefore the upward growth rate of Orbicella 

 annularis on the reef is critical. The data on it will be repeated : 



Upward growth-rate of Orbicella annularis 



Annual average 

 Location mm. 



Ft. Jefferson, tiles outside moat wall 6 .57 



Loggerhead Reef, tiles 5.28 



Loggerhead Reef, nat. att 6 .80 



Golding Cay, tiles 5.67 



Golding Cay, nat. att 5.00 



The highest figure is for naturally attached specimens on 

 Loggerhead Reef, but the average is based on only 5 measure- 

 ments which are not so accurate as those of specimens on tiles. 

 The specimens attached to tiles all thrived and gave an annual 

 average of 5.28 mm. for 14 measurements; while the Golding 

 Cay specimens, which also thrived, gave an annual average of 

 5.67 mm. for 6 specimens, 2 years growth each. An estimate of 

 6 mm. for upward growth per year is probably somewhat liberal. 



25 4 X 12 



This would indicate for an upward growth of a foot, — '- = 



6 



50.8 years. Should 7 mm. be taken as the average the rate 

 would be 1 foot in 43.54 years. Using these figures as the basis 

 of a further computation, a reef by the continuous upward growth 

 of corals might attain at a rate of 6 mm. per year a thickness of 

 25 fathoms = 150 feet in 7620 years; and at a rate of 7 mm. per 

 year it might attain the same thickness in 6531 years. 



Should the growth rate of Acropora palmata be taken as a 

 measure, the time to accumulate such a thickness would be con- 

 siderably less. This species forms spreading, palmate fronds, 

 rising from stout bases. As age advances the fronds thicken 

 and can withstand the pounding of surf and breakers. The 

 average upward growth is between 25 and 40 mm. per year, 



