IN THE FORMATION OF CORAL REEFS. 



351 



(5) In a series of counts on a line extending along the axis of White 

 Shoal, the average number of colonies to the square yard was 5.86 for 35 

 counts. On 5 squares no Gorgonians were found. In this series the condi- 

 tions on the southern end of the shoals were exceptional and were again due 

 to the hurricane of October 1910. At that time the larger portion of this 

 end of the shoal was covered by a mass of broken coral and shell to a depth 

 of 4 feet on the highest part of the reef. In January 191 1 an area, roughly 2 

 acres in extent, was laid bare at low tide. Across the entire crest of the reef 

 the water was 2 to 4 feet shallower than before the hurricane. In the course 

 of the next 18 months all of this loose material had been washed away, so 

 that the shoal was again back to its former level, but absolutely bare of Gor- 

 gonians. Within the interval since July 1912 a "set" of Gorgonians, almost 

 entirely of a single species, Gorgonia acerosa, has become established over 

 this area, so that a determination of the colonies on 75 square yards (includ- 

 ing 1 5 in the series along the axis of the reef) gave an average of 4 to the square 

 yard. On the northern three-fifths of this shoal, the Gorgonian fauna had 

 not suffered any extensive injury from the hurricane and was of the same 

 character as that found generally on the other reefs. 



Table 4. — Average weight oj a single Gorgonian colony. 



As a basis for the computation of the weight of Gorgonian colonies 

 occurring on any square yard of reef area, the figures given in table 4 show 

 the weight of a colony of the several species listed as determined by averaging 

 the weight of 20 colonies of medium size. 



Computed upon this basis, the average weight of the Gorgonian colonies 

 collected on the squares along the reef west of Loggerhead Key is 7.32 pounds. 

 Estimating by the average percentage of spicules (27.40 per cent) as deter- 

 mined for the II species as shown in table i, the average spicule content for 

 each square yard is 2 pounds. This result approaches very closely that 

 found by actual determination of spicule content of the Gorgonian colonies 

 on 20 square yards as given in table 2. Since the number of colonies per 

 square yard was in this series the smallest found in the counts on any reef, 

 the spicule content when estimated upon the same basis would be consider- 

 ably greater for many of the other reefs than the amount determined by 

 actual analysis as given in table 2. 



