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CARNEGIE INSTITUTION OF WASHINGTON. 



yard varied from to 32, while their weight varied from to 36.5 pounds. 

 The number and weight of the gorgonians with their spicule content growing 

 on a single dead coral (Meandra) head 26 inches in diameter is shown in the 

 following table : 



Gorgonians from a single coral-head. 



In order to obtain an estimate of the number of gorgonians over a large reef 

 area a line was run west-northwest from the laboratory on Loggerhead Ke}', 

 starting from the inner edge of the living reef, in about 1 fathom of water, 

 extending across the reef and down its outer slope to a depth of 6 fathoms. 

 Casts of the frame, a square yard in area, were made about every 30 feet so long 

 as the depth of water allowed of the determination of the specific identity 

 of the gorgonians with any certainty. Farther out, where the num])er only 

 of all the forms except Gorgonia acerosa and G. flabellum could be determined, 

 the casts were made from 50 to 60 feet apart. Along this line, which was 

 approximately 0.35 of a mile in length, in only 8 of the 45 casts did the square 

 fall on an area of bottom where no gorgonians were attached. The largest 

 number in any square counted was 17, and the average for the 45 casts was 

 5.72. Counts by means of the square-yard frame were made on nearly all 

 of the reefs about Tortugas over which the water was sufficiently shallow to 

 permit of the identification of the gorgonians. In many instances the counts 

 were continued down the slopes of the reef until soft bottom was reached 

 or the water became too deep for accurate counting. On the crests of the 

 reefs the proportion of squares where no gorgonians were found was in no case 

 higher than 1 to 10. The proportion of 1 to 5.6 for the long line previously 

 mentioned was due to the fact that on the outer and deeper portion of the 

 reef the gorgonians occurred in scattered patches over a sand}'- bottom. The 

 average of the determinations of the calcium carbonate (spicule) content of 

 the gorgonians from 20 square yards taken at random from the crests of several 

 reefs, where all of the gorgonians were removed, and the weight of their 

 spicules determined was 2.122 pounds per square yard or 5.28 tons per acre. 



These determinations show that on many of the reefs in the Tortugas group 

 the gorgonians are secreting an amount of calcium carbonate in their spicules 

 far in excess of that secreted by any other organisms (corals, mollusks, or 

 calcareous algae) living on the same reef. At present, however, sufficient data 

 are not at hand to warrant an estimate of the rate at Avhich this material is 

 actually added to the reef by the disintegration of the organic matter of the 

 gorgonian colonies and consequent liberation of their spicules. The facies of 

 the alcyonarian fauna on the reefs where studies on the ecology and growth 

 rate of these forms have been carried on for five years past has remained 

 practically unchanged during this period, except for the marked effects of the 

 hurricane of October 1910. At this time one section of reef south of Bush 



