350 THE GORGONACE^E AS A FACTOR 



Along this line, which was approximately 0.35 of a mile in length, in 

 only 8 of the 45 counts made did the frame fall upon an area of bottom upon 

 which no Gorgonians were growing. The largest number counted on any 

 square yard was 17. The average for the whole 45 counts was 5.72. Counts 

 upon a number of other reefs in different parts of the group show that the 

 proportion of squares on which no Gorgonians were found was considerably 

 higher along this line than that obtained by averaging all of the counts. 

 The average of one empty square to each 5.6 of those counted as found in 

 the series recorded in table 3 is almost twice as great as the average for all 

 the counts made on the reefs about Tortugas, which was one empty square 

 in each 10.03. Besides the counts along this line, other series were made on 

 nearly all of the shallow reefs in the Tortugas group. The most important 

 were the following (Plate 100): 



(i) 1 A line about 2.5 miles in length running nearly northeast along the 

 crest of the West Reef from opposite Loggerhead Key to the northwest 

 channel. The average number of Gorgonian colonies for the 150 counts 

 along this line was 8.97. In only 14 casts did the frame fall upon an area of 

 barren bottom. 



(2) A series of counts on 4 small reefs east of the northwest channel 

 where in each instance the line of countings was extended from deep water 

 on one side of the reef over its crest and down to deep water on the other 

 side. The average number of Gorgonian colonies for the 30 counts made 

 on 3 of the reefs in this locality was 10.86. In 3 casts the frame fell upon 

 barren bottom. 



(3) Along a line running north-northwest from the Pulaski Shoal buoy, 

 from the edge of the Rebecca Shoal channel over the reef and to deep water 

 on its inner side, 25 counts were made. The average number of Gorgonian 

 colonies for 20 counts along this line was 7.62, while in only one of the casts 

 did the frame fall upon an area of barren bottom. 



(4) In a series of counts along the outer side of Long and Bush Keys, 

 starting from the northwestern end of the former, extending along the north- 

 east channel, and then down the outer face of the long reef to the southward, 

 the average number of Gorgonian colonies found in 40 counts was 13.27. 

 The number of squares upon which no Gorgonians occurred was 7. This 

 series of counts extended over an area upon which there was a very unusual 

 destruction of Gorgonians during the severe hurricane that had its center 

 in the Tortugas region on October 17, 1910. The unusually large number of 

 colonies found is probably due to the fact that the normal conditions for the 

 Gorgonian fauna have not as yet been re-established. Nearly all of the 

 colonies occurring on this section of the reef were of small size, so that the 

 spicule content of the Gorgonians upon any square yard would be below the 

 average found for the det ermination based upon the counts from other reefs. 



'Details of the counts along these lines are given in tables 10 to 14 in an appendix to this paper. 



