344 THE GORGONACE^ AS A FACTOR 



On many reefs, e. g., on portions of the Great Barrier Reef of Australia 

 (Saville-Kent) and those of the Philippine Islands,^ the Alcyonaceae, whose 

 skeletons consist of loose spicules, constitute a large part of the lime-secreting 

 fauna. Their spicules are, however, so small and so easily broken apart that 

 they have not been recognized in samples of the coral rock from these reefs. 

 Saville-Kent, in writing of the "Alcyonarian reefs" of Australia, states that 

 the amount of lime secreted as spicules by these forms must be large, but is 

 not available for addition to the reef until the death of the colony and the 

 disintegration of the coenenchyma have set free the spicules. Although a con- 

 siderable portion of his work is devoted to a consideration of the rate at 

 which reef-formation takes place, he dismisses the matter of the contribution 

 of lime by the Alcyonaria with the above statement. 



In the Florida-Antillean region the most abundant representatives of 

 the Alcyonaria are the plume-like Gorgonaceae; but in this region the only 

 forms which have a dense lime-bearing axial skeleton belong to the family 

 Isidae. All other forms have free spicules which are scattered on the disinte- 

 gration of the living tissues. 



On all the coral reefs of the Florida-Antillean region which the writer 

 has visited, the area occupied by living coral is so small, in proportion to the 

 entire reef area, that it has seemed to him beyond question that some other 

 organisms must be more actively participating in the laying down of lime on 

 the reef. In many localities the Gorgonians growing on the shallow portions 

 of the reef — down to 6 fathoms — constitute by far the largest part, either 

 numerically or in bulk, of the organisms permanently attached to a given 

 reef area. Besides, the presence of Gorgonian spicules in nearly all bottom 

 samples from the reef, and even in the soft mud from the channels between 

 the reefs, indicates that they remain in a recognizable condition for a con- 

 siderable time after the disintegration of the colony and might be incorporated 

 in the reef limestones before they had undergone marked erosion. On the 

 basis of the two last-mentioned facts it seemed to me evident that the Gor- 

 gonians must be an important contributing factor in reef limestone formation. 

 The greater part of the time during a stay of six weeks at the Marine Labora- 

 tory of the Carnegie Institution of Washington at Dry Tortugas, Florida, 

 during the summer of 1914, was therefore devoted to a study of this problem. 



Three factors must be taken into consideration in order to determine the 

 amount of material contributed to reef-formation by the Gorgonians during 

 any given time: First, the amount of lime held as spicules in the tissues of 

 these colonies; second, the number of Gorgonians present on any reef area; 

 and third, the number of colonies which will set free their spicules on account 

 of the death and subsequent disintegration of their coenenchyma. 



'Based upon a private communication from Mr. S. F. Light, instructor in biology at the University of the 

 Philippines, Manila. 



