DEPARTMENT OF MARINE BIOLOGY. 



197 



The Alcyonaria as a Contributing Factor in Coral-Reef Formation. 



Among the alcyonaria, representatives of those families alone — Tubiporidse, 

 Helioporidse, and Corallidse — which form a massive skeleton are the only ones 

 which have received any serious attention as contributing actively to the 

 accumulation of calcium carbonate in coral-reef regions. The remaining 

 Alcyonacese and Gorgoniacese — the so-called flexible corals — have been in 

 general neglected from this point of view, although in many regions they are 

 the only representatives of the alcyonaria occurring on the reefs. 



Since practically all alcyonaria are restricted to hard bottoms, their distri- 

 bution in the Florida- Antillean region corresponds to that of the coral-bearing 

 reefs, so that the calcium carbonate accumulated in their spicules will be 

 deposited directly on the gro^ving reef. The spicules will, in any case, be set 

 free only after the disintegration of the organic tissues of the colony, but the 

 almost universal presence of such spicules in bottom samples taken over the 

 surface of the reefs shows that they must remain on the bottom for some time 

 without undergoing marked erosion. 



In order to determine the amount of calcium carbonate held as spicules in 

 the tissues of gorgonian colonies, specimens of the 10 forms occurring in 

 greatest abundance about the Tortugas were collected, weighed while still 

 wet, and the organic matter of the colony disintegrated by treatment with 

 a strong solution of caustic soda. After repeated washings in rain-water the 

 clean spicules were collected on a weighed filter, dried at 100° C. in a water- 

 bath, and their weight determined. By this procedure both the actual amount 

 of spicules and their proportion to the fresh weight of the colony was deter- 

 mined. The percentage of spicules in reference to the fresh weight of the 

 entire colony made it possible to estimate with a fair degree of accuracy the 

 amount of calcium carbonate held as spicules in any given mass of fresh 

 gorgonians. 



The following table gives the percentage by weight of spicules for 10 of 

 the most common forms of gorgonians found about Tortugas, as determined 

 by averaging five analyses: 



Percentage of weight of spicules to fresh weight of gorgonians. 



Collections of the gorgonians were made on several reefs in water sufficiently 

 shallow to permit wading, and separate determinations were made of the total 

 weight of the mass taken from one square yard and that for each of the com- 

 ponent species. The spicule content was determined separately for each 

 species, either by direct analysis or by multiplying the fresh weight of the 

 colonies by the percentage of spicules previously determined by several 

 analyses of the same species. In deeper water a square frame, made from 

 iron pipe with sides one yard in length, was lowered to the bottom and the 

 specific identity, number, and size of the gorgonians determined by use of a 

 water glass. On the shallow reefs the number of gorgonians found on a square 



