ZOOLOGY: L. R. CARY 
289 
There is no evidence that gorgonian colonies ever die from old age 
and to the agencies mentioned above is to be attributed the destruction 
of all those colonies the skeletons of which are found on the reefs. The 
fascies of the gorgonian fauna on any reef remains practically unchanged 
from year to year except for the introduction of the unusual factor of 
extensive destruction of the colonies by severe storms. The determina- 
tion of the number of skeletons of dead colonies on any reef area will, 
therefore, afford the most practicable method of obtaining the death- 
rate of these organisms. This method unfortunately has the serious 
drawback that the results will always be too low because when the 
colonies are torn from their attachment on the reef by severe storms 
some of them will be carried so far from their original location that 
they will not be included in a count of skeletons on any given area. 
The percentage of axial skeletons to living colonies on a small reef 
where the entire number of colonies has been counted each year since 
1910 has varied from 11.67% to 24.80% with an average of 17.22% for 
the six counts. On other reefs in the Tortugas region the destruction of 
gorgonians was nearly complete in the hurricane of October 17, 1910. 
In some restricted areas the amount of spicules set free from disinte- 
grating gorgonian colonies was as much as 25 pounds to the square yard. 
On the basis of all the recorded observations it seems probable that, at 
a conservative estimate, about one-fifth of the gorgonian colonies on 
any reef area will be destroyed annually. 
Since the fascies of the gorgonian fauna on the reefs remains relatively 
constant, and it is estimated that about one-fifth of the number of 
colonies are destroyed annually, it is important to determine the growth 
rate of the several species of these organisms which make up the most 
important elements in the gorgonian fauna. 
Growth records for the species entering into this study have been 
kept for a period sufficiently long to cover the period from the time 
of their attachment as planulae to the attainment of the normal average 
size of the colony. The time necessary for this growth varies from two 
years (Gorgonia citrina), to five years (Gorgonia acerosa). The time 
necessary for any of these colonies to reach the average size falls well 
within the limit marked by the observed rate of destruction which 
would be necessary to maintain the constancy of the gorgonian fauna 
of any reef. Some few of these species appear to keep growing for an in- 
definite period after the medium size for the colony has been reached, 
but in such instances the growth is very slow after this time and would 
not greatly influence the general results. 
