DEPARTMENT OF MARINE BIOLOGY. 



143 



OBSERVATIONS ON GORGONIANS. 



A series of measurements to ascertain the rate of growth of several species 

 of gorgonians was begim in June 1910. In so far as was possible, on account 

 of the weather conditions, the specimens for which measurements were re- 

 corded at that time were remeasured on January 10 to 12, 1911, when the 

 writer visited Tortugas in company with Dr. Mayer. The same colonies 

 were measured again on July 22, 191 1. 



The following table shows the actual lengths of a number of gorgonians 

 on a single coral-head at the dates when measured and the percentage of 

 increase in approximately one year : 



♦Could not be niea>ured. 

 t Not measured. 



The measurements made in January 1911 are incomplete and to a greater 

 extent inaccurate, on account of the difficulties caused by the roughness of 

 the water. Specimens i, 2, and 4 of G. Hahellum had been exposed to the air 

 at an unusually low tide on June 6, 1910, and as the result the uppermost end 

 of each colony was killed. When they were measured in January 1911 all 

 evidence of this injury had disappeared. 



With all of the other colonies measured the results were, in general, the 

 same. Those which were smallest when first measured showed the largest 

 percentage increase in size, while the smallest increase, actual as well as 

 by percentage, was found in those colonies which were largest when first 

 measured. 



During the present summer the measurements were extended to include a 

 much greater number of colonies of the two species previously mentioned, 

 and to specimens of 5 other forms. Specimens of all the forms were ce- 

 mented to tiles, measured, photographed, and fastened by iron pins on the 

 reef near Loggerhead Key. On one small reef all of the colonies of Gor- 

 gonia flabellum, G. acerosa, and Plexaura Hexuosa (148 in number) were 

 measured and classified in arbitrary groups, according to size, as follows : 

 Group I, o to 6 inches ; group 2, 6+ to 12 inches ; group 3, 124- to 18 inches ; 

 group 4, 18+ to 24 inches ; group 5, 24+ to the largest specimen found. 

 The percentage of each size for each of the three species is shown in the 

 following table : 



