within the sponge itself so that the skeletal 

 spongin fiber makes up a much larger per- 

 centage of the central mass after egg produc- 

 tion has actively begun. Loss of living material 

 causes a darkening of the internal portion of 

 the sponge, and the beginning of this darkening 

 can be observed in figures 3a and 3b, which 

 are sections of sponges just attaining egg- 

 producing size. 



Relationship Between Sponge Con- 

 centration and Larval Production 



Field observations of the number of eggs 

 produced by individual sponges and the per- 

 centage of sponges producing eggs in any one 

 area point to important relationships between 

 sponge concentration and reproduction. During 

 July 1956, more than 50 test dives of approxi- 

 mately 2 hours each were made. The relative 

 concentration of the sponges on each rock bar 

 was calculated from the number of sponges 

 taken on each dive. 



Although the information shown in table 2 

 does not lend itself to detailed analysis, some 

 tentative conclusions can be obtained from the 

 data gathered, supplemented by direct observa- 



tion of other sponging areas. Verification of 

 these can be established in future work. 



1. There may be a critical density of 

 sponges required for optimum pro- 

 duction of larvae . — If the concentra- 

 tion of sponges of 5-1/2 inches or 

 over was of the order of 11 per acre, 

 over 85 percent were producing larvae. 

 Of more significance is the fact that 

 the density of the larvae in these 

 sponges was approximately 500 per 

 cubic inch. At some stations where 

 the concentration of sponges was three 

 or less per acre, only 30 percent or 

 less of the sponges were producing 

 larvae and in these cases the density 

 of the larvae in the sponges was never 

 more than 50 per cubic inch. This 

 would give a total ratio of reproductive 

 potential of the sponges in the two 

 areas of about 30 to 1. 



The data must be interpreted with 

 reserve. Concentration of the sponges 

 is not the only factor in assuring opti- 

 mum fertilization and production of 

 larvae. A sperm-producing sponge is a 

 necessary element in the concentra- 

 tion. 



Table 2. — Concentration of wool sponges collected in July 1956 for determination 



of larval content 



[Number of sponges] 



'^ Locations of these stations are shown in figure 10. 

 ^ Very few larvae in any one sponge. 



10 



