Piney Point, Florida (personal 



observation) 2,27 



Abaco Island, Bahamas (Crawshay, 



1939) 2.34 



Turneffe, British Honduras 



(Crawshay, 1939) 2.94 



Growth Formula 



When the annual rates of increase between 

 units of diameter were plotted, it was found 

 that for growth beyond a diameter of 3-1/2 

 inches the growth factor could be expressed 

 by the standard formula: 



y= Ae^'^ 



where y = annual rate of increase - the 

 growth factor 

 X = radius of the sponge in inches at 

 beginning of a year 

 and A and B are constants, while 

 e is the base of the Naperian 

 logarithms. 



This is assuming a regular spherical shape 

 for the sponge. 



For the particular values obtained on the 

 growth rate off the Piney Point area the 

 formula, modified for ease in working, be- 

 came: 



y = 1 + 11. 2e 



■1.07X 



Since the data gathered were for diameters 

 of from 2 to 7 inches, the use of this formula 

 for extrapolation of the curve beyond 7 inches 

 was particularly useful (fig. 8). The formula 

 indicates that growth will almost completely 

 stop when the sponge reaches a 12- inch diam- 

 eter. This is confirmed in the observed 

 growth of wool sponges by the death of the 

 central portion of the sponge when this diam- 

 eter is reached. The form of the sponge from 

 then on becomes more and more doughnut in 

 shape. Continued growth beyond a 12-inch 

 diameter suggests that one other growth factor 

 operates as the sponge approaches the limit 

 of growth indicated by the formula. Since the 

 sponge is uniform in structure and the intake 

 of water carrying the food is through the sides, 

 the greatest amount of food uptake is in the 



RADIUS (INCHES) 



Figure 8.- -Growth factor for wool sponges. Radius in 

 inches vs. the logarithm of the growth factor. The 

 upper curved broken line is comprised of the per- 

 centage volume increase plus 1, which gives the fac- 

 tor of growth for any size of sponge from 3-1/2 to 12 

 inches in diameter. 



periphery of the sponge. This area, therefore, 

 continues to grow vigorously, but the rate of 

 food intake is not sufficient nor the rate of 

 food transfer through the sponge efficient 

 enough to support active metabolism in the 

 central portion of the sponge when the diam- 

 eter of the sponge is 12 inches or over. The 

 growth formula obtained would probably be 

 directly applicable to the rate of sponge growth 

 except for this phenomenon of sponge physi- 

 ology. It has been observed in doughnut- 

 shaped sponges of large size that the ring is 

 little more than 6 to 9 inches thick. 



The rate of growth in diameter indicated by 

 the growth formula (fig. 7) appears to be valid 

 for the first 5 or 6 years. Beyond this point 

 the growth rate must be assumed to be some- 

 what less than indicated by the formula, 

 the increase in diameter gradually approach- 

 ing a uniform rate as the sponge assumes the 

 doughnut shape. 



Life Span 



Little is known of the life span of wool 

 sponges although the records have indicated 

 that they can live at least 25 years. Presum- 

 ably, the limiting factor to continued growth is 

 the capability of the sponge to draw in suf- 

 ficient food for self-maintenance. Any lack of 

 food intake is counteracted in part by the dying 

 of the central portion of the sponge so that 

 after a certain point in growth in diameter, the 



18 



