of the 700 examined) less than 5-1/2 inches 

 were found to be producing larvae. In the Key 

 Largo area, the minimum size for mature wool 

 sponges was 3 inches; in the Bahamas, W. 

 Smith (personal communication) reported that 

 the minimum size was 4 inches. In British 

 Honduras sponges as small as 2 inches in 

 diameter may produce eggs. 



When in each area the size at maturation of 

 the wool sponges was compared with the water 

 temperature, there was a very close relation- 

 ship between the number of months per year 

 in which the temperature in an area was greater 

 than 80° F. and the minimum size of mature 

 wool sponges (fig. 5). The curve in figure 5 

 represents a relationship between size at 

 maturation (larval-production size) and the 

 variation of temperature at different geograph- 

 ical points. It is likely that a very similar 

 relationship exists between size at maturation 

 and the variation of temperature with depth of 

 water. Bathythermograph recordings show that 

 in the upper Gulf, for example, temperatures 

 of more than 80° F. are to be found as deep as 

 120 feet during July. Insufficient data exist to 

 plot the duration of this temperature at various 

 depths throughout the year. It is possible that 

 dispersion of wool sponges to deep water areas 

 in the Gulf may be retarded by the effect of 

 temperature on the sexual maturation of the 

 sponges. 



NUMBER OF MONTHS TEMPERATURE > 60* F 



Figure 5, — Temperature - size at maturation relation- 

 ship for wool sponges in various areas. (See appen- 

 dix a for areas.) 



Since temperature is a factor in the breeding 

 cycle of the wool sponge, variation of water 

 temperature from year to year will affect 

 larval production. It is possible also that long 

 periods of optimum temperature could bring 



about an earlier maturing of the sponges and 

 total egg productivity would be increased as 

 a result (fig. 5). 



GROWTH OF SPONGES 



Method of Determining Growth 



Sponge growth was studied during the investi- 

 gation by a series of underwater field tests in 

 the northern Gulf. In all, 108 sponges of the 

 three principal species (wool, grass, and 

 yellow) were measured and tagged for growth 

 rate studies. Eleven were cut off, measured, 

 and tagged for regrowth study. One hundred 

 sponge cuttings were set out to observe their 

 growth rate, and a number of plain cement 

 bricks were placed in the areas to try to ob- 

 tain sponge settings. Sufficient data were 

 obtained to construct a growth curve only for 

 the wool sponge. 



The sponges were tagged by running a 

 stainless steel or Monel wire through the 

 sponge and around a brick. Each cement brick 

 was code numbered by cuts in the edges (fig. 

 6b). The three dimensions of the attached 

 sponge was then measured with a modified 

 sliding square. 



It was necessary to examine seven or eight 

 sponging bars before locating one that had a 

 sufficient number of sponges growing on it to 

 justify establishing a station. When located, 

 each of the five selected stations was posi- 

 tioned by (a) placing a buoy, the most practical 

 method, (b) making compass sightings, (c) 

 timing course runs from stationary objects in 

 the water, e.g., the coastal bird racks (plat- 

 forms constructed in the shallow water for 

 collecting guano), and (d) laying of wires on 

 the bottom in set directions from the bar for 

 locating by dragging later. 



Losing buoys, changing work boats and com- 

 passes, taking of sponges by sponge fisher- 

 men (even though more or less unintentional), 

 and dying from adverse ecological conditions 

 contributed to our inability to recover a con- 

 siderable number of tagged sponges. Despite 

 these losses, I obtained enough data to establish 

 a growth rate for the sponges in the Gulf area 



15 



