270 THE SPONGES OF THE WEST-CENTRAL PACIFIC 



The relative abundances shown by the six numbers pertain only to depths of 

 less than 10 meters, chiefly less than 5 meters. In such shallow water wave 

 action is effective. 



It will be observed that the maximum abundance, as shown by the 

 number 1, is in the twice sheltered locality to the lee of the miniature reef 

 within the larger lagoon. This situation was brought out in my field collecting 

 conspicuously at Ailing-lap-lap and Ebon Atolls and not so definitely at 

 Majuro Atoll. I did not find exactly such a place anywhere in Likiep Atoll ; 

 but this is not significant, because I was unable to explore carefully the west- 

 ern part of Likiep Atoll. 



Ponape presents a very interesting layout in terms of the ecological situa- 

 tion now under consideration. The lagoon surrounds the entire island with 

 only relatively insignificant exceptions. Yet this lagoon is everywhere so 

 narrow that wave action cannot build up to great activity within its confines. 

 To use the scale of abundances from 1 (maximum) down to 6 (minimum) for 

 Ponape would merely involve placing the figure 1 in practically every portion 

 of the lagoon. Everywhere that we went in the Ponape lagoon, we found 

 sponges flourishing. 



A second factor for sponge success is also well exhibited in Ponape. This 

 concerns the ratio of land drainage to sea area. 



This relationship was brought out strikingly in my studies at Bermuda 

 (de Laubenfels, 1950 "Ecology"). There are no permanent freshwater 

 streams in Bermuda, but there are little gullies down which temporary streams 

 flow during and immediately after a hard rain. Right at the mouth of such a 

 gully, there is consistently an area with no sponges at all, doubtless due to the 

 lethal effects of sudden flushing with fresh water, which causes violent 

 changes in osmotic relationships. Yet, just farther out than this blank area, 

 there occurs one of extremely great sponge success. Sponges may even cover 

 the bottom and all available solid surfaces, crowding each other and making a 

 continuous mass more than 10 cm thick. The landward side of this crowd is 

 fairly sharp. The "twilight" zone may be less than 10 meters wide. At the 

 seaward side, however, the sponge abundance diminishes gradually over a 

 much longer distance. 



Only rough estimates are available for sponge abundance in the Gulf of 

 Mexico, but the reports of divers for commercial sponges are unanimous as 

 to the general picture that a certain region south of the western prolongation 

 of Florida, represented by the star in Figure 186, has been the second great- 

 est area for sponge yield in the whole world and is excelled only slightly by 

 that in the eastern Mediterranean. 



It might at first be thought that the region of maximum abundance would 

 be at the place marked with the figure 1, then less abundance at 2 and still less 

 at 3. That this is not the case is obviously due to the fairly strong currents, 

 which in this inland sea sweep from Texas toward Florida. Taking these into 



