THE SPONGES OF THE WEST-CENTRAL PACIFIC 269 



The Palaus, Carolines and Marshalls are not immune from hurricanes, 

 but suffer much less typhoon damage over a long period than is true of the 

 Marianas. 



In all three of these archipelagos, observation of relative sponge abund- 

 ance showed a consistent relationship to exposure. A conventionalized diagram 

 of an atoll may be used to illustrate the comparative suitability of locations 

 as follows : 



— J5.. 



^'''~ 3 ^"-- .>• DIRECTION 



,' ■*„ %/ OF PREVAKU- 



' N iNGr WINDS, 



/ 



' 2 J 6 



2l * * 



\ 



' 1 i ' 



^ J 



4 \ » 



3 

 5 



Text Figure No. 185. Diagram of relative sponge abundance in a generalized atoll. 

 1 : Greatest abundance. 6 : Least abundance. 



The numbers represent six degrees of sponge abundance, number one 

 being the maximum and number six the minimum. 



McDougall (1945) and I (de Laubenfels, 1947) have shown that water 

 currents are vital to sponge success. In general, from zero up to a point 

 somewhere between 2 and 3 kilometers per hour of usual current speed, the 

 faster the motion the more the sponges prosper. The most cursory observation, 

 however, shows that water movement is often above 2 kilometers per hour in 

 the area here studied. The equatorial and counter equatorial ocean currents 

 (see de Laubenfels, 1950) produce widespread streams in the open ocean 

 about the Marshall Islands, which movement is consistently near or even over 

 2 kilometers per hour. 



The violent or destructive motion probably responsible for relative 

 showings in Figure 185, is due to wind action and especially to wave action. 



