266 THE SPONGES OF THE WEST-CENTRAL PACIFIC 



Graphs or curves are very impressive but would be misleading if forcibly 

 applied to sponge abundance. Nevertheless, it is possible to use such words 

 as rare, uncommon, common, and abundant. 



The term abundant may be used when nearly every square meter has a 

 sponge or sponges whose gross size would approximate that of a human fist. 

 Such areas are frequently found throughout the West Indian region and 

 Mediterranean. The only places in the world that I know of where they 

 reach a greater abundance are in the Bermudas as, for example, at Walsing- 

 ham Pond. In that place they may fairly be called superabundant. 



The term common may be used when nearly every four square meters 

 contains a sponge, and in 25 square meters a double handful could be found. 

 Such areas are world wide. Probably half of the rocky coasts on earth have 

 such an abundance just below low tide. 



The term uncommon may be used when there is only about one easily 

 found sponge for each hundred square meters. 



The term rare may be used when one must hunt for hundreds of meters 

 to find even one sponge. 



In discussing the abundance of separate species, a more liberal allowance 

 is taken. If a single species is represented in each hundred square meters, it 

 is a decidedly abundant one. If in any search of one hour at least one specimen 

 can be found, that species is common. Uncommon species are represented by 

 5 to 15 specimens altogether, and rare species by only one or two specimens. 



The requirements of sponges for physical and chemical factors are only 

 moderately well known. Pertinent data are given in such literature references 

 as the following, which are here cited with comments. 



Sponges require protection from burial or smothering. Thus, they 



require clean water and suitable attachment. 



McDougall, 1943 de Laubenfels, 1947 



Parker, 1910 de Laubenfels, 1950 



Verrill, 1873 Vosmaer, 1882 



Sponges require moving water but not excessive current. Often 2 to 3 

 kilometers per hour seems ideal. This may have particular significance for 

 the initial attachment of sponge larvae. Oxygen needs are also certainly 

 involved. 



Tewell, 1935 Hyatt, 1877 



"Bidder, 1896, 1923 Rathbun, 1887 



McDougall, 1943 de Laubenfels, 1947, 1950 



Sponges require proper osmotic pressure, which is usually that of full 

 oceanic salinity. Only exceptions are a few genera, which are tolerant of 

 fresh or brackish water. Sponges, as a rule, cannot endure more than a frac- 

 tion of a per cent of excess salinity. 



Annandale, 1914 ("Chilka") de Laubenfels, 1947 



Galtsoff, 1925 de Laubenfels, 1950 



