21 



Aside from occasional samples which have been recovered 

 from the bottom with pitch globules, there have been no 

 indications of repellent bottoms such as have been des- 

 cribed in British Seas (Wilson, 1953). Sediments of 

 nonpolluted areas have been classed as attractive, 

 neutral, or repellent in their reactions to settling of 

 larvae^ According to this theory, attractive factors 

 derived from organic activity, such as a coat of living 

 microorganisms as bacteria, can be too abundant or too 

 few for settling of some species. Bottoms with dead 

 organisms and non-living organic matter can be actually 

 repellento 



Where compositions of sediments appear about the 

 same (such as fine mud), the kinds, proportions, and 

 densities of animal species may vary considerably in 

 adjacent areaso Exception can be made to the more immediate 

 areas of the outfalls, where differences in kinds of 

 associations are more accurately expressed in terms of 

 distance (within 1 to 3 miles) from the end of the pipe 

 and with kinds of sediments » 



Because of patchiness in shallower bottoms, it is 

 difficult to repeat samples with like results, even 

 though they presumably come from identical bottoms. 

 It should be noted, however, that the associations of 

 species, rather than individual kinds and amounts, share 

 the common characteristics and can provide an index of 

 productivityo Beyond these shallower depths the assemblages 



