

STUDIES IN MARINE ECOLOGY. 247 



The ecological age of the different associations has been 

 repeatedly mentioned. This idea clearly and repeatedly stated 

 by such workers as Cowles, Shelford and Adams, is apparently 

 not yet fully understood. Briefly, it means that the Melampus 

 association as it exists at present is an old association which has 

 passed successively through the other stages standing before it 

 in the series. Thus at one time the spot on which a Melampus 

 association is now located was bare sand, which, as it became 

 finely ground and somewhat packed, began to support a Scoloplos 

 fragilis colony much as is found on Blind Gutter Bar at the 

 present time. With accumulation of the organic products of 

 these animals in the absence of a scouring current, other animals 

 came in until the Scoloplos fragilis association began to resemble 

 a Phascolosoma association. As more muck was deposited the 

 older associations were passed one by one until the present old 

 Melampus association resulted. With further deposition the land 

 will be raised above tidal level and the Melampus association 

 will gradually give way to strictly land animals. In this region 

 the muck that accumulates is almost entirely of organic origin 

 (cf. Survey, p. 32) so that the animals themselves have played a 

 considerable part in causing ecological succession to take place. 



Transitional stages between the different associations are 

 abundant. A particularly noticeable one was studied that be- 

 longs between the Scoloplos acutus and Thy one associations. 

 This is located near the gravel spit at the Uncatena side of the 

 Northwest Gutter passage. There the Scoloplos acutus occur in 

 the muck, but Thyone are absent as yet, although they are found 

 nearby in greater numbers each year. Of the eight comparisons 

 that have been made in the summary tables, four would place 

 this location with the Thyone association, three place it as 

 younger than Phascolosoma association, and the other with 

 Scoloplos acutus where it belongs according to its animal inhab- 

 itants, and according to the average of these physical factors. 



The wharf pilings present a specialized Amarcecium type of 

 association that is obviously younger than the rook.- Amarcecium 

 community, although closely related to it both in animals present 

 and in physical conditions. It represents more nearly the type 

 of habitat that might be found where large rocks extend up out 



