198 



J. E. G. Raymont 



on the Danish waddens, with some dense patches of mostly young worms exceeding 

 2,000 per m-. 



The average population of Arenicola over North Bay varied between 30 and 70 

 per m^ apart from the marked decline in July 1946 (Fig. 4). Densities up to 400 per 

 m- occurred over part of the shore (Table XIV). However, Arenicola was absent from 



1200 — 



1000 — 



800 — 



K 

 u 

 a. — 



tc 

 ui 

 m 

 S 600— 



3 



O — 



< 



> 



< 4 00 — 



'OTHERS 

 NEPHTHYS 



ARENICOLA 

 PHYLLODOCIDS 



NEREIS 



HETEROMASTUS 



•^oo— 



PYGOSPIO 



t I t t 1 I 



NOV 

 43 



JULY 

 44 



NOV 

 44 



JULY 

 45 



NOV 

 45 



JULY 

 46 



Fig. 4. Fluctuations in the density of polychaetes over North Bay. The changes in the total popula- 

 tion and in the main species are shown. AH numbers represent densities per m^ calculated as averages 



of the populations at 14 sampling stations 



a considerable number of stations; possibly it was commoner above mid-tide level, 

 but there was no clear distribution pattern. Many authors have shown that lugworms 

 generally avoid soft substrata and live in essentially sandy bottoms. Thus in Spooner 

 and Moore's work, Arenicola hardly ever appeared in the samples. However, in the 

 Exe and off the Northumberland coast small populations of Arenicola occurred 

 (Table XIV), and Stephen (1930) found a rich ground in Loch Gilp. Thamdrup 



