194 J- E- G. Raymont 



gastropod. Smidt quotes Mytilus edulis and Littorina littorea as the two most import- 

 ant members of the epifauna — a composition that accords well with the North Bay 

 mud flat. One marked difference was the very low numbers of Corophium found in 

 North Bay. Thamdrup (1935), Smidt (1951), Beanland (1940), Spooner and Moore 

 (1940) all quote this species as an important member of the Macoma community. 

 Beanland, and Spooner and Moore, suggest that one factor which limits its 

 occurrence is lack of shelter, so that its maximum density is usually near high-water 

 mark. Nevertheless Corophium might have been expected to occur abundantly at 

 least at the higher levels of North Bay, which is at the end of a long, sheltered sea-loch. 

 Moreover, Hydrobia, which is also said to be sensitive to water movement, was very 

 abundant— in fact dominant numerically — in North Bay. There have been some 

 suggestions that Corophium may occur only as a temporary visitor on shore; perhaps 

 sampling only in July and November missed its abundant season. Possibly also 

 Corophium competes with other members of the fauna that were plentiful in North 

 Bay (cf. Thamdrup, 1935). 



Another difference between other described Macoma communities and North Bay 

 was the importance of chironomid larvae in the latter area. These larvae are not 

 mentioned by Thamdrup (1935), Smidt (1951), Fraser (1932), Brady (1943) or 

 Rees (1940). Spooner and Moore (1940) do list " dipterous larvae " on a few occasions 

 in their tables, but the numbers are very low, and clearly if there were Chironomidae, 

 they were never of importance. Wohlenberg (1937) also mentions chironomid 

 larvae in a small area near a fresh water stream, but they did not apparently occur 

 generally over the mud flat. Nicol (1935) found high densities (maximum 39,000 

 per m^) in muddy salt pools. Over the North Bay the average population varied 

 between 300 and 1,500 per m^ from 1943 to 1946, but individual samples gave densities 

 of 2,000-3,000 per m^ (maximum >9,000 per m^). 



Oligochaetes (chiefly Peloscolex) were also very abundant in North Bay ; the average 

 population for the shore ranged near 1,000 per m^ for a considerable period, and 

 individual samples amounted sometimes to several thousands (maximum 13,900 per 

 m^). Smidt (1951) comments on Ohgochaeta (including Peloscolex benedeni) as being 

 exceedingly numerous on the higher parts of the waddens, and Brady (1943) found 

 they occurred in muds off the Northumberland coast, though the densities in North 

 Bay were very much higher. Peloscolex was also found by Wohlenberg (1937). 



Most authors state that Hydrobia is concentrated in the upper tidal areas (cf. 

 Spooner and Moore); in North Bay the lowest stations usually had few. However 

 Rees (1940) found it in greater density towards low water, and Smidt states that the 

 young Hydrobia occurred in great numbers in summer and autumn anywhere over the 

 mud flats. This could account for the very dense patches occasionally encountered in 

 North Bay, even at the lowest tidal levels (cf. p. 1 85). The maximum densities recorded 

 by most workers in Great Britain do not usually exceed 20,000 per m- (Table XIV); 

 though Nicol (1935) found up to 32,000 per m^ at Aberlady, Scotland. The richness 

 of North Bay is therefore apparent. However, the densities there were not as high as 

 those at Skalling (Table XIV). Smidt (1951) recorded even higher densities for the 

 Danish waddens when O-Group Hydrobia were also counted (Maximum 600,000 per 

 m^). 



Of the bivalves typical of the Macoma community, Mya was taken only rarely in 

 North Bay. Macoma seemed able to live over a very broad zone of the shore, though 



