The fauna of an inter-tidal mud flat 



189 



The counts for November 1943 are not entirely reliable, as the sampling method was 

 still being worked out then. Nevertheless, the order of magnitude of the population 

 is probably correct, and it is important, since that population represents a pre-fertiliza- 

 tion autumn density for the North Bay area. Probably the data for July 1944 can also 

 be taken as approximating to a mmmer pre-ferti/ization density, since, although fertili- 

 zation began over Kyle Scotnish early in 1944, little effect may be expected for some 

 months (cf. Raymont, 1947). In November 1945 the density increased to a relatively 

 high level, but once more declined in the following summer, when there was a 

 particularly marked drop (Tables IV, VIII and IX). In all three years therefore the 

 July population was smaller than in the previous autumn. 



40 



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1943 1944 1945 



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Fig. 3. A comparison of the total populations in November 1943, 1944 and 1945 at each of the 14 

 regular sampling stations. (Numbers per m'^.) (The figures at Tr. 2, St. 4 and Tr. 4, St. 3 are doubtful 



owing to imperfect sampling) 



In considering the changes at individual stations it is probably necessary to omit 

 Transect 2, St. 4, and Transect 4, St. 3, since on some occasions the samples could be 

 obtained only by a grab. Of the remaining twelve stations, nine show an increase in 

 population in November 1945 as compared with November 1943 (pre-fertilization), 

 and two stations a decrease (Table VIII; Fig. 3). Owing to the patchiness of the 

 fauna and to sampling errors, small differences (e.g. Transect 1, St. 2; Transect 3, 

 St. 3) should probably be disregarded. If changes exceeding — 30°„ be regarded as 

 significant, six stations showed a real increase in population — three being really large, 

 while only one station showed a significant decline. 



If the July populations are now considered, from Summer 1944 to Summer 1945 

 there is no obvious change. The total populations when averaged differ by only 4%, 

 and of the individual 14 stations four only show a real increase and five a decrease. 



The decline in bottom fauna densities which appeared in every July sampling seems 

 to be more obvious in the summer of 1946. If the population then is compared with 



