Papers in Marine Biology and Oceanography, Suppl. to vol. 3 of Deep-Sea Research, pp. 178-203. 



The fauna of an inter-tidal mud flat 



By J. E. G. Raymont 



Zoology Department, University of Southampton, England 



Summary — 1 . An account is given of the fauna of an inter-tidal mud flat (North Bay) in Kyle Scotnish, 

 Loch Sween, Argyllshire. 



2. The distribution of the more important species of the fauna over the shore is discussed. 



3. Some indications are given of the growth rates of four lamellibranchs, Macoma, Scrobicularia, 

 Cardium and Mytilus. 



4. The changes in the density of the fauna are followed from 1943 to 1946, and the possible 

 beneficial effects of the fertilization of Kyle Scotnish on the bottom fauna of the inter-tidal zone are 

 reviewed. 



INTRODUCTION 



Some account has already been given of the bottom fauna of Kyle Scotnish — a 

 northern arm of Loch Sween, Argyllshire (Raymont, 1950), but that investigation 

 was confined to the fauna below low water mark. Very little inter-tidal shore exists 

 in Kyle Scotnish, but near the head of the loch there is a fairly extensive mud flat 

 which is designated in the text North Bay (Fig. 1). Although a small stream enters 

 the area, most of the flat is not estuarine. It was thought desirable to investigate the 

 fauna of the mud flat, since most of the work done on muds in Great Britain concerns 

 estuaries (e.g. Eraser, 1932; Rees, 1940; Beanland, 1940; Spooner and Moore, 

 1940). Since also the main work in Kyle Scotnish has been concerned with the effect 

 on general productivity of the addition of nitrate and phosphate fertilizers, it was 

 decided to attempt to correlate population changes in the mud flat with the effects of 

 fertilization. 



The investigation extended over three years commencing in November 1943. 

 Sampling over such a short period cannot give results on which very definite con- 

 clusions may be based. Nevertheless, as the work at Loch Sween had to be ended in 

 1946, the samples have been worked through and some account of the work is 

 presented. 



METHODS 



Sampling was confined to an autumn (November) and summer (July) period each year. Four 

 transects were planned across North Bay, sited on permanent marks on shore, and three or four 

 stations were selected at approximately equal distances along each of the four lines, beginning near 

 High Water and extending to Low Water (Fig. 1). Altogether fourteen stations were regularly 

 sampled. No exact tidal levels were taken, as the tidal range right at the head of Loch Sween is small, 

 and moreover the tides are irregular, the periods of exposure of the flat being very largely dependent 

 on the prevailing wind. 



Various sampling techniques were tried during November 1943 involving the digging of a square 

 (side 0-5 metres) and sieving the material, but such a procedure proved too laborious. In the method 

 finally adopted a quadrat (side 0-5 metres) was dug to a depth of 10-12 cm, the material passed through 

 a coarse (9-5 mm) sieve, and only the larger bivalves exceeding 10 mm length retained in the sieve were 

 counted. At the same station three small " auger " samples were also taken. The auger consisted of a 

 metal cylinder 10 cm diameter, 23 cm height, with a handle at the top. The auger was pushed into the 



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