The fauna of an inter-tidal mud flat 



183 



Of the bivalves, Macoma was fairly evenly distributed across the shore, while 

 Scrobicularia was somewhat more abundant at upper and middle levels (Fig. 2). 

 Mytilus was absent near high- and mid-tide levels, and increased towards low water. 

 In Transect 4, however, it was abundant in the middle region as well as towards low 

 water, but still avoided the upper levels (Fig, 2). This difference may possibly be 

 explained by the fact that Transect 4 was taken on a difierent portion of the shore 

 close to a small permanent stream which ran across the mud (Fig. 1). This difference 

 in distribution was also seen for Cardium: while in Transects 1-3 this bivalve was 

 practically absent near high water mark and was common from mid-tide levels and 

 towards low water, in Transect 4 Cardium was commonest at the uppermost levels 

 and decreased in abundance down the shore (Fig. 2), 



Fig 1 Sketch map of North Bay mud flat at head of Kyle Scotnish, showing positions of the four 

 TmnsecrsNuSs along Transects indicate Stations. Flagged dots = permanent poles on road- 



side used for bearings 



Some of the polychaetes also showed fairly obvious distributions. Nereis diversi- 

 color was hardly represented below mid-levels on the shore and was at its maximum 

 at the uppermost stations (Fig. 2). This distribution applied to Transects 2 and 3; 

 along the other Transects Nereis occurred hardly anywhere throughout the sampling 

 period. Nephthys contrasted sharply with Nereis in that it was practically absent 

 from the upper levels and increased sharply towards low water (Fig. 2). Nephthys 

 also occurred quite commonly below low water mark. There is again the suggestion 



