128 Mussel Beds; their Frodiictlvity and Maintenance 



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It will be interesting to note briefly the 

 manner in which portions, at least, of this scar 

 were formed, and how the mussels maintain 

 themselves there (Fig. 2). The substratum is of 

 moderately firm, clean sand, the surface of which 

 is somewhat broken up into sand ripples. The 

 steep (lee) faces of these front in an east-north- 

 easterly direction. Against these ridges, cockle 

 shells (which have been transported downstream 

 by the river current from the extensive beds 

 within the estuary), have accumulated, together 

 with stones, water-logged wood, etc. On these 

 materials, spat liberated by the mussels higher 

 up the river has settled, and continues to settle 

 year by year. As the shellfish develop, their 

 byssus fibres fasten the whole together with a 

 certain degree of firmness. As individual mussels 

 die, they become covered by sand, and their 

 shells afford a still better anchorage to their suc- 

 cessors. Thus the bed is composed of a number 

 of small colonies of mussels, clinging to the 

 steeper sides of the sand wave ripples, and 

 sheltered from the direct influence of the tidal 

 currant from the sea. Whether the whole of this 

 somewhat "ragged" bed presents the same aspect 

 is doubtful, but there is reason to beUeve that its 

 deeper portions, which are always submerged, are 

 rather more densely populated. 



Lying, as it does, in the narrow neck of the 

 estuary, where the tidal currents race most 

 strongly 1, portions of the scar are probably al- 

 ways covered more or less with sand. This sand 

 may be simply washed oyer it in quantity, from 

 the river bed, or from banks of shifting sand, 

 or else deposited from that held in suspension 

 by the current, which is considerable (see para- 

 graph on this subject in another place). 



Although the sea mussel is an animal of 

 rapid growth, yet, considering the relatively small 



^ Captain Enoch Lewis, of Aberdovey, informs me that, 

 during spring tides, the current in the seaward portion of the 

 estuary reaches a speed of about three miles an hour. 



