202 J- E. G. Raymont 



Nereis diversicolor and Arenicola marina (Fig. 4). Not a single Arenicola was taken 

 in July 1946, and Nereis and Heteromastus occurred only in one auger sample (Tran- 

 sect 4, St. 1), at that time. The decline in the polychaete population affected the other 

 species also, though not quite so obviously (Fig. 4) ; the only exception was Nephthys. 



The increase in Heteromastus and Pygospio in 1944, and in Pygospio and Phyllo- 

 docidae in the following year, may be " natural " fluctuations, though probably the 

 increased food supply in Kyle Scotnish due to fertilization in the early years may have 

 helped in their success. The decline in 1946, in contrast to the rise in the polychaete 

 population below low-water mark, (Raymont, 1950) may be attributed to the adverse 

 conditions over the exposed inter-tidal mud flats in the winter. It may not be without 

 significance that Nephthys was the only polychaete which did not suffer the decline. 

 This species was sharply limited to the lowest tidal limits on the shore, and it therefore 

 would not be long exposed to freezing. Over the same period Nephthys was increasing, 

 together with other polychaetes, in the areas below low water in Kyle Scotnish. 



It would appear that fertilization, with the resulting increase in food over the North 

 Bay area, had little lasting effect on the density of the bottom fauna. While some 

 increase did occur when other environmental conditions were also favourable, the 

 beneficial effect was more than wiped out by other adverse conditions, and the increase 

 in density was at the most temporary. It is clear, therefore, that increase in food supply 

 alone cannot compensate for other adverse features in the environment. Any attempt 

 at fertilization in inter-tidal areas should therefore be made only in those areas where 

 the species of animals whose increase is desired are either naturally " hardy ", or 

 where the environmental conditions such as temperature, salinity, and so on are 

 constantly favourable. 



ACKNOWLEDGEMENTS 



I wish to thank Imperial Chemical Industries Ltd., Billingham, for their generous 

 financial assistance during the work at Loch Sween, and D.S.I. R. for a grant for an 

 assistant for one year. 



I am indebted to Dr. Gauld and Mr. Nutman for assistance in the taking of samples, 

 and to Dr. A. C. Stephen of the Royal Scottish Museum for the identification of some 

 specimens. 



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