Fig. 36. Chart showing the route and times of approach to the British Isles of Atlantic and 

 'Lusitanian' plankton indicator species. 



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sense of annual pulsation of the current which is not necessarily a true one. 

 The currents have periods of maximum and minimum inflow of their own 

 which are not always connected with the abundance of nidicators. 



To follow the further penetration of the mixed water into the North Sea 

 the true oceanic species are no longer so useful as indicators as they have mostly 

 died out, but the mixed water indicators take their place and a picture such 

 as that given by Glover (Fig. 35) is seen. Taking a general view of the whole 

 example, one can produce a chart (Fig. 36) which gives an idea of the 

 average route taken and the times of arrival of the indicator species. 



This principle applies elsewhere of course, and passing mention can be 

 made of the inflow of salps into Norwegian waters in September 1955 and 

 the inflow of salps west of Iceland in September 1958 which even continued 

 round the North Cape. 



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