The Plankton Production of the Skager Rak at various seasons 



from August 1912 to April 1914. 



The following work is a survey of the principal results that were obtained during 

 a series of quantitative investigations, carried ont upon a large number of watersamples 

 from the Skager Rak. The material was collected by the Swedish Hydrographical 

 Commission under the superintendance of Prof. D:r Otto Pettersson, and I have dealt 

 with it in my quality of biological assistent of the Commission. Along the customary 

 route from the Swedish coast, across the mouth of the Kattegat, to Skagen and then 

 farther across the Skager Rak to Arendal in Norway (Fig. 1), samples of c:a 250 cc were 

 taken at every ten metre's depth at the stations recorded further on. As to their plan 

 and technical details, these investigations closely resemble those carried out by Mx H. 

 H. Gran and described in the newly published paper by this author on the Plankton 

 Production of the North European waters in the spring of 1912 (1915). I thus need not 

 dwell here at any length neither upon the development of the method used, nor upon the 

 results, hitherto won with it. Also the list of Literature, already complete in Mr Gran's 

 work, will not be reproduced here, with an exception for some few papers, necessary to 

 refer to. 



It will be sufficient to state that from 10 to 100 cc of the sea-water, that had pre- 

 viously been sterilised with 50 cc of strong Fleming's solution per 1, were centrifugated 

 and the sediment brought upon a glass for counting the organisms under the microscope 

 by means of a counting table. Even of waters very poor in plankton, larger samples 

 could hardly be used, because of the often considerable amount of inorganised detritus 

 and grains of sand. 



As Mr Gran's paper deals, among others, with two series of samples from exactly 

 the same stations of the Skager Rak route, that are the object of the present survey, it 

 will already be possible to make some interesting comparisons as to the various features 

 of the ruling plankton-vegetation not only at different seasons, but also, for a part, at 

 the same season in different years. The results are rather astonishing, in what concerns 

 the large and striking dif f erences, registered from one year to another, and of f ering a most 

 clear and uncontestable picture of the changing faces of microscopical meadows, growing 

 in moving waters. 



