46 



ASTRID CLEVE-EULER, QUANTITATIVE PLANKTON RESEARCHES IN THE SKAGER RAK. 



is quoted by him, p. 503 — 504, to be naturalised in the North Sea proper, from the Nor- 

 wegian Sea to the Belgian shore. Also Coscinodiscvs concinnus, not treated in the paper 

 just referred to, is known by previous investigations, as recorded already in Cleve's 

 Phytoplankton, to be a Scotland-form in spring, and is stated by Mr Gran in his last 

 work to occur at diffcrent North-Sea-stations, principally in the southern part of the Sea. 



Thus I think wc have to exj)lain the figures of S. Skag. 5, near Skagen, and S. Skag. 

 6, further out in the Skager Rak, by supposing a powerful inbreak of southern Atlantic 

 water through the English Channel having just taken place. This salt and heavy water 

 pushed before it, and between itself and the North-Sea-coast of the Continent, the ordi- 

 nary litoral waters of the region, which it invaded; and these last waters wc now find at 

 S. Skag. 5. It lies near to hand to suppose some connection between accidental and 

 strong migrations of southern Atlantic water like this to the Scandinavian coasts, and the 

 remarkable appearance of the large tunnyWest of Sweden in the last years, and it would 

 be of interest to make clear the relation between both phenomena. From the Director 

 of the Fishery Board, Dr Andersson, and from Dr Östergren I am told that the tunny 

 was observed in our waters, during the period dealt with, for the first time in the late 

 summcr of 1913, and was afterwards especially numerous in the summer of 1915. Whether 

 an import of southern Atlantic water took place also in 1915, we unfortunately do not 

 know, as no plankton-samples were gathered in the Skager Rak in that year. In the 

 spring of 1913, there is no trace of such currents, anyhow, as may be settled from the se- 

 ries III and IV, described abovc. It is seen at once from table 33 (p. 25) how the usual 

 northern Chaeto-plankton, mixed with some Sira-plankton, is ruling in April 1913 in 

 Central Skager Rak without any addition whatever of southern types. 



Already the very limited material treated as yet in a quantitative way is evidently 

 sufficient to prove in a convincing raaiiner what important differences and irregularities 

 in the composition of the Skager Rak-plankton and in its distribution are brought forth 







Table 70. S. Skag. 6. 57° 56' N., 9° 40' E. 18. IV. 1914. 







a. 



Q 



Tempera- 

 ture ' C. 



o 

 o 



o 



>> 



43 



'c 



"Ja 

 t» 



>> 



'ro 



a 

 o 

 Q 



"3 



-5 



o 



c 

 S 

 >, 

 O 



.2 



u 

 o 



O 



.2 



'c 



"C 



P4 



Peridiniales 



total 



numbers 



| 



o 



9> 



<D 

 fcH 



r-. 



8 

 o 

 o 



.Q 

 tö 

 (-1 



Protozoa 



total 

 numbers 







6,54 



27,45 



21,57 



840 



100 



200 



2,080 



2,260 



960 



3,400 



10 



6,04 



34,65 



27,29 



80 



310 



60 



710 



220 



180 



440 



20 



6,04 



34,65 



27,29 



120 



375 



120 



705 



100 



20 



160 



30 



6,01 



34,63 



27,28 





450 



70 



740 



130 



40 



240 



40 



6,05 



— 



— 



40 



270 



100 



590 



150 



50 



330 



60 



6,06 



34,63 



27,28 



100 



140 



30 



590 



200 





280 



80 



6,06 



34,65 



27,29 



20 



430 



70 



650 



70 



50 



180 



100 

 A 



6,04 

 verage 



34,72 

 numbc 



27,35 



rs 





320 



20 



420 



00 



40 



160 



10—1 

 20—1 



00 m 

 00 m 







51 



328 



67 



630 



111 



54 

 33 



255 

 225 







