26 



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



spore stage. Tliough Ch. sociale is generally termed neritic, as for instance in the recent 

 large work of Ostenfeld (1913), T cannot consider it neritic in the same meaning as, let 

 us say, Leptocylindrus. Truly, it has its largest, very considerable maximum at S. Skag. 

 9 close to the Norwegian land, but here a great depth gives the Atlantic water free access. 

 Nor is it a regular component of our coastal plankton, missing almost totally in the spring 

 of 1914. 



Chaetoceras dioderna occurs in the same way as Ch. sociale, but never copiouslv, 

 and accumulates, thanks to its heavy spores, in still deeper layers. The maximum of 

 2,526 ind. per 1 falls first at a depth of 50 m. 



Table 34. S. Skag. 6. 57° 56' N., 9° 40' E. 25. IV. 1913. 



o 



10 

 20 

 30 

 40 

 50 

 (50 

 80 

 100 



gö 



Q, 



5 £ 



cd B 

 c-, *> 



O 



O 



>> 



C 



"3 



6,79 



32,74 



5,58 



33,69 



5,35 



34,47 



5,19 



34,58 



5,19 



34,72 



5,14 



34,74 



5,10 



34,74 



5,13 



34,78 



5,12 



34,79 



a 



CD 



Q 



•i o 



a s 



e_ 



£ B 



<.2 

 a 



.5 

 'c 



O *j 



c O 



>> 

 o 



25,09 



100 



26,59 





27,25 



250 



27,35 



850 



27,45 



200 



27,48 



120 



27,48 



220 



27,51 



60 



27,52 



60 



1,970 



2,400 



5,100 



2,400 



850 



640 



580 



760 



440 



S <° B 

 | |.| 



2 c « 



CD O -° 

 O" . 



790 



650 

 950 

 200 

 340 

 120 

 120 

 100 



2 — 

 +3 "3 



o 



440 



500 



50 



250 



20 



80 

 60 



940 

 600 

 550 

 550 

 100 

 80 

 60 

 160 

 100 



CD B 

 fe C 



360 



300 

 100 



280 

 40 



- 



o g 

 - s 



3 



a 



'O 



o 



co 



OJ 



fe £ 



O «Ä 



° — u 



o ° 6 

 Ph C 



4,665 

 3,600 

 7,350 

 5,300 

 1,650 

 1,740 

 1,040 

 t 1,200 

 860 



3,500 



4,500 



1,600 



2,200 



4,100 



4,350 



6,050 



2,000 



950 



300 



440 



380 



100 



240 



200 



40 



60 



180 



8,120 



3,850 



8,450 



8,050 



1,450 



940 



400 



400 



620 



At a depth of about 30 m, two slightly different kinds of water meet, of which the 

 lower one is exceedingly uniform for at least 60 m downwards. The hydrographically 

 hardly perceptible limit is enhanced by more striking biological differences. It is in- 

 stantly seen from tables 33 and 34 how the moderately rich Chaeto-plankton (= Eastern 

 neritic plankton) is springing down abruptly, diatoms and peridinians as well as infuso- 

 rians, af ter having passed the 30 m-limit. The discs, as Thalassiosirae, are chiefly li- 

 mited to the undermost, Atlantic layer, that is still holding a good deal of plankton all 

 way down to the bottom. In the uppermost layer, Ceratia are comparatively frequent 

 (940 ind. per 1 in the surface), and their coming summer-development seems to begin here 

 right early. The ruling Ceratimn is C. longipes v. balticum Ostf. A new small Amphi- 

 dinium, that I ha ve named A. carota, is a regular inhabitant of these waters and belongs 

 perhaps to the association of Chaetoceras sociale, whose distribution it follows closely 

 enough. 



8. Skag. 8. (Tables 35, 36). 



The limit of the diluted water (less than 30 %o salinity) runs here about 10 m higher 

 up than in the Eastern Skager Rak (S. Skag. 0). Accordingly, LeptocyJindrus has its 

 maximum of 71,250 ind. per 1 already at 10 m. The number is no high one, compared to 

 those from the south-eastern Skager Rak. Chaetoceras sociale, that seems to have been 

 imported to this deepwater-station in the Norwegian f urrow by Northern Atlantic currents, 



