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



Table 2 gives the distribution of the peridinians, which have their maximum in the 

 ten uppermost metres, where they are until several times as numerous now as the dia- 

 toms. In the very surface, Prorocentrum micans is »flowering» with 1300 living indivi- 

 duals per 1; the more heavy species of Ceratium have their maximum first at 10 m, 

 with 1660 ind. per 1. The dominating species is C. fur ca, while C. tripos is rare and 

 C. longipes absent or in any case too sparse to be visible in the figures. Also Glenodiniuw 

 danicum is rather spread. 



Infusorians are remarkably scarce even in the surface-water, possibly in consequence 

 of the scanty amount of vegetable food now present. Only 340 ind. per 1 were noted at 

 m, for about the half part consisting of Tintinnus subulatus, which thus proves to be 



Table 3. S. Skag. 0. 57° 41' N., 11° 24' E. 16. VIII. 1912. 



Depth 



Tempera- 

 ture c C. 



o 

 o"" 



>> 

 a 



"3 



m 



o 

 >. 



'3 



c 

 o 



Paralia 

 sulcata 



Guinardia 

 flaccida 



Rhizosolenia 

 alata f. gra- 

 cillima 



Rhizosolenia 

 fragil issima 



Thalassiosira 

 decipiens 



Thalassio- 



thrix nitz- 



schioides 



Naviculoid 



diatoms and 



Nitzschiae 



Diatoms 



total num- 



bers 



Laboese 

 spp. 



Infusorians 



total mim- 



bers 







10,27 



29,07 



21,16 







260 



170 







10 



1,780 



4,030 



4,625 



10 



16,77 



32,72 



23,13 







20 



10 







10 



120 



280 



380 



20 



10,04 



33,35 



24,50 



30 



70 







20 



10 



100 



380 



40 



40 



30 



15,60 



33,51 



24,72 







10 





40 



70 



30 



180 



50 



50 



40 



15,3.') 



33,69 



24,91 





40 







30 



70 



50 



400 



00 



70 



50 



14,50 



33,75 



25,14 



150 



10 







30 



220 



40 



530 



80 



130 



00 



12,27 



33,69 



25,53 



250 



80 







00 



790 



80 



1,330 



100 j 140 



80 



10,35 



33,89 



20,05 



1 ,200 



20 







00 



340 



30 



1,820 



90 



90| 



characteristic of the Tripos-plankton. The Laboece, so frequent in spring, are almost 

 totally absent here as at the other southern stations; at the northern and eastern stations 

 they are a little more numerous, but still very sparse, compared to the April-numbers. 



At Skag. 0, the easternmost station near the Swedish coast, the water is a trifle 

 more diluted in the surface and less diluted in deeper layers than at the corresponding 

 levels of Extra II, thus somewhat less intermixed than here. From 20 m downwards 

 to 80 m, the salinity is very slowly creaping up from 33,4 to 33,9 %<>; the temperature 

 also decreases slowly at first, but more rapidly from about 50 m. To the not very sharp, 

 though perceptible hydrographical limit above 20 m, there is a corresponding undistinct 

 biological limit, the southern North Sea-forms stopping partly at this level, above which 

 we chiefly find the ordinary Tripos-plankton with Rhizosolenia gracillima. One southern 

 species, anyhow, has associated itself with the latter, viz. Rhiz. fragilissima, a delicate 

 form that has been able to spread upwards to the very surface, where it is f eebly, but quite 

 distinctly multiplying. This may also be supposed concerning Chaetoceras curvisetum. 

 Paralia shows a regular increasing downwards, especially towards the bottom, no doubt 

 owing to the exigences of this immigrant for a very salt and dense water (compare table 

 7) to keep it up f loating. 



Table 4, giving the vertical distribution of the peridinians, corresponds fairly well 

 with the similar table from S. Extra II, through the total numbers keep somewhat be- 



