KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 32. N:0 



2. North Sea April— May 1897. 



The samples collected by the Swedish steamers at the end of April and in the 

 beginning of Maj' prove that considerable changes had occurred since the winter. 



1. Chaeto-plankton. The broad tongue of water with a salinity of 35 p. inille 

 and temperature 5,6 to 7,5^ contains chceto-plankton chiefly. This kind extends to the 

 Shetlands, Fftröes and south Iceland. It occurs also abundantlj' in Skagerak. It was not 

 found at Plymouth, but occurred there abundantly in November and December of 1896, and 

 remnants lingered there still in January and February of 1897. At Iceland and at the 

 Färöes it began to appear in March. 



In the Southern North Sea (i. e. above the 50 metre plateau) Chcetoceros decipiens did 

 not occur to any important extent, but its place was there taken by the flagellate 

 Phceocystis Pouchetii, which I consider as connected with the ch^to-plankton. The slimy 

 masses of the last named organism were found at Helder and north of that station in 

 immense quantities. 



It is from the above apparent that the choäto-plankton already began to develop in 

 the mouth of the English Channel in December 1896, arrived at the Färöes and Iceland 

 in March and was enormously developed in April and May. As to the origin of the 

 chajto-plankton I defer the discussion to a future publication. From the collections of 

 the Swedish Expedition to Spitzbergen it is evident that the chasto-plankton appeared 

 there in the middle of July and as it had then disappeared on the route Iceland — Färöes — 

 Shetlands and from the North Sea, it might be assumed that it had migrated towards 

 Spitzbergen, where it was found abundantly in the middle of August, in Hinlopen Strait, 

 but this hypothesis would presuppose a greater velocity of currents than is usually admitted. 



2. Northern and arctic neritic plankton. The chteto-plankton of the North 

 Sea is bordered by a band containing a number of arctic and northern forms, belonging 

 to the sira-, tricho- and northern neritic types. As these forms are all derived from the 

 north-west and occur interiningled, I treat of them in the following as noi^tliern neritic 

 plankton. This plankton appears abundantly at the north end of Scotland and in a band 

 above the limit between the 50 metre and 100 metre plateaus. It continues along the 

 west of Scotland to the south of Iceland, and to the east along the Norwegian coast in- 

 to Skagerak. Similar neritic plankton also occurs sparingly in water of 35 p. mille sa- 

 linity from the Shetlands along the 60th degree of lat. to the region of the submarine 

 ridge, discovered by the Ingolf expedition and called »Reykianäs Ryg» which extends to 

 the south west from Iceland. West of the Reykianäs Ryg, which seems to have a great 

 influence upon the currents, styliplankton is the ruling type. 



As it is of considerable interest to examine the distribution of the forms which 

 constitute the northern neritic plankton as defined above, I will treat of each species 

 separately. 



1 See 0. Petteksson and G. Ekman. Bih. t. K. Sv. Vet. Akad. Handl. Vol. XXV. Part II. No 1. 1899. 



