I. Plankton of the North Sea in 1897. 



I have already^ reported on the stete of the North Sea in winter (January and 

 February). The region has since then been explored by Swedish steamers during April — 

 May, July — August and October — November, and a quantity of material has been ob- 

 tained which affords a good insight into the annual changes in the plankton of the North 

 Sea. To understand these changes it must be borne in mind that, as proved by hydro- 

 graphical researches, the water of the Atlantic enters the North Sea both by the north 

 of Scotland and through the English Channel. Of considerable importance ai^e also the 

 researches of Mr. Wemyss Fulton on the currents of the North Sea.^ The results of 

 these investigations are summarised as follows: 



1. »There is at all seasons a fairly constant slow circulation of the surface water iii 

 the North Sea, Atlantic water entering round the north of Scotland, and passing south- 

 wards along the east coasts of Scotland and England, as far as the neighbourhood of the 

 Wash, then in an E.N.E. direction towards the coast of Denmark, and then northerly 

 along the Danish coast. The surface water may or may not enter the Skagerak and 

 penetrate to the west coast of Sweden and Norway, according to the prevailing wind 

 The main body passes up the west coast of NorAvay and joins the Atlantic stream. The 

 limit between the north-going eastern stream and the south-going western stream varies 

 greatly, probably according to the prevailing wind; but as a rule the extent of the former 

 is greater.» 



2. »The movements of the surface water in confined areas, like the western part of 

 the Moray Firth, and the Firth of Forth, is irregular, and depends upon variations in 

 the winds and the tides.» 



3. »The speed of the movement is usually about two or three geographical miles a 

 day, but may be much accelerated or retarded by the action of the wind.» 



From the above hydrographical statements it appears that the plankton of the 

 northern part of the North Sea (i. e. above the 100 and 200 metre plateaus) is furnished 

 by the Atlantic, north of Scotland. The plankton of the southern part (i. e. above the 

 50 metre plateau north of the continental coast) which I have called the didymus-plankton, 

 on the other hand, is derived partly at least, from the English Channel. A part of it 



^ A treatise on the phytoplankton of the Atlantic and its tributaries, Upsala 1897. 4°. 

 ^ Fifteentli annual report of the Fishery Board for Scotland. 1897, pag. 334, 



