APPENDIX A: PETTERSSON _ 20 — 



phenomena, the existence of which have been fully proved by authentic observations 

 conducted according to the claims of science. 



The manner in which prevaihng hydrographie conditions affect the living organisms 

 of the sea is twofold. They either depend entirely on the motions of the water for their 

 temporary residence, in which case they are drifted by the sea-currents f inst. from higher 

 into lower lats., or being stationary within certain geographic limits, their physiologic 

 functions are affected by modifications resembling chmatic changes in the salinity and 

 temperature of the surrounding water. Plankton, animal and vegetal, fish-eggs and larvse 

 belong to the former, fishes to the latter category. For instance we may assume, that 

 the atlantic plankton found by "Michael Sars" Febr. 1903 in the neighbourhood of Jan 

 Mayen was conveyed thither by the retarded flood of Atlantic water. Another example 

 is this: 

 Annual changes Accotdiug to obsetvations made by the Swedish Greenland-expedition in 1899 the 

 of the Plankton plaukton-character on the northern slope of the North Sea plateau had completely 

 changed from June to September. The list of principal forms given below is compiled 

 by Professor Cleve and is illustrative of this condition. 



Norwegian Sea 61° — 62° Lat. N., o°-37— i°i9 Long. E. 

 31. May — 2.Junei899. 



Phaeocystis Poucheti, Chaetoceras decipiens, Calanus finmarchicus from 25 m. depth 

 and in deeper layers. 



8. September 1899. 



Ceratium macroceros, tripos, Paracalanus parvus, Centropages typicus. 



Calanus finmarchicus was met with at a depth of 100 m. only and in abundance in 

 greater depths at 6o°55' Lat. N. and o°2o' Long. E. 



As the hydrographie situation exhibited corresponding modifications it may be 

 inferred, that the plankton of September entered the Norwegian Sea with the 

 Atlantic water ^. 



All plankton-biologists agree, that the hydrographie state of the Norwegian Sea is 

 closely connected with the character of the plankton pervading it. As to the ultimate 

 cause of the annual variations in the character and distribution of plankton, opinions 

 differ. From the observations of the "Michael Sars" during her first cruise in 1900, it 

 is evident that, judging by the specimens of chief species collected, the boundaries of 

 the different plankton regions are nearly concurrent with those of the three waterareas, 

 that we discern, i.e. the Atlantic, the Arctic and the littoral or bank water. 

 According to Cleve each kind of water is predominated by a special type of plankton. 

 Thus Trieho- and Sira-plankton (T and Ti) denotes Arctic, Chaeto- and Styli- 

 plankton (C and S) Atlantic, Tripos -plankton (Tp) littoral water. 



To the annual variations in the hydrographie state correspond modifications in the 

 distribution of plankton-types. This feature is wellknown in the Skager Rak. Cleve 's 

 analytic studies of plankton collected monthly during the past 10 years at two stations 

 on the Skager Rak coast, have proved beyond doubt the correspondence of hydrographie 



I Specimens of the wellknown southerly form Velella spirans were in September collected even east 

 of the Shetlands. 



