1036 



CLEVE, P. T., PLANKTON FROM THE RED SEA. 



also agrees with the salinity-determinations, carried out by 

 Prof. 0. Pettersson on the samples of water collected by Dr. 



AüRIVILLIUS : 



Nr. 



1 



. rc 



51' 



N. 



33° 



34' 



E. 



temp. 



19,65 



salin. 



40,82 



» 



2 



. 25^ 



22' 



» 



35° 



31' 



» 



» 



22,25 



» 



40,22 



» 



3 



. 22^ 



25' 



» 



37° 



25' 



» 



» 



23,65 



» 



39,5 



» 



4 



. 19° 



22' 



» 



39° 



15' 



» 



» 



25,5 ' 



» 



38,8 



» 



5 



. 16° 



16' 



» 



41° 



12' 



» 



» 



24,5 



» 



37,41 



» 



6 



. 13° 



16' 



» 



43° 



3' 



» 



» 



24,8 



» 



36,35 



The water N. 1 and 2 was almost sterile in plankton, the 

 high salinity evidently being inimical to the plankton-organ- 

 isms. Most organisms noted in the above derive from No. 3 — 6. 



Almost all copepoda (92 %) occur in the Indo-pacific region, 

 many, or 38 %, also in the tropical Atlantic, both having a 

 very large number of plankton-organisms in common. 



Of the diatoms 29 % only occur in the tropical Atlantic, 

 but 64 % in the temperate and northern Atlantic, which is a 

 fact of great interest, as many among these diatoms are the 

 same as occur in the spring in the area N. of the Azores. 

 There can scarcely be any doubt that the water, which expands 

 in the spring N. of the Azores and during the summer moves 

 towards Iceland and the Färöe Channel, derives from the southern 

 Atlantic, in parts from the Antarctic Ocean. ^) The same is 

 probably the case, at least to some extent, with the water that 

 enters the Red Sea, as we find among the plankton-organisms 

 Thalassiothrix longissima, an arctic and antarctic species, which 

 scarcely can live permanently in a water of so high a salinity 

 and temperature as that of the Hed Sea. The occurrence of 

 Pseudoeunotia doliolus in the Gulf of Aden strongly corroborates 

 this hypothesis, as the said diatom is characteristic for the 

 southern Atlantic and southern Indian Ocean. 



1) ÖfVers. K. Sv. Vet. Akad. Förh. 1900, N:o 7, p. 921. 



