526 DEPTHS OF THE OCEAN 



on the west, but in regard to individuals they are very much 

 exceeded by the attached forms. 



A great difference between the arctic region in high 

 latitudes, where the Gulf Stream has lost its warming influence, 

 and the boreal region, is to be found in the littoral, or more 

 correctly in the strand, zones. The luxurious growth of fucus 

 and laminaria which covers the rocks along the coasts in the 

 boreal region, both above and below low-water mark, is wanting 

 in depths less than about 6 metres. This is due to the ice 

 blocking up the shore for a great part of the year and prevent- 

 ing the development of animal and plant life. The strand 

 zones in high arctic latitudes accordingly exhibit nothing but 

 naked rock, in contradistinction to the rocks of the boreal 

 region, where we find numbers of attached animal-forms right 

 up to high-water mark. As soon, however, as we descend 

 below the limit of the baneful effects of the ice, we meet 

 with a profusion of both plants and animals, sometimes even 

 in greater abundance than in the boreal region. 



Though we are thus unable to speak of an actual strand- 

 fauna in high arctic latitudes, we can distinguish, to a certain 

 extent, between the littoral, or rather sub-littoral, and the deeper 

 non-littoral forms. The former, however, appear to be compara- 

 tively few in number, taking 40 metres as the lower limit as we 

 did in the boreal region, while on the other hand most of the 

 non-littoral forms reach nearly up to or actually pass the littoral 

 limit. Generally speaking, the limits between a littoral and 

 non-littoral zone seem to be less clearly defined in the arctic 

 than in the boreal region.^ The reason for this is obvious 

 enough, if we remember that temperature largely controls 

 distribution. In high arctic latitudes the difference in tempera- 

 ture between deep and shallow waters is inconsiderable 

 compared with that at corresponding depths in boreal areas. 

 As a result the forms find favourable conditions of existence, 

 so far as temperature is concerned, at very different depths, and 

 the vertical distribution of most of the arctic forms is far more 

 extensive than that of boreal forms. A few instances may be 

 cited : Hymenaster pellticidus in the Norwegian Sea deep 

 basin is found even below 2000 metres, while on the east side 

 of Spitsbergen it occurs at 27 metres; Antedon eschrichti v(\2.y 

 be met with in the cold area of the Norwegian Sea at very 

 considerable depths, whereas at Spitsbergen it flourishes in 



^ Cf. Stuxberg, "Evertebratfaunan i Sibiriens ishaf," Vega-exped. vetenskap. iakttagelser, 

 Bd. i. pp. 730, etc. 



