MARINE ALGAL VEGETATION 93 



Lower Limits of Growth in metres (see Table 7). 



About 60 

 About 3—10 About 15-20 About 25-30 About 35—45 and more 



Red algae 13 10 10 15 7 



Brown algae 19 8 4 5 3 



Green algae 16 .. 1 2 



Total... 48 18 15 22 10 



37 



In the above table 113 species are mentioned, of which 48 do 

 not extend to a greater depth than about 10 metres, 18 extend to 

 about 20 metres, 15 to about 30 metres, 22 to about 40 metres and 

 10 to about 60 metres and more. Thus there appears to be a flori- 

 stic boundary at a depth of about 10 metres; while another boundary 

 can be faintly distinguished at a depth of from about 30 to 40 

 metres, as there are 37 species which appear not to extend further 

 downwards; and here, also, is situated the lower limit of growth 

 of most of the Laminariacece which play the same role on the sub- 

 littoral bottom as the Fucacece play in the littoral zone. Exactly 

 where the lower limit of growth, as regards the marine algse in 

 Iceland, is situated — whether it lies at a depth of about 60 to 80 

 metres or deeper — I cannot at present decide, but it is most pro- 

 bable that the vegetation at greater depths than 60 metres is, in 

 any case, extremely poor in species. 



According to the above statements the lower limits of the alga? 

 are as follows : — 



The littoral limit (Upper Littoral Zone) 53 species 26.77 % 



The limit of low-tide 32 — 16.1 7 % 



At about 10 metres 48 — 24.24 % 



At about 20 metres 18 — 9.09 % 



At about 30— about 40 metres 37 — 18.68 % 



At about 60 metres and more 10 — 5.05 % 



198 species. 



By future investigations all these figures will undoubtedly be 

 altered and many of them to no inconsiderable extent; but the four 

 principal boundaries, namely the littoral limit, the 10-metre limit, 

 the 30—40 metre limit and the absolute depth -limit will always 

 remain evident. 



As regards the absolute depth-limit I cannot make any definite 

 statement. The dredgings which I myself have undertaken have all 

 been conducted with a small dredge from a small rowing boat. 



