The Botany of Iceland - 01.12.1912, Side 107

MARINE ALGAL VEGETATION
93
Lower Limits of Growth in metres (see Table 7).
About 5—10 About 15-20 About 25-30 About 35—45
Red algæ........ 13 10 10 15
Brown algæ. . . . 19 8 4 5
Green algæ...... 1 (i . . 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 apjiear not to extend further
downwards; and here, also, is situated tlie lower limit of growtli
of most of the Laminariaceœ which plajr the same röle on the sub-
littoral bottom as the Fucaceœ play in the littoral zone. Exactly
where the lower liinit of growth, as regards the marine algæ in
Iceland, is situated — whether it lies at a deptli 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 stateinents the lower limits of the algæ
are as follows: —
The littoral limit (Upper Littoral Zone)........... 53 species 26.77 %
The limit of low-tide.............................. 32 — 16.17%
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 flgures 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 deflnite
statement. The dredgings which I myself have undertaken have all
been conducted with a small dredge from a small rowing boat.
About 60
and more
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