The Botany of Iceland - 01.12.1912, Side 102

88
H.JÓNSSON
If \ve reckon, in percentages, the nuraber of species of each
group of the total number of species in the upper littoral zone \ve
obtain the following figures. The strictly littoral species (58 in all)
are indicated by a, the other species (20 in all) not strictly littoral
are indicated by b, but no attention is paid to those species which
may be found in the upper littoral zone and appear to grow by
preference in pools.
Rhodophyceie Phæophyceæ Chlorophyceíe Cvanophyceæ
a.................... 5 (9 °/o) 14 (24%) 33 (57 %) 6 (10%)
a + b................ 18(23%) 18(23%) 36 (46 %) 6(8%)
So far as the abundance of species is concerned I lay special
stress on the red algæ, green algæ and blue-green algæ. It would
be confusing, especially as regards the red algæ, to reckon the b-
species as strictly littoral, nor can this be done, because they are
not adapted for life in the open liltoral zone. As regards the brown
and green algæ, on the other hand, it is of no essential importance
whether the fc-species are included or not, as they are so few in
number.
If we calculate how great a proportion the strictly littoral
species form of the combined number of each group we obtain the
following íigures: —
Rhodophyceæ Phæophyceæ Chlorophyceæ Cyanophyceæ
Species known at pre-
sent from Iceland.. 76 67 51 6
Strictly littoral species 5(6.6%) 14(20.9%) 33 (64.7 %) 6(100%)
a + b (see above).. . . 18 (23.7 %) 18 (26.8 %) 36 (70.6 %) 6 (100 %)
B. The Lower Littoral Zone and the Belt below down to
a depth of about 10 metres.
1. The Lower Littoral Zone. From this are recorded 93
species in all (Table 7), viz. 39 Rhodophyceœ, 37 Phœophyceœ and
17 Chlorophyceœ. Of these 93 species, the upper and lower littoral
zones have 15 species in cornmon (8 red, 5 brown, 2 green) which
do not extend further downwards; the greater number of these
belong, strictly speaking, to the lower littoral zone, as, in the upper
littoral zone, they usually occur in pools or very shady spots. 19
species (8 red, 11 brown) have been found only in the lowær littoral
zone; but the majorily of them probably occur also below the limit
of low-tide, and, in any case, some have their area of distribution