The Botany of Iceland - 01.12.1912, Side 101

MARINE ALGAL VEGETATION
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phyte; the remaining 4 species are common in the lower littoral
zone, and occur in pools in the upper littoral zone, consequently
they cannot, strictly^ speaking, be reckoned as belonging to the upper
littoral zone.
Chlorophyceæ. In tlie table, 36 species of green algæ are
mentioned from the upper littoral zone. Of these, 15 are charac-
terized as common and 21 as rarer. 31 species are recorded ex-
clusively from the upper littoral zone; 2 species, Entoderma and
Bolbocoleon are more frequent in the lower littoral zone; one species
Chlorochytrium dermatocolax is as frequent in the lower littoral zone
as in the upper littoral zone, one species Ulothrix ftacca, which
must be considered a decidedly littoral species, grows to a depth
of about 10 metres. Utvella fucicola also grows to a depth of 5
metres, but must nevertheless be considered littoral. In addition
to these 36 species, others may be found in the upper littoral zone,
which have a more downward extension (e. g. Monostroma Greuitlei
var. arctica, M. fuscum, Acrosiphonia incurva, and others), but thev
generally keep to the pools.
Cyanophyceæ. All the species hitherto found (6) grow in
the upper littoral zone.
The species which are recorded from the upper littoral zone
may be put into two divisions. The one eomprises the species
wliich are connnon in the upper littoral zone and are adapted to
growtli in places exposed to the light and the wind during the
period of exposure; these species, then, might be termed strictlyr
littoral. The other division comprises species which are common
in the lower littoral zone or extend even further downwards. Tlie
greater number of tliese species does not occur in the open littoral
zone, but is found as an undergrowth or in shady clefts, or in
pools. The real home of these species is lower down than in the
upper littoral zone, and for this reason they can scarcely be de-
signated littoral species.
According to the above, there are in all 58 strictly littoral species:
Rhodophyceœ 5 species, Phœophyceœ 14 species, Chlorophyceœ 33
species and Cyanophyceœ 6 species.
The upper littoral zone is thus essentially characterized bv a
paucitv of species of red algæ, by many sjiecies of green algæ and
by a preponderance of Fucaceœ. The number of the species of
brown algæ is of less importance; it is three times as large as that
of the red algæ and about half as large as that of the green algæ.