The Botany of Iceland - 01.12.1912, Blaðsíða 150

136
H. JÓNSSON
the autumn and winter, both because the light is feeble, and be-
cause the increased high seas following stormy weather to some
extent compensate for the difference in height. But it is in the
spring and summer that it is most evident that Corallina lias
really extended too high up. According to Börgesen’s description
(12) it appears to extend still higher up in the Færöes.
In the Corallina-association an abundant epiphytic vegetation
may occur, both of small algæ like Chantransia and of larger algæ
such as Monostroma Grevillei, Spontjomorpha vernalis, Acrosiphonia
alhescens and also the Aea//ies/a-associations. Furthermore, Ceraminm
rubrum, Cijstoclonium, Delesseria sinuosa and D. sanyuinea occur, and
other red algæ, often in great quantities. When to this is added
the foct that Gigartina is often ahundantly intermingled with tliose
already mentioned, it is easily seen tliat this mixed vegetation as-
sumes quite a diíferent character, according as to whether the
brown-red Gigartina and Ceramium or the light-green Monostroma
and Spongomorpha predominate. This characteristic appearance dif-
fers entirely from the usually monotonous appearance of the Coral-
lina-belt. This epiphytic vegetation must be considered to form as-
sociations which do not really belong to the Corallina-\egetation in
any other respect than that of having it for a substratum.
The Gigartina-association is widely distributed on very
exposed coasts; it often is of very great breadth and, as already
frequently mentioned, extends in under the Fucaceœ as undergrowth.
Where the exposure is less, it does not reacli so high; hut yet, in
the lower littoral zone there is, as a rule, a distinct Gigartina-belt,
which most frequently occurs above the limit of low-tide. The
Gigartina-\egetation extends also below the limit of low-tide, but it
seems to belong most closely to the lower littoral zone. The belt
is quite characteristic, and can often be seen from a distance, as
tlie colour is in sti’ong conti’ast to that of the Fucaceœ-community.
The species is of very social growth and is usually dominant where
it occui’s; not rarely, lxowever, a few species occur intermingled
with it, especially in the Vestmannaeyjar and at Öndverðarnes, two
very exposed localities. In the Gigartina-belt Coratlina may occur
lowest, Callithamnion Arhusciila is sometimes plentifully intermixed
witli the Corallina and occurs also in abundance as an epiphvte,
and Ceramium acanthonolum occurs i’ather frequently and often
abundantly. In the Vestmannaeyjar Callithamnion scopulorum occurs
rather fx-equently as undergrowth. In addition, Ceramium rubrum,