The Botany of Iceland - 01.12.1912, Blaðsíða 121

MARINE ALGAL VEGETATION
107
connected with each other tlian thej' are with the remaining asso-
ciations, which also are mutually very closely connected. In this
way the community may he divided into two belts, of which the
first comprises the two first-mentioned associations, and the second
the remaining four. The Pelvetia- Fucus - spiralis-belt is narrow. It
is situated in the upper part of tlie littoral zone, at, and just below,
lowest high-water mark, i. e. flood-mark at neap-tide. It has only
one layer of vegetation, as tliere is no undergrowth wortli men-
tioning, and it is entirely devoid of epipliytes; it is submerged in
normal conditions for a very short time.
The second, the Fucus-belt is broad; it occurs in the lower part
of the upper littoral zone, just above low-water mark of neap-tide.
The vegetation occurs in two, and sometimes in three, layers and
epiphytes are present in abundance. The vegetation is submerged
much longer than in the íirst belt. Thus, these two belts differ so
greatly that they cannot be treated together.
The Pelvetia-Fucus-spiralis-belt.
This belt is of common occurrence, and its vegetation is luxuriant
in S. and SW. Iceland, but in the other parls of the country is
sparse and devoid of Pelvetia. This belt is not continuous except
along sliort distances, and its vertical lieight is inconsiderable; but
tlie breadth may sometimes be fairly considerable, especiallv on
very gently sloping coasts. It grows on rocky coasts, and in places
where these consist of a talus of debris the vegetation is distributed
in patches wliich is a natural consequence of the surface, tlie limit
of the association being rather sharply defined downwards. Petvetia
and Fucus spiratis do not grow intermixed, but occur in two pure
and distinct associations. They gnnv luxuriantly on exposed coasts;
in the most exposed parts of the coast, however, they seem to
recede. Thus, tliis belt was either absent from, or was poorly re-
presented on tlie most exposed points at the extremity of Snæfellsnes
and of the Vestmannaeyjar and at the extreme end of Reyðarfjörður;
but there occurred in its place surf-forms of Fucus inftatus (f. ex-
posita and f. dendroides).
The Pel vetia-association (Fig. 3) always occurs highest of all.
As already mentioned it is found in S. and SW. Iceland only, but
there it occurs in great abundance in many places; in some places its
vegetation is poor, and sometimes only a few scatlered individuals
are found. This is more particularly the case in places where Petvetia