The Botany of Iceland - 01.12.1912, Síða 126

112
H. JÓNSSON
Fucus vesiculosus grows highest and F. inflatus lowest. How the
species behave when left dry is mentioned in connection with each
association.
Tlie Fucus vesiculosus-association, as already mentioned,
is uppennost and often borders closely on that of Fucus spiralis.
It varies extremely in extent, aecording to tlie character of the coast.
The breadth may vary from about one foot on vertical rocks to
several fathoms on a gently sloping coast.
Fucus vesiculosus extends right into the innermost part of the
fjords, which is generally considered a protected coast; if there is
a favourable substratum tliere, its growth may be fairly luxuriant.
It also grows very luxuriantly on slightly exposed coasts, i. e. where
a landward wind is sometimes both frequent and tempestuous, but
wliere breakers are extremely rare. If the exposure is increased, it
seems tliat F. vesiculosus not only decreases in nurnber of individuals
but also seeks for shelter between tlie rocks. Then, gradually, it re-
treats lower into the Iittoral zone, and Ascophijllum, which is evidently
better able to withstand the lieavy seas, advances. Tliis is seen
very distinctly at Reykjavík, wliere tlie coast must be considered
somewhat exposed, because tlie south-west, west, and north winds
are frequently stormy and occasion heavy seas. If we take a bay
which is bounded by a rockjr promontory, we see at the head of
it a luxuriant Fucus vesiculosus-association; this extends out upon
tlie promontory, growing gradually narrower as it extends outwards;
in the vicinity of the point itself, tlie alga has commenced to seek
for shelter, and at the extreme end of tlie point it lias disappeared
and Ascophyllum has occupied its place, and tlien Fucus vesiculosus
is either found not at all or only a few individuals of it occur
high up in the Ascophyllum-be\t. What is here seen on a small
scale is repeated on a larger scale on proceeding' from the head of
the fjord outwards to the extreme point of tlie peninsulas. Thus,
Fucus vesiculosus was not observed on exposed points at 0ndverð-
arnes (the extreme point of Snæfellsnes), while Ascophyllum and,
naturally, Fucus inftatus also, were found in abundance. On the
most exposed points of the Vestmannaeyjar Fucus vesiculosus was
also absent, while both of tlie otliers occurred plentifully.1 Thus,
Fucus vesiculosus behaves in Iceland precisely as it does in the
Færöes (Börgesen, 12, 11).
1 Strömfelt (70) records AscophyUum as growing above Fucus vesiculosus
at Hólmanes in E. Iceland.