The Botany of Iceland - 01.12.1912, Page 149

MARINE ALGAL VEGETATION
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12. The Community of Corallina.
Tlie members of this communily are Corallina officinalis, Gigar-
tina mamillosa, Chondrus crispus and Ahnfeltia plicata. These species
occur as a rule in luxuriant and more or less sharply detined as-
sociations, which very frequently occur together, and may therefore
be regarded as nearly related to each other.
The fronds are branched, and their consistency is on the whole
flrm because, as is known, Corallina is encrusted with calcium car-
bonate, Ahnfeltia is horny and Gigartina and Chondrus are car-
tilaginous.
Gigartina and Corallina generallv occur in a belt at the limit
of extreme low-wTater; in my diary I have always called this belt
the Gigartina-Corallina-belt. Gigartina, howTever, extends higher up;
on exposed coasts right up to the Fucus-belt, and even into that
as under-vegetation; but, where Gigartina and Corallina meet, there
is most frequently a mixed belt. Tliese associations belong to S.
and SW. Iceland.
The Corallina-association occurs most luxuriantly about lowT-
wTater mark. The species growTs extremely socially, and entirely
covers depressions in the littoral zone which are more or less filled
with wTater. The association occurs on somewThat exposed and also
on verv exposed coasts, but almost always in depressions surrounded
by rocks upon w'hich the wTaves break; yet I have seen it, wThere
the exposure is but slight, covering the face of rocks below low-
water mark. Only rarely have I obtained Corallina by dredging in
greater depths, as, for example, on the north coast, at a depth of
about. 14 metres, wThere it seems to be present in abundance. It
may be assumed with certainty, however, that this association has
a much wider distribution belowT the limit s of lowT-tide than is
shown by the dredgings, and wTith exceptional lowT-tides it can be
seen that in rnany places the Corallina-vegetation covers the í’ocks
as far as the eye can reach.
On a very exposed coast I have met with Corallina growdng
socially in water-filled depressions at a considerable liigher level,
sometimes on a level with the upper part of the í’ucus-belt. Here,
however, with the exception of the lowTest part of the frond, it is
quite wThite in colour, and has evidently strayed outside its real
domain. The spores have been carried to this height above the true
Cor«//inu-belt by the beat of the waves, and have been retained in
the depressions. It can also thrive fairly well at this height during