The Botany of Iceland - 01.12.1912, Síða 153

MARINE ALGAL VEGETATION
139
these depressions which fact will be mentioned again later on.
Some of the depressions are occupied by semi-littoral associations,
thus, Corallineta, Gigartineta, Chondreta, Monostrometa, Ceramieta, etc.
frequently occur, and, in addition, several of the species which be-
long to these associations are found growing in a scattered manner.
As mentioned above (p. 125), the vegetation in the pools is
highly heterogeneous, and, in the large pools it can frequently be
seen that the associations or their representatives arrange them-
selves in belts, here on a small scale in the same manner as they
do on a larger scale outside the pools.
c. The Sublittoral Zone.
The sublittoral vegetation covers the sea-bed from the limit of
low-tide down to a deptli of 40—60 metres, and perhaps to an even
greater depth. Under normal circumstances it is not exposed during
low-tide; yet it may happen that the uppermost Laminariœ, espe-
cially when small, become exposed during extreme low-water, but
this must be considered exceptional. What especially characterizes
this zone is the circumstance that the associations are always sub-
merged. The associations are certainly few in number, but most of
them liave a remarkably wide horizontal distribution, and tlie vege-
tation, taken as a whole, is homogeneous. With the exception of
illumination the conditions ol' life must be supposed to be stable;
in any case, compared with the conditions of life in the littoral
zone, they are unstable to a very slight degree. In the littoral zone
the change of season is noticeable, but in the deep, under normal
circumstances, these changes are very slight. The character of the
vegetation is therefore nearly the same all the year round.
The Laminariaceœ vegetation, as previously mentioned, is do-
minant in this zone and stretches in a broad belt along the coasts.
Beyond the La/iu'narfa-belt another narrower belt occurs composed
almost exclusively of Rhodophijceœ.
14. The Community of Laminariaceæ.
This community occurs especially on a rocky substratum, and
extends over large areas of the sea-bed from about the limit of low-
tide to a depth of about 30 metres. It forms a belt round the
coasts, and varies in breadth according to the conditions of depth
and the nature of the substratum. This belt is for the most part