The Botany of Iceland - 01.12.1912, Blaðsíða 104

90
H. JÓNSSON
number of red algæ in Ihe lower littoral zone. This can be dis-
tinctly seen from the following figures: —
Upper Littoral Zone Lower Littoral Zone
58 species (a) 93 species
not comnion common not common
51 (35.42 %) 7 (4.86 %) 86 (59.72%)
Upper Littoral Zone Lower Littoral Zone
78 species (a -t- b) 93 species
not common common not common
54 (36.73 %) 24 (16.33 %) 69 (46.94 %)
Lower Littoral Zone From the limit of low-tide to a
93 species depth of about 10 m. 103 species.
not common common not common
34 (24.82 %) 59 (43.06 %) 44 (32.12 %)
The figures show that the upper littoral zone is very unlike
the lower littoral zone, especially if only the species which are
characteristic of the latter, or which occur in the open littoral zone
(a), are taken into consideration, which is most correct, as the
shade-loving species in the upper littoral zone must be regarded
as stragglers from associations lower down. As previously mentioned,
the lower littoral zone bears the greatest resemblance to the belt
which exists lower down (to a depth of about 10 metres).
The species which have their lower limit of growth at a depth
of about 10 metres and which are commonly distributed in the
lower littoral zone I designate semi-littoral because they are found
both laid bare during low-tide in the lower littoral zone and con-
stantly submerged in the belt below; as these species especially
characterize the lower littoral zone and the belt below to a depth of
about 10 metres I designate this area the semi-littoral zone. It must
not be concluded, however, that semi-littoral vegetation covers the
bottom everywhere down to a depth of 10 metres; below the limit
of low-tide the semi-littoral vegetation appears rather to consist of
stragglers from the lower littoral zone into the Laminaria-belt. Thus
the semi-littoral zone is situated between the Facns-belt and the La-
minaria-he\t. The species which specially occur in the semi-littoral
zone I designate on the whole as semi-littoral, also those which are
found in the lower littoral zone and are not found below the limit of
low-tide; they will probably be found also below this limit. Species
which are common in the lower littoral zone and are rare in the