Biology Reference
In-Depth Information
Compared to the cold-temperate regions in the northern hemisphere, the south-
ern hemisphere has been characterized by the greater importance of the prevailing
ocean currents for the seaweed distribution as well as by a more pronounced
geographical isolation of the seaweed flora (L
uning
1990
). In the southern hemi-
sphere, the cold temperate regions have more island-like or peninsular character,
thus resulting in a higher endemism. In the northern hemisphere, migrations at
higher latitudes are possible mainly along coastlines. Since its formation the ACC
has been the dominating biogeographical element at cold-temperate latitudes of the
southern hemisphere and has served as a migration route for floating seaweed
species (e.g.,
Macrocystis pyrifera
and
Durvillaea antarctica
) creating similarities
in floras between these regions (L
€
uning
1990
; Fraser et al.
2009a
; see also Chap.
17
€
by Roth
ausler et al.).
One of the striking differences between the northern and southern cold-
temperate regions is the almost exclusive dominance of species of the order
Laminariales in littoral systems in the northern hemisphere, whereas in the southern
hemisphere the only genera of the Laminariales, i.e.,
Macrocystis
,
Lessonia
,
Ecklonia
,
Eisenia,
and
Laminaria
, grow intermixed with various dominant fucalean
species. Nearshore reef assemblages in temperate New Zealand and Australia differ
from those in other parts of the world: fucalean seaweeds dominate in the shallow
subtidal zone, the kelp
E. radiata
forms dense beds at middle depths, and the giant
kelp
M. pyrifera
occurs in the southern regions, but is abundant at only a few sites
(Schiel et al.
1995
). In the mid-intertidal zone,
Chondrus crispus
, a common
dominant rhodophyte in the northern hemisphere, is replaced in regions of southern
South America and many sub-Antarctic islands by species of
Nothogenia
and by the
brown alga
Adenocystis utricularis
(Westermeier and Rivera
1986
; Ing
´
lfsson
2005
). Among the main similarities between the northern and southern hemisphere
cold-temperate floras is the presence of various members of the order
Desmarestiales. In the coast of southern Chile, South Africa, and many sub-
Antarctic islands several species of
Desmarestia
are regional endemics, and some
species such as
D. ligulata
and
D. confervoides/D. viridis
exhibit a disjunct amphi-
equatorial distribution (Wiencke et al.
1994
; Peters et al.
1997
). Species such as
D. anceps
,
D. menziesii,
and
Himantothallus grandifolius
are dominant in the
Antarctic, but absent from the cold-temperate region. These species are regarded
as ecological equivalent of Laminariales in the northern hemisphere (Moe and Silva
1977
; Clayton
1994
; Wiencke et al.
1996
).
€
14.5 Concluding Remarks
Seaweed flora in the cold-temperate regions of the southern hemisphere has been
modified not only by large-scale geological and paleoclimatic processes but also by
long-distance dispersal events and an inherent capacity of the species to adapt to
new habitats. Diverse present and future threats arising from anthropogenic
activities will impose new challenges for these seaweeds communities. Many
