Biology Reference
In-Depth Information
et al.
1994
). In general, factors determining the ecological functions of seaweeds
have been well described for the ecosystems at 30-40
S (reviewed by Santelices
1989
). At intertidal sites, trophic interactions with gastropods, such as the limpet
Fissurella
, the polyplacophoran
Chiton granossus,
and the snail
Tegula atra
, have
important consequences for the seaweed communities (Moreno and Jaramillo
1983
;
Jara and Moreno
1984
; Ota
´
za and Santelices
1985
). At subtidal sites, the interac-
tion between
M. pyrifera
and the sea urchins
Loxechinus albus
and
Tetrapygus
niger
defines the ecological process of southern kelp forests (Santelices and Ojeda
1984
; Dayton
1985
). Unlike the situation for kelp forests of California, sea urchins
from southern region preferentially consume algal drifts and act regulating the
biomass of recruits (Moreno and Sutherland
1982
;V´squez et al.
1984
; Graham
et al.
2007
). Some gastropods, such as
Tegula atra
, graze also on subtidal kelps
(Moreno and Sutherland
1982
; Buschmann
1992
).
14.2.2 Southeastern South America Region (Argentinean
Patagonia)
Approximately 400 seaweed species have been reported for the Atlantic coast of
Argentina (reviewed by L
uning
1990
). Two main biogeographical provinces have
been proposed: (1) the Magellan province with cold water covering the southern
Patagonia, and (2) the Argentinean province with warmer waters extending from
North Patagonia (around Peninsula Vald
´
s at 42-43
S) northwards (Lutz et al.
2003
). In this region, species richness has been characterized as being relatively
poor (Bolton
1994
). Intertidal rocky shores here are characterized by a depauperate
seaweed flora, mainly due to harsh physical conditions (Paruelo et al.
1998
;
Bertness et al.
2006
), calcareous algae covering low tidal height in wave-protected
sites (Bertness et al.
2006
). Northwards from the Gulf San Mat
´
as (41
S), the
massive runoff and sedimentation from Rio de la Plata limit the availability of
hard substrates for seaweeds. In this region, temperate chlorophytes adapted to
estuarine conditions dominate (Acha et al.
2004
). Southwards, in the limit between
the Argentinean and the Magellan biogeographical regions, subtropical species,
such as
Dictyota
, are mixed with sub-Antarctic (e.g.,
Bryopsis australis
) and
endemic (e.g.,
Myrogloia major
) components. The kelps
Macrocystis pyrifera
,
Lessonia flavicans,
and
L. vadosa
occur continuously from the Pacific to the
Atlantic coast (up to 42
S for
Macrocystis
, 47-48
S for
Lessonia
) (Barrales and
Lobban
1975
; Searles
1978
). The fucoid
Durvillaea antarctica
has its northern limit
around 51
S in the Argentinean side of Tierra del Fuego (Boraso and Zaixso
2011
).
The invasive kelp
Undaria pinnatifida
has been associated with a decrease of
species richness and diversity of native seaweeds in Patagonia (Casas et al.
2004
;
see also Chap.
12
by Andreakis and Schaffelke).
In the Falkland Islands, a total of 169 seaweed species (55% Rhodophyta, 29%
Phaeophyceae, 16% Chlorophyta) were recently listed (Ram
´
rez
2010
). The lower
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