Cold-Temperate Seaweed Communities of the Southern Hemisphere - Seaweed Biology - page 291

intertidal zone is dominated by Durvillaea antarctica , while the subtidal zone is
characterized by extensive Macrocystis pyrifera forests (van Tussenbroek 1993 ).
Other large kelps, such as Lessonia flavicans , are also present (Ram ´ rez 2010 ).
Based on phylogenetic analyses, a highly diverse flora of bladed Bangiales (at least
nine species) has been reported for the Falkland Islands (Broom et al. 2010 ). A high
floristic similarity (60%) is found with the flora from Magellan-Tierra del Fuego
region, principally due to species with a sub-Antarctic origin. The Falkland Islands
and Magellan-Tierra del Fuego region form a group that separates from the
Antarctic region (Hommersand et al. 2009 ; Ram´rez 2010 ). These studies do not
support the previously proposed biogeographic province with continuity of the
marine flora in the Antarctic region and the sub-Antarctic South American region
(John et al. 1994 ).
Ecological studies on seaweeds from the southeastern South American region
are scarce, and thus the understanding of the distribution and abundance patterns as
well as the functional roles of the seaweeds in these ecosystems is poorly known.
Apparently, intertidal seaweed communities are strongly regulated by physical
factors, as grazing pressure is weak due to the absence of common predaceous
crabs and snails and the limited impact by limpets (Bertness et al. 2006 ). In subtidal
environments, evidence based on population dynamics from Argentinean mainland
and the Falkland Islands indicates that giant kelp beds are regulated by storms and
nutrient availability (Barrales and Lobban 1975 ; van Tussenbroek 1989 ). In the
kelp ( Macrocystis ) forests no consistent grazers, such as sea urchins, were reported
either (Barrales and Lobban 1975 ). However, growth patterns and demography of
these forests show considerable local variation (van Tussenbroek 1993 ).
14.2.3 Victoria-Tasmania Region
The seaweed flora of the southern Australia is characterized by high species
richness and endemism (Bolton 1994 ; Phillips 2001 ; Kerswell 2006 ), resulting
from a complex interaction of biogeographical, phylogenetic, and ecological pro-
cesses (reviewed by Phillips 2001 ). Over 1,100 species (Bolton 1994 ) and four
major floristic elements, i.e., endemic, widely distributed temperate, tropical, and
polar elements, have been identified (Phillips 2001 ). Endemic (40-77%) and widely
distributed temperate (17-45%) species account for the majority of the seaweeds,
whereas species with tropical (4.5-9.7%) and polar (1.5-5.1%) affinities are much
less represented. In Rhodophyta and Phaeophyceae, endemic elements dominate
(77% and 59%, respectively), while in Chlorophyta widely distributed temperate
(45%) flora account for the majority (Phillips 2001 ). Recent quantitative seaweed
analyses confirmed the traditionally recognized Peronian (eastern), Flindersian
(western), and Maugean (south-eastern) marine biogeographic provinces of the
southern coast of Australia (Waters 2010 ). Furthermore, differentiation of marine
communities in eastern and western elements has been associated with the Bassian
Isthmus as a historical vicariant barrier (Waters 2008b ; Fraser et al. 2009a ).