Biology Reference
In-Depth Information
Peters et al.
2005
; see Chap.
4
by Gordillo). Not surprisingly then, protein levels in
Antarctic macroalgae are also higher than reported for most other places in the
world (Peters et al.
2005
). Since protein levels are important determinants of the
nutritional value and palatability of seaweeds to herbivores (e.g., Horn and
Neighbors
1984
), this suggests that were it not for the common occurrence of
chemical defenses in these algae they would likely be more valuable foods for
herbivores than seaweeds from other regions. In the only study we are aware of in
the Arctic,
L. solidungula
and
S. latissima
were shown to also have relatively low C:
N ratios early in the growing season which increased as stored nitrogen was used for
biomass gain during the summer (Henley and Dunton
1995
).
13.4.3 Defenses Against Herbivory and Biofouling in Polar
Seaweeds
Many seaweeds deter herbivores with organic compounds that make them unpalat-
able and/or interfere with the animals' digestion, and similar compounds can also
be used to deter the settlement of biofouling spores or larvae (see also Chap.
8
by
Iken and Chap.
9
by Amsler). In addition or as an alternative to chemical defenses,
seaweeds can also decrease their palatability to herbivores by increasing their
physical toughness (e.g., Lowell et al.
1991
).
Chemical defenses against herbivores are very common in Antarctic seaweeds
(Amsler et al.
2005a
,
2008
,
2011
; Aumack et al.
2010
). All of the dominant brown
seaweeds along the western Antarctic Peninsula described and most of the common
red seaweeds in the subtidal community elaborate chemical defenses against
herbivores. Although physical toughness may play a role in some species, particu-
larly against amphipods, chemical defenses appear to be far more important overall
in deterring herbivory (Amsler et al.
2005a
,
2008
,
2011
). Hence, although these
communities are similar to temperate kelp forests in being dominated by large,
perennial brown seaweeds, they differ from many such communities in that the
seaweeds are able to resist herbivory directly rather than relying on top-down
control of herbivores by their predators (e.g., Elner and Vadas
1990
; Estes and
Duggins
1995
).
Both of the dominant red seaweeds in the Ross Sea,
I. cordata
and
P. antarctica
,
are also chemically defended against a sea urchin which is the most obvious
potential algal consumer in that system (Amsler et al.
1998
). However, the sea
urchins preferentially cover themselves with detached seaweeds when they are
available, which in turn provides a physical barrier for defense against their main
predator, large sea anemones (Amsler et al.
1999
). This benefits the seaweeds since
it keeps a large population of drift algae in the photic zone where they continue to
photosynthesize and reproduce (Amsler et al.
1999
; Schwarz et al.
2003
).
The palatability of 19 seaweeds to herbivorous sea urchins and amphipods has
been examined in the Arctic at Svalbard (Wessels et al.
2006
). Of these, 17 seaweed
