Biology Reference
In-Depth Information
species were unpalatable. By comparing assays on fresh seaweed thallus with
artificial foods which removed physical defenses, it was concluded that 15 of the
17 seaweeds rely primarily on physical toughness to deter herbivores and that only
two elaborate chemical defenses (Wessels et al.
2006
). In one of these chemically
defended seaweeds,
Desmarestia viridis
, the defensive compound has been shown
to be sulfuric acid (Molis et al.
2008
).
D. viridis
provides associational defense to
other seaweeds growing near because it so strongly repels sea urchins (Molis et al.
2008
).
To date, no studies—we are aware of—have examined polar seaweed chemical
defenses against biofouling in an ecologically relevant context (see also Chap.
9
by
Amsler). However, Antarctic seaweeds do produce compounds which are toxic to
epiphytic diatoms in vitro (Amsler et al.
2005b
; Iken et al.
2011
; Sevak
2010
).
Grazing amphipods appear to be very important in reducing diatom fouling of these
seaweeds in nature (see also Chap.
8
by Iken). However, when held in experimental
mesocosms without amphipods, one of four species,
Desmarestia anceps,
still had
only very low diatom coverage even though the other three species were heavily
fouled (Aumack et al.
2011
).
D. anceps
is one of the many species which have anti-
diatom bioactivity in vitro, and it is possible that some of these compounds are also
playing a role in controlling fouling in nature.
13.4.4 Trophic Interactions
Antarctic seaweeds appear to play important roles in benthic food webs in both
shallow and deeper waters along the northern portion of the Antarctic Peninsula and
they are likely to be of particular importance to benthic detrital food chains. A
majority of the mid-water and, in particular, deep water carbon flux along the
western Antarctic Peninsula can be composed of seaweed material, which also
forms a significant part of the sediments (Liebezeit and von Bodungen
1987
;
Reichardt
1987
; Fischer and Wiencke
1992
). Seaweeds are also important in
Antarctic coastal and maritime detrital food chains along the western Antarctic
Peninsula (Zielinski
1981
; Dawson et al.
1985
). Drift seaweeds can be abundant in
pockets on the coastal sea floor (Neushul
1965
; Brouwer
1996b
; Amsler, personal
observations). A major portion of the primary production of
Himantothallus
grandifolius
is lost as blade erosion and, in contrast to phytoplankton, this carbon
input to the detrital communities continues throughout the year (Dieckmann et al.
1985
). Although living, drift
Desmarestia anceps
decays fairly slowly via fragmen-
tation, carbon from dead
D. anceps
is recycled relatively quickly (Brouwer
1996b
).
Stable isotope techniques have shown that macroalgal carbon makes important
contributions to invertebrates via the detrital food webs in both shallow hard bottom
communities where they grow (Dunton
2001
) and in nearby, soft bottom
communities (Corbisier et al.
2004
) along the western Antarctic Peninsula. In
McMurdo Sound,
Phyllophora antarctica
appears to be a similar, important source
