Seaweeds and Their Communities in Polar Regions - Seaweed Biology - page 273

of carbon to hard and soft bottom communities, likely via the detrital food web
(Norkko et al. 2004 ).
Antarctic seaweeds also provide food and cover to large numbers of
invertebrates and fishes (e.g., DeLaca and Lipps 1976 ; Richardson 1977 ; Iken
1999 ; Huang et al. 2007 ; Zamzow et al. 2011 ). Amphipods occur on these seaweeds
at exceptionally high densities. Richardson ( 1977 ) reported over 10,000 amphipods
per single Desmarestia anceps while Amsler et al. ( 2008 ), combining datasets from
the same community collected by Amsler et al. ( 1995 ) and Huang et al. ( 2007 ),
estimated densities of amphipods in solid stands of D. menziesii at over 300,000
individuals m 2 of the benthos with densities in solid stands of D. anceps and
Plocamium cartilagineum of approximately 30,000 individuals m 2 . All the sea-
weed species that have been reported with very high amphipod densities are also
chemically defended against amphipod herbivory (Amsler et al. 2005a ; Huang et al.
2007 ; Aumack et al. 2010 ) and as such are almost certainly not being consumed by
the amphipods. Instead, the amphipods are grazing epiphytic diatoms and other
macroalgae, as well as filamentous algal epiphytes and emergent filaments from
algal endophytes (Aumack et al. 2011 ). Removing these biofouling algae undoubt-
edly benefits the host seaweeds. The amphipods also benefit from associating with
the chemically defended seaweeds as they are much less likely to be consumed by
omnivorous fish (Zamzow et al. 2010 ). Therefore, the seaweeds, which are the
dominant, habitat-forming organisms in the community and the amphipods, which
are by far the most numerous animals in the community, exist in a community-
wide, mutualistic relationship.
Filamentous algae growing as epiphytes are very rare along the western Antarc-
tic Peninsula (Peters 2003 ). However, filamentous algae growing as endophytes
within the larger, chemically defended seaweeds are unusually common, which has
probably been selected for as a refuge from the dense amphipod assemblage (Peters
2003 ; Amsler et al. 2009 ; see also Chap. 9 by Amsler and Chap. 11 by Potin).
Although endophytes do not necessarily harm their hosts, serious pathogenic effects
of filamentous algal endophytes on their seaweed hosts are well known (e.g., Apt
1988 ; Correa and S´nchez 1996 ; Peters and Schaffelke 1996 ). Whether or not, and
if so how frequently, the abundant algal endophytes in Antarctic seaweeds are
deleterious to their hosts and whether or not Antarctic seaweeds use chemical
defenses against endophytes are important areas for future study.
Although seaweeds in Arctic Spitsbergen support a diversity of macrofauna
(Lippert et al. 2001 ; Włodarska-Kowalczuk et al. 2009 ), only 2 of 19 such species
examined were shown to consume the seaweeds (Wessels et al. 2006 ). However, it
is likely that, as in Antarctica, seaweed carbon is important in this system via the
detrital food web (Hop et al. 2002 ). In the Alaskan Beaufort Sea, stable isotope
techniques have shown that kelps are an important carbon source to many inverte-
brate species including direct herbivores and animals deriving the carbon via
detritus (Dunton and Schell 1987 ).