Biology Reference
In-Depth Information
Table 8.3
Algal defenses against grazing
Defense
mechanism
Selected example
Non-coexistence strategies
Escape in time The highly palatable green alga
Ulva
forms early spring blooms from an
overwintering propagule bank in the Baltic Sea, thus avoiding intense
herbivore pressure, which efficiently suppresses
Ulva
later in the season
(Lotze et al.
2000
)
Escape in space Turf algae on the Great Barrier Reef thrive in regions of reduced herbivory,
but are readily consumed when transplanted to regions of high herbivore
abundance (Bonaldo and Bellwood
2010
)
Escape in size
The chiton
Katharina
is very effective in removing new recruits of the low
intertidal kelp
Hedophyllum
in the Northeast Pacific but does not graze on
the adults (Markel and DeWreede
1998
)
Associational
defense
The palatable red alga
Gracilaria
is protected from sea urchin grazing when it
occurs associated with the unpalatable brown alga,
Sargassum,
in the
temperate Atlantic (Pfister and Hay
1988
)
In tropical coral reefs, seaweeds persist even under high herbivore abundances
when they are covered with epiphytic cyanobacteria (Fong et al.
2006
)
Coexistence strategies
Structural
defense
Fucus
produces adventitious branches after grazing damage, which act as
structural defenses against further grazing, although high phlorotannin
content in these branches may also present a chemical defense (Van
Alstyne
1989
)
Padina
on coral reefs exhibit morphological plasticity with an erect, foliose
morphology in the absence of grazers and a more resistant turf morphology
under high grazing pressure (Lewis et al.
1987
)
Chemical defense
Tropical systems A large variety of green, red, and brown seaweeds deter feeding in many
invertebrate and vertebrate grazers using a rich arsenal of terpene and
acetogenin metabolites (see Table 2.1 in Pereira and da Gama
2008
). For
example, the Brazilian brown alga
Stypopodium zonale
(Dictyotales)
produces a diterpene mixture that chemically differs depending on
location, and some compounds of the mix deter urchin and crab feeding
more than others (Soares et al.
2003
)
Temperate
systems
While generally less rich in natural products active against grazers than
tropical algae, temperate seaweeds are often chemically defended, with
phlorotannins in brown algae being the most-studied group (Jormalainen
and Honkanen
2008
). However, phlorotannins are not always the deterrent
compound; in
Fucus vesiculosus
, a galactolipid and uncharacterized non-
phenolic compounds are active in deterring an urchin grazer (Deal et al.
2003
)
Polar systems
Extracts of 20 macroalgae along the Western Antarctic Peninsula deter
sympatric grazers, although responsible compounds are often unidentified
(Amsler et al.
2005
). Phlorotannins are abundant in most of the dominant
brown algae and some deter feeding in sea star, amphipod, and/or fish
grazers (Iken et al.
2007
,
2011
)
Many coralline algae also contain defensive chemicals in addition to calcification.
For example, chemical defenses instead of calcification were the driving mecha-
nism for reduced grazing of urchins, amphipods, and parrot fishes on the tropical
