Chemical Ecology of Seaweeds - Seaweed Biology - page 175

of this in the context of the biofilm environments they settle within in nature is
unknown (Amsler 2008b ). Interestingly, although Ulva spores given the choice
between alternating hydrophobic and hydrophilic surfaces settle preferentially on
the hydrophobic patches (Callow et al. 2000 ), when presented with a hydrophobicity
gradient they settle more in hydrophilic regions (Chaudhury et al. 2006 ). In the brown
alga Hincksia irregularis , surface hydrophobicity interacts with light and light
gradients (Greer and Amsler 2002 , 2004 ) and with potential antifouling compounds
(Greer et al. 2003 ) to influence spore settlement patterns.
Some brown algal spores respond to inorganic nutrients in their swimming and
settlement behaviors. Spores from several species of kelps (Order Laminariales)
demonstrate chemotactic swimming responses toward or away from nutrients
(Amsler and Neushul 1989 ; Fukuhara et al. 2002 ). Spores themselves probably
have no need for inorganic nutrients, but the filamentous gametophyte stage into
which they germinate after settlement certainly does. Because these gametophytes
are microscopic and confined to the biofilm environment the spore settles in, the
nutrient microenvironment in which they settle likely has a profound influence on
the ultimate growth and reproduction of the gametophyte. Macrocystis pyrifera
spores are attracted to ammonia concentrations which stimulate gametophytic
growth but not to high concentrations which inhibit it (Amsler and Neushul
1989 ). The spores are also attracted to low concentrations of iron which stimulate
gametophytic reproduction, but not to higher, inhibitory concentrations (Amsler
and Neushul 1989 ). Independent of chemical gradients, and apparently via a
somewhat different sensory mechanism, kelp spores also settle more rapidly in
the presence of nutrients which are necessary for gametophytic growth and repro-
duction (Amsler and Neushul 1990 ).
9.3 Chemical Defense
9.3.1 Defenses Against Predation
Seaweed chemical defenses against herbivores have received the bulk of attention
in seaweed chemical ecology. They have been the subject in whole or large part of
numerous recent reviews appearing in journals (e.g., Pohnert 2004 ; Amsler and
Fairhead 2006 ; Ianora et al. 2006 ; Amsler et al. 2009b ; Paul et al. 2011 ) and in six
chapters of a recent topic (Amsler 2008a ). They are also discussed in Chap. 8 by
Iken, particularly with respect to their population or community level importance.
This section focuses on selected sets of studies which illustrate defenses from a
more mechanistic perspective.
Seaweeds utilize a variety of chemical compounds for defense (Maschek and
Baker 2008 ) and these may be spread throughout the alga or be localized to
particular parts of the thallus (Jormalainen and Honkanen 2008 ). Chemical
defenses can be produced constitutively, only when a seaweed is attacked by a