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clear-cut as biofoulers may also have characteristics of pathogens or competi-
tors, and individual defensive metabolites may have multiple defensive roles
(e.g., Schmitt et al. 1995 ).
It would be impossible to comprehensively review seaweed chemical ecology in
a short chapter such as this. Indeed there is a recent topic devoted entirely to algal
chemical ecology (Amsler 2008a ) and it could not be comprehensive with respect to
most subjects. Rather, I have attempted to highlight studies that illustrate the
various aspects of seaweed chemical ecology while providing references to more
detailed reviews.
9.2 Sensory Chemical Ecology
9.2.1 Chemical Communication
Chemical communication is important in sexual reproduction of brown seaweeds.
This has received a great deal of research attention and been the subject of
numerous reviews (e.g., Maier and M
uller 1986 ; Maier 1995 ; Amsler and Iken
2001 ; Pohnert and Boland 2002 ; Amsler and Fairhead 2006 ). Comparatively,
virtually nothing is known about such phenomena in green or red seaweeds
although similar mechanisms are well documented in some freshwater and micro-
scopic green algae (Sekimoto 2005 ; Amsler 2008b ).
Brown seaweeds utilize pheromones released by female gametes both as male
gamete attractants and, in some taxa, for stimulating the release of male gametes.
Although this behavioral attraction was first observed in the 1800s, the specific
pheromones responsible did not begin to be identified until the 1960s (cf. Amsler
and Fairhead 2006 ). The 12 known pheromones from over 60 brown algal species
in 13 orders are all C 8 or C 11 hydrocarbons or epoxides (Maier 1995 ; Pohnert and
Boland 2002 ). These diffuse rapidly away from the female gametes and the range at
which perception by males is possible has been estimated at up to several
millimeters (Maier and M
uller 1986 ).
Gamete attraction in brown algae is probably best understood in Ectocarpus
siliculosus , where a responsible pheromone was first identified (M
uller 1967 ,
1968 ). Upon settlement, female gametes secrete the C 11 pheromones ectocarpene
and pre-ectocarpene (M
uller 1978 ; Pohnert and Boland 2002 ), which cause a
complex response in male gametes that has been described as a chemo-thigmo-
klinokinesis [reviewed by Maier and M
uller ( 1989 )]. Upon
sensing the pheromone, the male gametes remain in contact with a surface (the
“thigmo” component) and slow down. As the pheromone concentration increases,
the gametes make sharp, nearly U-turns more and more frequently (hence a
“chemokinetic” response; cf. Amsler and Iken 2001 ) and thereby are effectively
trapped in the area of the female gamete until they contact it. In contrast, male
gametes of the kelp Laminaria digitata are able to swim directly toward female
uller ( 1986 ) and M
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