Biology Reference
In-Depth Information
that inhibit bacterial biofouling (Nylund et al.
2008
). The green alga
Ulva reticulata
appears to release a water soluble antifouling defense. Water collected from the
vicinity of the seaweeds in nature inhibits attachment of larvae of fouling bryozoans
and hydroids (Harder et al.
2004
). Some, but not all, of this could be the result of
compounds actually produced by a bacterial species colonizing the surface of the
algae (Harder et al.
2004
).
9.3.4 Allelopathy
Allelopathy (chemical defense against competitors) is relatively widely studied in
freshwater systems including in macrophytic algae, vascular plants, and phyto-
plankton (Gross
2003
; see also Chap.
11
by Potin). In marine systems there have
been studies showing allelopathic effects of water-soluble compounds from
seaweeds on the growth of phytoplankton in laboratory conditions, but the signifi-
cance of such interactions in natural populations is unclear. On the other hand,
seaweeds often compete with other sessile, macroscopic organisms for space (see
Chap.
7
by Edwards and Connell) and the advantages of being able to inhibit the
growth of such competitors are obvious. There have been at least two studies of such
interactions under ecologically relevant conditions. The red alga
Plocamium
hamatum
causes tissue necrosis in soft corals upon physical contact due to allelo-
pathic effects of the monoterpene chloromertensene (de Nys et al.
1991
). In a study
of the effects of contact by multiple seaweed species on two species of hard corals,
Rasher and Hay (
2010
) reported that in nearly half the interactions, seaweeds caused
bleaching (loss of symbiotic microalgae) of the corals. This was due to the physio-
logical stress imposed on the microalgal symbionts (measured as photosynthetic
efficiency). In nearly every interaction where the intact seaweed caused this effect,
so did lipophilic chemical extracts of the seaweed (Rasher and Hay
2010
).
9.4 Outlook
If this chapter were about the chemical ecology of terrestrial organisms rather than
of seaweeds, the relative lengths of the above sections would be vastly different.
Terrestrial chemical ecology is currently dominated by studies of sensory chemical
ecology, including intentional or unintentional communication among or between
prey species, their predators, and their predators' predators. Such studies are in their
infancy in seaweed chemical ecology and represent important areas for future
studies. Likewise, we are just starting to learn about seaweed defenses against
pathogens and biofoulers in ecologically relevant contexts. Doing the necessary
experiments in an ecologically relevant manner is difficult, but many more such
studies are needed to advance the field. Important work is ongoing in all areas
