Biology Reference
In-Depth Information
The community context where macroalgae are susceptible to multiple natural
enemies, including herbivores and epibionts, and where the susceptibility to one
enemy may depend on the occurrence of others, implies that the patterns of natural
selection for resistance to epibiotism and resistance to herbivory may be correlated.
When enemies tend to coexist on the same hosts, generalized defenses, i.e., traits
that provide resistance to assorted enemies, are expected to evolve (Rausher
1996
).
There are some data supporting such multiple functions of macroalgal secondary
metabolites
:
The diterpene alcohols pachydictyol A and dictyol E from
Dictyota
menstrualis
, which provide resistance to herbivores (reviewed in Hay and Steinberg
1992
), also prevent fouling organisms from colonizing the surface (Schmitt et al.
1995
). Similarly, brown algal phlorotannins have been suggested to have multiple
functions, e.g., to act both against herbivores and epibiota (reviewed in Amsler and
Fairhead
2006
). This is also the case of some oxylipins, which are allelopathic
substances and were also shown to deter herbivores (Hay et al.
1998
).
Epibiosis and grazing are very likely to be intimately interdependent in the
influence of both community dynamics and the evolution of resistance traits.
11.4.2
Implications to Seaweed Mariculture
Epiphytes, endophytes, and parasites are well involved in human affairs, as when
they increase the cost for mariculture of economically important seaweeds
(Friedlander
1992
; see also Chap.
22
by Buchholz et al.). Epiphytism has been
considered one significant problem in seaweed cultivation (Fletcher
1995
; Oliveira
et al.
2000
; Ask and Azanza
2002
;L
uning and Pang
2003
). Massive monocultures
of algae offer ideal conditions for the growth of epiphytes and propagation of
diseases (Wheeler et al.
1981
; Fletcher
1995
;Luning and Pang
2003
). Epiphytes
also produce a series of undesired effects in the production of the host depending on
the extent of the contamination (Fletcher
1995
). Some important problems with
epiphytes have been attributed to (1) competition for nutrients (Buschmann and
G´mez
1993
), (2) shading (Fletcher
1995
), (3) increased weight and drag (Kuschel
and Buschmann
1991
; Buschmann and G´mez
1993
), (4) the possible liberation by
the epiphyte of growth inhibiting compounds that affect the host (Santelices and
Varela
1993
), and (5) a decrease in the reproductive output of the infected host
(D'Antonio
1985
).
Methods for controlling epiphytes have been described and utilized in cultures of
Gracilaria
(cf. Fletcher
1995
). However, many of these methods can only be used
in cultivation tanks and are more difficult to apply to open ocean cultivation.
The concern in seaweed mariculture with epiphytism has led to special attention
being directed to the selection of resistant strains and to knowledge of the strategies
developed by the host to avoid epiphytism (e.g., Santelices and Ugarte
1990
;
Santelices 1992; Fletcher
1995
; Ask and Azanza
2002
). For example, the ability
to produce compounds, which deter the settlement and growth of epiphytic
organisms, has been described in some algae of commercial value (Santelices
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