Biology Reference
In-Depth Information
Macroalgae represent approximately 20% of the world's marine introduced
species. High-profile seaweed taxa such as
Caulerpa taxifolia
(Vahl) C. Agardh,
Codium fragile
(Suringar) Hariot ssp.
tomentosoides
(Van Goor) Silva,
Sargassum
muticum
(Yendo) Fenshold, and
Undaria pinnatifida
(Harvey) Suringar have led to
well-documented economic and ecological consequences in their introduction
range (Schaffelke et al.
2006
; Schaffelke and Hewitt
2007
; Williams and Smith
2007
). Following establishment, these species are able to directly affect the habitat
profile by monopolizing space and acting as ecosystem engineers and can signifi-
cantly modify the composition of local communities by altering competitive
interactions and trophic networks (Wallentinus and Nyberg
2007
).
Terms such as “pest” or “invasive” are often used to describe introduced taxa.
A “pest” has been defined as an introduced species with a documented negative
economic effect (Williamson and Fitter
1996
), while an “invasive species” spreads
rapidly from its point of introduction and becomes highly abundant (Kolar and
Lodge
2001
). In this topic chapter, we mainly use the term “invasive” because the
economic consequences, and hence the pest status, of an introduced species are
generally not well understood (reviewed in Schaffelke and Hewitt
2007
).
Global climate change plays a pivotal role in the perpetuation and evolution of
organisms and populations, for example, by slowly changing ecological niches and
triggering evolutionary events at the species and population levels (Howden et al.
2003
; Mainka and Howard
2010
). However, it is difficult to predict how climate
change will influence species introductions in the near future (Occhipinti-Ambrogi
2007
). For instance, changes in environmental conditions may turn a species into
an invasive species in its introduced or even in its native range by revealing certain
biological traits of that species that were previously not expressed and confer inva-
siveness (Mueller and Hellmann
2008
;Willisetal.
2010
). Conversely, environmental
changes may decrease the suitability of the ecosystem for newly established or even
well-adapted invasive marine species (Mainka and Howard
2010
). Although popula-
tion growth and dispersal potential can be modeled, it is nearly impossible to predict
whether a newly introduced species will become invasive, or where and when.
12.2 Biological Traits of Invasive Seaweeds
Seaweeds are good candidates for becoming invasive given their potential to
survive long-range relocations via maritime transport (Flagella et al.
2007
;upto
intercontinental scales; see also Chap.
17
by Rothh
ausler et al.) and because many
species have a set of biological traits that make them highly competitive. Functional
traits that are recognized to facilitate successful invasions include:
€
1. High growth rates and in some cases large individual sizes (most invasive green
and brown macroalgae are larger than their native counterparts)
2. Vegetative propagation (e.g., red and green invasive macroalgae such as
Kappaphycus
sp.,
Ulva
sp.,
Caulerpa
sp.)
3. Spectacular growth strategies (e.g., invasive species such as
Caulerpa
spp. form
dense covers of siphonous single-cell individuals several meters long and inhabit
