Environmental Engineering Reference
In-Depth Information
natural migration of organisms due to climatic variations is becoming
superimposed by anthropogenic vectors, facilitating a much faster and
wider distribution into new habitats (Diederich et al. 2005).
Biological invasions can have many ecological impacts, including the
modifi cation of benthic communities and displacement of native species, and
for this reason are considered to be one of the major causes of biodiversity
loss (Soulé 1991). Some invasions may affect the overall functioning of
an ecosystem in terms of material fl ow between trophic groups, primary
production, the relative extent of organic material decomposition, and
extent of benthic-pelagic coupling (Occhipinti-Ambrogi 2007). The decline
in existing populations of native species can sometimes be overlooked
because of taxonomic mistakes or lack of available information on species
richness, diversity and composition (Geller 1999).
The past few decades have witnessed an accelerated rate of
establishment of introduced species in coastal waters (Ruiz et al
.
2000).
The enhanced global transport of species together with increasing coastal
ocean temperatures could provide a fuller explanation for these increasing
rates of invasion by nonindigenous species (Stachowicz et al
.
2002). Mass
mortalities in benthic organisms as a result of anomalous temperature stress
(Cerrano et al
.
2000, Pérez et al
.
2000, Garrabou et al
.
2001) open up niches
for new colonizers (Occhipinti-Ambrogi 2007). The competition for open
space on the substrate is heavily infl uenced by the timing of recruitment,
which in turn is highly dependent on temperature; changing seasonal
patterns of temperature may therefore favor the settlement of invasive
species at a particular time of the year and have long-lasting consequences
in preventing the recruitment of native species (Occhipinti-Ambrogi
2007). Increasing coastal ocean temperatures may therefore accelerate the
homogenization of global biota by favoring the growth and recruitment and
hence dominance of non-native species over native species (Stachowicz et
al
.
2002, Ricciardi 2006).
Sharp differences have been found over the past 12 years in the response
of native and introduced ascidians (sea squirts) to interannual variations
in temperature in the eastern Long Island Sound (North America). Total
annual recruitment of introduced ascidian, the solitary
Ascidiella aspersa
and
the colonial
Botrylloides violaceous
and
Diplosoma listerianum,
was positively
correlated with the mean winter water temperature (Fig. 2; slope=0.280,
R
2
=0.02, R
2
=0.46) and a strong negative correlation was found between the
timing of the initiation of recruitment and winter water temperatures. The
magnitude of native ascidian recruitment on the other hand, was negatively
correlated with mean winter temperature (more recruitment in colder
years) (Fig. 2; slope=0.151, R
2
=0.08, R
2
=0.30) and its timing was unaffected
(Stachowicz et al
.
2002), suggesting that invaders arrived earlier in the
season in years with warmer winters. Ocean warming therefore facilitates
