Environmental Engineering Reference
In-Depth Information
south, bringing colder conditions to an area formerly unfavorable for
C
.
hyperboreus
(Johns et al. 2001, Richardson 2008).
Large-scale changes in the biogeography of calanoid copepods in
the Northeast Atlantic Ocean and adjacent seas were also attributed to
regional changes in sea surface temperature (Beaugrand et al. 2002).
Strong distributional shifts in all copepod assemblages have occurred
with a northward extension of more than 10° latitude of warm-water
species associated with a decrease in the number of colder-water species
(Beaugrand et al. 2002). The biological associations showed consistent
long-term changes that appear to refl ect a movement of marine ecosystems
towards a warmer dynamical regime (Beaugrand 2005). As an example,
the cool-water assemblage is dominated by
Calanus fi nmarchicus
, a large
calanoid copepod species (Richardson 2008). As water warmed over
recent decades and the assemblage retracted northward, this species has
been replaced by
Calanus helgolandicus
, the dominant species of the warm-
water assemblage (Richardson 2008). Given that larval stages of Atlantic
cod feed on
C. fi nmarchicus,
the replacement of this species could have a
detrimental effect on cod stocks because both copepods are abundant at
different times of the year (Beaugrand et al. 2003). In fact, cod recruitment
decreased from the mid-1980s, coincident with unfavorable change in the
plankton ecosystem. All of these changes in the plankton ecosystem may
be the cause of temporal predator-prey decoupling and hence, reduced cod
recruitment (Beaugrand 2005).
The distribution of two individual copepod species in the Northeast
Atlantic has also been studied in relation to ocean warming (Lindley
and Daykin 2005).
Centropages chierchiae
and
Temora stylifera
both moved
north from the vicinity of the Iberian Peninsula in the 1970s and 1980s to
the English Channel in the 1990s (~ 6° of latitude). Concurrent with the
expansion polewards of warm-water copepods, the Arctic assemblage
has retracted to higher latitudes (Beaugrand et al. 2002). Although these
translocations have been associated with regional warming of up to 1°C,
they may also be partially explained by stronger north-fl owing currents
on the European shelf edge. These shifts in distribution have had dramatic
impacts on the foodweb of the North Sea (Beaugrand et al. 2003).
Biogeographical shifts may have severe consequences for exploited
resources, especially fi sheries. During the last 20 years, there has been
an increasing interest in the scientifi c community in understanding the
relationship between zooplankton and climate change due to the fact that
several marine fi sh and invertebrates feed on zooplankton at some stage
of their life (Drinkwater et al. 2003). If changes continue, it would lead to
important modifi cations in the abundance of fi sh, with a decline or even a
collapse in the stock of species (Beaugrand et al. 2002).
