Climate Change and the European Water Dimension - Agri ...

eastern and western side of the North Atlantic indicate that the response of the
biosphere to climate change may exhibit complex behaviour. This kind of response is
mediated through complex regional interactions with existing hydro-climatic channels
such as the NAO. Indeed, the inverse response of ecosystems to climatic features on
the two sides of the North Atlantic Ocean is consistent with the spatially
heterogeneous nature of the climatic manifestations induced by this dominant mode
of atmospheric variability (Dickson et al. 1996; Drinkwater 1996).
These large-scale biogeographical changes have deeply impacted the diversity of
calanoid copepods in the North Sea (Beaugrand 2003; 2004). Calanoid copepod
diversity has increased in that region due to an increase in warm-water species
(Figure IV.C.11). These modifications seem to be a response of pelagic ecosystems
to an augmentation in sea surface temperature positively correlated to Northern
Hemisphere Temperature anomalies and may have a strong impact for the
functioning of the ecosystems, biogeochemical cycles and exploited resources
(Figure IV.C.12). Using a plankton index indicator of the quality and quantity of prey
available for larval cod survival in the North Sea, Beaugrand et al. (2003) showed
that long-term changes in the index paralleled changes in cod recruitment at age 1
and therefore larval cod survival (Figure IV.C.12). The index revealed a clear
distinction between the periods 1963-1983 and both the periods 1984-1999 and
1958-1962 (Figure IV.C.12). The period 1963-1983 (‘Gadoid Outburst’, Cushing
1984) was characterized by high abundance of prey for larval cod (positive
anomalies in the biomass of calanoid copepods, in the abundance of C.
finmarchicus, euphausiids and Pseudocalanus spp.) and a high mean size of
calanoid copepods. Larval cod survival decreased from the mid-1980s, coincident
with unfavourable changes in the plankton ecosystem, compared to the earlier period
1963-1983. The change in the quality and quantity of plankton prey was related
negatively to fluctuations in sea surface temperature. Increasing sea temperature
may have had a double negative impact on larval cod survival in the North Sea.
Figure IV.C.12. The regime shift in the
North Sea. Long-term changes in fish
abundance in relation to year-to-year
changes in calanoid copepod
composition and hydrometeorological
forcing. a. Long-term
changes in gadoid recruitment
(especially cod). b. Long-term changes in
calanoid copepod species composition
(in red: warm-water copepod calanoid
species; in blue: cold-water calanoid
copepod species). c. Changes in
hydrological variables (sea surface
temperature). d. Changes in large-scale
hydro-climatic forcing (Northern
Hemisphere Temperature anomalies).
From Beaugrand (2004).
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