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

(1) Are we already observing a response of ecosystems to climate warming?
(2) What could be the consequences for ecosystems, exploited resources and
biogeochemical cycles?
Effects of both global warming and the increase in CO2 concentration on ecosystems
have just started to emerge in the scientific literature and many aspects of this
influence are still poorly understood (Hughes 2000). Such effects may influence
organisms in a direct way by acting on the physiology, e.g. photosynthesis (Keeling
et al. 1996; Myneni et al. 1997) or on the species phenology (e.g. seasonal cycle;
Crick et al. 1997; McCleery and Perrins 1998). It may also influence biological
systems in indirect ways by modifying abiotic factors involved in interspecific
relationships between organisms (Pounds 2001). This, in turn, may affect the spatial
distribution of species and modify the whole community at the ecosystem level.
Long-term datasets are essential to identify relationships between climate
fluctuations and both changes in species abundance and biodiversity and changes in
the structure and functioning of both aquatic and terrestrial ecosystems. These
datasets should also encompass a large range of regions in order to appreciate the
spatial variability in the response of ecosystems to climate change. Such datasets
are unfortunately rare. For the marine pelagic environment, the Continuous Plankton
Recorder (CPR) survey is the only plankton-monitoring programme that allows
examination of the long-term changes of more than 400 plankton species or taxa
over many regions in the North Atlantic Ocean and its adjacent seas. The CPR
programme is operated by a high-speed plankton recorder that is towed (about 20
km h -1 ) behind voluntary merchant ships at a depth of approximately 6-7m (Warner
and Hays 1994; Reid et al. 2003).
Results from the CPR survey have shown that major changes have taken place in
the biodiversity of plankton over the last few decades mainly in the northeastern part
of the North Atlantic Ocean, including the North Sea.
Using species assemblage indicators of calanoid copepods (Beaugrand et al. 2002a;
Beaugrand et al. 2002b) have recently reported substantial changes during the
period 1960-1999 in the spatial distribution of calanoid copepod assemblages at an
ocean basin scale and have provided evidence that this might have been influenced
by the combined effect of the climatic warming of the Northern Hemisphere and the
North Atlantic Oscillation. Maps of the mean number of species present in an area for
all species assemblages (Figure IV.C.11) demonstrate that major biogeographical
shifts for all species assemblages have taken place since the early 1980s to the
southwest of the British Isles and from the mid 1980s in the North Sea.
The mean number of warm-temperate, temperate pseudo-oceanic species increased
by about 10° of latitude. In contrast, the mean number of cold-temperate mixed
water, sub arctic and arctic species have decreased towards the north. All the
biological assemblages show consistent long-term changes, including neritic species
assemblages that seem to have also slightly moved northwards.
These changes have been correlated to the Northern Hemisphere Temperature
(NHT) anomalies and to a lesser extent to the winter NAO index. These
biogeographical modifications paralleled a northward extension of the ranges of
many warm-water fishes in the same region (Quero et al. 1998; Stebbing et al. 2002).
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