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

available light to the bottom modifying thus the offshore limit of plant growth to
shallower depths. According to Short and Neckels (1999), a scenario of 50cm sea
level rise over the next century would cause a 30-40% reduction in seagrass growth
as result of 50% reduction in light availability. The propagation of marine waters onshore
may compensate that loss and provide new opportunities for the plants to
extend shoreward, assuming that progression is not perturbed by specific
infrastructures. The penetration of light can also be reduced through increasing
turbidity resulting from sediment re-suspension or eutrophication of the water column
above. In the latter process, phytoplankton and epiphytes organisms on seagrass
leaves are acting as strong competitors for the use of macronutrients and inorganic
carbon, reducing by as much their availability to the growth of seagrass plants.
As the light penetrates into the water column, its quality is modified with higher
penetration at lower wavelengths, in the blue and UV part of the spectrum. Accordingly,
seagrass beds are expected to be very sensitive to the highly penetrating UV-B
radiations that are increasing as a result of a reduction in the stratospheric ozone. The
impact of these radiations on the physiology of the plants is similar to those reported for
phytoplankton, i.e. bleaching of the photosynthetic pigments and damaging the cellular
DNA pool (Häder 1997; Helbling et al. 2001). The net effect of UV-B radiations on
seagrass plants remains, however, difficult to assess because of the ability of some
species to produce UV-B blocking compounds (Short and Neckles 1999) and the
protective role of epiphytes organisms on the plant surface to filter UV-B radiations
(Brandt and Koch 2003).
Conclusion
There is no doubt that the concerted scientific efforts conducted over the last decade
through international and European programmes have led to significant progress in
our understanding of the coastal system and ecosystem processes. A signal of
change is reflected in the various components of the system, ranging from its
physical structure, hydrography and water circulation, to the nutrient and carbon
cycle and organisms physiology. Some causes and indirect impacts have been
thoroughly analyzed, owing to joint actions of multidisciplinary teams.
However, the coastal system is complex and operates through multiple and nonlinear
interactions between all its components, as well as each component reacting
and providing feedbacks to external forces. In addition, the reactions of the coastal
biota and elemental cycles on meteorological variations and increasing
anthropogenic pressure encompass a wide variety of spatial and temporal scales.
Under such situation, assessing the effect of climate change, extricating the natural
variability of the system from human-induced changes, still represents a formidable
challenge which remain to be constantly addressed to develop and improve
integrated management tools that would protect as much as possible the coastal
environment and its invaluable resources.
Coastal eutrophication is, for example, a process that has been extensively studied
worldwide. Nevertheless, questions are still open on e.g., the contribution of
groundwater seepages to the coastal inorganic and organic loads; how does the
benthic community interact with the nutrient cycles and changes in elemental
stoichiometry? Although some climate change impacts have been identified on the
several components of the system, further attention needs to be given to response
mechanisms that would allow more confidence in predictive scenario.
Scientific programmes continue to provide data and information for application in
modeling and monitoring. However the complexity of coastal systems requires that
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