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

In the last decade, a general model has been proposed considering pristine coastal
lagoons as dominated by extensive meadows of seagrass species, which are
assumed to take advantages of nutrient supply from sediment (de Wit et al., 2001;
Schramm and Nienhuis, 1996, Castel et al., 1996, Hemminga, 1998). These
communities are naturally productive and, to a certain extent, resistant and resilient.
However, an increasing nutrient input is thought to favour in a first phase
phytoplankton and epiphytic microalgae, and later floating ephemeral macroalgae. In
the later stages of this succession, when internal equilibria undergo a short circuit,
the imbalance of phosphorus to nitrogen ratio can favour cyanobacteria and/or
picoplankton species. Macroalgal blooms have been recognised as one of the most
catastrophic symptoms of community degeneration (Morand and Briand, 1996,
Valiela et al., 1997, Flindt et al., 1999). These changes have been particularly
severe in the Mediterranean coastal lagoons with summer events of anoxia and
dystrophy (Sfriso et al., 1992, Chapelle et al., 2001, Viaroli et al., 2001,), see Figures
IV.D.4-5. More recently, harmful algal blooms (HABs) and bacterial contamination
have become a growing concern not only for aquaculture and tourism exploitation but
also for the natural planktonic communities (e.g. change in the trophic relations,
nutrient uptake).
Figure IV.D.4: Thau lagoon during a dystrophic episode (malaïgue). In August 1997,
nearly one third of the annual oyster annual production was lost.
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