13 France - The Mediterranean Lagoons
M.-L. DE CASABlANCA
13.1 Introduction
The Mediterranean lagoons can be characterized by their salinity regimes, which are determined by the balance between freshwater input by
land run-off, or rainfall, mainly from November to May, and seawater
input between the periods of rainfall, particularly from May to November.
Evaporation in the summer accentuates these variations and may even
isolate the lagoon from the sea. The extremes vary from year to year,
therefore pluriannual variation data give a better insight into the characteristics of a lagoon (Fig. 13.1).
The range of salinity variations is usually wider in the shallow, littoral
lagoons that are more influenced by fresh water input, compared to the
deep marine-type lagoons of tectonic origin. The average salinity determines the type of plant communities, whereas the species diversity is
inversely proportional to the amplitude of the salinity variations (De
Casabianca-Chassany et al. 1973).
Usually the lagoons with pronounced salinity variations are more eutrophicated, compared to those with a balanced salinity regime. There
may be two major reasons for this. First of all, a highly physico-chemically variable environment is usually characterized by population fluctuations. This also means production of plant material, accumulation and
breakdown of organic matter together with regeneration of nutrients,
which favour the development of macrophytic algae in shallow, littoral
lagoons. The second reason is the additional supply of nutrients and
other materials with the fresh water input.
It is therefore possible to define different degrees of "natural eutrophication" for each type of lagoon, depending on the extent to which it is
Station Mediterraneenne de l'Environment Littoral, Universite Montpellier II, 1, Quai de
la Daurade, 34200 Sete, France
Ecological Studies, Vol. 123
Schramm/Nienhuis (eds) Marine Benthic Vegetation
© Springer-Verlag Berlin Heidelberg 1996
M.-L. DE CASABlANCA
13.1 Introduction
The Mediterranean lagoons can be characterized by their salinity regimes, which are determined by the balance between freshwater input by
land run-off, or rainfall, mainly from November to May, and seawater
input between the periods of rainfall, particularly from May to November.
Evaporation in the summer accentuates these variations and may even
isolate the lagoon from the sea. The extremes vary from year to year,
therefore pluriannual variation data give a better insight into the characteristics of a lagoon (Fig. 13.1).
The range of salinity variations is usually wider in the shallow, littoral
lagoons that are more influenced by fresh water input, compared to the
deep marine-type lagoons of tectonic origin. The average salinity determines the type of plant communities, whereas the species diversity is
inversely proportional to the amplitude of the salinity variations (De
Casabianca-Chassany et al. 1973).
Usually the lagoons with pronounced salinity variations are more eutrophicated, compared to those with a balanced salinity regime. There
may be two major reasons for this. First of all, a highly physico-chemically variable environment is usually characterized by population fluctuations. This also means production of plant material, accumulation and
breakdown of organic matter together with regeneration of nutrients,
which favour the development of macrophytic algae in shallow, littoral
lagoons. The second reason is the additional supply of nutrients and
other materials with the fresh water input.
It is therefore possible to define different degrees of "natural eutrophication" for each type of lagoon, depending on the extent to which it is
Station Mediterraneenne de l'Environment Littoral, Universite Montpellier II, 1, Quai de
la Daurade, 34200 Sete, France
Ecological Studies, Vol. 123
Schramm/Nienhuis (eds) Marine Benthic Vegetation
© Springer-Verlag Berlin Heidelberg 1996