312
M.-L. De Casabianca
For a spatial analysis of the shores, a pluri-annual time scale was chosen
because the extremes of the physico-chemical parameters play an important role in determining the nature and composition of the populations.
The populations selected for this study are those with upper salinity
tolerance limits close to seawater salinity (cf. Fig. 13.2). We have analyzed the marine and brackish-water areas of the Corsican lagoons, before and after the agricultural development of the western plain which
was still surrounded by bush land in 1975.
13.2.2 The Shores of Corsican Lagoons (1975-1980)
The Corsican lagoons were studied during 1975-1980. An investigation
of Urbino basin (western shore) followed in 1980-1990 in view of the
developing agricultural exploitation.
Figure 13.3 shows some chemical parameters determined for the four
large lagoons Biguglia, Diana, Urbino, and Palo during the first investigation period from 1975-1980, and for the western Urbino basin from
1980-1990.
The greatest differences were observed at the brackish sites with a
shallow slope (3 -10%) and fluctuations in temperature, salinity as well
as oxygen levels during summer. In addition, for all of the lagoons with
comparable slope, a decrease in the detritic plant material and other
particulate matter was noted from the shoreline towards the seagrass
beds. Particulate organic C and N decreased from 13 to 4 mg dm - 3 and
from 2 to 0.04 mg dm -\ with an increase in the C/N ratio from 6.2 ± 0.6
to 10.3 ± 0.2, respectively.
The various aquatic nearshore communities studied in 1975-1980
have been classified in relation to the different environmental
parameters. Annual salinity variations act on the community structure in
two ways: the average salinity level determines the type of community
(brackish or marine), while the amplitude or extremes of the salinity
variations controls species diversity.
Communities of the marine type correspond to salinities between 26
and 39 PSU (De Casabianca-Chassany 1988). In Corsica this applies
mainly to the shores of the large marine-type lagoons Diana and Urbino,
as well as Stagnolo sud and Balistra. Brackish water communities correspond to much wider salinity variations (1.8 to 39 PSU) than can be
found at the shores of the large brackish lagoons of Biguglia and Palo,
the small lagoons of Stagnolo Nord, Gadugine, Terrenzana, Pinarello and
Arasco, or at the shores of shallow, marine-type lagoons subject to irregular freshwater input or high degree of emersion (Pompugliani
M.-L. De Casabianca
For a spatial analysis of the shores, a pluri-annual time scale was chosen
because the extremes of the physico-chemical parameters play an important role in determining the nature and composition of the populations.
The populations selected for this study are those with upper salinity
tolerance limits close to seawater salinity (cf. Fig. 13.2). We have analyzed the marine and brackish-water areas of the Corsican lagoons, before and after the agricultural development of the western plain which
was still surrounded by bush land in 1975.
13.2.2 The Shores of Corsican Lagoons (1975-1980)
The Corsican lagoons were studied during 1975-1980. An investigation
of Urbino basin (western shore) followed in 1980-1990 in view of the
developing agricultural exploitation.
Figure 13.3 shows some chemical parameters determined for the four
large lagoons Biguglia, Diana, Urbino, and Palo during the first investigation period from 1975-1980, and for the western Urbino basin from
1980-1990.
The greatest differences were observed at the brackish sites with a
shallow slope (3 -10%) and fluctuations in temperature, salinity as well
as oxygen levels during summer. In addition, for all of the lagoons with
comparable slope, a decrease in the detritic plant material and other
particulate matter was noted from the shoreline towards the seagrass
beds. Particulate organic C and N decreased from 13 to 4 mg dm - 3 and
from 2 to 0.04 mg dm -\ with an increase in the C/N ratio from 6.2 ± 0.6
to 10.3 ± 0.2, respectively.
The various aquatic nearshore communities studied in 1975-1980
have been classified in relation to the different environmental
parameters. Annual salinity variations act on the community structure in
two ways: the average salinity level determines the type of community
(brackish or marine), while the amplitude or extremes of the salinity
variations controls species diversity.
Communities of the marine type correspond to salinities between 26
and 39 PSU (De Casabianca-Chassany 1988). In Corsica this applies
mainly to the shores of the large marine-type lagoons Diana and Urbino,
as well as Stagnolo sud and Balistra. Brackish water communities correspond to much wider salinity variations (1.8 to 39 PSU) than can be
found at the shores of the large brackish lagoons of Biguglia and Palo,
the small lagoons of Stagnolo Nord, Gadugine, Terrenzana, Pinarello and
Arasco, or at the shores of shallow, marine-type lagoons subject to irregular freshwater input or high degree of emersion (Pompugliani