Evolution of the Biological and Edaphic Features in the Oliveri-Tindari Lagoon
307
In particular, Marinello and Mergolo pools,
which were geo-morphologically stable and well
defmed since ancient times (Abbruzzese and
Arico 1955), in 1978 already showed a pelitic substratum. The mud increase in these basins, which
mainly receive continental inputs, was regular
but low. Different sedimentary evolution
occurred at Verde and Fondo Porto pools, the
more north-westerly ones, where the effect of
sea-storms has produced an important rise of
mud, recorded in the second investigation cycle.
In these pools, during the considered twenty
years, the primary sandy substratum slightly
covered by mud (Verde: 29.60%, Fondo Porto:
0.50%, Crisafi et al. 1981), became a sandy mud,
with a pelitic fraction ranking 76.33% and
66.28%, respectively (Fig. 2). Finally, in Porto
Vecchio and Nuovo pools, which have became
established in the last decades, the substratum is
still heterogranular and badly sorted, also in
relation to the continuous modifications of the
littoral bar separating it from the sea. For this
reason the pelitic fraction content in these pools
is also low in the third investigation cycle
(64.60% and 40.97%), although a progressive
increase has been observed.
It is important to point out that the noted
fluctuations of the sedimentary budget, are linked
to some human interventions executed in this
area over the last thirty years, and have caused
considerable modifications in the littoral dynamics of the system (Amore and Randazzo in press).
The total organic carbon content (TOC) is
generally elevated in all pools (min: 0.99%; max:
3.18%), with remarkable variations during the
100
Mud %
75
50
25
a
A
B
C
D
period considered. In the Verde and Fondo Porto
pools, the organic content greatly increased in
1987, in concomitance with a marked rise of the
pelitic fraction. On the contrary, in the other
pools, the higher TOe values were recorded in
the first investigation cycle (1978), with a more
or less noticeable decrease during the two successive periods. Therefore TOC space-temporal
trend does not show a clear relationship with the
pelitic fraction content, even if some significant
coincidences have been observed. In fact the
Toe content generally decreases from the first
investigation cycle to present day, in opposition
to the pelitic trend, save the case of marked
increase of sedimentary rate (Fig. 2c,d).
As far as the soft bottom mollusc communities are concerned, the data collected describe a
generalized oligotipic situation in all the periods
under investigation. An extreme case is shown by
the Marinello pool, where mono specific communities, observed in 1978, became extinct later on
(Table). Also in the Nuovo pool, after a period of
high oligo specificity (1978-97), the mollusc communities became extinct. The causes which
determined such extinctions are different. In the
Marinello pool this is probably linked to the
marshy vegetation growth (Raimondo and
Rossitto 1978), which has progressively invaded
all the soft bottoms. However in the Nuovo pool
the continuous morphological changing of the
littoral bar, which determined the burying of the
pre-existing communities (Table), now hinders a
new colonization.
Setting aside these two extreme cases, the
highest values of specific richness were recorded
TOC% 3,5
Mud %
\
3
1978
2,5 _
1987
2
~ 1997
1,5
TOC%
•
1978
0 ,5
•
1987
a •
1997
E
F
Fig.2. Mud and total organic carbon (TOe) percentage evolution in the investigated pools
307
In particular, Marinello and Mergolo pools,
which were geo-morphologically stable and well
defmed since ancient times (Abbruzzese and
Arico 1955), in 1978 already showed a pelitic substratum. The mud increase in these basins, which
mainly receive continental inputs, was regular
but low. Different sedimentary evolution
occurred at Verde and Fondo Porto pools, the
more north-westerly ones, where the effect of
sea-storms has produced an important rise of
mud, recorded in the second investigation cycle.
In these pools, during the considered twenty
years, the primary sandy substratum slightly
covered by mud (Verde: 29.60%, Fondo Porto:
0.50%, Crisafi et al. 1981), became a sandy mud,
with a pelitic fraction ranking 76.33% and
66.28%, respectively (Fig. 2). Finally, in Porto
Vecchio and Nuovo pools, which have became
established in the last decades, the substratum is
still heterogranular and badly sorted, also in
relation to the continuous modifications of the
littoral bar separating it from the sea. For this
reason the pelitic fraction content in these pools
is also low in the third investigation cycle
(64.60% and 40.97%), although a progressive
increase has been observed.
It is important to point out that the noted
fluctuations of the sedimentary budget, are linked
to some human interventions executed in this
area over the last thirty years, and have caused
considerable modifications in the littoral dynamics of the system (Amore and Randazzo in press).
The total organic carbon content (TOC) is
generally elevated in all pools (min: 0.99%; max:
3.18%), with remarkable variations during the
100
Mud %
75
50
25
a
A
B
C
D
period considered. In the Verde and Fondo Porto
pools, the organic content greatly increased in
1987, in concomitance with a marked rise of the
pelitic fraction. On the contrary, in the other
pools, the higher TOe values were recorded in
the first investigation cycle (1978), with a more
or less noticeable decrease during the two successive periods. Therefore TOC space-temporal
trend does not show a clear relationship with the
pelitic fraction content, even if some significant
coincidences have been observed. In fact the
Toe content generally decreases from the first
investigation cycle to present day, in opposition
to the pelitic trend, save the case of marked
increase of sedimentary rate (Fig. 2c,d).
As far as the soft bottom mollusc communities are concerned, the data collected describe a
generalized oligotipic situation in all the periods
under investigation. An extreme case is shown by
the Marinello pool, where mono specific communities, observed in 1978, became extinct later on
(Table). Also in the Nuovo pool, after a period of
high oligo specificity (1978-97), the mollusc communities became extinct. The causes which
determined such extinctions are different. In the
Marinello pool this is probably linked to the
marshy vegetation growth (Raimondo and
Rossitto 1978), which has progressively invaded
all the soft bottoms. However in the Nuovo pool
the continuous morphological changing of the
littoral bar, which determined the burying of the
pre-existing communities (Table), now hinders a
new colonization.
Setting aside these two extreme cases, the
highest values of specific richness were recorded
TOC% 3,5
Mud %
\
3
1978
2,5 _
1987
2
~ 1997
1,5
TOC%
•
1978
0 ,5
•
1987
a •
1997
E
F
Fig.2. Mud and total organic carbon (TOe) percentage evolution in the investigated pools