342
S. Schiaparelli et al.
(VP: Peres and Picard 1964) (Carpine 1970;
Picard 1972; Chardyet al. 1973).
Differently, significant variations were
observed taking into account the contribution of
the different phyla to total biomass (Fig. 3): in
particular polychaetes showed a marked
decrease in biomass values, dropping from 2.1 to
0.1 gWW/m2.
Moreover, taking into account the species
composition of the whole two data sets, large
variations may be stressed. A total of 156 species
was found on the whole, only 25 of which were
others
molluscs 6%
echinodenns
49%
polychaetes
32%
recorded both in 1981 and 1996 cruises. These
species showed quite different dominance values, as evidenced by the Cabioch index (Fig. 4).
In Table 2a,b the characterising species of
the two data sets are reported with their numerical dominance values in respect of the whole
community and of the phylum, to which they
belong.
Trophic structure stressed an increase of carnivorous and scavenging species in 1996
(grouped together in Fig. 5) at despite of typical
deposit-feeding species.
others
3%
polychaetes
2%
echinodenns
70%
Fig.3. Percent dominance of different taxa to total biomass in 1981 (left> and 1996 (right)
60
50
rJ) 40
.~
(,)
Q)
c.
rJ) 30
- 0
... Q)
.D 20
E
:::J
t:
10
0
Fig. 4. Frequency distribution of Cabioch index