Biology and Ecology of Opeatogenys gracilis from Western Mediterranean
223
Table 4. Food preferences of Opeatogenys gracilis throughout the year. Percentage of number (N%) and percentage of occurrence (F%) are reported for each food item
Spring
Summer
Autumn
Wroter
N%
F%
N%
Acarina
0.38
10
0.00
Amphipoda
0.96
20
2.67
Copepoda Colonoida
0.00
0
0.67
Chironornidae
0.38
10
0.00
Cumacea
0.38
10
0.67
Copepoda Harpacticoida
95.79
100
77.33
Isopoda
0.19
5
0.00
Ostracoda
0.19
5
0.00
Polychaeta
0.38
15
0.67
Tariaidacea
1.34
25
18.00
d.m. a
0.00
5
0.00
• (a.m.. digested material)
Stomach Content Analysis
The simple index values for each food item are
reported in Table 4. In the Figure the relative
importance index values are shown. Prey richness was highest in spring where 9 prey taxa
were identified and declined to 3 taxa in winter
(Table 4). Copepoda Harpacticoida represent the
preferential and most important food item
throughout the year (F%= 100%; IRI% ranges
from 53% to 97%). Tanaidacea are also important components of the diet in summer and
autumn (F%=80%. 95%; IRI% = 28.27% and
34.33%). Polychaeta worms, Cumacea and
Amphipoda were a lesser component of the diet.
Figure. Index of relative
importance (IRI%) of the
main food items
100
40
Spring
F%
N%
F%
N%
F%
0
0.53
5
0.00
0
10
0.00
0
0.00
a
5
0.00
0
0.00
a
0
4.28
55
2.44
25
5
5.88
35
0.00
0
100
64.44
100
95.12
100
0
0.00
5
0.00
a
0
0.80
15
0.00
0
10
3.48
45
2.44
25
80
20.59
95
0.00
0.00
10
0.00
15
0.00
0.00
Discussion and Conclusions
Biometric and Meristic Characters
When compared with the literature data, a large
number of specimens of Opeatogenys gracilis
were collected from both study sites. The small
sizes of the specimens, benthic habit and the
high habitat complexity of Posidonia oceanica
beds make it difficult to assess the distribution
and abundance of this species along western
Mediterranean coasts. Although O. gracilis is
considered to be an uncommon species (Bini
1968; Tortonese 1975), the fact that such a large
number of individuals was collected leads us to
D
Sumner
Autwm
W inter
223
Table 4. Food preferences of Opeatogenys gracilis throughout the year. Percentage of number (N%) and percentage of occurrence (F%) are reported for each food item
Spring
Summer
Autumn
Wroter
N%
F%
N%
Acarina
0.38
10
0.00
Amphipoda
0.96
20
2.67
Copepoda Colonoida
0.00
0
0.67
Chironornidae
0.38
10
0.00
Cumacea
0.38
10
0.67
Copepoda Harpacticoida
95.79
100
77.33
Isopoda
0.19
5
0.00
Ostracoda
0.19
5
0.00
Polychaeta
0.38
15
0.67
Tariaidacea
1.34
25
18.00
d.m. a
0.00
5
0.00
• (a.m.. digested material)
Stomach Content Analysis
The simple index values for each food item are
reported in Table 4. In the Figure the relative
importance index values are shown. Prey richness was highest in spring where 9 prey taxa
were identified and declined to 3 taxa in winter
(Table 4). Copepoda Harpacticoida represent the
preferential and most important food item
throughout the year (F%= 100%; IRI% ranges
from 53% to 97%). Tanaidacea are also important components of the diet in summer and
autumn (F%=80%. 95%; IRI% = 28.27% and
34.33%). Polychaeta worms, Cumacea and
Amphipoda were a lesser component of the diet.
Figure. Index of relative
importance (IRI%) of the
main food items
100
40
Spring
F%
N%
F%
N%
F%
0
0.53
5
0.00
0
10
0.00
0
0.00
a
5
0.00
0
0.00
a
0
4.28
55
2.44
25
5
5.88
35
0.00
0
100
64.44
100
95.12
100
0
0.00
5
0.00
a
0
0.80
15
0.00
0
10
3.48
45
2.44
25
80
20.59
95
0.00
0.00
10
0.00
15
0.00
0.00
Discussion and Conclusions
Biometric and Meristic Characters
When compared with the literature data, a large
number of specimens of Opeatogenys gracilis
were collected from both study sites. The small
sizes of the specimens, benthic habit and the
high habitat complexity of Posidonia oceanica
beds make it difficult to assess the distribution
and abundance of this species along western
Mediterranean coasts. Although O. gracilis is
considered to be an uncommon species (Bini
1968; Tortonese 1975), the fact that such a large
number of individuals was collected leads us to
D
Sumner
Autwm
W inter