160
M. Campolmi et al.
occurred exclusively at night (Table 3b). Some
rare hyperbenthic calanoid species were collected: Pseudocyclops spp. and Stepho! spp. The former were not abundant during the day. showing
a clear peak at night. while the latter were collected only at night (Table 3b).
July 1996
The zooplankton community showed fairly large
day-night variations in abundance (110 - 5211
indo m- 3 ) (Fig. 2; Table 4a). There were relatively
low values during the day (average 185 indo m- 3 )
and a sharp peak at night (03:00 h; during low
tide), mainly due to the increase in Acartia copepodids, A. margalefi and harpacticoids (Table
4b). Hydromedusae and nematodes showed significant variations in abundance (P<0.05),
increasing respectively at night and during the
day, while both mysids and decapod larvae
exhibited a clear peak at night (Table 4a).
Eighteen copepod species were identified, six of
which were found only occasionally. Among
these, Ridgewayia marki minorcaensis, a hyperbenthic calanoid. was found only at night. The I.
clavipes adults and copepodids were more abundant at night (P<0.05) (Table 4b), The same trend
was shown by Pseudocyclops species (Table 4b).
October 1996
The diel variation in abundance was lower in
October (139-2531 indo m- 3 ) than in the other
months. However the pattern of a sharp increase
during the dark period (during both low and
high tide) was the same (Fig. 2; Table Sa). Mysids
showed two significant (P<0.05) nightly peaks
(Tab. 5a), Decapod larvae increased slightly at
21:00 h (Table Sa), The structure of the copepod
assemblage was characterised by coastal species,
mainly Acartia copepodids and A. margalefi.
which were significantly (P<0.05) more abundant
from 21:00 to 7:00 h (Table 5b). Harpacticoids
and I. ciavipes followed in rank. order, both showing a significant (P<0.05) increase during the
dark period (Table 5b). Among the hyperbenthic
Thble 3a,b. a May 1996: diel variation of average abundance (ind. m- 3 ) for the main systematics groups. b May 1996: diel variation of average abundance (ind. m- 3 ) for the main copepod species (SD, standard deviation)
Time (h)
13:00
18:00
3:00
8:00
15:00
Average ±SD
Average ±SD
Average
±SD
Average ±SD
Average ±SD
a
Copepoda
1067.29 574.9
806.86 319.6
6368.33
1375.8
1399.58 391.3
3506.30 1359.2
Copepoda nauplia
157.00 133.5
54.79
32.6
145.33
98.4
121.53
57.6
332.28 235.7
Ostracoda
117.95 143.9
21.94
16.4
96.18
161.6
9.60
5.3
846
5.5
Polychaetalarvae
33.98
37.5
8.60
5.3
23.60
22.8
4.80
2.6
0.73
0.6
Mysidacea
0.79
1.0
2.14
3.7
55.70
29.9
0.37
0.4
0.46
0.7
Amphipoda
5.40
3.2
13.36
19.1
20.66
12.9
2.50
2.7
2.76
2.6
Decapoda larvae
3.53
3.3
1.10
0.5
24.35
15.0
8.00
5.4
5.38
1.1
Total abundance
1426.2
783.7
938.3
340.3
6845.8
1509.9
1561.0
391.8
3864.1
1593.2
b
Acartia copepodites 615.49 442.8
301.11 136.7
5009.97
1183.4
1115.40 442.0
3084.50 1238.8
Harpacticoida
353.53 163.4
460.69 429.5
897.01
163.3
234.45
67.8
239.00
45.2
lsias copepodites
58.94
46.3
21.74
10.1
19S.12
106.4
20.75
15.9
86.S0
0.8
Acartia margalefi
14.58
10.1
8.08
8.4
63.80
55.4
10.75
9.1
76.10
75.2
lsias clavi pes
120.96
80.6
Pseudocyclops spp.
2.45
3.3
0.57
0.9
29.30
U.S
0.07
0.1
Pseudocyclops
2.1S
3.8
copepodite.s
Stephos spp.
0.18
0.3
Total abundance
1067.3
574.9
S06.9
319.6
636S.3
1375.S
1399.6
391.3
3506.30 1359.24
M. Campolmi et al.
occurred exclusively at night (Table 3b). Some
rare hyperbenthic calanoid species were collected: Pseudocyclops spp. and Stepho! spp. The former were not abundant during the day. showing
a clear peak at night. while the latter were collected only at night (Table 3b).
July 1996
The zooplankton community showed fairly large
day-night variations in abundance (110 - 5211
indo m- 3 ) (Fig. 2; Table 4a). There were relatively
low values during the day (average 185 indo m- 3 )
and a sharp peak at night (03:00 h; during low
tide), mainly due to the increase in Acartia copepodids, A. margalefi and harpacticoids (Table
4b). Hydromedusae and nematodes showed significant variations in abundance (P<0.05),
increasing respectively at night and during the
day, while both mysids and decapod larvae
exhibited a clear peak at night (Table 4a).
Eighteen copepod species were identified, six of
which were found only occasionally. Among
these, Ridgewayia marki minorcaensis, a hyperbenthic calanoid. was found only at night. The I.
clavipes adults and copepodids were more abundant at night (P<0.05) (Table 4b), The same trend
was shown by Pseudocyclops species (Table 4b).
October 1996
The diel variation in abundance was lower in
October (139-2531 indo m- 3 ) than in the other
months. However the pattern of a sharp increase
during the dark period (during both low and
high tide) was the same (Fig. 2; Table Sa). Mysids
showed two significant (P<0.05) nightly peaks
(Tab. 5a), Decapod larvae increased slightly at
21:00 h (Table Sa), The structure of the copepod
assemblage was characterised by coastal species,
mainly Acartia copepodids and A. margalefi.
which were significantly (P<0.05) more abundant
from 21:00 to 7:00 h (Table 5b). Harpacticoids
and I. ciavipes followed in rank. order, both showing a significant (P<0.05) increase during the
dark period (Table 5b). Among the hyperbenthic
Thble 3a,b. a May 1996: diel variation of average abundance (ind. m- 3 ) for the main systematics groups. b May 1996: diel variation of average abundance (ind. m- 3 ) for the main copepod species (SD, standard deviation)
Time (h)
13:00
18:00
3:00
8:00
15:00
Average ±SD
Average ±SD
Average
±SD
Average ±SD
Average ±SD
a
Copepoda
1067.29 574.9
806.86 319.6
6368.33
1375.8
1399.58 391.3
3506.30 1359.2
Copepoda nauplia
157.00 133.5
54.79
32.6
145.33
98.4
121.53
57.6
332.28 235.7
Ostracoda
117.95 143.9
21.94
16.4
96.18
161.6
9.60
5.3
846
5.5
Polychaetalarvae
33.98
37.5
8.60
5.3
23.60
22.8
4.80
2.6
0.73
0.6
Mysidacea
0.79
1.0
2.14
3.7
55.70
29.9
0.37
0.4
0.46
0.7
Amphipoda
5.40
3.2
13.36
19.1
20.66
12.9
2.50
2.7
2.76
2.6
Decapoda larvae
3.53
3.3
1.10
0.5
24.35
15.0
8.00
5.4
5.38
1.1
Total abundance
1426.2
783.7
938.3
340.3
6845.8
1509.9
1561.0
391.8
3864.1
1593.2
b
Acartia copepodites 615.49 442.8
301.11 136.7
5009.97
1183.4
1115.40 442.0
3084.50 1238.8
Harpacticoida
353.53 163.4
460.69 429.5
897.01
163.3
234.45
67.8
239.00
45.2
lsias copepodites
58.94
46.3
21.74
10.1
19S.12
106.4
20.75
15.9
86.S0
0.8
Acartia margalefi
14.58
10.1
8.08
8.4
63.80
55.4
10.75
9.1
76.10
75.2
lsias clavi pes
120.96
80.6
Pseudocyclops spp.
2.45
3.3
0.57
0.9
29.30
U.S
0.07
0.1
Pseudocyclops
2.1S
3.8
copepodite.s
Stephos spp.
0.18
0.3
Total abundance
1067.3
574.9
S06.9
319.6
636S.3
1375.S
1399.6
391.3
3506.30 1359.24