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350 ind.m-3 H'(loge) 4.00
300 3.50
250 3.00
2.50
200
2.00
150
1.50
100 1.00
50 0.50
ind. m-3
H'
0 0.00
1 2 3 4 5 6 7 8 9 10 11 12
Sampling stations
Fig. 3 - Horizontal trends of copepod diversity (Hƍ) and abundances (ind m-3) integrated on
the water column.
4.3. Vertical distribution
Abundances decreased with increasing depth with a maximum in surface layers
(mean abundance 138.57 ind m-3) and a minimum at 200-300 m (mean abundance 9.19
ind m-3; Fig. 4). An abrupt abundance decline from 98.86 to 48.76 ind m-3, occurred
between 80-60 and 100-150 m layers. The vertical pattern of Shannon-Weaver index
showed two peaks: the former (3.19) in the 40-60 m layer and the latter (2.98) at 150-
200 m depth (Fig. 3). The minimum (2.42) was observed in the 0-20 m layer. It was
possible to distinguish a surface (0-30 m) from a subsurface (30-80 m) assemblage; the
former was characterized by the strong dominance of C. furcatus, O. atlantica, A.
negligens and T. stylifera that accounted on average for more than 57.6 % of copepod
population both in inshore and in offshore stations; in the latter, the contribution of
Ctenocalanus vanus, Centropages typicus, Nannocalanus minor, L. flavicornis, C.
arcuicornis and C. jobei was more important (45.8 %). Corycaeus furcifer, Lucicutia
flavicornis were dominant on the epipelagic copepod assemblage constituting about 30
% of the whole population in the 80-200 m layer. With the previous two species,
Haloptilus longicornis and Pleuromamma abdominalis were the typical assemblage of
mesopelagic depths.
DISCUSSION
The copepod assemblages in the Egadi Islands is high diversified as observed in
adiacent regions such as the Tyrrhenian Sea (Scotto di Carlo et al., 1984) and the Sicily
Channel (Siokou-Frangou et al., 1997). This is probably due to their geographical
position at the entrance of Sicily Channel and the exchanges of water masses between
eastern and western basins. With respect to Sicily Channel, in this area Acartiidae was
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