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zooplankton was performed in aliquots ranging from 1/10 to 1/25 of the original
sample, depending on the sample richness, while the whole samples were observed for
the identification of rare species. Adult copepods were counted and identified at species
level, while copepodids were identify at genus level. Other groups were classified at
higher taxonomic levels. Abundance was expressed as individuals per cubic metre (ind
m-3). Biodiversity were evaluated by using Shannon index (H') (Shannon Weaver,
1963), taking in account only the adult copepods.

4. RESULTS

4.1. Environmental parameters

Vertical distribution of temperature, salinity, dissolved oxygen and fluorescence
showed similar patterns in many of the stations with 80m depth. A clear halocline was,
generally, localized at the 40-80 m layer. Chlorophyll maximum (mean value 0.61±0.30
μg l-1) was observed between 60 and 80 m depths. On average, vertical distribution
patterns of temperature showed higher values (21.07±2.48 °C) on surface (0-40 m
layer). Termocline was found from 40 to 80 m depth. Salinity vertical distribution
showed increasing values from surface (on average, 37.74±0.13 psu at 0-40 m) to
deeper layers (on average, 38.38±0.19 psu at 80-200 m and 38.71±0.05 psu at 200-300
m) reaching the highest value (S>38.70 psu) at 200-300 m, in the stations 10, 11 and 12.
In figure 2, vertical profiles of physical and chemical parameters of one station on each
transect are reported.

4.2. Horizontal distribution

Copepods were the dominant group ranging from 295,14 to 22,09 ind m-3 and
represented on average 75 % of all zooplankton. A total of 110 species were identified
in the investigated area. The highest number of species (72) was found at st. 7. The
stations between the islands of Marettimo, Levanzo and Favignana showed higher
diversity levels (Hƍ Uanging from 2.79 to 3.18) and lower abundances than typical
coastal stations (2 and 3) (H’= 2.30, 2.57; 295.14; 244.88 ind m-3) (Fig. 3).
Clausocalanus furcatus, Oithona atlantica, Temora stylifera, Centropages typicus and
Acartia negligens were the most representative species at coastal station accounted for
68.75 % of total copepod community. Acartia adriatica occurred with slightly lower
abundances than Acartia clausi. Occurrence of Acartia danae was observed at st. 4, 5,
6, 7, 8 and 9 stations and in most of them substituted the congener species A. clausi.
Nannocalanus minor (7.57%), Clausocalanus arcuicornis (4.72 %) Clausocalanus jobei
(4.00 %) and Ctenocalanus vanus (3.77 %) contributed more in the area between the
islands together with typical neritic species. In the pelagic area, Corycaeus furcifer,
Lucicutia flavicornis, Pleuromamma gracilis and Corycaeus typicus, with the above
species accounted for 69.5 % of copepod population. Shannon index showed the
maximum (3.38) at st. 7. The lowest abundances (22.08 ind m-3) were observed at st.10.

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