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Sarà et al: Dispersal of fish farm waste 267
(a) –20 0 m sites 500 m sites 1000 m sites (b) –16 0 m sites 500 m sites 1000 m sites
500 m sites 1000 m sites
–21 –17 C < M; M > CO; C < M; M > CO; C > M; M < CO;
–18 EI > ALL EI > ALL EI > ALL
–22 –19
δ 13C, ‰ δ 13C, ‰ –20
–23 –21
–22
–24 –23
–25 –24
–25
–26 –26
(c) 7 0 m sites (d) 6 0 m sites 500 m sites 1000 m sites
6 5 C = M; M > CO; C < M; M > CO; C < M; M = CO;
5 EI > C
4 EI > CO EI > C-CO
3
2δ 15N, ‰ δ 15N, ‰ 4
1
3
2
1
0 0
C M CO EI -- C M CO EI -- C M CO EI --
C M CO EI -- C M CO EI -- C M CO EI --
Location
Location
Fig. 5. Mean (± SE) isotopic values of carbon (δ13C) and nitrogen (δ15N) for distance categories and locations. (a) POM δ13C;
(b) SOM δ13C; (c) POM δ15N; (d) SOM δ15N. Comparisons using Student-Newman-Keuls tests reported inside SOM graphs. C =
Gulf of Castellammare; M = Menfi Bay; CO = Capo d’Orlando; EI = Egadi Islands (control)
after referred to as SOM A) represented 3 sites, which Bray-Curtis similarity70
could be categorized as pristine sites in the cage areas: 75
CAST HYDRO 1 (500 m), CAST HYDRO 1 (1000 m), 0m80
and MEN HYDRO 2 (0 m). The third group included 500 m85
the impacted locations (hereafter referred as SOM B), 1000 m90
which were further grouped into 2 subgroups: a low H2 (500 m)95
impact subgroup represented by MEN HYDRO 2 H3 (500 m)100
(500 m), MEN HYDRO 2 (1000 m) and CORL HYDRO H2 (1000 m)
3 (0 m); and a high impact subgroup that included H3 (0 m)
CAST HYDRO 1 (0 m), MEN HYDRO 2 (500 m), and H1 (0 m)
CORL HYDRO 3 (1000 m). The highest level of aver- H3 (1000 m)
age dissimilarity was recorded in the pair-wise com- H2 (0 m)
parison of CTRL sites with SOM B sites; SOM A exhib- H1 (500 m)
ited an intermediate level of Bray-Curtis dissimilarity H1 (1000 m)
(Fig. 7). In all comparisons, the sources contributing
most to dissimilarities were SM and PEL (Fig. 7). CTRL (EI) POM A POM B
DISCUSSION Avg. dissim.: 29.7 Avg. dissim.: 16.8
Our study highlighted that the effect of waste from PEL (32.2), PHY (28.1) PHY (39.6), PEL (26.7)
fish farms on the area surrounding fish cages was a EJE (22), TER (17.6) EJE (18.8), TER (14.8)
Avg. dissim.: 47.7
PHY (34.2), PEL (30), EJE (21), TER (14.8)
Fig. 6. Cluster analysis of POM mixing model percent data
(Bray-Curtis similarity index). Average dissimilarity (Avg. dis-
sim., %) between groups, and results of SIMPER procedure
for contribution of each POM source (TER, PEL, EJE, PHY; cut
off: 100%), also reported. EI: Egadi Islands (control). For
acronyms, see Figs. 2 & 3
