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270 F. Espinosa et al.

TABLE 3 PERMANOVA analysis of the effect of substrate and protection on the size (measured on the longitudinal axis) structure of P.
ferruginea populations. The matrix used was the same as for the MDS analysis (Fig. 3).

Source Df SS MS Pseudo-F P
Substrate 1 421.56 421.56 0.36 0.786
Protection 1 3,516.30 3,516.30 2.96 0.042
Substrate×protection 1 29.90 29.90 0.03 0.994
Residual 17 20,164 1,186.10
Total 20 24,111

FIG. 3 MDS ordination of populations
(only those with .10 individuals) of
P. ferruginea based on the number of
individuals per size class. Groups of
samples determined by the SIMPROF test
are enclosed by ellipses. Populations
include six from this study (Table 2) and
15 from published data (Table 4).
Designation as unprotected (circles) or
protected (triangles) indicates the
likelihood or not, respectively, of
exploitation, based on accessibility. ANP,
artificial substrate, non-protected; AP,
artificial substrate, protected; NNP,
natural substrate, non-protected; NP,
natural substrate, protected. Arrows
indicate artificial substrates.

threatened status of the species (Paracuellos et al., 2003; there has also been a noticeable decline on these islands,
Bazairi et al., 2004; Guerra-García et al., 2004; Espinosa, with a large decrease in mean density at several sites from
−1
2006; Cristo & Caronni, 2008; Espinosa et al., 2009a,b, and 1985 to 2009: 0.933 to 0.02 m at Tizzano (Laborel-Deguen
references therein), mainly a result of human pressure, these & Laborel, 1990; present study) and 2.334 to 0.13 m −1 at
studies were at a local or regional scale. The information Gáleria (Laborel-Deguen & Laborel, 1991b; present study;
summarized here demonstrates that the range of this Fig. 4). Exploitation in Corsica during summer has been
threatened mollusc has contracted severely and that the reported by Laborel-Deguen & Laborel (1990, 1991b).
remaining populations are scarce and generally sparse. In Tunisia P. ferruginea is restricted to the north-
The species has not been reported from the Italian eastern shores, as also reported by Tlig-Zouari et al. (2010).
mainland since the 1980s, when it was recorded in low num- The largest and most structured population (i.e. presence
bers at a few locations in Tuscany (Curini-Galletti, 1979; of different size classes) is on the Zembra archipelago,
Terreni, 1981; Biagi & Poli, 1986) and one location in Liguria although Tlig-Zouari et al. (2010) reported lower densities
(Porcheddu & Milella, 1991). However, we did not find the at Zembra than at Cap Bon. However, on Zembra they
species at any of these locations. The situation on the Italian surveyed at a location with the lowest densities, which is
islands of Egadi, Sicily and Pantelleria is also critical. probably not representative of the archipelago. The species
Giaccone & Sortino (1974) reported P. ferruginea on the shows great variability in recruitment (Guallart et al., 2006;
Egadi islands with a relative abundance of II, within a range Rivera-Ingraham, 2010) and the high densities found at
from I (rare) to V (abundant), but it is now extremely scarce, some sites at Cap Bon by Tlig-Zouari et al. (2010) could be a
having also declined in density. Giaccone et al. (1973) result of good recruitment from the Zembra population
reported the species in a general phytobenthos study at during 2006.
Pantelleria but we detected only one small specimen there, Many authors have demonstrated the influence of
despite the focus on this species. There are some specimens exploitation on the mean size and presence of large repro-
from Palermo, Sicily, in Locard’s 1892 collection at the ductive individual molluscs (Keough et al., 1993; Branch &
Muséum national d’Histoire naturelle, Paris, but the species Odendaal, 2003). Patella ferruginea is used as food and
no longer occurs on the island. fishing bait and as a collector’s item (Laborel-Deguen &
The Corsican and Sardinian populations were greater in Laborel, 1991a, b; Templado & Moreno, 1997; Ramos, 1998),
density than those on the Egadi islands and Pantelleria but the latter confirmed by our observations of shells being sold

© 2013 Fauna & Flora International, Oryx, 48(2), 266–275

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