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704 BIOLOGICAL CONSERVATION 141 (2008) 699–709

Fig. 3 – Fish species response to protection, measured as the natural log ratio of density between reserves and fished areas, in
relation to the enforcement level. Bars indicate 95% confidence intervals. Black circles: significant ratios; grey circles: non-
significant ratios. See Section 2 for details on the analysis.

providing suggestive evidence of the role that enforcement In addition, we demonstrated the importance of taking into
exerts in enhancing average fish biomass values relative to lo- account the enforcement at the reserves studied when proce-
cal conditions that may change from place to place. dures are used to summarize or generalize the effectiveness
of multiple reserves (e.g. in meta-analysis studies and
As a general rule, finally, the density of Diplodus fish was reviews).
above the threshold ($12 individuals per 125 mÀ2) required
to control sea urchin populations only at the reserves where Many target fish species clearly responded to protection in
enforcement is high. The threshold was not achieved when well-enforced marine reserves, similar to what has been ob-
all reserves were considered (Fig. 6). Looking at each reserve, served in other Mediterranean reserves (e.g. Harmelin et al.,
the density of Diplodus fish was above the threshold at all 1995; Garc`ıa-Charton et al., 2004; Claudet et al., 2006; Guidetti
three well-enforced reserves (i.e. Miramare, Torre Guaceto and Sala, 2007). However, in the present study the response of
and Portofino) and at Tavolara. The maximum value was ob- fish was to some extent variable among reserves, which could
served at Torre Guaceto and the minimum at Ustica. also be attributed to their different reserve age (Gerber et al.,
2002; Dufour et al., 2007; Guidetti and Sala, 2007).
4. Discussion
Protection effects were evident for large predators like the
This study evaluated the consequences of different levels of dusky grouper E. marginatus, a species that is included in the
enforcement on the ecological effectiveness of 15 Italian mar- IUCN red list as endangered and at risk of dramatic reduction
ine reserves on fish, in terms of direct effects on target fish (see http://www.iucnredlist.org). Fish predators of sea urchins
and their potential of indirectly influencing entire rocky reef also clearly responded to protection. The critical threshold of
communities (Guidetti and Sala, 2007 and references therein). $12 adult individuals per 125 mÀ2 (Guidetti and Sala, 2007)
was exceeded only at the three well-enforced reserves (Mira-