Background

Only in the last decade has there been recognition that marine ecosystems worldwide are suffering massive and acute declines in biodiversity and irreparable alterations to ecosystem functioning (Boersma and Parrish, 1999; Millennium Ecosystem Assessment, 2005). Marine protected areas (MPAs) and other forms of marine spatial closures are increasingly common components of management programmes for living marine resources (NRC, 2001). The use of MPAs has been primarily advocated for protection of sensitive marine habitats and associated species (Roberts et al., 2001; Willis et al., 2003). Increasingly, these management tools have been proposed and implemented for use in achieving traditional fishery management goals, for limiting by-catches, and for increasing biomass in adjacent fished areas (Horwood et al., 1998; Piet and Rijnsdorp, 1998; Frank et al., 2000; Gell and Roberts, 2003; Sissenwine and Murawski, 2004). By protecting defined areas, including both resident species and their biophysical environments, MPAs offer an ecosystem-based approach to conservation or fisheries management, which is distinct from the traditional focus on single species conservation or management (Browman and Stergiou, 2004; Sissenwine and Murawski, 2004).

Various types of MPAs exist, all of which can be defined based mainly upon the level of protection and their primary goals. Some MPAs such as no-take marine reserves, prohibit all extractive and damaging anthropogenic activities, with the aim of protecting individual features of the marine environment, as well as restoring or maintaining the natural ecological balance within the ecosystem. Alternatively, multiple-use marine areas seek a balance between biodiversity protection and continued human use. Despite the beneficial effects of marine reserves for enhancing biomass and density of exploited species within reserves (Garcia-Rubies and Zabala, 1990; Garcia-Charton et al., 2004; Guidetti et al., 2005), rehabilitating community structure (Castilla, 1999; Shears and Babcock, 2002), enhancing reproductive output (Planes et al., 2000; Goni et al., 2003) and biomass exportation through adult migration (Chapman and Kramer 1999; Gell and Roberts, 2003), prohibiting all extractive activities in certain areas can have socio-economic costs. Indeed, even if reserves benefit fisheries (e.g. higher revenue per unit effort in the vicinity of the MPA boundary for haddock fishery, (Murawski et al., 2005)), local fishers may be negatively affected by the loss of fishing grounds, decreased catches and increased travelling time, at least in the short-term (Fiske, 1992). Consequently, marine reserves may face strong opposition by extractive users, making the process of reserve implementation and subsequent enforcement difficult. MPAs imparting partial protection from certain types of fishing are often advocated by groups with direct fishing interests and promoted as a ‘compromise’ solution allowing both protection and fishing (Denny and Babcock, 2004).

Ecological effects of MPAs are typically measured in terms of changes in biomass, abundance, species richness and body size (age) of species that occur within and outside the protected area (Pelletier et al., 2005). There is some evidence that the response of a species to protection depends, in part, on its life-history parameters (Blyth-Skyrme et al., 2006). For example, species that demonstrate a positive and rapid response to protection are often relatively sedentary and spend much of their life in the MPA (Boersma and Parrish, 1999; Murawski et al., 2000; Tawake et al., 2001). In contrast, for species of greater mobility or that utilize a variety of habitats, there is some debate over whether MPAs would be an effective conservation measure (Murawski et al., 2000; Kaiser, 2005), and what size MPA is required to achieve effective conservation of fish stocks (Mangel, 2000; Halpern, 2003; Claudet et al., 2008). In addition, characteristics of MPAs such as age (years since establishment), location, enforcement, regulation, size, distance from other protected areas have often been invoked as potential sources of heterogeneity in the response of marine assemblages to protection (Cote et al., 2001; Halpern, 2003; Halpern and Warner, 2002; Micheli et al., 2004; Guidetti et al., 2008).

While there have been numerous reviews of the effects of marine reserves on target and non-target species (Roberts and Polunin, 1991; Cote et al., 2001; Fraschetti et al., 2002; Halpern, 2003; Ojeda-Martinez et al., 2007; Claudet et al., 2008; Garcia- Charton et al., 2008; Lester et al., 2009), only one review examined the efficacy of partially protected MPAs to date (Lester and Halpern, 2008) and none of these reviews were done systematically (but see Stewart et al., 2008). Whereas the systematic review by Stewart et al. (2008) examined the impacts of temperate zone no-take areas on biological measures of marine biota, the systematic review to be undertaken will encompass a global synthesis of studies that have examined the efficacy of MPAs that confer varying levels of protection from extractive activities. Data on the life-history traits and ecological parameters of the reported species will be extracted and if correlations between effects on the response variable (e.g. fish biomass or abundance) and species characteristics (e.g. maximum body size, mobility) can be determined this may enable us to generate predictions about the response of particular species to spatial management measures.