Can marine reserves restore lost ecosystem functioning? A global synthesis

Abstract

Marine protected areas (MPAs) have grown exponentially, emerging as a widespread tool to conserve biodiversity and enhance fisheries production. Although numerous empirical studies and global syntheses have evaluated the effects of MPAs on community structure (e.g., biodiversity), no broad assessment concerning their capacity to influence ecological processes (e.g., species interactions) exists. Here, we present meta-analyses that compare rates of predation and herbivory on a combined 32 species across 30 MPAs spanning 85°of latitude. Our analyses synthesize the fate of 15,225 field experiment assays, and demonstrate that MPAs greatly increased predation intensity on animals but not herbivory on macroalgae or seagrass. Predation risk, quantified as the odds of prey being eaten, was largely determined by predator abundance and biomass within reserves. At MPAs with the greatest predator accumulation, the odds of predation increased to nearly 49:1, as opposed to 1:1 at MPAs where predators actually declined. Surprisingly, we also found evidence that predation risk declined with increased sea-surface temperature. Greater predation risk within MPAs was consistent with predator and prey population abundance estimates, where predators increased 4.4-fold within MPAs, whereas prey decreased 2.2-fold. For herbivory, the lack of change may have been driven by functional redundancy and the inability of reserves to increase herbivore abundance relative to fished zones in our sample. Overall, this work highlights the capacity of MPAs to restore a critical ecosystem function such as predation, which mediates energy flows and community assembly within natural systems. However, our review of the literature also uncovers relatively few studies that have quantified the effects of MPAs on ecosystem function, highlighting a key gap in our understanding of how protected areas may alter ecological processes and deliver ecosystem services. From a historical perspective, these findings suggest that modern levels of predation in the coastal oceans may currently only be a fraction of the baseline prior to human exploitation.

Mediterranean marine protected areas have higher biodiversity via increased evenness, not abundance

“…What mechanisms could underlie changes in species’ relative abundances following protection? Similar to existing work describing reduced total abundance of prey species within MPAs (Cheng, Altieri, Torchin, & Ruiz, ; Claudet et al, ), we hypothesize that increased evenness among prey species could reflect stronger top‐down control inside protected areas. We found a trend towards lower abundances of prey species (see Figure for the positive relationship between sensitivity and trophic level) in MPAs, and lower abundances were accompanied by increased evenness (and a reduction in the relative abundance of the most common prey species of almost 10%; Figure ).…”

Assessing the effectiveness of a national protected area network for carnivore conservation

“…rotected areas (PA) are perceived as key conservation instruments 1-3 yet we know very little about their effectiveness at safeguarding biodiversity against increasing human pressures 4 . Given the utmost importance of these instruments for the protection of species 5 , the maintenance and restoration of ecosystem functioning 6 and their contribution to human well-being and poverty alleviation 7,8 , it appears as even more urgent to improve our understanding of the effectiveness of PAs worldwide. The last two decades have put more attention on PA efficiency (e.g., coverage of species ranges within protected areas 9 ) than on ecological effectiveness 10 .…”

Multi-zone marine protected areas: Assessment of ecosystem and fisheries benefits using multiple ecosystem models

“…Similarly, the temporal dynamic model of Medes Islands highlighted decreasing trends for white seabream, common two-banded seabream and common dentex, while groupers slightly increased. These results evidence that under protection the food-web effects can play an important role and there are winners and losers as a result of the new ecological state, where results of protection can include cascading effects of predators on preys species (Edgar, Stuart-Smith et al 2014;Cheng, Altieri et al 2019) as well as an increase in competitive interactions (Micheli, Halpern et al 2004).…”

“…Larger abundance and sizes could entail higher reproductive potential of species, and eggs and larvae from recovered populations could then be exported to external unprotected locations, including adjacent ones (Gell and Roberts 2003;Harrison, Williamson et al 2012). In addition, MPAs could restore ecosystem functioning (Cheng, Altieri et al 2019). Although some of our temporal results showed potential recoveries (some target species, increases of predators and declines of prey, and some ecological indicators), our study evidences that they are still far from what we would expect from the temporal protection effects of MPAs, highlighting an overall modest historical positive effect of protection on these MPAs.…”

“…Within the EBM, ecological modelling has been proven to be a suitable tool to merge available ecological information into a coherent form to obtain insights about how ecosystems are structured and impacted by human activities and environment, and delivering ecosystem services Christensen and Maclean 2011). Although quantitative models have become a key tool to assess the extent to which MPAs are able to achieve their conservation targets (Fulton, Bax et al 2015), the understanding of MPA effects on ecological processes and ecosystem function is still scarce (Cheng, Altieri et al 2019). For instance, it is mostly unknown if protection benefits inside fully protected areas extend to partially areas and beyond, and if those benefits have the potential to cascade through the ecosystem components.…”