Marine protected areas' positive effect on fish biomass persists across the steep climatic gradient of the Mediterranean Sea

Abstract

1. The positive effect of fully protected Marine Protected Areas (MPAs) on marine biodiversity, and specifically on fishes, has been widely documented. In contrast, the potential of MPAs to mitigate the impact of adverse climatic conditions has seldom been tested.2. Here, we test the effectiveness of MPAs, quantified as increasing fish biomass, across wide geographic and environmental gradients across the Mediterranean Sea. For this, we performed underwater visual surveys within and outside MPAs to characterize fish assemblages in 52 rocky reef sites across an extent of over 3,300 km. We further use the steep spatial temperature gradient across the Mediterranean as a 'space-for-time' substitution to infer climate-driven temporal changes.3. We find that, as expected, Mediterranean MPAs increased fish biomass. At the same time, higher seawater temperatures are associated with decreased fish biomass, changes in species composition and shifts towards more thermophilic species.Importantly, we also found that the rate of decrease in fish biomass with temperature was similar in protected and fished sites.4. Taken together, these results suggest that the capacity of MPAs to harbor higher fish biomass compared to surrounding areas is maintained across a broad temperature range. At the same time, MPAs will not be able to offset larger-scale biotic alterations associated with climate.5. Policy implications. Our results suggest that sustained warming will likely reduce fish biomass in the Mediterranean Sea and shift community structure. At the same time, protection from fishing should remain an important management tool even with future high water temperatures, and MPAs will continue to provide local-scale benefits to conservation, and fisheries.

A marine protected area network does not confer community structure resilience to a marine heatwave across coastal ecosystems

“…It is not surprising that community shifts occurred inside and outside MPAs simultaneously for most habitats, since many of the species exhibiting the biggest changes are not directly targeted by fishing activities (e.g., invertebrates and algae). In cases where MPAs do not confer ecological resilience to marine heatwaves, it is important to note that the capacity of MPAs to harbor higher biomass than unprotected sites can still be maintained (Frid et al, 2023). Other studies have documented increases in targeted species biomass inside of MPAs within this system, which is a focal MPA conservation objective (Caselle et al, 2015; Hamilton et al, 2010; Ziegler et al, 2022).…”

“…Our results highlight the need for management frameworks that include climate adaptation strategies, the protection of range‐shift corridors, and consideration of the compounding effects of both fishing and marine heatwaves on resilience (Burrows et al, 2014). More investigation is needed to better understand the drivers that can help MPAs to maintain higher fish biomass than unprotected sites under climate change (Frid et al, 2023).…”

Quantifying the ecological consequences of climate change in coastal ecosystems

“…But other arriving taxa can have equally profound impacts (de et al, 2022). Despite evidence that "healthy" ecosystems with relatively intact biodiversity can resist climate change of the magnitude already witnessed (Bates et al, 2014;Frid et al, 2023;Ziegler et al, 2023), the inevitability of range shifts identifies the network effects of tropicalisation and deborealisation as an urgent research priority.…”

Marine protected areas can increase the abundance of invasive lionfish (Pterois miles)

“…In the Mediterranean Sea, MPAs are strongly affected by climate change associated impacts such as the spread of warm‐water invasive alien species (IAS) that arrive through the Suez Canal (D'Amen & Azzurro, 2020; Frid et al, 2023; Giakoumi, Pey, et al, 2019). Conversely, species that are particularly vulnerable to climate change may not benefit as expected from the protections MPAs offer, creating a ‘Protection Paradox’ (Bates et al, 2019).…”

“…Invasive species can synergistically interact with climate change to alter species interactions and food‐web dynamics, potentially leading to the collapse of sensitive species populations that MPAs are designed to protect (Chaffin et al, 2016; Corrales et al, 2018; IPBES, 2023). There are concerns that MPAs in the Mediterranean, where IAS are a chronic and expanding issue, may not function as biodiversity conservation areas but as breeding grounds for IAS (Frid et al, 2023; Galil et al, 2017; Giakoumi, Pey, et al, 2019). Impacts of IAS are expected to worsen as other human pressures intensify (Geraldi et al, 2020).…”