Effective full protection and increasing temperatures make thermophilic native species future conservation winners in the Mediterranean SeaBroad-scale Spatial Patterns

Antonio Calò^1,2, Elena Desiderà^3,2, Manfredi Di Lorenzo^3,2, Paolo Guidetti^3,2, Marco Milazzo^1,2, Federico Quattrocchi^1,2, Antonio Di Franco^2,3

¹University of Palermo, Italy - ²National Biodiversity Future Center (NBFC), Italy - ³Stazione Zoologica Anton Dohrn, Italy

Marine protected areas (MPAs) have been proposed as potential tools to counteract the direct and indirect effects of climate change and enhance the resilience of marine ecosystems. However, this aspect remains unclear and poorly studied. In this study, we assessed protection effects on the native, range-expanding, Mediterranean parrotfish (Sparisoma cretense), a thermophilic herbivore whose proliferation may lead to significant alterations to coastal benthic assemblages. Specifically, we 1) evaluated the effect of protection and temperature on S. cretense biomass, implementing a zero-inflated model controlling for depth, habitat complexity and spatial variables and 2) compared the magnitude of protection effects between the native range-expanding species and other fish trophic groups, using a meta-analytical approach. Underwater visual censuses were conducted to assess fish biomass across sites with different protection levels (i.e. fully, partially and unprotected) in 16 Mediterranean MPAs. Findings indicate a significantly higher biomass of S. cretense in fully protected areas compared to partially and unprotected areas. Additionally, higher mean summer temperatures over the past decade positively and significantly correlate with increased biomass of S. cretense. Finally, we showed that the positive effect of protection on S. cretense biomass mirrors that of large predatory fishes in well-managed MPAs. Our results highlight the dual advantage that S. cretense gains from effective protection and increasing seawater temperatures, suggesting potential unwanted early ecological implications for MPAs in the future and emphasizing the need for adaptive management against species, native or non-indigenous, sharing similar traits and rapidly spreading in the warming Mediterranean Sea.