<p>Human activities are rapidly eroding the biodiversity of most ecosystems, threatening the myriad contributions they provide to nature and people. Protected areas are often seen as key management tools for their conservation. However, the lack of historical baselines hinders our ability to fully assess these declines and the extent to which protected areas can compensate for decades of human-mediated degradation. Using a Bayesian framework, we modelled 22 fish community contributions across 2,800 tropical reefs and predicted their levels under counterfactual scenarios to compare the relative benefits of marine protected areas (MPAs) and anthropogenic impacts on unprotected reefs. We show that human activities have significantly reduced fish biodiversity- and biomass-related contributions with, for example, a 120% decline in piscivore biomass, corresponding to a net loss of 19 kg per hectare of reef. In contrast, the benefits of MPAs appear comparatively low, with conservation efforts potentially offsetting only 5% of this decline. Ultimately, only old and fully protected areas provide marked benefits to nature and people. This suggests that even if we drastically increase our protection efforts across the ocean (30% coverage by 2030), we cannot expect short-term socio-ecological benefits to counterbalance a long history of human footprint. A desirable future for nature and people thus requires a paradigm shift in our relationship with ecosystems and their biodiversity, beyond MPA establishment.</p>