Marine protected areas regulate the structure of fish communities threatened by global warming and human impact

Protecting and restoring the structure of marine communities is critical for supporting many bio-physical processes including human well-being. Marine Protected Areas (MPAs) can successfully help to protect the abundance of target marine species, however, we know little about the cause-effect relationship between MPAs and community-wide properties of fish communities under the context of climate change and anthropogenic disturbances. Here, we show that MPAs mediate anthropogenic and climatic effects on fish diversity, while they directly increase by 28% the probability that a fish community displays a higher-than-average pyramid-like structure: energetically efficient systems with small basal species as the most abundant and large apex predators as the least abundant. To quantify these causal effects, we integrate a nonparametric causal-inference approach with ecological theory and observational data from 286 geographical sites with more than 1,400 fish species. Our work provides a quantitative platform to study how different factors may protect and restore marine communities.