Marine protected areas maintain pyramid-like structures of coral-reef fish communities
Tabi, Andrea; Gilarranz, Luis J. ; Saavedra, Serguei
Maintaining the species composition 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 their ability to protect the composition of entire communities. This is a challenging task given that the effects of MPAs on community structure can be intertwined with numerous internal (e.g., species interactions) and external factors (e.g., thermal stress). Here, we show that on average MPAs increase by 23% the chance that a community displays a stronger pyramid-like structure: energetically efficient systems with small basal species as the most abundant and large apex predators as the least abundant. We show that this effect is done indirectly by regulating the interaction constraints within a community, which in turn regulate the community structure. To test these effects, we follow a nonparametric causal-inference approach using observational data from 286 coral-reef fish communities, comprising a total of 1,548 fish species together with spatial, temporal, and climatic factors across 286 sampling sites worldwide. We estimate the interaction constraints by inferring the effect of species interactions on the tolerance of a community to structural perturbations following theoretical population dynamics. Our findings provide a quantitative platform to differentiate the role of internal and external factors affecting the composition of marine communities, and provide additional evidence of the importance of MPAs.