Deserts have been historically regarded as ecologically simplified systems; however, growing evidence suggests that long-lived plants can sustain diverse and multilayered interaction networks even under extreme abiotic constraints. Here, we provide a comprehensive description of the biotic interactions associated with 19 coastal Copiapoa species in the hyper-arid Atacama Desert (northern Chile), based on direct observations, camera traps, and thermal imaging. We recorded a taxonomically diverse assemblage of flower visitors, florivores, pre-dispersal seed predators, myrmecochorous seed dispersers, insectivorous birds, parasitic plants, climbing plants, epiphytic lichens, and ectothermic vertebrates using cacti as thermal refugia. Many of these interactions were organized across different trophic levels, including predators targeting herbivorous larvae inside cactus fruits and frugivores foraging on fruits of parasitic plants growing on cacti. Thermal imaging further revealed that Copiapoa stems buffer temperature extremes, providing thermal refugia for fauna across the day-night cycle. Together, these results demonstrate that Copiapoa species concentrate interactions at multiple trophic levels, functioning as hubs of biological activity in an otherwise resource-scarce landscape. These findings highlight the disproportionate ecological importance of foundation cacti in desert ecosystems and the cascading consequences their decline may entail.