Marine Parasite Biogeography Mirrors Host Patterns Across Latitude, Area, and Diversity

Parasites are integral components of biodiversity, yet they remain poorly represented in large‐scale biogeographic theory. In this study, we test whether marine parasites follow three macroecological patterns established for free‐living taxa, namely that parasite species richness: (1) scales positively with area (both host body size and geographic area) and (2) follows the latitude diversity gradient and (3) increases with host species richness. We assembled a spatially explicit dataset of parasites of cartilaginous fish, which were relatively well‐sampled, and consisted of 7198 host–parasite associations involving 778 host species and 2093 parasite species. We found strong support for all predictions. Host traits (notably body size and range size) explained significant variation in parasite richness across host species. Parasite richness followed a bimodal latitudinal gradient, with richness peaks in both hemispheres—consistent with emerging patterns in marine biodiversity. Finally, parasite richness covaried with host species richness across space. These results provide robust, global‐scale evidence that parasite distributions are shaped by the same large‐scale processes as free‐living organisms.