Parasites represent a critically understudied component of reef communities-a knowledge gap that has become more evident as infectious diseases emerge. Here, we test the roles of competing ecological and evolutionary factors in driving infections by an emerging infectious phenomenon: Black spot syndrome (BSS) in Caribbean reef fishes. BSS, a condition associated with localized hyperpigmentation in the dermis and fins of fishes, has recently been linked to infection by trematode parasites in the genus Scaphanocephalus. Using phylogenetic generalized linear mixed models, we evaluated the influence of host phylogeny, habitat preference, body size, and trophic position on infection abundance. Metacercariae of Scaphanocephalus were recorded in 29 of 41 fish species, including 21 new host species records, and within 306 fish (62.3% prevalence). Among species, infection load increased significantly with host body size and decreased with host trophic level, such that large-bodied herbivores tended to support the most infection. There was no significant effect of host phylogeny on infection load. These results suggest the parasite is a generalist in its use of fish intermediate hosts and emphasize the influence of local variation in parasite exposure risk. Overall, the count of visible spots per fish was a positive predictor of Scaphanocephalus abundance among species and individuals, although not all fish species exhibited spots, even when infection loads were high. Findings from this study indicate that Scaphanocephalus infections are far more prevalent in reef fishes than previously recognized and highlight the importance of investigating infection patterns beyond the external symptoms of BSS.
