DAO 161:39-46 (2025)  -  DOI: https://doi.org/10.3354/dao03834

ABSTRACT: Bonamia (Haplosporida) are oyster parasites capable of devastating oyster populations. The near-circumglobal distribution of the host generalist B. exitiosa has previously been associated with the natural and anthropogenic dispersal of broadly distributed non-commercial oysters in the Ostrea stentina species complex. Here, we took a global snapshot approach to explore the role of the widely introduced Pacific oyster Magallana gigas, a commercially important species that can be found on every continent except Antarctica, in transporting Bonamia. We screened 938 M. gigas individuals from 41 populations in this oyster’s native and non-native geographic range for presence of Bonamia DNA using PCR. B. exitiosa was the only species detected and only within 2 of 5 populations from southern California, USA (10 and 42% PCR prevalence). Therefore, M. gigas could have played a role in transporting B. exitiosa to California (if introduced) and/or maintaining B. exitiosa populations within California, but morphological confirmation of infection needs to be done to better understand the host-parasite dynamics within this system. We detected no Bonamia DNA within any other non-native M. gigas populations (n = 302) nor within native M. gigas populations in Japan and Korea (n = 582) and thus found no evidence to support the co-dispersal of M. gigas and other Bonamia species. Lower sample sizes within some populations and the non-systematic nature of our sampling design may have led to false negatives, especially in areas where Bonamia are known to occur. Nevertheless, this global snapshot provides preliminary guidance for managing both natural and farmed oyster populations.

KEY WORDS: Non-native introductions · Bivalves · Haplosporidian · Crassostrea gigas · Bonamiasis