Bivalve Diseases and Pests

Farming of oysters, mussels, and clams are important activities throughout California, particularly in Humboldt, Tomales, and Morro Bays and Carlsbad Lagoon. This form of aquaculture contributes to California’s economy and provides a sustainable, efficient source of seafood in an era when overfishing threatens the world’s marine ecosystems. Our lab works with shellfish growers to diagnose disease and monitor pathogen presence in farms and wild bivalve populations across the state.

Since nearly all oyster larvae or seed for commercial farming is imported from out-of-state hatcheries, our lab approves source facilities and inspects shipments of seed for non-native pests. These activities ensure long-term sustainability of wild native shellfish populations and the shellfish culture industry.

Three of the diseases we monitor and investigate:

Oyster Herpesvirus (OsHV-1)

This virus affects Pacific oysters and has caused devastating disease in oyster populations worldwide. The disease is highly temperature dependent, occurring most frequently in warm water and can cause high mortality rates in larvae and juveniles. Increased seawater temperatures associated with climate change may increase occurrences of the disease.

Denman Island Disease

Caused by the protistan parasite Mikrocytos mackini, Denman Island Disease can affect Pacific (Crassostrea gigas) and Kumamoto oysters (Crassostrea sikamea), particularly older individuals in cold waters. Although the disease is named for an island in British Columbia, the causative pathogen has been found in Washington State and California. It appears that the waters in California are typically not cold enough to cause expression of the disease.

Bonamia spp. Microcell

Protistan parasites of the genus Bonamia cause disease that affects oysters in the genus Ostrea, including the California native oyster Ostrea lurida and the European flat oyster Ostrea edulis. We are currently investigating the identity and distribution of Bonamia parasites in native oyster populations throughout the state.

staff inspecting oyster in farm
Inspecting oysters at farms in California
A farmed Pacific Oyster