Effects of starvation and macroalgae extracts on the survival and growth of quahog parasite unknown (QPX)

Quahog parasite unknown (QPX) is a relatively poorly characterized protistan parasite that causes QPX disease in infected hard clams (Mercenaria mercenaria). Most prior studies presented descriptive reports of the occurrence and the characteristics of the disease in cultured and wild clams, while several basic aspects of the biology and ecology of the parasite remain obscure. In an attempt to better understand factors affecting the persistence and growth of QPX in marine environment, we investigated the ability of QPX to survive in seawater and the potential role of macroalgae in supporting its growth. An association with macroalgae is particularly relevant because several members of the phylum to which QPX belongs are known to live in association with marine macroalgae and vascular plants. Results indicate that while QPX did not appear to grow in seawater under laboratory conditions, the parasite may be capable of long-term survival in seawater without growth. QPX was able to grow using macroalgae homogenates as a source of nutrients, although extracts from certain macroalgae species significantly inhibited the in vitro growth of QPX. Overall, our results suggest that macroalgae might be an important factor for the survival, growth and spread of QPX in the marine environment.