Project: Biogeochemical and Ecological Impacts of Amphipod Circoviruses in Benthic Habitats

Description from NSF award abstract:
This project will investigate how circoviruses influence the herbivory/detritivory rates of benthic amphipods through the study of an experimental gradient of viral prevalence and by addition of cultivated viruses. The hypotheses to be tested are:
H1: Circoviruses cause decreased detritivory and herbivory by infected amphipod hosts;
H2: Circoviral impacts on amphipods result in decreased growth rate of sediment bacteria, decreased extracellular cellulose activity of sediment microorganisms, and decreased fluxes of oxidized inorganic nutrients from sediments into overlying waters;
H3: Circoviruses negatively impact the nutritional quality of their hosts. These hypotheses will be tested by conducting sediment-water mesocosm experiments to assess the impacts of circoviruses on aquatic vegetation breakdown, and subsequent impacts on biogeochemistry, including bacterial production, efflux of reduced N into overlying waters, and production of dissolved organic C.

Finally, this project will examine how circoviruses influence the nutritional quality of amphipods by examining elemental ratios of amphipod populations from high to low circoviral prevalence and experimentally infected amphipods. Data from these three approaches will be used to form a model of how circoviruses influence benthic foodwebs and biogeochemical cycles in sediment habitats. This study focuses on circoviruses within two ecologically sensitive amphipods that are crucial to ecosystem function: Diporeia (in Lake Michigan), which has experienced dramatic decline in abundance over the last 20 years within the Great Lakes, and Peramphithoe femorata, which is a major consumer of the environmentally threatened giant kelp Macrocystis pyrifera on the US West Coast.

Decades of research have identified the importance of viruses in aquatic ecology and biogeochemistry. However, most studies have focused on bacteriophage and viruses of eukaryotic microorganisms. Metazoa are important drivers of benthic biogeochemistry, where they cause bioirrigation of anoxic sediments, resuspension, settlement of particulate matter, facilitating nutrient fluxes from sediments to overlying waters, and potentially influencing ocean-scale processes like sediment denitrification. Circoviruses have been identified as a common constituent of crustacean viral assemblages, where they are well correlated with host death rates and population decline, and cultivated circoviruses cause death of arthropod cells. There is therefore a strong need to investigate how viruses impact the ecology of their crustacean hosts, and how in turn those impacts influence ecosystem function. Amphipods are important epifaunal constituents of benthic habitats, where they consume settled particulate matter and aquatic vegetation, which in turn influences its conversion to dissolved organic matter through microbial degradation. In turn their feeding activities stimulate benthic mineralization rates, and they are consumed by higher trophic levels. Therefore, amphipods link microbial to macrobial food webs in coastal and lake habitats. This project investigates how circoviruses infecting amphipods influence the flux of C through benthic ecosystems as a model of how viruses of metazoa influence biogeochemistry of aquatic ecosystems. The research will provide insight into how viruses influence aquatic biogeochemistry, opening up a new area of research into metazoan viruses in benthic ecosystems.