Fish farming is a large and important industry in Norway. In today's semi-closed systems, a significant amount of feed and faeces is discharged directly into the free water mass. Most of these by-products settle on the bottom in the direct proximity to the farmed fish. If the sedimentation of organic waste exceeds the carrying capacity of the seabed, this can lead to negative consequences such as oxygen depleted environments and production of hydrogen sulphide. Integrated multitrophic aquaculture (IMTA) is a way to manage and maximize the yield of the nutrients added during fish production. Previous studies at the Institute of Marine Research in Bergen have indicated that some species of polychaetas are particularly suitable for use in IMTA as they have been observed in high densities and that they contain high quality fats and protein valuable as feed ingredients. In order to integrate polychaetas in large-scale fish production in the future, more knowledge is required about the polychaetas succession, expected biomass and population dynamics.
This PhD project will build on earlier indications that have been made and further evaluate the potential for the use of polychaetas in handling by-products from fish farming. The project is a collaboration between the University of Bergen, Lerøy and the Institute of Marine Research and consists of three work packages. The first part is a field study that will document biomass and succession of polychaetas at an trout farming production site. Part two is a laboratory study that will estimate the turnover of organic carbon from polychaetas fed with either fish feed or faeces. The last part will estimate some basic life history features of the species that previously has indicated great potential for use in IMTA systems.
Fish production in open-net cages release a substantial amount of organic co-products (waste) consisting of faeces and uneaten feed, that may settle on the seafloor beneath cages. High organic loading can lead to decreased benthic species diversity, abundance, and eventually loss of benthic fauna. Farm co-products can be considered a resource that can be recycled. Integrated multitrophic aquaculture is one approach for utilizing co-products by the incorporation of organisms from different trophic levels such as kelp, mussels and benthic deposit feeders that benefit from the different fractions of co-products. Polychaetes can be a component in the benthic part of integrated aquaculture systems for handling and recycling farm co-products. This project will investigate the farm co-product mitigation of polychaetes observed on artificial hard bottom substrates. A few species of polychaetes have been found to occupy hard bottom under fish farms, and preliminary investigations indicate a large capacity to degrade organic matter as well as high abundance. To evaluate the polychaetas ability to mitigate organic co-products, their biomass, abundance and nutrient turnover beneath fish farms needs to be further investigated and quantified. This project will combine field surveys at a trout farm, documenting biomass and succession, and laboratory experiments will be defining turnover capacities and exploring the life cycle of one species given specific interest, Ophryotrocha craigsmithi.
This project aims to contribute to our understanding on how polychaetes that occupy artificial hard bottom substrates beneath fish farms can recycle and mitigate organic deposition to the seabed.