Mussel farming production capacity and food web interactions in a mesotrophic environment

Abstract

Low trophic aquaculture (LTA), such as bivalve farming, offers promising avenues to supply sustainable seafood and aquafeed. While bivalve farming usually occurs in highly productive coastal areas which already support numerous human activities and suffer from environmental pressures, numerical tools offer a promising avenue to explore and assess biomass production potential and associated ecosystemic impacts for further development of the industry and prospection of new exploitation sites. In this study, we coupled an ecophysiological model, the dynamic energy budget theory (DEB), with an ecosystem model (NORWECOM.E2E) to simulate blue mussel Mytilus spp. farming production and effects based on the food web in the mesotrophic Hardangerfjord in western Norway. We tested several levels of fjord-scale farming intensity and assessed 2 production purposes: aquafeed and human consumption. Results suggested the Hardangerfjord could host large-scale mussel farming for both purposes. However, large exploitation schemes displayed detrimental effects on individual mussel growth (39% less wet mass after 2 yr) and especially on secondary production (decrease of 33% after 1 yr) due to acute trophic competition. Simulations showed short production cycles for aquafeed were more efficient to exploit primary production, since young and small mussels have lower maintenance and reproduction costs. Dissolved nutrient inputs from salmonid farms had marginal effects on primary production (<2%). However, salmonid and mussel farming activities could compete for the sites with the highest production potential.

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“…When increasing the extent and density of LTA, the ecological carrying capacity issues should also be considered to avoid unacceptable changes to the ecosystems [65][66][67][68] . Extensive mussel farms can potentially make plankton food unavailable to other nature values with potentially negative consequences for both ecosystems and fishery 69,70 . Further, sedimentation of mussel bio-deposits can cause accumulation of organic matter underneath the farms leading to local hypoxia, inhibition of denitrification, and increased nutrient fluxes [71][72][73] .…”

“…Moreover, offshore areas have strong currents diluting the negative effects of sedimentation from LTA 76 . The carrying capacity of any LTA solutions can be estimated by 3D modeling and must be site-specific due to the interactions with local environmental conditions 68,70 . However, in other offshore areas, nutrient concentrations can become relatively low, and the advantage of OWF-LTA may be less obvious considering the negative effects (e.g., fuel) from longer transportation time.…”