Spatial differences in growth rate and nutrient mitigation of two co-cultivated, extractive species: the blue mussel (Mytilus edulis) and the kelp (Saccharina latissima)

Cultivation of extractive species, such as bivalves and seaweeds, provides opportunities for food production while removing excess nutrients in eutrophic coastal waters. However, to optimize these ecosystem services, selecting aquaculture sites that affect growth and nutrient uptake is important. In a transplant experiment we assessed spatial growth patterns of the blue mussel Mytilus edulis and the kelp Saccharina latissima, which were used to estimate nutrient removal. Optimal locations for growth and nutrient extraction differed, mussels grew better in relatively sheltered inner coastal areas, whereas seaweed growth increased in outer more exposed coastal areas. Estimates of mitigatory capacity indicated that under the best available conditions, mussels remove approximately 700 kg N and 6600 kg C ha⁻¹yr⁻¹, whereas seaweed removes approximately 100 kg N and 1000 kg C ha⁻¹yr⁻¹. We identified the importance of site selection for the overall capacity of two extractive species (bivalves and seaweeds) in order to synergistically maximise their growth and nutrient mitigation.