Artificial upwelling to stimulate growth of non‐toxic algae in a habitat for mussel farming

Large-scale artificial upwelling was tested as a method to enhance the environmental conditions for the growth of non-toxic algae in a Norwegian fjord (61°0′N, 6°22′E). The experiment was designed to evaluate if nutrient-rich seawater, brought up from below the mixed zone of a stratified fjord to the euphotic zone by air bubbling, would stimulate the growth of non-toxic relative to toxic algae. Pumping 44 m3 min−1 of air at 1 atm through a pipe diffuser submerged at 40 m depth formed a buoyancy flux that lifted 60 m3 s−1 of deep water to the upper 17 m over a period of 21 days. The supply of silicate, inorganic nitrogen and phosphate to the upper 10 m in the fjord increased, and a significant increase in the biomass of non-toxic algae was observed. The upwelling gave an increased growth of the non-toxic dinoflagellates Ceratium furca and C. tripos. After termination of the experiment, the phytoplankton biomass decreased significantly, whereas a distinct increase occurred in the relative biomass of the potentially toxic Dinophysis spp. The result is considered promising when it comes to creating controlled geographical areas with non-toxic food for mussel production.