Recycling of macronutrients from sea to land using mussel cultivation

The presence of diarrheic shellfish toxins (DST) has been the main obstacle to mussel cultivation in Sweden. Monitoring of DST concentrations in mussels by HPLC for 12 years has shown great geographical and seasonal differences. Furthermore, individual mussels on the same farming strip may differ by a factor as great as 16. DST levels are usually low in summer, rise in September, remain high in the winter and vanish after the start of the spring bloom. A part of the Bohuslan fjord system north of the island Orust, which is secluded from the open sea by shallow sills, regularly shows low DST concentrations. This basin is among the most eutrophicated parts of the Bohuslan coastline. Cultivation of mussels in this area has been calculated to reduce the eutrophication, and results of field-tests support this view. As a consequence, a strategy for sea-gardening is being developed in which the presence of nutrients with primary production in the sea and cultivation of mussels are planned to balance one another.