Mussel Mytilus edulis (L.) filtering of the Baltic Sea outflow through theOresund - An example of a natural, large-scale ecosystem restoration

Investigations were undertaken to quantify the filtering capacity of mussel s at the sill in Oresund, one of the straits connecting the Baltic Sea with the Kattegat. The investigations included observations of hydrography and currents and measurements of nutrients, chlorophyll-a. and phytoplankton. T racing the water over the vast mussel banks at the sill, we found that abou t 75% of the phytoplankton biomass was removed from the water. The clearanc e rate, defined as the water volume cleared of organic matter per unit time and unit ash-free dry-weight of soft tissues of the mussels (AFDW), was es timated at 7 L/h/g. Based on the mussels present at the sill (Madsen and Ho jgard Petersen 1996), we determined that the mussels could clear the outflo w from the Baltic Sea through Oresund almost completely of phytoplankton bi omass. We also found that the plankton biomass recovered after the passage of the sill.