The impact of juvenile mussels on Wadden Sea plankton
To better protect natural mussel beds in the Wadden Sea, fishing for juvenile mussels is replaced by harvest from collectors. The pelagic collectors consist of ropes or nets facilitating the attachment of mussel larvae, and increase the number of young mussels present. Since mussels remove large amounts of plankton by means of filtration, this thesis tried to answer the question whether an aimed harvest of 40 M kg will affect the plankton community.
Juvenile mussels removed larger organisms faster than smaller ones. Size-selective filtration initially resulted in lower mortality rates of phytoplankton and increased bacteria growth rates. However, within the time frame of the average water resident time in the western Wadden Sea (9 days) we reported a decrease in small algae, while larger plankton were able to recover to pre-filtration biomasses on some occasions. The total daily filtration pressure exerted by these collector mussels was estimated at 3 percent.