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Blue mussel beds can clean fjords and bays

Agricultural fertilizers leaching into aquatic environment can cause massive algae blooms leading to oxygen depletion. Banks of blue mussels can get the algae populations under control, Danish researches have demonstrated.
Credit:   Peter Symes
Blue mussels, edulis mytilus, are effective filter feeders
A project conducted by researchers from Denmark's Technical University showed that 18 hectares of blue mussels in Skive Fjord reduced the levels of algae low enough to prevent oxygen depletion.
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The main issue with fertilization of coastal waters causing algae bloom stems from the massive amounts of dead algae sinking to the bottom in thick layers. As they rot, they consume and deplete oxygen, choking huge swathes of seabed, leading to widespread bottom death. This is a big issue along coasts of agricultural areas.

Shallow waters with a limited exchange of water, such as deep fjords, are in particular at risk, but also bigger seas, such as the Baltic, are severely affected by oxygen depletion and huge areas regularly die off.

In an attempt to prevent algae to completely dominate the ecosystems, researchers have looked into using blue mussels, which are effective filter feeders, to bring the blooming algae populations under control.

Normal feeding in Mytilus edulis, and many other suspension-feeding bivalves, depends on the cirri-trapping principle, where bands of lateral cilia produce the main water transport through interfilamentary canals of the gill where suspended particles are separated. In experiments it has been demonstrated that the mean individual filtration rate of 21.5mm shell length mussels was about 15 milliliter per minute. This equates to 22 centiliter, or a quarter liter per 24 hours, just for one small mussel.

Consequently, as many divers can testify, there is often a much clearer layer of water just above dense mussel beds.

The Danish researchers used 90km (56mi) of lines from which the blue mussels were suspended. After a year, the scientists saw significant improvement in water quality in a surrounding area that was ten times bigger than the mussel beds. This effect has been attributed solely to the blue mussels.

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