Thursday, 29 November 2012

Darkened Fjord Waters Mean Fewer Fish, More Jellyfish


ScienceDaily (Nov. 19, 2012) — The seawater in the Baltic Sea, the North Sea, and Norway's coastal waters and fjords is gradually getting darker. Researchers are observing signs similar to those from overproduction of organic compounds. The result may be fewer marine areas with fish, and more jellyfish.

Marine biologist Dag L. Aksnes of the University of Bergen has analysed the impacts of the declining optical conditions in Norwegian coastal waters. The process has likely been taking place over many decades, and there is strong evidence that changes in weather and climate are causing it to accelerate. And it could prove difficult to reverse.

Coloured matter from fresh water causing problems
Fresh water from rivers and lakes flows into the sea, mixing with coastal seawater. "This fresh water contains far more coloured dissolved organic matter (CDOM) than marine water, so our coastal waters are darkening," explains Professor Aksnes.

His research project receives some of its funding from the Research Council of Norway's research programme on the Oceans and Coastal Areas (HAVKYST).

Major differences between fjords
For many years, Professor Aksnes and his colleagues have been studying two fjords, Lurefjorden and Masfjorden, in northern Hordaland county on Norway's western coast. The fjords are similar and located close to each other, but with one important difference: Masfjorden contains far more seawater than Lurefjorden, which contains lower-salinity coastal water all the way down to its seabed. The study shows that while Masfjorden still has an ecosystem dominated by fish, its darker neighbouring fjord is heavily populated by the jellyfish Periphylla periphylla.

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