Where the water is cleaner, there are more animals – one might think. A research team from the Senckenberg am Meer Research Institute and the University of Oldenburg has now shown that this is not always and everywhere the case. The group led by Anja Singer investigated how species diversity and total biomass have changed in the East Frisian Wadden Sea compared to the 1980s. They note a clear downward trend: Stocks of the then-dominant species, the common mud snail, tree tubeworms and mud crustaceans, have fallen by more than 80 percent. According to the study, the total biomass has almost halved, and the number of individuals per square meter has shrunk by 31 percent. In the journal Frontiers in Marine Science. has been published.
Experts see why the food supply is declining. Restrictions on the use of fertilizers and more stringent requirements for wastewater treatment plants have greatly improved water quality over the past 40 years, but at the same time have reduced the nutrient content of rivers such as the Elbe, Weser and Rhine. As a result, algae blooms, for example, became much rarer — and at the same time the food supply of many once widespread species shrank.
However, this is not synonymous with ecosystem impoverishment. “What may be a disadvantage to mud snails is a clear benefit to other organisms: Better water quality has a positive effect on seagrass meadows and oyster reefs, for example,” says study co-author Ingrid Kroenke in one. Senckenberg Society press release. The total number of species found in the study area has remained roughly constant since the 1980s.
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