They mitigate climate change and prevent algal blooms — and they can also reduce concentrations of potentially harmful bacteria in seawater, according to the latest research: seagrass beds provide another ecosystem service for us humans, according to a study now published by researchers in Kiel. The findings provide further incentive for the protection and restoration of these long-underrated ecosystems in the German Baltic Sea.
It has been known for some time that seagrass beds can absorb nutrients and thus prevent over-fertilization of the seas and thus algal blooms. In addition, their important role as a marine carbon sink is also increasingly recognized, which means they can counteract the greenhouse effect. In a study now published in the journal Marine Biology, a team of researchers from GEOMAR Helmholtz Centre for Ocean Research Kiel has demonstrated that native seagrass meadows can also improve water quality with respect to potentially harmful bacteria: Water from the densely vegetated submarine areas contains fewer vibrios — naturally occurring bacteria that can be harmful to health in high concentrations.
At five locations in the Bay of Kiel, divers took targeted water samples from overgrown and vegetation-free sandy bottoms. In the laboratory, these were placed on a plate coated with nutrient solution. After a few days, the Vibrio colonies that formed were counted. Analyses showed that water from seagrass beds contained an average of 39 percent fewer Vibriones and 63 percent fewer of the potentially harmful Vibrio vulnificus/cholerae type compared to unvegetated areas.
The underlying mechanism of action will be studied in more detail in the future. “It is conceivable both that the increased sedimentation in the dense meadow leads to the settling of fine particles to which vibrions also adhere,” explains Professor Thorsten Reusch, marine biologist at GEOMAR and leader of the study. “But it could also be that chemical substances from the seagrass leaves inhibit the growth of the bacteria.”
“Our pilot study was motivated by a 2017 Science publication that showed a reduction of coral and human pathogens for tropical meadows wherever dense seagrass meadows grow between human settlements and reefs. Now, for the first time, we have been able to demonstrate similar functions for our native waters.”
- Prof. Thorsten Reusch
The new results are of particular importance because all climate models predict above-average warming in the future in combination with a sweetening of the Baltic Sea. “These are exactly the environmental conditions that will lead to the further spread of vibrios also on bathing beaches in summer,” said Professor Ute Hentschel Humeida, microbiologist at GEOMAR and co-author of the publication. The study also highlights the crucial importance of seagrass beds as a nature-based solution for the health of shallow water ecosystems and their water quality. Thus, it provides further incentives for the protection and restoration of these long underestimated coastal ecosystems.
