seagrass meadows grow in shallow coastal seas worldwide and cover a total area of almost 18 million hectares. Also in the North sea and the Baltic sea they occur. The billowing forests of this water plants, as many marine animals as an important habitat. Fish and shellfish use seagrass meadows as a nursery, turtles and manatees graze in them. With your the roots of the sea grasses will strengthen the Sediment on the sea floor and thus prevent coastal erosion. Because the seagrass meadows, large quantities of the greenhouse gas carbon dioxide to bind – more even than the rain forests, you also for the climate a meaning.
eutrophication
threatened But how many other coastal ecosystems, seagrass meadows are highly threatened. Since 1980, their area has decreased by around seven per cent per year, around a quarter of the seagrass species are now on the Red list. The cause for the decline is mostly due to the Eutrophication of the seas is in addition to the warming of the sea water, displacement by invasive species and destruction by human activities. Because sea grasses draw their nutrients mostly through their roots, they thrive in clear, nutrient-poor water is best.
however, When eutrophication increases, the Seaweed, increasingly, competition from sea algae. This coating its leaves often with a dense algae layer that allows hardly any light through, and the Seaweed, resulting in the death of. When the eutrophication reaches a threshold, the ends of the seagrass meadows, fatal, has now been researched by a Team of the Leibniz centre for tropical Marine research (ZMT). “We managed, for the first time to determine a limit value of the nitrogen load from the habitat, seagrass meadow not more of this environmental stress can recover and dies,“ says senior author Tim Jennerjahn.
the sea off the coast of Hainan reveals relationships
this was made Possible because Jennerjahn and his Team seagrass meadows more than a decade before the island of Hainan in the South China sea to explore. In this area, as in many places in Southeast Asia, perch by the number of aquaculture facilities, especially for shrimp and Zack since the 1980s, the explosive increase. From these Aqua cultures are constantly washed large amounts of uneaten feed and excreta of the animals in the surrounding ocean areas. Because the nitrogen-rich wastewater is left untreated, discharged into the coastal sea. This nutrient performs fine current to a Eutrophication of the water and impacted meadows of the seagrass.
Jenner Jahn and his colleagues noted, is meadows the biomass of seagrass off the coast of Hainan, within the last ten years to 87 percent. Isotopic analyses of seagrass leaves and algae stored nitrogen showed that this nutrient was not reached with the rivers from the Inland to the sea, directly from aquaculture came from. Compare the nitrogen values, the state of the plant and other factors, the researchers were able to determine the level at which it is for the Seaweed, critical: “He reported is Jennerjahn at a concentration of 112 micrograms of dissolved inorganic nitrogen per Liter of water, which acts over a period of at least ten years”.
According to the scientists, this threshold value is now an important point of reference to meet, especially in South East Asia better protection measures for the threatened seagrass meadows.
source: Leibniz-centre for tropical Marine research (ZMT); technical article: Marine Environmental Research, doi: 10.1016/j. marenvres.2020.104986
*published The article “seagrass meadows at the Limit” of Wissenschaft.de. Contact with the executives here.
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