To prevent some beaches on the North Sea and Baltic Sea from being washed away by wind and weather, they have to be regularly replenished. This type of sand replenishment is convenient for tourists, but it has significant consequences for the beach ecosystem and its microscopically small inhabitants. Biologists in Mecklenburg-Western Pomerania have now investigated how devastating the coastal protection measure is for them.
As a bather, the beaches where you spend your holidays seem obvious, but at least on the North Sea and Baltic Sea, a lot of work goes into maintaining them. Because storms, waves and currents continually erode the sand on some shores, it has to be replenished every few years. In such so-called sand replenishment, dredging ships suck up sand from the seabed and transport it to the coast, where it is unloaded and distributed by bulldozers.
Census in the sand
But how much does this active intervention in the beach ecosystem affect its inhabitants? Biologists led by Iryna Kapshyna from Senckenberg am Meer in Wilhelmshaven have now investigated this in Ahrenshoop in Mecklenburg-Western Pomerania. The beach there is refilled every five years over a four-kilometer stretch. To find out how this affects the local meiofauna – organisms less than a millimeter in size – the team analyzed the biodiversity before the sand was refilled and then for the entire year afterward.
To do this, Kapshyna and her team analyzed a total of 246 sand samples from the shoreline – both using a classic microscope and using so-called metabarcoding. The DNA of all animals in a sample is analyzed together and their species-specific gene segments are automatically recognized, similar to barcodes at the supermarket checkout. The fact that the biologists limited their analysis to meiofauna organisms is related to their important role in the ecosystem. They are the most numerous animals on the sea floor and essential for the food webs there. The composition of their communities therefore provides information about how intensively an ecosystem has been disturbed by human intervention.
Landfill disrupts ecosystem
In the case of the beach at Ahrenshoop, this disruption was initially massive: “The meiofauna communities initially changed drastically after the sand was replenished. Immediately after the sand was replenished, mites (Acari) and annelids (Annelida) had almost completely disappeared from the wash zone, copepods (Copepoda) decreased significantly, while the number of flatworms (Platyhelminthes) increased significantly,” reports co-author Gritta Veit-Köhler. In the following year, the communities recovered slowly, but still not completely.
It is still unclear how exactly this regular reorganization of the meiofauna affects the ecosystem as a whole. But regardless of this, senior author Sahar Khodami emphasizes: “When it comes to the effects of coastal protection measures on ecosystems, the smallest marine animals should not be overlooked!”
Source: Senckenberg Society for Natural Research; Article: Metabarcoding and Metagenomics, doi: 10.3897/mbmg.8.127688