Parasites aren’t exactly popular, but they’re an important part of biodiversity and ecosystems. It is therefore all the more gratifying what biologists have discovered in five reservoirs along the Ruhr: the water snails living there contain a surprisingly large variety of suction worms. These parasites of fish and birds show that the lakes and their ecosystems are in very good condition, as the researchers explain.
Living in a foreign organism at its expense is widespread in nature. Humans are also often plagued by parasites. But despite their rather bad reputation, parasites play an important role in nature: “They take on important ecological functions: They regulate the populations of intermediate and final hosts and structure the network of food relationships,” explains senior author Bernd Sures from the University of Duisburg-Essen. “They are part of the biodiversity and provide valuable information about the state of the water.”
Parasite detection in five Ruhr area lakes
That is why Sures, his colleague Christian Selbach and their team have now investigated the frequency and variety of suction worms in five artificially created, interconnected lakes. “This is the first large-scale study of trematode diversity in a connected freshwater system,” they explain. The place of investigation was the Baldeneysee and Hengsteysee lakes, which were dammed up along the Ruhr, and the Sorpe, Verse and Hennetalsperre dams. For their study, the researchers collected a total of 5347 water snails from these waters, because these animals are the main hosts for the larvae of the suction worms.
“Trematodes are dependent on several hosts,” explains Sures. “They spend part of their complicated life cycle as larvae in water snails and leave them again to continue growing in another living being – for example a fish. Often this is just a stopover: a bird or other animal eats the fish and is then infected by the suction worms. The worm eggs are later excreted through the end host’s droppings. The cycle can start again. ”But because the water snails are the first stop for all suction worms, they give the best insight into the frequency and species distribution of these parasites in a body of water.
36 different types of trematodes
The evaluation showed: Of the 5000 water snails, more than 1000 were infested with sucking worm larvae. In total, the researchers identified 36 different types of trematodes from nine families – a surprisingly large variety: “This is a considerably greater diversity in water snails than was found in most of the other freshwater systems examined so far,” report Selbach and his colleagues. “This high biodiversity is in strong contrast also described in the literature.” By far the most suction worms, the researchers found in the mud snail (Radix auricularia), it housed 23 different types of trematodes and also the largest number of parasite larvae. “This supports the assumption that Radix auricularia is the most important trematode host among the water snails in larger lakes,” said the researchers.
According to the scientists, the high diversity of the suction worms in the Ruhr lakes is definitely a reason to be happy. Because it indicates that these waters are in good condition. “A healthy ecosystem is rich in parasites,” explains Sures. At the same time, this result underlines that parasites such as the suction worms make up an important but often overlooked part of the earth’s biodiversity. “They can often be found in secret – right on our doorstep in the reservoirs and dams of the Ruhr,” said the researchers.
Source: University of Duisburg-Essen; Technical article: Scientific Reports, doi: 10.1038 / s41598-020-59548-5