Mud Crab Discovery in Matsalu Bay May Disrupt Marine Ecosystems | New

Rhithropanopeus harrisii, the estuarine mud crab, is native to the northwest Atlantic, ranging from Canada to northern Brazil. The crab was discovered in Pärnu Bay off the Estonian coast in 2011.

Redik Eschbaum, a researcher in ichthyology and fisheries science at the University of Tartu, said the crab must have arrived in the Baltic Sea with the ship’s ballast water and has since established itself there. “The seabed of Pärnu Bay is completely covered with these crabs. There are so many of them,” said the researcher.

Jonne Kotta, a marine biologist at the University of Tartu, said the crabs are now breeding successfully and their population is increasing rapidly due to recent hot summers. When they were first discovered in Parnu Bay, there were only a few crablets on the seabed, but a year later there were many more in the same place. “This summer we again assessed the density of the crab population in Pärnu Bay and found a number of places with more than 100 crabs per square meter. This is a huge volume,” said the searcher.

“Last year, we only found a small juvenile in the Matsalu Bay area. Based on the recent discovery of an adult specimen, it appears that the crab has also successfully established itself. in Matsalu Bay, and there is now a risk that its population will reach the same size as in Pärnu Bay,” Kotta added.

Kotta doesn’t think it’s possible the crabs were brought there from another country. It most likely came from Pärnu Bay, as baby crabs can attach themselves to seaweed and float with it throughout the sea, such as, for example, in Matsalu Bay, Kotta said. “All it takes is a weather story to remove seaweed from rocks, and wherever the seaweed floats, the crab follows,” the marine expert said. If the conditions are right, the crab will most likely settle in its new environment.

Matsalu Bay, Kotta said, is a very suitable habitat for them, as the river flowing into the bay is rich in nutrients and the bay is shallow enough to help retain the summer heat.

According to Kotta, the conditions in Estonia are ideal for these crabs.
Not only Pärnu and Matsalu berries, but also Haapsalu and Narva berries are suitable for them. Although a little colder, the latter is fed by the Narva River, which provides the crab with abundant food.

Mud crabs do not attack humans and therefore pose no direct threat to us. Nevertheless, its spread in coastal seas could have serious environmental consequences. Kotta said crabs in Pärnu Bay ate almost all the shellfish on the seabed, and because the mussels in the bay provided a self-cleaning habitat, acting as natural filters, the water quality deteriorated significantly. . “Water treatment facilities now need to clean water much more efficiently to achieve the same results,” Kotta said. And as the natural balance shifts, the Gulf of Parnu could become more vulnerable to flooding, she added.

As crabs also feed on eggs and small fish, they can negatively impact fish stocks. “They eat anything they can get their claws on,” Kotta joked about the crab’s eating habits.

Both Kotta and Eschbaum say the mud crab is here to stay and unlikely to go away. “We’ll have to wait and see what this expansion brings,” Kotta added, “but there’s no reason to anticipate anything particularly positive.”

Eschbaum said the mud crab isn’t really edible even though it isn’t poisonous. “It’s a 2 euro coin, which is so small you can’t really eat it.”

Rhithropanopeus harrisii, the estuarine mud crab, can grow up to two centimeters wide. It has olive-brown or greenish-brown claws with white tips of unequal size and shape.

Follow ERR News on Facebook and Twitter and never miss an update!