Bucca ragwort – an overlooked invasive species in Poland

In early August of this year, the list of invasive alien species that pose a threat to the European Union (IGO) expanded with the addition of three more: the rosette pistia plant (Pistia stratiotes), the ribbed adelgid fish (Fundulus heteroclitus) and the clawed platypus frog (Xenopus laevis). All live in aquatic environments. So does an invasive species of bivalve mollusc – the Bukhian rockfish – which seems to go completely unnoticed. Its presence in our waters – specifically the Szczecin Lagoon – was written about as early as 2016. [4, 5, 6]. A plague of gillnets of the Oder River due to a catastrophe in 2022. revealed that the species can also be found in the lower sections of the river [3]. However, unlike the invasive bivalves themselves, information about them has not spread further.

Overlooked invasion

In the shadow of the mass mortality of fish, mussels and other gill-bearing animals of the Oder River is hidden another drama, which had its beginning a nice few years earlier – the invasion of the Bug River rockfish(Dreissena rostriformis, syn. D. bugensis, D. rostriformis bugensis, colloquially ang. “quagga mussel”, quagga mussel). One can search in vain for entries about this species in the Polish Wikipedia, in textbooks for students of fisheries or in the database of IOP PAN on alien species recorded in Poland. EU and national regulations on how to eradicate IGO are silent about it.

None of the hundreds of environmental assessment reports I’ve analyzed mentions this invasive mussel, although it could theoretically have been present throughout Poland for a nice couple of decades before being officially identified. It’s been 20 years since it was detected in the Romanian section of the Danube, 19 since it appeared in the canals connecting the Rhine and Main rivers to the Danube, and 10 since it wandered into the Thames near Heathrow. The damage it causes has been known for decades from neighboring countries, Switzerland and the Great Lakes of the US and Canada [2].

This quagga will not die out, rather others will die out because of it

The Bucasian ragwort is native to the Southern Bug in the Dnieper River basin. Like many other Pontocaspian species, it has become extremely expansive in Western Europe, Canada and the United States. It differs from the well-known Dreissena polymorpha variegated crayfish, among other things. larger size (adult male fingernail, 2 cm wide), more rounded shape and lighter shell with fading (smudging) stripes.

Hence its English name, “quagga mussel,” referring to the coat of the quagga Equus quagga quagga (an extinct relative of the zebra, in which the stripes faded on the belly, instead of remaining equally pronounced throughout its length). The previously imported variegated rockfish is called “zebra mussel,” because its stripes remain more pronounced. Nevertheless, both are highly variable in shape and color; for example, many pale and even albino specimens are found in Lake Erie [1].

“Quagga-thrasher” is able to inhabit deeper waters than “quagga-thrasher”, with less stable, muddier substrates. It can displace it in several ways: by sucking up its larvae, competition for space and complete deprivation of food, known as “starvation. stunting.

Great purge, great famine

One adult crayfish filters at least a liter of water a day. Huge reserves of phosphorus and calcium are deposited in the pseudofecal matter and shells of dead clams. Pseudo-fecal matter is particles taken up by the clam that are too large or inedible and are excreted through a gully trap (rather than a spout trap, which is different from true fecal matter). The Bucca ragwort has become the most important regulator of the phosphorus cycle in at least four Great Lakes of North America [2].Their bodies can accumulate 300,000 times more toxins than either water or sediment. And since for every kilogram of predatory fish there are 3-4 kilograms of biomass and necromass of crayfish, you can guess what kind of threat this poses to the animals that feed on these mollusks [2].

Sail and bag

The success of the invasion is facilitated by the biology of the crayfish. They are the few lamellate bivalves in our freshwaters, in which the wildly swimming larva stage, called veliger (sailor), typical of oceanic forms, is preserved. The rest of the bivalves from the rivers and lakes of Central Europe and North America do not have a larvae stage at all (the globefish) or produce a glochidium, parasitizing fish (the scaphopods and pearlfishes). The lack of larvae severely limits its ability to expand. Having glochidia makes reproduction dependent on specific types of fish, their condition and the quality of the watercourse.

The native scaphopods suffer from the invasion of Sinadonta woodiana, because the fish, after contact with its larvae, become hypersensitive and drop or otorrhize the young of the native bivalves. It is worth noting that free-swimming veligers will be encountered in other expansive bivalves of the order Veneroidae: Corbicula corbicula and the Atlantic rank of Rangia cuneata, discovered in the Gulf of Gdansk. Corbicula corbicula also belongs to the veneroidae. They are such “bagworms of the mollusk world” – their eggs, and later embryos, develop in nesting bags in the gills of both parents, after which they are released in the form of miniature bivalves. In negligible numbers, add, for example, 2 to 10 in the deep-sea pea mollusk, and an average of 20-24 in the ribbed scoop [1, 2, 4, 5].

In a pile of strength

Another distinguishing feature of crayfish in freshwater fauna remains their ability to form colonies (shoals) on hard substrates, a thing typical of true mollusks (mussels) or oysters, unique in lakes and rivers. Culicoids and scaphopods burrow in soft or loose sediments. Racicids like sea mussels (with which, by the way, they are notoriously confused in popular science works translated by translators) can clog hydro installations.

Adults of D. bugensis are able to survive 3-5 days of exposure to the air (drying out of a body of water/stream, transport on boats or fishing equipment). In the States, stocking with native fish or reintroducing rare species is increasingly being abandoned precisely because of the risk of importing quagga into waters previously free of them. The golden remedy against this “Bug infestation” is supposed to be the red-eared sunfish Lepomis microlophus – a fish particularly fond of mussels and snails, and highly valued by anglers [1, 2, 4].

Other preadaptations to invasion are similar to many other kenozoans (invasive alien species, analogous to plant kenophytes): tremendous fecundity, high survival rates at all life stages, a certain plasticity of the life cycle and of individual individuals [1].

The glories and shadows of the presence of the crayfish

When I was a young boy, schools organized student debates and judgments over the variegated crayfish. The term “useful pest” was coined for it. The damage to hydropower in Poland was not as significant as in other countries with more strongly developed sewage treatment plants and their own nuclear power. The beaches remained sandy, unlike behind Big Water. Instead, the advantages of the presence of rockfish were emphasized, such as the extraordinary cleanliness of the water, the return of macrophytes and valuable fish sorts, the increase in numbers and changes in the migration routes of game birds, especially shrikes.

Of course, not all the changes introduced by these mollusks were good. Declining oxygen concentrations, increasing acidification of the water, and finally the decreasing availability of phosphorus and calcium for the remaining organisms were cause for concern. There is a similar argument to be made about the Bukhian rockfish. It affects the established ecosystems in a similar way as the variegated rockcress, only more strongly. Finally, it is larger and heavier.

Photo. main: Public Domain/commons.wikimedia.org

In the article, I used, among other things. z:

[1] Imo, M., Seitz, A., & Johannesen, J. (2010). Distribution and invasion genetics of the quagga mussel(Dreissena rostriformis bugensis) in German rivers. Aquatic Ecology, 44, 731-740.

[2] Li, J., Ianaiev, V., Huff, A., Zalusky, J., Ozersky, T., Katsev, S. (2021). Benthic invaders control the phosphorus cycle in the world’s largest freshwater ecosystem. Proceedings of the National Academy of Sciences, 118 (6), e2008223118.

[3] Szlauer-Lukaszewska, A., Ławicki, Ł., Engel, J., Drewniak, E., Ciężak, K., & Marchowski, D. (2024). Quantifying a mass mortality event in freshwater wildlife within the Lower Odra River: Insights from a large European river. Science of The Total Environment, 907, 167898.

[4] Wozniczka, A., Wawrzyniak-Wydrowska, B., Radziejewska, T., & Skrzypacz, A. (2016). The quagga mussel(Dreissena rostriformis bugensis Andrusov, 1897)-another Ponto-Caspian dreissenid bivalve in the southern Baltic catchment: the first record from the Szczecin Lagoon. Oceanologia, 58(2), 154-159.

[5] Wozniczka, A., Wawrzyniak-Wydrowska, B., Radziejewska, T., Soroka, M., & Skrzypacz, A. (2016). Dreissena rostriformis bugensis in the Gulf of Szczecin-the first record in the waters of Poland. Folia Malacologica, 24(1).

[6] Wawrzyniak-Wydrowska, B., Radziejewska, T., Skrzypacz, A., & Wozniczka, A. (2019). Two non-indigenous dreissenids(Dreissena polymorpha and D. rostriformis bugensis) in a southern Baltic coastal lagoon: variability in populations of the “Old” and a “New” immigrant. Frontiers in Marine Science, 6, 76.