Polski
“Once the fish, frogs and crayfish,
came up with this idea,
to leave the pond…”
Jan Brzechwa
All watermen (and non-watermen) have been following the situation in the Oder River for a year in suspense. Leaving aside its direct and indirect causes, the ecological disaster that hit the river in the summer of 2022 showed us the consequences of ecological invasions in a very drastic and blunt way. It may have been especially shocking to those who have not yet realized the dangers that invasive species can bring. And ecological invasions happen all the time. Only most often they are quiet, unspectacular. Often unnoticed by the layperson. Until…
To invade, a species must first hit an area, find favorable conditions, establish itself, and then spread. It can be brought in unintentionally, as a “stowaway,” in ballast water, attached to the hull of a ship (the canonical example is the variegated crayfish clam Dreissena polymorpha) or misplaced in transported goods (remember the stories about spiders in bananas?). But it can also be brought in completely intentionally, as an object of trade. This is how exotic plants and animals, for example, come to us. From there, it’s only a step to invasion.
Although well over 1,000 alien species have already been identified in Poland, only a few threaten biodiversity and ecosystem services and have been designated as invasive species. They belong to a number of taxonomic groups and range from large, easily recognizable mammals or trees to tiny, unnoticeable viruses, both terrestrial and aquatic organisms. Due to the thematic specificity of “Water Matters,” I will skip here the (otherwise very important) issue of terrestrial species, escapees from home gardens, crops or farms, and focus on aquatic species whose migrations affect our rivers and lakes.
How do alien species get into our waters?
Species migrate, that much is obvious. Only that these migrations usually take place within the limits of natural ranges, determined by biogeographical factors. Even if their range is changing for various reasons, such as climate change, the process is usually slow enough to be hardly noticeable on a human life scale. The situation is quite different when humans contribute to the movement of the species.
Routes of spread of alien species in Europe have been analyzed by scientists for at least two decades (the European Strategy for Invasive Alien Species was adopted in 2003. [1]) and generally fairly well recognized [2]. However, many people are unaware of this phenomenon, and some of us even unknowingly contribute to it.
One well-known example of the deliberate introduction of alien species into the aquatic environment is stocking for fishing or angling purposes, or the reintroduction of crayfish (e.g., brindle crayfish) to bolster the crayfish population, which has been depleted by the crayfish plague. Another lesser-known example might be the planting of ornamental mushroom cultivars in natural reservoirs for landscape beautification purposes (indeed, I have seen such practices myself). These plants can interbreed with our native mushrooms, creating taxa with intermediate characteristics of the parents. And the ornamental turtles? Bought as a large coin diameter pet, they suddenly turn out to be quite large, demanding and troublesome to maintain, and end up in the environment dumped in a nearby pond or ditch.
Have you wondered how many diasporas or survival forms of various alien species may be in the water left over after aquarium cleaning, and what happens to them when such water enters the environment?
As long as the climate is relatively harsh, probably most of them do not survive the low temperatures of winter and are naturally eliminated (although the small azolla fern Azolla filiculoides in ice-covered waters can survive – in the form of peak buds – temperatures down to -20°C). As the climate warms, with milder winters, more and more species are likely to survive, and who knows what will survive and stay with us for longer. This can be seen by studying ecosystems with heated waters, such as those resulting from the operation of power plants, such as the Konin Lakes (included in the cooling system of the Konin-Pątnów power plant), where more than 40 alien species have been found, including a massive occurrence of Vallisneria spiralis and numerous alien species of benthic macroinvertebrates, red-footed turtle and Nile tilapia [3].
Once introduced into the environment, alien species can spontaneously spread or be spread further via various vectors. Plant fragments are carried from one reservoir to another on the proverbial duck’s feet, entangled in fishing nets, with bait, stocking material, stuck to watercraft or on caltrops. Animal vectors are not much influenced by us, but our behavior is. When using the waters, it’s a good idea to remember to rinse your boating, fishing or research equipment properly before using it in another body of water (guidance on recommended practices can be found in codes, such as those for recreational fishing or boating).
Algae cells can move in a similar way. In truth, the list of invasive species does not include representatives of this group, but phycologists have published papers on the effects of the emergence of invasive algal species outside their natural range, such as the tropical blue-green alga Cylindrospermopsis raciborskii or the brackish haptophyte Prymnesium parvum. The latter can hardly be considered an alien species to Europe, since it is recorded in the marine coastal waters of the Baltic Sea (in Poland described from the Gulf of Gdansk by Bursa in 1938 [4]), but for inland waters it is. And on top of that, it is highly invasive.
Therefore, as many times as I hear the question, “Where did the golden alga come from in the Oder River?”, I feel like answering that the question is of the silly kind. Of course, it is possible to have some assumptions, based on more or less rational premises, but in the case of most of the species that have been swamped and spread, no one can responsibly and with certainty answer such a question.
Not every alien species is invasive
The mere appearance of a species outside its natural range is not yet a problem. The problem begins when such a species, for various reasons, finds a niche there to develop and reproduce. And if it gets too comfortable, multiplies too abundantly and spreads too widely, it can gain invasive status (known as IGO). For example, the widespread in Polish waters Canadian urea Elodea canadensis has lived with us for more than 100 years, and yet it does not show aggressive behavior. Even when it appears as part of the flora, it remains in small numbers [5, 6]. Moreover, it has been reported to be phasing out in many countries in recent years.
In contrast, its relative, the delicate soak E. nuttallii, which entered Europe with a delay of a century or so, and has already managed to spread aggressively in many waters, massively displacing native species, behaves quite differently. It can also happen that an alien species, originally not showing invasive traits, begins to multiply and behave aggressively. The key to this phenomenon is a change in environmental conditions, such as an increase in temperature or water salinity. If the factor blocking the reproduction and invasion of the woolly-eyed crab is that the salinity of inland waters is too low, what happens if that salinity increases?
The total number of alien species of plants, animals and fungi included in the database of the Institute of Nature Protection of the Polish Academy of Sciences is 1771(IOP PAN, accessed in June this year), but there are probably more in reality. The vast majority of them are recorded incidentally, and only some form reproducing populations. And only some have been recognized as invasive species and listed as IGOs in accordance with the Decree of the Council of Ministers of December 9, 2022 on the list of invasive alien species posing a threat to the Union and the list of invasive alien species posing a threat to Poland, remedial actions and measures aimed at restoring the natural state of ecosystems (Journal of Laws 2022 item 2649).
Of the 88 plant and animal species included in the regulation as posing a threat to the Union (including 68 species subject to rapid eradication and 12 widely distributed), about athird are aquatic species. Fortunately, not all of them are listed in Poland.
Among those widely distributed in our waters are primarily fish – Amur cheekbait, sun bass or grasshopper (gobies and dwarf catfish were not included in the list, but the black catfish, which is rare in our country, was included), striped and California crayfish, woolly-eyed crab and ornamental turtle. Others, such as the delicate soak and the marbled crayfish, are dangerously increasing their numbers and expanding their range, which means a worsening ecological problem. Other species on the list have either been recorded incidentally, occur sporadically, in single habitats, or have not yet been identified in Poland at all. Let’s not delude ourselves, sooner or later they will appear in our country as well.
How do aquatic IGOs affect the nature and ecosystem services of our waters?
Each invasive species is actually a topic for a separate story. However, the primary impact of IGOs on the natural environment is similar in nature, regardless of species, and concerns competition with native species for environmental resources. Thanks to a lack of natural enemies, greater tolerance to unfavorable conditions, faster reproduction rates or other reasons that are not always fully explained, invasive species fare better in their new environment than indigenous ones, gaining a competitive advantage over them in the struggle for food, light, development and reproduction sites.
Submerged hydrophytes, such as the delicate soak, Carolinian cabomba or (as yet unrecorded) great lagarosyphon, as well as Brazilian and pink-leafed decoys, show the ability to grow massively and produce huge amounts of biomass. Abundant populations of these species can overgrow the entire water column or form detached, free-floating mats that cut off light access to deeper zones of the reservoir. By competing with native species for food resources and light, they cause them to recede until they are completely displaced. For example, in Probarskie Lake, the delicate urea, from its first listing in 2017, took over the dominance in the phytolittoral within 2 to 3 growing seasons, occupying 80% of its area and reducing the biocenotic diversity index by half [7].
Invasive pleustophytes, or plants with floating leaves, such as the aforementioned small azolla or water hyacinth Eichhornia cressipes (so far recorded only sporadically, for example, in the heated waters of the Konin Lakes), are able to form extensive mats of considerable density and thickness, floating on the surface of the reservoir and cutting off the flow of light and oxygen to the deeper layers. Beneath the surface of such dross, under oxygen-deficient and light-limited conditions, many species are unable to cope.
American crayfish (brindle, signal) or ornamental turtles compete with European species (the former with the noble and mud crayfish, the latter with the pond turtle) for space and food resources. They are also vectors of pathogens and parasites, posing a threat to animals and even humans. Foreign crayfish are primarily carriers of the Aphanomyces astacilarvae , causing crayfish plague,which has decimated European crayfish and is still a threat to them. Also, invasive fish are food competitors to native species because they deplete the food base. Locally, they can cause drastic changes in trophic systems and species composition, reducing abundance, among other things. species of special concern. They are also transmitters of numerous parasites.
Those who think that biological invasions are a purely natural issue, affecting only flowers and birds, but not humans, are mistaken. Well, no, because the negative impact of IGOs on ecosystem services can be just as severe.
The nuisance of invasive aquatic plants is related to their massive growth. Dense, dense populations create difficulties for recreational and commercial use of reservoirs, impair boat engines, make fishing and commercial fishing difficult. If they are highly constricted, they can lead to pipe clogging, hinder water abstraction in hydropower systems (clogging turbines and causing them to corrode) or water abstraction for public supply for food and other needs (negative impacts on water quality and the infrastructure associated with the abstraction of this water).
Thick mats formed by rapidly multiplying plants restrict the flow of water in watercourses, reduce the effectiveness of drainage channels, blocking them, which necessitates maintenance work. By growing en masse in farm ponds, they can hinder the growth of fish and, in extreme cases, lead to reduced or collapsed production.
Alien fish species have a negative impact on native species of economic importance, harvested from the wild and raised in ponds and fishing grounds. Through competition, predation on eggs and fry, and as a vector for parasites, they can reduce the production (abundance and biomass) of species used to supply the population with food. As a parasite vector, they increase the risk and frequency of infecting cultures.
Invasive species of invertebrates also cause various types of economic losses, mainly due to the overgrowth of hydraulic facilities or fishing nets. Such behavior is exhibited, for example, by the crayfish clam Dreissena polymorpha or the eastern bollworm Chelicorophium curvispinum.
Fighting the invader – do we stand a chance of winning in a clash with IGOs?
Attempts to eradicate aquatic IGOs from the environment have met with moderate success or have not had the lasting, desired effects. It’s a bit like weeding a lake of weeds or picking potato beetles from a potato crop. To make things even more difficult, the role of alien species, even invasive ones, at least in the aquatic environment, is not unequivocally negative. There has been controversy over the use of the variegated crayfish as a reservoir cleansing organism, popular especially in Northern Europe. Large colonies of this mollusk with a high filtering capacity significantly reduce the turbidity of the water, producing a positive ecological effect.
The delicate soak behaves similarly, with its mass occurrence contributing to the maintenance of a clear-water state in lakes. This species has a higher tolerance to elevated trophic conditions and thrives where perhaps our native species would not persist anyway due to eutrophication. Of course, the mass emergence of an invasive species leads to a drastic decrease in taxonomic diversity. The question is whether we prefer the dominance of alien macrophytes or a phytoplankton-dominated turbid water state.
However, a foreign species, especially an invasive one, is generally an undesirable element. The term ” biopollution” is sometimes applied to IGOs, mainly aquatic ones. The concept was introduced by Elliott in 2003. [8] and accepted in biological invasion science. They were used to develop the concept of assessing the level of biological pollution [9], as well as to define criteria for good ecological status in accordance with the Marine Strategy Framework Directive.
Polish methodologies for assessing the ecological status of waters address the problem of alien species very little, and remain largely blind to them [7]. Perhaps because they were developed 10 to 15 years ago, when the problem of ecological invasions in our waters was not so pressing. It looks like it’s time to review this approach.
In the article, I used, among others. From the works:
[1] Genovesi P., Shine C., 2004. European strategy on invasive alien species. Bern Convention, Nature and environment No. 137, Council of Europe Publishing.
[2] Harrower CA, Scalera R, Pagad S, Schönrogge K, Roy HE. 2018. Guidance for interpretation of CBD categories on introduction pathways. https://circabc.europa.eu/sd/a/738e82a8-f0a6-47c6-8f3b-aeddb535b83b/TSSR-2016-010%20CBD%20categories%20on%20pathways%20Final.pdf.
[3] Najberek K., Solarz W., 2011. Konin Lakes as an outbreak of alien species invasion in Poland. [w:] Głowaciński Z., Okarma H., Pawłowski J., Solarz W. (eds.) Gatunki obce w faunie Polski. II: 614-623.
[4] Bursa A., 1938. A note on several noteworthy plankton species hitherto unknown from the Gulf of Gdansk. Hel Marine Station Bulletin, 3: 63-68.
[5] Kolada A., Kutyla S., 2016. Elodea canadensis (Michx.) in Polish lakes: a non-aggressive addition to native flora. Biological Invasions 18: 3251-3264.
[6] Ceglowska A., Jusik S., Samecka-Cymerman A, Klink A, Szoszkiewicz K., 2017. Habitat requirements of Elodea canadensis Michx. In Polish rivers. Oceanological and Hydrobiological Studies 46: 363-378.
[7] Kolada A., Pasztaleniec A., Bielczynska A., Kutyla S., 2022. Taking over the dominance of the macrophyte community by Elodea nuttallii (Planch.) H. St. John is poorly reflected in ecological status assessment results. Aquatic Invasions 17(4): 516-542.
[8] Elliott M., 2003. Biological pollutants and biological pollution – an increasing cause for concern. Marine Pollution Bulletin 46, 275-280.
[9] Olenin S., Minchin D., Daunys D., 2007. Assessment of biopollution in aquatic ecosystems. Marine Pollution Bulletin, 55 (7-9), 2007, 379-394.
