Por Ramón Álvarez.
E-mail: gthsem@gualtierianus.com
Miembro de la Sociedad Española de Malacología
1.- What is the zebra mussel and how is it identified?
The zebra mussel (zebra mussel in English), whose scientific name is Dreissena polymorpha, was described by Pallas in 1771 from some specimens found in the Caspian Sea . Due to their resemblance to marine mussels, they were originally named with the genus Mytilus, but they are not phylogenetically related.
The zebra mussel is a freshwater bivalve mollusk, which also resists brackish waters, from the Black and Caspian Seas, where it lives in biological balance. It is not edible. Starting in the 19th century, it spread throughout Europe with the river navigation of the rivers in that area and in the eighties of the 20th century it began to invade North America with the maritime transport of goods. It has currently colonized numerous continental waters (rivers, lakes, lagoons and reservoirs) of North America and central and western Europe.
Its shell is triangular in shape and has a blunt outer edge, resembling a small marine mussel, but it only reaches three centimeters in length and has an irregular pattern of white and dark zigzag bands. It is attached to the substrate by a byssus, forming extensive and dense clusters similar to marine mussel plants. It has a preference for stagnant waters with little current. To learn more about its biology and reproductive cycle, you can consult the book by Castagnolo, Franchini e Giusti (1980: 56-59).
2.- How did the zebra mussel arrive in Spain?
Since the beginning of the 20th century there has been speculation about the possible presence of the zebra mussel in the Iberian Peninsula. There are quotes from the late 19th century that refer to its appearance in the Douro River near Porto (Portugal), but it was probably some accidental introduction of dead specimens by sea (Azpeitia Moros, 1933: 750-756). However, young specimens of zebra mussels were detected in a specific point in the middle basin of the Llobregat River, whose origin is unknown but knows that they disappeared with the floods of October 1982 (Altaba, 1992: 95).
Finally, fears about the possible invasion of this exotic bivalve have come true when in August 2001 a group of malacologists from Catalonia specialists in naiads and naturalists from the Freixe de Flix Nature Group (Tarragona) detected their presence in the lower Ebro (Catalonia), from Xerta to the Ribarroja reservoir.
But how could it reach the Ebro? It is not really known, but it is most likely that everything began recently with the arrival in the Ebro of a boat infested with zebra mussels or loaded with ballast water infested with larvae of this species. This supposed vessel would have spread zebra mussels to various points in the lower Ebro or perhaps only in the Ribarroja reservoir, the planktonic larvae rapidly expanding downstream with the river current. But other hypotheses cannot be ruled out either.
3.- Are there scientific studies on the zebra mussel?
In the US and Europe, hundreds of scientific works have been carried out on the biology and ecology of the zebra mussel, especially in relation to the ecological and socioeconomic damage it causes. The scientific literature on this matter is very abundant and there are many scientists specialized in the study of this species. However, in Spain hardly any work has been published on the zebra mussel because until now its presence had not been confirmed continuously.
The first specific article on the presence of the zebra mussel in Spain has been published in the magazine Quercus of October 2001 (Altaba, Jiménez and López, 2001), precisely to report the news of the appearance of this species for the first time in the lower reaches of the Ebro River in Catalonia. Another article that can be consulted is the text of a press release from the Spanish Society of Malacology that was issued as soon as it received news of this discovery, to provide general information on the seriousness of the introduction of this species (Álvarez Halcón, 2001 ).
Currently we are waiting to know the results of a research commissioned by the Ministry of Environment to the Freixe Natura Group of Flix (Tarragona) to study in detail the extent and speed of the biological invasion of the zebra mussel in the Ebro. Members of the Aiguabarreig Biological Station confirmed in mid-November 2001 the appearance of the zebra mussel from Fayón to Mequinenza, already in Aragón. This means that the zebra mussel is advancing rapidly upstream of the Ribarroja reservoir.
Dreissena polymorpha
4.- How does the zebra mussel invasion occur?
The entry route for the zebra mussel into an ecosystem free of this species is usually the release of water with larvae of this invasive mollusk transported in a boat or container from another place where it is present. Once the zebra mussel is introduced into an ecosystem, it may adapt perfectly to the environment and proliferate more or less quickly, but it may not be able to survive and disappear. This depends on the interaction of various environmental factors. The truth is that it has been introduced into the Ebro, successfully adapting to the new habitat and is now a true pest.
The larvae of the zebra mussel have a great capacity for dispersal, which favors a rapid expansion of this species up and down the river from the point where it was introduced into the river, covering all wet areas in lakes, lagoons and reservoirs. They grow rapidly and reproduce practically every month, in this way they soon form the characteristic mussels made up of numerous individuals per square meter, and their empty shells usually accumulate on the banks and bottoms of the channels. In the Great Lakes area of the United States, in 1988 there were 200 zebra mussels per square meter in one lake, the following year the density increased to 4,500 individuals per square meter in said lake, while in another lake it reached 750,000. per square meter in a few months (Schloesser, Nalepa & Mackie, 1996).
The first known data on the situation of this species in the Ebro in September 2001 gave the figure of about 500 zebra mussels per square meter (Altaba, Jiménez and López, 2001), after a few months the density of their populations can already be very serious. If these mussels are used as bait for river fishing, there is a risk of increasing the distribution area of this species. But in addition, river navigation in a channel partially infested with zebra mussels can cause a rapid and drastic expansion of this exotic mollusk in other unaffected places in the Ebro Basin. As if this were not enough, the capacity of many invertebrates to to colonize relatively distant places attached to the legs of birds. The Ebro is an important biological corridor, also for exotic species such as Dreissena polymorpha, and may be the definitive entry route for the zebra mussel to the rest of Spanish rivers and wetlands.
5.- What harmful effects does the zebra mussel produce?
The zebra mussel feeds on phytoplankton, competing with other native species for this food and increasing the level of organic matter, thus affecting the quality of continental waters. Therefore, it affects all wild fauna and flora due to the alteration of ecosystems. The zebra mussel is characterized by causing a great ecological imbalance by covering and carpeting the entire substrate in its path: river bed, boulders and rocks, riverside vegetation, shells of native bivalves (which are highly endangered, such as Margaritifera auricularia), hydraulic constructions of all types, turbines, drains, tanks, hulls, engines and ship anchors, piers, industries, hydroelectric plants, water purification plants, dams, weirs, irrigation ditches and canals, entry and exit channels of energy plants, etc.; and even completely obstructs pipes, pipes, irrigation conduits and hydraulic conduits in general.
The accumulation of thousands and thousands of shells of dead zebra mussel specimens modifies the substrate of river bottoms, riverside beaches and river sediments.
6.- Is there a real environmental risk caused by the presence of the zebra mussel?
When the zebra mussel is successfully introduced, and taking into account the precedents from other places in the world, we can speak of a serious environmental risk. This risk must be counteracted through preventive measures to avoid its introduction into unaffected areas and its proliferation where it is already present. But you can quickly go from being in a situation of environmental risk to suffering the harmful effects and observing them directly. The great demographic explosion that Dreissena polymorpha experiences once introduced, reaching high population densities, makes the progressive colonization of the different natural and artificial substrates that are in contact with the freshwater environment practically unstoppable (Hunter & ; Bailey, 1992). This threat to river ecosystems represents a serious risk of ecological and socioeconomic disaster in the short or medium term wherever it occurs, as evidenced by the extensive scientific literature that deals with the problem of the introduction, expansion and negative effects of the mussel. zebra.
7.- How can you avoid the harmful effects of zebra mussels?
Manual, chemical, thermal or radio wave methods to eradicate this species once introduced are very expensive and not always satisfactory for the conservation of ecosystems. In the US, the presence of this invasive bivalve is causing multimillion-dollar losses (2 billion dollars in about 10 years). Throughout the world, the efforts of scientists and public administrations have intensified to investigate and combat the introduction and proliferation of this species, with alert and control centers having been created for this purpose (Nalepa & Schloesser, 1993).
Efforts are focused on the effective protection of naiads or large freshwater bivalves, most of which are in danger of extinction, which are removed from their habitat and bred in captivity while the threat of the zebra mussel remains, to prevent them from cover them, preventing them from opening the valves. The clogging of hydraulic pipes is controlled by maintaining periodic checks and applying chemical or thermal methods to eliminate zebra mussel clusters. In addition, vessels sailing through infested areas must be fumigated with molluscicides before moving to unaffected areas, as well as the use of zebra mussels as fishing bait must be expressly prohibited. Special care must be taken with cleaning the surface of the boats and fishing equipment. Any route of natural or artificial introduction of the zebra mussel into an ecosystem or area free of its presence must be eliminated.
8.- What should be done when detecting the presence of zebra mussels in a new place?
The zebra mussel has already been detected in the lower Ebro in Catalonia and Aragon. In the coming months it is possible that its appearance will be detected in the Ebro upstream of Mequinenza and in the tributaries of the Ebro. If exhaustive control of navigation of all types in continental waters (rivers, canals, reservoirs, lakes and lagoons) and the use of live baits for fishing, it is possible that the zebra mussel can colonize unexpected places very far from the current focus of invasion. Public Administrations should act in coordination by creating alert and control centers as they already exist in other countries, with emergency telephone numbers for these cases. While these centers do not exist, as soon as their presence is detected in other places, the Nature Protection Service of the Civil Guard (SEPRONA) must be urgently notified to inform them of this fact, and in turn it is necessary to notify the Department of the Environment of the Autonomous Community where this species is detected.
9.- Can the presence of the zebra mussel affect the National Hydrological Plan?
Everyone is aware of the social and political discussion surrounding the National Hydrological Plan, recently approved in Spain; But the intention here is not to argue about it, but only to give a simple objective explanation about how the presence of the zebra mussel can affect this project.
The implementation of the National Hydrological Plan implies a transfer of Ebro waters to other Spanish Mediterranean hydrographic basins. If this transfer is carried out without avoiding the elimination of the zebra mussel at the point where the waters to be transferred are taken, it is normal for this dangerous exotic mollusk to colonize the continental waters of the Autonomous Communities that receive those waters infested with larvae of Dreissena polymorpha.
From a legal point of view, the introduction of exotic species that alter the ecological balance of ecosystems is illegal, and this could occur with the water transfer provided for in the National Hydrological Plan. But in the case of the zebra mussel, there would not only be the risk of altering ecosystems, but also the risk of seriously damaging the normal functioning of hydraulic infrastructure.
In this sense, the presence in the Ebro of this non-native invertebrate may negatively affect the National Hydrological Plan, unless the Ministry of the Environment can guarantee that said transfer will not cause the introduction of the zebra mussel into other hydrographic basins. In any case, the final decision adopted cannot be exempt from technical and political responsibilities, subject to a rigorous environmental impact assessment.
10.- Where can you find more information about the zebra mussel?
Given the scarce information on the zebra mussel in Spain, due to its very recent introduction, in addition to the cited bibliography, it is recommended to consult the data on the Internet using the search option <zebra mussel>, <zebra mussel> or <Dreissena polymorpha>. The zebra mussel should not be confused with another similar species called the "golden mussel" (Limnoperna fortunei), which causes the same type of damage.
One way to obtain information about the measures that the competent Administrations are adopting to prevent the introduction and proliferation of the zebra mussel is to request this information through the procedure established in Law 38/1995, of December 12, on the right to access to information on environmental matters.
Cited bibliography
Altaba, C. R. 1992. "La distribució geográfica i ecológica dels bivalves d'aigua dolça recents dels Països Catalans". Butlletí de la Institució Catalana d'História Natural, 60: 77-103.
Altaba, C. R., Jiménez, P. J. y López, M. A. 2001. "El temido mejillón cebra empieza a invadir los ríos españoles desde el curso bajo del río Ebro". Quercus, 188: 50-51.
álvarez Halcón, R. M. 2001. "El mejillón cebra: una amenaza para el Ebro". Ibón, Revista de naturaleza y divulgación ambiental, 15: 16-20.
Azpeitia Moros, F. 1933. "Conchas bivalvas de agua dulce de España y Portugal". Memorias del Instituto Geológico y Minero de España, 38(1): 1-458, y 39(2): 459-763, láms. I-XXXVI.
Castagnolo, L. Franchini, D. e Giusti, F. 1980. Bivalvi (Bivalvia). "Guide per il Riconoscimiento delle Specie Animali delle Acque Interne Italiane", 10. Verona, Consiglio Nazionale delle Ricerche.
Hunter, R. D. & Bailey, J. F. 1992. "Dreissena polymorpha (zebra mussel): colonization of soft substrata and some effects on unionid bivalves". The Nautilus, 106(2): 60-67.
Nalepa, T. F. & Schloesser D. W (Eds.). 1993. Zebra mussels: Biology, impacts, and control. Lewis Publishers, Boca Raton, Florida.
Schloesser, D. W., Nalepa, T. F. & Mackie. G. L. 1996. "Zebra mussel infestation of unionid bivalves (Unionidae) in North America". American Zoologist, 36: 300-310.
Recommended Internet pages:
http://www.fut.es/~freixe/novetats.htm
http://www.ngpc.state.ne.us/fish/whatsnew/zebra.html
http://www.science.wayne.edu/~jram/zmussel.htm
http://www.wes.army.mil/el/zebra/zebra.html
http://nas.er.usgs.gov/zebra.mussel/
http://www.usbr.gov/zebra/wzmtf.html
http://www.great-lakes.net/envt/flora-fauna/invasive/zebra.html
http://water.usgs.gov/wrri/96grants/seir1ar.htm
http://www.abi.org/publications/leastwanted/mussel.html
http://animaldiversity.ummz.umich.edu/accounts/dreissena/d._polymorpha$narrative.html
http://pflbau.boku.ac.at/private/wf/Dreissena%20polymorpha.html
http://lionfish.ims.usm.edu/~musweb/nis/Dreissena_polymorpha.html
http://www.vims.edu/adv/ed/zm/zmbkinfo.html
http://www.siue.edu/OSME/river/ZMMain.html
http://www.wa.gov/wdfw/fish/nuisance/zmegctf.htm
http://www.earthwave.org/zmussel.htm
http://www.schoolnet.ca/vp-pv/ces/e/zebra/zebrahom.htm
http://biology.usgs.gov/s+t/noframe/x274.htm
http://www.georgianbay.ca/gbafoundation/zebra/
http://www.siue.edu/OSME/river/ZMTTrunk.html
http://www.schoolnet.ca/revue/e/archives/january97/contents/page7a.html
http://www.rpi.edu/dept/bio/fwi/zebralinks.html
http://www.nationalatlas.gov/zmussels2t.html
http://www.dnr.state.oh.us/odnr/watercraft/brochures/zebra.html
http://www.zebra-mussels.com/zebra-mussels/index.html
Other information about MOLLUSCS
- Introduction
- Monoplacophores
- Polyplacophora
- Scaphopods
- Gastropods
- Bivalves or lamelibranchs
- Freshwater clams
- Daisy (Margaritifera auricularia)
- Zebra mussel (Dressenia polymorpha)
Other information about fauna in Aragón:
A small list of species in Aragon would be the following:
| Vertebrates | Invertebrates |
|---|---|
MammalsBirdsReptilesAmphibiansFishes |
MetazoansProtozoa |
|
images about the fauna in Aragon. photographs on invertebrates. beneficial animals for agriculture. | |
Also Aragon enjoys a diverse and varied Nature where passing by plants, animals, Geology, or landscapes we can arrive at a fantastic bestiary that lives in its monuments.
The information will not be complete without a stroll by its three provinces, with shutdown in some of its spectacular landscapes like Ordesa, the Moncayo, Monegros or by opposition the Ebro.
Also you can dedicarte to the intangible ones: from the legend compilation that also does to universal Aragon.