Once the Asian clam, Corbicula fluminea, colonizes a habitat, its eradication is impossible. Therefore, it is in education, awareness, prevention and control that the scientific community demands attention. This invasive species has been present in Galicia since 1989, when it was first identified in the Miño River and can currently also be found in other rivers, such as the Ulla or the Sil. The researcher from the University of Vigo Noé Ferreira has spent three years analyzing its pattern and speed of dispersion, as well as the ecological characteristics that can be applied in the management, prevention and control of this exotic species in Galicia. The conclusions of his study are included in his doctoral thesis, supervised by the professor of Ecology Isabel Pardo, within the doctoral program Marine Science, Technology and Management, Do*Mar.
Currently, this invasive species has already colonized the Ulla, Mero, Deva, Sil rivers and isolated environments such as the Centeáns lagoons, although since 2008 there seems to have been a period of stagnation in terms of its extension to new rivers, as the researcher highlights.
97 sampling points in Galicia and Portugal
To carry out his study, Ferreira established a total of 97 sampling stations in 30 rivers and three lagoon systems, both in Galicia (71 points in the Anllóns, Avia, Eume, Eo, Ladra, Landro, Lérez, Louro, Masma, Mandeo, Miño, Neira, Sil, Sor, Tambre, Tea, Ulla and Umia rivers and in the artificial lagoon systems of Centeáns, in Porriño) and in northern Portugal, where he established 26 stations. The results confirm the presence of C. fluminea in the Miño river from its mouth in the Guarda to Ribadavia, and show that the species has also colonized the Sil river. The researcher explains that more recently this invasive species has colonized new basins and, he adds, “today we can find it in the Ulla and Mero rivers, where year after year it has advanced upstream to the Cecebre reservoir”. In the north of Portugal they found it in the Alva, Douro, Ferro, Limia, Mondego, Rabaçal, Tamega, Tuela and Vouga rivers, as well as in the Mira and Pateira de Fermentelos lagoons.
Field data collected in Ferreira’s study show an average upstream dispersal of 3.6 km yr-1 in the Miño, Ulla and Mero rivers, results he explains, are similar to those obtained in other European basins, such as the Elbe and Rhine (2.4 km yr-1). In the Miño-Sil basin, the Asian clam colonized 197 km upstream from the mouth, indicating a maximum dispersal rate of 9.2 km yr-1. “This colonization of the upstream basin occurs despite a succession of reservoirs that exceed 25-30 m in height, which can only be explained by the association of the species with human activities, for example its use as bait for sport fishing,” he notes.
Prevention strategies
One of the main routes of entry of exotic freshwater aquatic species occurs through the ballast water of large ships. To address this problem, the exchange of ballast water at sea has been identified as an effective tool but can be improved if the temperature in the tanks is increased and with it the metabolic rate of the potential invasive species transported. Another route of entry of invasive species is the animal trade. “To address biological invasions, good prevention is key and for this, an assessment of the invasive potential of the species before their commercialization as companion/ornamental animals is necessary, in addition to a joint effort between administrations, NGOs and the different actors involved in the dispersal.”
Consequences of the invasion
When prevention strategies fail and the arrival and establishment in the new habitat occurs, the environmental risk assessment allows the establishment of management strategies that provide a rapid response to biological invasions. In this sense, the work developed allows factors never evaluated until now, such as calcium, to be taken into account in the establishment and dispersal of the Asian clam.
In his thesis, the researcher also evaluates the impact that these invasive species have on other species, such as freshwater mussels (naiads), one of the most threatened animal groups worldwide. One of these native mollusks, the Unio delphinus, “has recorded a decline of up to 30% in its populations in the last 30-40 years”. With an eye on the future, and given that global warming “is a reality today”, Ferreira also evaluates the impact of these invaders in a warming scenario during increasingly frequent heat waves and based on the predictions made by the IPCC. “The results are worrying, since the introduction of the Asian clam decreases the capacity of native naiads to overcome extreme climatic events such as heat waves”. However, ecosystems have their own biological control strategies without human intervention. In this sense, part of the community has adapted its diet to this new resource, increasing its numbers in response to the invasion of C. Fluminea. One consequence is the increase in the population of species such as the Oystercatcher (Haematopus ostralegus), a wading bird that feeds mainly on molluscs in the Miño estuary.
But this new trophic resource is not only used by native species, and generates new challenges for the future. The introduction of exotic toad conchs could pose a new conservation problem for native toad conch species due to a better use of this abundant resource. However, while the distribution of the Asian clam throughout Galicia is increasing, other species such as the zebra mussel have not been recorded in the community. In this sense and although of limited application, the current plans for the reintroduction of sturgeon in Europe could represent a tool for biological control of the zebra mussel at least in the early stages of invasions.
Source: DUVI
