An updated assessment of Cabomba caroliniana in the Netherlands
Cabomba caroliniana (Cabombaceae, EPPO List of Invasive Alien Plants) is considered an invasive alien plant in Australia, Canada, China, India, Japan and in the USA and is also present in the EPPO region in Belgium, France, Hungary, the Netherlands and the United Kingdom. There was initially a lack of information on the probability of entry, establishment, spread and impacts of this species in the Netherlands, where its recorded distribution in this country has been classified as ‘restricted range’. A report has been produced to provide further information.
The probability of entry of C. caroliniana in the Netherlands is largely determined by the plant trade. C. caroliniana is one of the most frequently imported aquarium plants in the Netherlands, representing over 30% of the total import volume, and is widely available from Dutch and Belgian online retailers and in shops. The species is discarded from aquaria or deliberately planted in natural waterways. Although the Dutch Code of conduct includes this species, retailers have not included information on the invasiveness of this species on the plant labels, and in addition this species is often mislabeled as Cabomba aquatica.
Between 1986 and 2013, C. caroliniana has been recorded growing in water bodies covering a total area of 65 km² in the Netherlands. After 2006, there has been a rapid increase in the number of records. All shallow slow flowing and still waters in the Netherlands are considered to be potentially at risk of future colonization by C.;caroliniana. The species only reproduces vegetatively through plant fragments, and it has a strong reproductive potential. The probability of establishment of the species in the Netherlands was considered to be medium. Pathways of spread of the species are the following, ordered by importance: the plant trade, hobbyists, boats and water flow (high), aquatic weed harvesters, fishing equipment (medium) and aquatic birds (low). Concerning environmental impacts, C. caroliniana has been recorded in 3 Natura 2000 areas. Although the species has been recorded to have smothered native aquatic plants, in most instances there was no other macrophyte growth in areas where C. caroliniana became established. The plant exhibits an induced chemical response that reduces its palatability to herbivores. Regarding alteration of ecosystem functions, mass C.;caroliniana death and decay may deplete the available dissolved oxygen, which may then cause foul-smelling water and mortality of fish and other aquatic organisms. The risk for ecological impacts was ranked as high.
Evidence of socio-economic impacts of this species are limited to one site, and the cost of management action over a single year was 350 000 euros.
Future habitat alteration due to climate change and with high concentrations of phosphate in substrate may result in local widening of C. caroliniana’s distribution. Overall, the distribution classification of C. caroliniana is expected to remain as ‘restricted range’.
Sources
Matthews J, Beringen R, Lamers LPM, Odé B, Pot R, van der Velde G, van Valkenburg JLCH, Verbrugge LNH, Leuven RSEW (2013) Risk analysis of the non-native Fanwort (Cabomba caroliniana) in the Netherlands. 46 pp.