Information on measures and related costs in relation to species included on the Union list – Cabomba caroliniana This note has been drafted by IUCN within the framework of the contract No 07.0202/2017/763436/SER/ENV.D2 “Technical and Scientific support in relation to the Implementation of Regulation 1143/2014 on Invasive Alien Species”. The information and views set out in this note do not necessarily reflect the official opinion of the Commission, or IUCN. The Commission does not guarantee the accuracy of the data included in this note. Neither the Commission nor IUCN or any person acting on the Commission’s behalf, including any authors or contributors of the notes themselves, may be held responsible for the use which may be made of the information contained therein. Reproduction is authorised provided the source is acknowledged. This document shall be cited as: Bickel, T.O. 2019. Information on measures and related costs in relation to species included on the Union list: Cabomba caroliniana. Technical note prepared by IUCN for the European Commission. Date of completion: 07/08/2019 Comments which could support improvement of this document are welcome. Please send your comments by e-mail to [email protected]. Species (scientific name) Cabomba caroliniana A.Gray Species (common name) cabomba, fanwort, Carolina fanwort, Carolina water shield Author(s) Tobias O. Bickel, Department of Agriculture and Fisheries, Brisbane, Australia Date Completed 07/08/2019 Reviewer Andreas Hussner, Duisburg, Germany Summary Highlight of measures that provide the most cost-effective options to prevent the introduction, achieve early detection, rapidly eradicate and manage the species, including significant gaps in information or knowledge to identify cost-effective measures. Cabomba caroliniana A.Gray (Cabombaceae) is a submersed aquatic macrophyte native to freshwaters of South and North America (Ørgaard, 1991). It is a popular aquarium species that has been introduced to the wild worldwide through unintentional disposal of surplus aquarium material and escape from culture for the trade. Today, it is a serious aquatic invasive species in many countries including Australia, USA (outside its native range), Canada, China and some European countries (e.g. the Netherlands and Germany) (Ørgaard, 1991; Les & Mehrhoff, 1999; EPPO, 2007; Wilson et al., 2007; van 1 Valkenburg et al., 2011; Hussner, 2012; McCracken et al., 2013). Another cabomba species, Cabomba furcata, is altering wetland ecosystems in Malaysia (Sharip et al., 2012). C. caroliniana can be found in a range of freshwater systems, but prefers still to slow moving waters (Ørgaard, 1991). Water clarity permitting, it can grow to considerable depths, but biomass is highest at 2-4 m (Bickel & Schooler, 2015). C. caroliniana readily grows from small stem fragments comprising only a single node and predominantly reproduces asexually in its introduced range (Bickel, 2016). While C. caroliniana can flower prolifically, seed production is rarely observed in its introduced range (Mackey & Swarbrick, 1997). However, even in its native range, seed production is low (Ørgaard, 1991). The history of the C. caroliniana invasion in Australia is an example of the potential of this plant for rapid spread and to become a significant aquatic weed. It was first recorded in Australia in 1967 and is today naturalised in four states (Victoria, New South Wales, Queensland and the Northern Territory), with populations spanning the entire eastern half of the continent from temperate to tropical regions (Mackey & Swarbrick, 1997; Schooler et al., 2006). It is considered a Weed of National Significance in Australia and considerable amount of financial effort and manpower is spent annually for management of this aquatic invader. C. caroliniana is currently not widely naturalised in the EU, but populations are present or have been recorded in Belgium, Croatia, Denmark, France, Germany, Hungary, Netherlands, Poland, Romania, Serbia, Sweden and the UK (EPPO, 2007; Hussner et al., 2010; Hussner, 2012; EASIN, 2019). The most detailed published information about C. caroliniana invasion and management in the EU comes from the Netherlands, where it was first recorded in 1986 (Matthews et al., 2013), but did not become problematic until 2005 (van Valkenburg et al., 2011). Cabomba caroliniana is legally prohibited to be imported, cultivated and traded under EU legislation. However, C. caroliniana was well established in the aquarium hobby for many decades (EPPO, 2006, 2007) and therefore it is likely that the plant is still cultivated in private aquaria and passed on between hobbyists. In addition, there are several C. caroliniana cultivars known in aquarium hobby circles, so the possibility that enthusiasts could illegally introduce and move specific cultivars within and from outside the EU cannot be excluded. As Cabomba species are morphologically difficult to distinguish unless flowering (Ørgaard, 1991), C. caroliniana can be incorrectly identified as C. aquatica or C. furcata, and unintentionally introduced into the EU (Matthews et al., 2013). Even for experts, the Cabomba species are difficult to distinguish unless flowering, therefore it is very difficult to prevent accidental importation of C. caroliniana through morphological screening of Cabomba material imported to the EU. Additional training of customs officials at borders on identification of these species is needed and, once DNA-barcoding techniques can be carried out routinely by non-specialists, this technique could also be used. The rapid spread and potential to become a serious aquatic weed highlights the importance of containment and management of existing populations of this species in the EU. As C. caroliniana has been a weed worldwide, there is a range of control options available that have successfully been used. In general, no single method is superior in the control of aquatic invasive plants, but they all have their strengths and limitations, and have to be used within the right context (e.g. management goals, scale) (e.g. Hussner et al., 2017). Furthermore, experience shows that the integration of various tools greatly improves aquatic plant control. The choice of control methods used to manage C. caroliniana in EU member states will be similar options for 2 other submersed aquatic weeds, but specific control tools and costs will always be situation and location dependent. Therefore, the control options, their costs and limitations described in this document are only intended as a reference. A detailed management plan needs to be developed for individual infestations to increase control efficiency and chance of success. Due to the difficulty of controlling cabomba once it is established, containment of existing populations and prevention of further spread is critical. Containment can be achieved through user access restrictions, strategic control of C. caroliniana to reduce the risk of fragment uptake and transport, the provision of weed hygiene facilities and public awareness campaigns. Similarly, early detection of new invasions is critical. This can be achieved through active government surveillance in high risk areas and through citizen science monitoring programs. Early detection of new infestations will increase the chance of eradication when populations are still small. Herbicides are effective in controlling C. caroliniana, but due to the legal restrictions prohibiting the use of herbicides in aquatic habitats in the EU, other control methods listed in this document need to be selected. Choice of control method mainly depends on the size of the infestation and the local situation. Small populations can be removed manually through divers or by mechanical means, e.g. suction dredging. Once fully established in larger systems, maintenance and prevention of spread can be achieved through the application of mechanical mowers, harvesters and strategic manual harvesting, or the installation of physical barriers such as benthic blankets. Currently, there are no biological control options available, but these could complement management in the future - the use of grass carp could be a useful tool to manage C. caroliniana. This review of C. caroliniana control options is not exhaustive. Further methods are described in the literature that could become novel tools, such as the example of pH manipulation through the addition of lime (liming). The pH of water determines the chemical form in which carbon is available for photosynthesis. C. caroliniana depends on free CO2 for photosynthesis, which is only available sufficiently in neutral to acidic water. Experimental work found significant biomass reduction in C. caroliniana when the pH in aquaria was elevated to pH 9-10 by addition of lime (James, 2011). The environmental effects of elevating the pH to such high levels in a natural water body would have to be weighed against any benefits of removal. However, even an elevation of the pH to 8 might be enough to reduce the competitive advantage of C. caroliniana and thus potentially reduce its abundance (Bickel & Perrett, 2014). The rapid advance in DNA technologies also means that in the near future there might be routine tools available for rapid species identification through DNA-barcoding on border entry points (Ghahramanzadeh et al., 2013) and eDNA methods for the detection of C. caroliniana in the environment (Edmunds & Burrows, 2019). The availability of eDNA techniques would be invaluable for monitoring to prevent spread and reappearance post