Preventing Further Introduction and Spread of Aquatic Weeds Through the Ornamental Plant Trade

Sixteenth Australian Weeds Conference Preventing further introduction and spread of aquatic weeds through the ornamental plant trade Andrew Petroeschevsky1 and Paul Champion2 1 NSW Department of Primary Industries, PMB 2 Grafton, New South Wales 2460 2 National Institute of Water and Atmospheric Research, PO Box 11-115, Hamilton, New Zealand Email: [email protected] Summary The trading of aquatic plant species for The aquatic plant trade distributes large numbers aquarium and pond plant purposes poses an ongoing of potential weeds throughout Australia, thus increas- risk of both future introductions and spread of aquatic ing propagule pressure and the potential for new natu- weeds in Australia. Over 400 species of freshwater ralised populations to occur (Kolar and Lodge 2002). aquatic plants have been legally traded in Australia There is also a direct link between the aquatic plant over the last 30 years. Some of these have been known trade and infestations due to wild harvesting opera- weeds whilst little was known about the weed potential tions by aquatic plant suppliers. To meet consumer of others. demand, aquatic plant suppliers traditionally ‘seeded’ To address this concern the National Aquatic waterways and returned later for wild harvesting. Weeds Management Group, in partnership with state This practice resulted in many aquatic weed governments, aquatic plant trade industries and New infestations in waterways on the eastern seaboard, Zealand’s National Institute of Water and Atmospheric particularly in or near urban areas. Some aquatic Research, initiated a Weed Risk Assessment (WRA) suppliers still continue this practice, despite several of aquatic plants within the ornamental plant trade. recent industry initiatives to raise awareness amongst Using a WRA model tailored to aquatic plants the their constituents regarding responsible aquatic plant process has to date identified 25 high-risk aquatic trading. Subsequent spread by water movement or plant species for recommended national bans. Twenty via contamination of watercraft, nets and drainage one other species with significant weed potential were machinery led to further dispersal from these initial identified but require further data to conduct an ac- weed sources. curate evaluation. The process ensures declarations will be based on BACKGROUND research conducted under Australian conditions and Previous attempts at national bans In 1982 the made in consultation with industry. National Committee on Management of Aquatic Keywords Aquatic weeds, Weeds of National Weeds developed a list of undesirable aquatic plants Significance, weed risk assessment, ornamental plant for aquaria purposes. This process used tier I and tier II trade. lists; the former recommending national ban from sale and the latter requiring further monitoring. In recent INTRODUCTION times the Australian Weeds Committee considered The contribution of the aquatic plants trade to the in- national bans on sale on more aquatic plants, include troduction and spread of aquatic weeds is significant. those on the 1982 tier II list, and had agreed to ban a Over 85 percent of declared and naturalised aquatic number of aquatic plant taxa. weeds in Australia were historically traded as aquari- The 1982 lists and the Australian Weeds Commit- um or pond plants. Studies in New Zealand identified tee recommendations removed, or proposed to remove, that 75 percent of their declared aquatic weeds were some of the worst aquatic weeds from sale. How- introduced through the aquatic plant trade (Champion ever, they didn’t address the issue of wild harvesting and Clayton 2000). practices potentially introducing and spreading new Natural transfer of introduced aquatic weeds species. The potential for plant suppliers to replace between catchments is uncommon, with few weed banned species with other species with similar weed species having seed spread by birds or wind, or being potential remained as little was known about many of solely asexual in their naturalised range (Champion et the plants within the trade. al. 2002). Thus human transfer between catchments, which are analogous to ‘islands in a sea of land’, Towards a risk assessment based approach The is the major dispersal mechanism for these species Weeds of National Significance cabomba strategic (Champion et al. 2002). plan acknowledged wild harvesting issues and 399 Sixteenth Australian Weeds Conference recommended promotion of safer alternative species as various weed lists (e.g. Csurhes and Edwards 1998, one solution (Agriculture and Resource Management Champion et al. 2002, Randall 2002, Randall and Council of Australia and New Zealand, Australian Kessal 2004, Groves et al. 2005, Barker et al. 2006, and New Zealand Environment and Conservation ISSG 2007) and recent reports of naturalisation (e.g. Council and Forestry Ministers 2001). However, this Weed Spotter Newsletters, CRC Weed Management process was later deemed to be unfeasible by National 2007). These species were further assessed by Weed Aquatic Weeds Management Group (NAWMG) due Risk Assessment (next section) and through discussion to difficulties of identifying and recommending safe amongst the TAG. alternatives on a national scale. In place of the ‘safe list’ the NAWMG recom- Risk assessment In New Zealand an aquatic weed mended a risk assessment and consultative-based risk assessment model (Champion and Clayton 2000) approach to plants currently within the trade. The aim has been used as a decision support tool to determine of this approach was, in cooperation with industry, to which cultivated freshwater plants should be banned identify those plants with high weed risk potential and from entry, or prevented from deliberate dispersal recommend through the Australian Weeds Committee through the nursery trade. The model scores attributes national sales bans for each. This concept utilises more such as habitat versatility, competitive ability, repro- science and consultation in aquatic plant declarations ductive output and dispersal, impacts, resistance to and is supported by the Pet Industry Association of management and potential distribution. Australia (A. Ramsey pers. comm.). A similar use of this model was envisaged in this The inclusion of industry representatives in the project, with modifications to cater for south-eastern project was also likely to provide assistance in the mainland Australian conditions as discussed by the evaluation process with information on aquatic plants TAG. Changes included removal of attributes such in their cultivation, length of time traded in Australia, as impedance of hydro-electric power generation and volume of trade and early identification of potentially impacts of freezing while increasing the importance weedy species. of competitive ability, the importance of fluctuating Funds were obtained from the Defeating the water levels, turbidity, increased salinity (southern and Weeds Menace Program to identify the extent of inland areas), irrigation and flood control. Additional potential weeds in the aquatic ornamental plant trade information specific to the trade was included, with and a technical advisory group (TAG) of industry, assessment of length of time and volume in the trade regulatory and scientific members. and whether the species is traded as an outdoor (i.e. pond) or aquarium plant. Length of time and volume MATERIALS AND METHODS in the trade were scored as having a decreased likeli- A project steering committee consisting of state gov- hood of a species becoming weedy if it had been ernment and aquatic plant trade industry representa- traded for over 25 years without naturalising. Pond tives developed and endorsed a project approach. plants were seen as a much greater risk of naturalising than tropical aquarium species, normally grown at a Identification of species in the trade An extensive constant 28°C. compilation of historic and current sales lists for Species with a weed risk assessment score greater aquatic plants in Australia was provided by Ed Fra- than 50 were recommended for a national ban from ser of Pisces Enterprises, Brisbane. Price lists from sale in Australia. A score less than this could still other Australian companies such as Wormborough, indicate significant weed potential and if a plant not Aquadepot and Austral Gardens were sourced and a known to be present in Australia scored greater than compilation of species made. Wherever possible iden- 40 (e.g. Stratoites aloides (47)) then its importation tification of these traded species was checked. A list should be prevented. of internationally traded plants was collated from an extensive database of aquarium species (Booth 2002) Competition trials Many of the currently traded and various texts (e.g. Slocum and Robinson 1996, species are not reported as weeds internationally and Oriental Aquarium 2002, Kasselmann 2003). Correc- some species that are weedy overseas may not be as tions for illegal species combination and synonyms problematic in Australian conditions. A series of ex- were made based on IPNI (2004). periments growing candidate species in competition with known weeds (WONS species) and indigenous Pre-screening of plants Lists of traded species plants have been initiated to assess potential weedi- present and absent from Australia were made. Amongst ness under a range of climatic conditions ranging from these lists, potential weeds were identified from central coastal Queensland to Central Victoria. These 400 Sixteenth Australian Weeds Conference experiments

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