Brazilian Elodea - Provincial EDRR Species(Egeria densa)
Brazilian elodea is the most aggressive aquatic aquarium trade plant species globally and it is recognized under the Province’s Early Detection Rapid Response program. At this time, the infestation is localized to one area. It was recently released into the Richmond’s open drainage system; likely from an unwanted aquarium. It forms dense mats up to 4 metres deep in still and flowing water sources.
Description and Identification
Brazilian elodea is easily confused with other similar-looking aquatic plants. It is usually submerged, but can form dense mats on the surface of water. Leaves grow in whorls around the plants stem, making it appear very leafy. In the spring and summer, Brazilian elodea blooms with small, white, three-petal flowers that float on top of the water or slightly above.
Impacts on the Environment
Brazilian elodea adversely affects aquatic ecosystems by forming dense mat canopies that shade out native vegetation. Extensive mono-specific stands of Brazilian elodea cause poor habitat conditions for fish and other wildlife. It restricts water movement and traps sediments subsequently altering the chemical and physical characteristics of the ecosystem and decreasing local biodiversity.
Brazilian elodea can also have negative economic impacts, as it clogs rivers and drainage canals which then require constant maintenance and attention. In ponds and rivers it makes recreational activities such as fishing, swimming and boating difficult or impossible. It impedes flood capacity and storm drain systems which increases municipal maintenance costs.
The City of Richmond, in partnership with the Province of BC, has been managing a large infestation of Brazilian elodea within a large water feature near the West Dike since 2014. Brazilian elodea is listed as a priority species in the City’s Invasive Species Action Plan, and is a candidate for eradication in the provincial Early Detection Rapid Response Program. There are currently only two confirmed sites of Brazilian elodea in waterbodies in BC. Its presence in BC is particularly concerning due to the plant’s extreme ability to regenerate. A monotypic stand of Brazilian elodea restricts habitat opportunities for wildlife and has the ability to negatively alter the physiological characteristics of an ecosystem. Infestations can clog waterways leading to increased maintenance costs and a loss of important fish habitat and recreational activities.
There are currently no formal best management practices in BC to manage infestations. With support from the Province, the City implemented an integrated pest management approach to managing Brazilian elodea in 2017. Primary management activities to control the infestation have included:
- Creating and preparing community engagement material and raising awareness of the program through local meeting with the public;
- Containment using mechanical suction dredging and nets;
- Designing, constructing and installing a project-specific weir system to control water levels in the drainage canal;
- Completing geo-spatial inventories to monitor regeneration;
- Controlling water levels each season during winter months to expose elodea and its roots to freezing temperatures;
- Manipulating the exposed soils to further expose and stress the plant roots;
- Removing biomass from the water column with specialized, custom-built diver-assisted suction dredge equipment never utilized in the Lower Mainland at the time
To date, the integrated management approach has successfully reduced the infestation by approximately 90%. In addition, the soil manipulation has acted to naturalize the area and the City has noted a resurgence of native vegetation and wildlife back to the area.