Oxygen Weed

Outside of its native range, oxygen weed only exists as a female plant. Thus, propagation occurs through the dispersal of female plant parts throughout the aquatic ecosystem. This can occur through water currents breaking a fragment of the plant off and bringing it to another spot in the system, where the fragment can become embedded in the substrate and begin growing. Fragments of plants can also be moved and propagated through the passing by of boats, nets, and other aquatic equipment. 

Oxygen weed is dormant in winter and emerges in the spring. The female plants’ flowers sprout from summer to early autumn. The growth rate of oxygen weed decreases as sunlight hours per day decrease during the fall.  

Oxygen weed grows strictly in aquatic habitats. Its preferred temperature is between 20°C and 23°C, with a maximum of 25°C. Under 10°C, oxygen weed will fail to grow, and an established population will become dormant, meaning it could still survive in cooler Canadian waters. Oxygen weed grows best in still water ecosystems with little water flow and can grow in depths of more than 6 meters deep. Growing in dense mats, oxygen weed will cover other aquatic plants, creating an ecosystem for where other plants find it difficult to grow. Oxygen weed is a hardy plant that can leech nutrients from deep in the soil, meaning it can grow and flourish in otherwise nutrient scarce aquatic ecosystems (Bickel, 2011). However, oxygen weed grows best when high sunlight is accessible, and therefore may not thrive in opaque or highly turbid waters. Given oxygen weed’s hardiness and ability to grow in low nutrient areas, it is able to spread and grow in a variety of water bodies, such as lakes, dams, streams, rivers, and canals which can lead to broader socio-economic impacts.  

Due to the growth structure of oxygen weed, an initial sign of infestation may be the dying off of native plants, coupled with the dense growth of the mat-like structure of oxygen weed. Oxygen weed’s growth behaviour and persistence will initially create a less biodiverse ecosystem, which in turn has initial short-term affects on the survivability of native species, such as plants and insects. Amphibian and reptile survival within an aquatic ecosystem also acts as a warning sign that a habitat is decreasing in health. Due to their permeable skin and important roles in the ecosystem, reptile and amphibian survival and health acts as an indicator for the health of their environment, and therefore may indicate an invasive species is taking over an ecosystem. 

Oxygen weed has not been documented as established currently in North America. Its native region is in Southern Africa, including Zambia, Zimbabwe, Botswana, Lesotho, and South Africa. Oxygen weed was introduced to New Zealand during the 1950’s as an ornamental aquatic plant. Since, oxygen weed has been found and eradicated in Southern Australia and has also been found in the UK and Europe. Due to the plants’ hardiness and ability to grow under tough conditions, oxygen weed can easily be distributed through accidental transplant of fragments of the plant from place to another. This transplant can be facilitated by water currents and recreational equipment like boats and water waders. Oxygen weed is available from online sellers and distributed to countries where the plant has yet to be introduced. It is assumed that this buying and selling of ornamental plants is how oxygen weed has been distributed internationally.  

Ecological Impacts: 

Due to oxygen weed’s growth structure, ability to grow quickly under harsh conditions, and ability to distribute, this plant often out-competes native plants for sunlight, space, and access to nutrients. Oxygen weed grows both tall and thick. The roots of oxygen weed form dense mats on the waterbody’s floor, and the tall stems grow to the surface of the water, blocking out sunlight for lower growing plants and space for other plant’s roots to form on the water’s floor. Oxygen weed’s persistence in growth and distribution will decrease the biodiversity of plants in an aquatic ecosystem, which can have long-term effects on the balance of the system’s food web. This decrease in biodiversity fosters an ecosystem with low oxygen and nutrient levels, causing aquatic invertebrates to die off, reptiles, amphibians, and fishes struggle to eat, and mammals and birds who rely on that waterbody strain to find food. 

Social and Economic Impacts:  

Due to the nature of oxygen weed’s growth, the thickness of its populations impede water recreational uses, such as boating and swimming. This plant can become wrapped around motor blades and can impede fishing, as it creates an uninhabitable ecosystem for fishes to survive. Outside of recreation, oxygen weed has been known to also increase flooding impacts, and can block waterways at hydro-electric dams, causing electrical generation issues.  

Oxygen weed is an internationally recognized invasive plant, and many provinces are working to restrict the introduction of this plant. The B.C. Inter-Ministry Invasive Species Working Group considers oxygen weed as a priority species. Although this species is not yet prohibited under the B.C. Wildlife Act, it is still very much under watch. Alberta, Saskatchewan, and Manitoba do not yet recognize oxygen weed as a species of concern, however, the awareness of this species is only growing. 

The Government of Ontario has proposed Oxygen weed be considered as a prohibited invasive species under the Invasive Species Act. Prohibited species are illegal to bring into the province, which includes the possession, sale, and propagation of the species within or into the province. This regulation would ensure this highly dangerous invasive plant does not make it into Ontario’s valuable waterways, causing dangerous effects on the ecosystem’s health and economic values. Prevention of species introduction is much easier and cost-effective than controlling a species once it is introduced.