Ecological significance: Aquatic plants, encompassing a diverse range of species from submerged macrophytes to emergent reeds, form the foundational trophic level in many Australian freshwater ecosystems. They convert sunlight into energy, providing food and habitat for invertebrates, fish, and waterfowl. Without aquatic plants, the entire food web collapses, leading to declines in fish populations crucial for both ecological balance and recreational fishing, and a significant reduction in water quality due to increased turbidity and nutrient levels. Their presence is intrinsically linked to the health and resilience of Australian waterways.
Species Profile
| Attribute | Data |
|---|---|
| Scientific name | Myriophyllum aquaticum (Vell.) Verdc. |
| Trophic level | Primary producer |
| Population estimate | Estimated to cover over 8000 hectares of waterways in south-eastern Australia, with ongoing expansion (Centre for Invasive Biologicals, 2023). |
| Native range | South America; introduced to Australia. |
| EPBC Act status | Not listed (considered a high-impact weed). |
Position in the Food Web
- Prey species: Myriophyllum aquaticum itself isn't directly ‘consumed' in the traditional sense, but provides a substrate for periphyton growth - microscopic algae, bacteria, and fungi - which are grazed upon by various invertebrate species like amphipods (e.g., Austrogammarus australis) and snails (e.g., Physa acuta). These invertebrates are then consumed by larger organisms.
- Predators: While not directly preyed upon, dense mats of M. aquaticum can impede the foraging efficiency of predatory fish like Murray cod (Maccullochella peelii), reducing their access to prey species. The introduced carp (Cyprinus carpio) will actively disturb and consume the plant material, though it doesn't represent true predation.
- Competitors: M. aquaticum aggressively competes with native aquatic vegetation such as Vallisneria americana (eelgrass) and Potamogeton tricarinatus (pondweed) for light, nutrients, and space. Its rapid growth rate allows it to quickly dominate waterways, displacing native species.
- Symbiotic partners: A commensal relationship exists between M. aquaticum and certain epiphytic algae. The algae gain a stable substrate for growth, while the plant is generally unaffected. However, the plant can also host parasitic fungi, impacting its growth and spread.
- Keystone role: While not a keystone species in its native habitat, M. aquaticum has become a significant ‘ecosystem engineer' in Australian waterways due to its invasive nature. It dramatically alters habitat structure, impacting water flow, light penetration, and oxygen levels, thereby influencing the entire ecosystem.
Habitat Requirements and Microhabitat Use
Myriophyllum aquaticum thrives in a wide range of freshwater habitats, including lakes, ponds, rivers, and irrigation channels. It prefers still or slow-flowing water with nutrient-rich sediments. It can tolerate a broad range of temperatures, from subtropical to temperate, and is commonly found in the Murray-Darling Basin, the south-east Queensland region, and parts of Victoria and New South Wales. It's particularly prevalent in disturbed habitats, such as those impacted by agricultural runoff or urban development. The plant is frequently found in the Riverine Plain bioregion, where irrigation channels provide ideal conditions for its proliferation. It can grow in water depths ranging from 0.5 to 3 meters, and prefers substrates of silt, clay, or sand.
Reproductive Strategy and Population Dynamics
Myriophyllum aquaticum exhibits a highly opportunistic, r-selected reproductive strategy. It reproduces primarily through fragmentation - small pieces of the plant readily break off and establish new colonies. This allows for extremely rapid colonization and spread. It also reproduces sexually via small, inconspicuous flowers, but fragmentation is the dominant mode of reproduction in Australian waterways. Juvenile survival is high due to the plant's ability to quickly establish roots and access nutrients. Population growth is primarily limited by water level fluctuations and, to a lesser extent, temperature. However, its tolerance to a wide range of conditions means it can persist even under challenging circumstances. The plant's ability to oversummer as turions (dormant buds) allows it to survive dry periods and re-establish rapidly with the return of water.
Threats and Vulnerability Analysis
- Introduced species pressure: The primary threat to native aquatic ecosystems is the continued spread of M. aquaticum itself. Introduced carp further exacerbate the problem by disturbing sediments and increasing turbidity, creating conditions favourable for the plant's growth.
- Land-use change: Agricultural runoff, containing high levels of nutrients (nitrogen and phosphorus), fuels the growth of M. aquaticum. Land clearing also increases sediment loads in waterways, providing suitable substrates for establishment.
- Climate projections: Climate change is predicted to increase the frequency and intensity of droughts and floods in many parts of Australia. While droughts may temporarily reduce plant biomass, floods will facilitate its dispersal and colonization of new areas. Increased water temperatures may also favour its growth. By 2050, modelling suggests a potential 30-50% increase in the area infested by M. aquaticum under a high-emissions scenario.
- Disease: While some fungal pathogens have been identified affecting M. aquaticum, they have not yet proven effective as biological control agents.
Recovery Actions and Research Gaps
Current management strategies focus on physical removal (hand-pulling, mechanical harvesting) and, in some cases, herbicide application. However, these methods are often costly, labour-intensive, and can have unintended consequences for non-target species. Biological control efforts, involving the release of the weevil Vossia sublineata, are underway, but their long-term effectiveness remains uncertain. A critical data gap exists regarding the genetic diversity of M. aquaticum populations in Australia. Understanding the genetic structure could inform more targeted and effective management strategies, potentially identifying populations that are more susceptible to biological control agents or less likely to spread.
Ecological FAQ
Why is aquatic plants terrestrial plants important to its ecosystem?
Despite being an invasive species, Myriophyllum aquaticum provides habitat for some invertebrates and small fish, albeit a degraded habitat compared to that provided by native vegetation. However, its dense growth significantly reduces water flow, leading to oxygen depletion and the creation of anoxic conditions, negatively impacting fish and other aquatic organisms. It also reduces light penetration, inhibiting the growth of other aquatic plants and altering the overall ecosystem structure.
How has the aquatic plants terrestrial plants population changed over the last 50 years?
The population of M. aquaticum in Australia has increased dramatically over the last 50 years, following its introduction in the 1960s. Initially confined to ornamental ponds, it has since spread rapidly throughout many waterways, particularly in the Murray-Darling Basin. This expansion is attributed to its efficient fragmentation-based reproduction, coupled with increased nutrient loads from agricultural runoff and the lack of effective natural controls.
What can individuals do to support aquatic plants terrestrial plants conservation?
Given that M. aquaticum is an invasive species, ‘conservation' efforts focus on its control and eradication. Individuals can help by: reporting sightings of the plant to local authorities; avoiding the transport of plant fragments on boats, trailers, or fishing gear; supporting sustainable agricultural practices that reduce nutrient runoff; and participating in community weed control programs. Never purchase or propagate this plant for ornamental purposes.