Invasive species

Water Primrose

What is it?

Water primrose will grow rapidly and stablish large, dense stands

Water primrose, Ludwigia grandiflora, is an attractive but highly invasive plant that grows in or alongside ponds, lakes and wetlands. Grows from fragments. Native to South America but is causing serious economic and environmental problems in France and England. It has recently recorded in a small number of artificial garden ponds in Co Kerry but has not yet been recorded in the wild.

How do you identify it?

• Long red stems that grow horizontally on water or mud; the stems will also emerge to 1 m above the water surface. Stems can grow to 5 m in length.
• Most plants have alternate dark green leaves of two types: emerged long and slender (willow like) and floating oval forms.
• Large yellow flowers, each with 5 petals.

Why are we concerned?

In suitable waters this plant grows very rapidly and establishes large, dense (often impenetrable) surface and sub-surface vegetation carpets. These can block watercourses and interfere with boating, cruising, angling, irrigation, drainage and other water uses. Dense stands will deplete dissolved oxygen from the water, resulting in fish kills, compete with native species for space and resources, and reduce biodiversity.

How do we stop the spread of this species?

Do not purchase from garden centres or accept cuttings.
If you see this invasive plant in a garden centre or in a garden pond, report the sighting immediately to the emergency response number 1890 347424.

Killer Shrimp Keep it out! Alert! Killer shrimp poster How you can help Killer shrimp   Killer Shrimp, Dikerogammerus villosus, is the latest freshwater invasive species which is threatening Irish waterways. The killer shrimp is much bigger than our own native freshwater shrimp at 30mm but is otherwise quite similar in appearance. Unlike our native shrimp it feeds aggressively taking large invertebrates and even small fish as prey.

Asian Clam The latest invader Underwater video Alert! See poster How you can help (Corbicula fluminea) The Asian clam has recently been discovered in Lough Derg. Like the Zebra Mussel (Dreissena polymorpha), Asian Clam has the ability to become highly invasive in a short period of time and at high densities it can alter the food web and compete with native mussel species. Asian clam are known to aggressively out compete native invertebrate communities, limit phytoplankton biomass, biofoul water intakes, alter benthic habitats, add biologically available nitrogen and phosphorus to systems, and impact aesthetic and recreational values of public beaches, lake front properties and swimming areas. Their high rates of filtration, metabolism, reproduction, tolerance to wide ranges of habitats, and juvenile dispersal allows Asian clam to aggressively expand ranges and to rapidly re‐invade areas; limiting management, reducing restoration efforts and impacting native benthic communities. Asian clam are capable of both filter feeding (feeding from the water) and pedal feeding (feeding directly from the sediment). One reason for why Asian clam is successful in so many different environments is that it can effectively filter phytoplankton and bacteria out of the water column and feed from the sediments when food from the water column becomes scarce. Water fern A dense mat of Azolla at a lock on the River Barrow (Azolla filiculoides) This is a small free floating fern that grows and proliferates in canals, ponds and sheltered aquatic habitats. It is tolerant of brackish water. In suitable watercourses Azolla can carpet the water surface over considerable areas. By excluding light it eliminates the native submerged flora. It also prevents diffusion of oxygen from air to water, which can produce anoxic conditions. This may cause fish kills. The physical biomass can prevent boat movement or angling. During the 2001 weed and water quality survey of the River Barrow, a large stand of Water Fern, was observed upstream of the lock gates at Milford. This was the first record of this species on the River Barrow. Following this  recording of what was thought of as an isolated colony of Azolla on the River Barrow at Milford, more extensive beds of this exotic, free-floating plant were identified upstream of Bagnelstown in early November of the same year. A subsequent survey revealed small stands of this plant in most canal cuts from Carlow downstream to St. Mullins Azolla has the capacity to rapidly over-grow static or slow flowing channels (e.g. canals or cuts on the Barrow), and may cause major problems for navigation, angling and other amenity activities on the waterway, as is evident from the photographs taken of the cut upstream of Bagnelstown. Careful monitoring of this prolific plant will be required for the coming seasons and all positive sitings will have to be looked at closely. As this plant is free-floating it poses a real threat of spreading to other stretches of this system and to other canals. Where Azolla is present it will be required to remove it from the channel to prevent the further spreading. New Zealand pigmyweed (Crassula helmsii) New Zealand pigmyweed can out-compete native aquatic plants in a short period This plant was first recorded in Ireland in 1994. It has spread very rapidly in watercourses in Britain and has the potential to do likewise here. It forms dense submerged and emergent stands in ponds, small lakes and canals. In suitable aquatic habitats the biomass produced is sufficient to eliminate native plants and create poorer conditions for macroinvertebrates and fish. Nuttall’s pondweed (Elodea nuttallii) Nutall's pondweed is commonly called Elodea This perennial submerged plant is native to North America and was first recorded in Ireland in the 1980s. It grows in still and slow flowing water and thrives in eutrophic habitats. It is a freshwater plant but is tolerant of moderately saline water. In recent years it has become widespread in Ireland and, where it establishes, can form exceptionally dense monocultures. These occupy the water column from bed to surface. No native flora can compete with this plant and, as a consequence, biodiversity suffers following its introduction. It also interferes with any form of amenity usage of infested waterways. Zebra mussel (Dreissena polymorpha) Zebra mussels are widespread in Ireland and continue to be discovered at new locations This small but prolific mussel is a native of the Caspian and Black Seas region and was introduced through ballast water to the Shannon Estuary in the 1990s. Zebra mussels live in freshwater and in the upper reaches of tidal estuaries. They have spread from this area, principally via boat movements, throughout the Shannon and Shannon-Erne catchments. The female mussel can release up to 1 million eggs each year. These are carried in water currents and settle out after approximately three weeks. They are filter feeders and remove much of the plankton that juvenile fish depend upon. Hence, they may cause an imbalance in fish communities. They attach to hard surfaces such as boats, buoys and water intake pipes, where they form very dense clusters. As such, they can cause problems by blocking intake pipes and clogging cooling systems.     Japanese knotweed (Fallopia japonica) Japanese knotweed is becoming a very common sight along river banks. Japanese knotweed was intentionally introduced as an ornamental plant. It has since infested a wide range of habitats, including the banks of rivers. The plant grows to 3 metres in height and forms very dense monocultures along river corridors. The rhizomes are very extensive and grow to 3 metres deep and up to 7 metres from the parent plant. Spread is by plant or rhizome fragments. Spread is rapid and the growth habit of the plant efficiently excludes native herbaceous species that function to maintain bankside stability. Giant hogweed (Heracleum mantegazzianum) Giant hogweed can cause severe skin burns as well as impact on the ecology of river banks. This statuesque plant can grow to a height of 4 metres and was introduced to Ireland as an ornamental in the late 1880s. It’s preferred habitat is wasteland and the banks of many rivers in the country. The plant produces a sap that is hazardous to humans, particularly in the presence of direct sunlight. The large leaves of the plant create sufficient shade to suppress indigenous herbaceous understorey plants along banksides. Giant Hogweed, in a non-native plant species that grows abundantly along the banks of rivers and streams. Hogweed is a cause for concern in that it is both a human health hazard, and exerts a negative ecological impact on infested river corridors. In 1998 the Office of Public Works commenced a four-year control/eradication programme, in the Mulcair River catchment, where hogweed was widespread and restricting angler access. Results to date are very positive with these dense stands no longer a feature of this catchment. Monitoring of the effects of control will continue until the end of 2001. A catchment approach to spraying with glyphosate is required, starting at the furthest upstream site for the plant. Spraying should commence in March/early April when leaf growth has occurred and the height is >15cm. Experience in Ireland has shown that seedlings are less susceptible to glyphosate treatment. A dose rate of 5 l/ha -1 is sufficient to kill treated vegetation. Sections treated in March/April should be re-treated in May. The catchment area should be surveyed again in July and any plants that have flowered or are likely to flower must be deheaded before seeds are produced. The cut umbels must be removed from the area and destroyed. The plant should be sprayed again with glyphosate or it will attempt to flower again and set seed. A further spraying of glyphosate throughout the catchment area in September will kill or suppress the growth of autumn flowering or late-developing plants. If the above protocol is rigorously applied over a four year period which is the normal lifespan of H. mantegazzianum the seed reserve will be depleted and the risk of serious re-infestation will be minimal. Chub (Squalius cephalus) Chub, a new invasive species in Ireland, was probably released into Irish waters by anglers. Chub is a cyprinid fish that is widespread throughout central and southern Europe. It is indigenous to England but, until 2004, had not been formally recorded in Ireland. It is a species that inhabits rivers with a moderate flow, but can also be found in lakes. It was probably intentionally introduced to Ireland by anglers. Chub feed on aquatic plants and invertebrates when young but, as they mature, they feed more selectively on larger prey items, including young fish. They could result in an imbalance among our native fish communities if they establish large populations.