24 research outputs found
The Water Lettuce, Pistia stratiotes L. (Araceae) in the lower Erft region in North-Rhine Westphalia: Dispersal ability and ecosystem impact
2008 konnte erstmals in der Erft ein ĂŒberwinterndes Vorkommen von Pistia stratiotes beobachtet werden, das sich seitdem immer weiter ausbreitet, in der Erft und in angrenzenden GewĂ€ssern dichte MassenbestĂ€nde ausbildet und die GewĂ€sseroberflĂ€che teilweise vollstĂ€ndig bedeckt. Die BestĂ€nde blĂŒhen reichlich von Juni bis in den November hinein und bilden viele Samen aus, die eine hohe Keimungsrate aufweisen. Aufgrund der bereits bestehenden Problematik der Beschattung ganzer NebengewĂ€sser und Seitenarme und des durch die Verdriftung von Pflanzen und Samen in den Rhein bestehenden hohen Ausbreitungspotenzials der Art fĂŒr den Rhein und angrenzende GewĂ€sser erscheint ein Management der Art notwendig.In 2008, an overwintering population of Pistia stratiotes has been observed for the first time in the river Erft in North-Rhine Westphalia. The species spreads quickly and forms dense monospecific populations within the stream network. The flowering period starts in June and ends in November, producing numerous and highly viable seeds. Due to the already existing problems caused by shade effects of dense Pistia populations as well as the high number of downstream drifting plants and seeds, particularly into the river Rhine, management strategies are needed in order to minimize the negative impact of this species on these river ecosystems
Report of a Pest Risk Analysis for Hydrocotyle ranunculoides
Hydrocotyle ranunculoides originates from the American continent and was introduced into the EPPO region as an ornamental plant for tropical aquaria and garden ponds, where it is still sold under its correct name, sometimes under other names (H. vulgaris, H. leucocephala, and H. natans which is a synonym of H. ranunculoides). The plant was first recorded as naturalised in the south-east of the UK in the 1980s (Newman, 2003). Naturalisation in the Netherlands and in Belgium was recorded in the last decade of the twentieth century (Baas & Duistermaat, 1999; Baas & Holverda, 1996; Krabben & Rotteveel, 2003; Verloove 2006, Invasive Species in Belgium Website). Deleterious impacts have been reported in these three countries. The species is also recorded in France, Ireland, Italy, Germany (see EPPO, 2009) but several EPPO countries are still free from H. ranunculoides and there are concerns that it may be able to enter and establish in further countries. This PRA assesses the risks of its further introduction into other EPPO countries and its current and predicted impact.
An initial EPPO PRA was performed and approved in 2005. After the proposal of listing this species in the Directive 2000/29, the European Food Safety Authority reviewed the initial PRA and made some comments. The initial PRA is therefore revised in the view of the EFSA comments and of information having become available after the initial PRA (EFSA, 2007)
Fish community composition in small lakes: The impact of lake genesis and fisheries management
Gravel pit lakes are common across Europe. These novel ecosystems serve as model systems to study humanâinduced and natural colonisation of isolated lakes by fish. Fisheriesâmanagement activities can quickly spread species over large distances, possibly homogenising fish communities across ecosystems, while fostering local fish diversity.
Our objective was to evaluate the effects of lake genesis (gravel pit lakesâ<â100âyears old vs. natural lakes of glacial genesis ~10,000âyears old) and fisheries management (fish stocking activities present vs. absent) on the fish community in small lakes, while controlling for key environmental variables known to affect lake fish communities.
We sampled fish communities by electrofishing and multimesh gillnetting in 47 isolated lakes managed for fisheries, and 19 unmanaged and isolated lakes of both natural and artificial origin in northern Germany. Unmanaged lakes were used as reference to assess fisheriesâmanagement impacts in small natural and artificial lakes.
We caught 178,506 fish from 30 species and found that the accumulation of native lake fish species in lakes was associated with fisheries management, which increased local species richness (αâdiversity) and number of predatory species, and reduced amongâlake variation in fish community composition (ÎČâdiversity; i.e., homogenisation). The homogenisationâeffect associated with fisheries happened with introduced native fish species, whereas nonânative species were rarely detected.
In unmanaged gravel pit lakes, the littoral fish community composition was substantially different to the communities present in both types of managed lakes and unmanaged natural lakes. Therefore, the relatively young unmanaged gravel pit lakes revealed evidence of ongoing, stochastic colonisation processes that resulted in comparatively speciesâpoor fish communities.
We concluded that fisheries management by anglers speeds up the colonisation of gravel pit lakes with native fish species in the study area. For planning initial fish introductions in newly created gravel pit lakes, it is recommended that fish communities from ecologically similar natural lakes within the same geographical region are used as references to maintain the biotic integrity of newly created fish communities.This work was jointly supported by the German Federal Ministry of Education and Research (BMBF) and the German Federal Agency for Nature Conservation (BfN) with funds granted by the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU; grant number: 16LC1320A).Peer Reviewe
Pest risk analysis for Myriophyllum heterophyllum
Myriophyllum heterophyllum presents an overall high phytosanitary risk for the EPPO region with a low uncertainty rating. The overall likelihood of M. heterophyllum continuing to enter the EPPO region is high. The plant is imported into the EPPO region as a misidentified aquatic species for aquaria and ponds and is already established in Austria, Belgium, France, Germany, Hungary, the Netherlands, Spain and Switzerland. The risk of entry into other EPPO countries through import is considered high. The risk of the species establishing in additional countries is high as movement through irrigation and river systems acts to connect countries, facilitating spread regionally. Spread may be accelerated by recreational activities in water bodies invaded by the weed. Impacts of the species within the EPPO region are likely to be severe (high score rating), including aquatic plant species displacement, habitat dominance and effects on other aquatic organisms
From introduction to nuisance growth: A review of traits of alien aquatic plants which contribute to their invasiveness
Invasive alien aquatic plant species (IAAPs) cause serious ecological and economic impact and are a major driver of changes in aquatic plant communities. Their invasive success is influenced by both abiotic and biotic factors. Here, we summarize the existing knowledge on the biology of 21 IAAPs (four free-floating species, eight sediment-rooted, emerged or floating-leaved species, and nine sediment-rooted, submerged species) to highlight traits that are linked to their invasive success. We focus on those traits which were documented as closely linked to plant invasions, including dispersal and growth patterns, allelopathy and herbivore defence. The traits are generally specific to the different growth forms of IAAPs. In general, the species show effective dispersal and spread mechanisms, even though sexual and vegetative spread differs strongly between species. Moreover, IAAPs show varying strategies to cope with the environment. The presented overview of traits of IAAPs will help to identify potential invasive alien aquatic plants. Further, the information provided is of interest for developing species-specific management strategies and effective prevention measures
Pest risk analysis for Alternanthera philoxeroides
Alternanthera philoxeroides presents a high phytosanitary risk for the EPPO region with a low uncertainty rating. A. philoxeroides is already present in the EPPO region in France and Italy. Further spread within and between EPPO countries is considered likely. The overall likelihood of A. philoxeroides continuing to enter the EPPO region is medium. It is not clear how this species entered the EPPO region and there are no clear pathways of further introduction, as the species is not widely traded as an aquarium plant or as any other type of living plant material. There may be confusion with A. sessilis, or other Alternanthera species traded for aquarium, ornamental or food purposes. The risk of the species establishing in other EPPO countries is considered high as movement through irrigation and river systems may act to connect countries, facilitating spread regionally, especially through high energy unstable river systems that may encourage fragmentation. Spread may be significantly accelerated by water based recreational activities. The potential high impact of the species within the EPPO region should be considered similar to that seen in other countries where the species has invaded and become established; i.e. Australia and the southern states of North America. Impacts are likely to be more pronounced in countries and regions where the climate most suited to population, establishment, growth and spread
Ăkologische und ökophysiologische Charakteristika aquatischer Neophyten in Nordrhein-Westfalen
Alien aquatic plants in a thermally abnormal river and their assembly to neophyte-dominated macrophyte stands (River Erft, Northrhine-Westphalia)
AbstractFloristic surveys, vegetation mapping, and detailed transect analyses rendered a macrophyte flora of 14 native and five alien taxa of flowering plants in the River Erft, a contributory of the River Rhine in Northrhine-Westphalia. Water temperatures of this river do not fall below 10°C all the year round, for reasons of geothermically heated water discharged from nearby opencast mining areas. Macrophyte stand structures, composed of the neophytes Azolla filiculoides and Lemna minuta (floating) and Myriophyllum aquaticum, Egeria densa, and Vallisneria spiralis (rooted in the muddy or sandy ground of the river) are described and the ecological requirements of these taxa are characterized. The alien species can be seen as elements that increase the α-diversity of the aquatic vegetation of the River Erft. They do not replace any of the native species, even if shifts in the competition dynamics occur. The colonization by neophytes of the abnormally warmed River Erft can be appreciated as paradigmatic for trends in the macrophyte vegetation of medium-sized rivers in Central Europe when climate-related or discharge-based heating of the waterbody occurs and propagules of alien plants imported by waterfowl or â more important â plants from aquarium waste will find suitable places of existence and spread
Effects of water nutrients on regeneration capacity of submerged aquatic plant fragments
Aquatic plants play a substantial role in almost all freshwater habitats throughout the world. Even though submerged aquatic plants dominantly spread by the dispersal of vegetative plant fragments, most aquatic plant species show a broad distribution range. Here we studied the differences in the regeneration capacity and the regeneration type of fragments (by root and/or shoot growth) of eight submerged plant species (Ceratophyllum demersum, Egeria najas, Elodea canadensis, Elodea nuttallii, Hydrilla verticillata, Myriophyllum aquaticum, Myriophyllum heterophyllum and Myriophyllum spicatum) under different water nutrients in sediment-free conditions. Overall, M. spicatum showed the highest regeneration (82±2%) in this study, followed by C. demersum (73±2%) and M. aquaticum (47±4%), whereas M. heterophyllum showed the lowest (1±1%). The shoot fragments of E. canadensis, H. verticillata, E. najas and E. nuttallii regenerated by 40±2, 23±2, 16±2 and 7±1%. The nitrate concentration affected the regeneration capacities of E. najas (P=0.05), M. spicatum (P=0.013) and C. demersum (P=0.001), whereas phosphate had no significant effect. Additionally, the different nutrient concentrations had a significant effect on the portion of the regeneration types within E. canadensis, E. nuttallii and H. verticillata. Summarizing, submerged plants differ significantly in their regeneration capacity, and water nutrients have a potential effect on the regeneration of submerged plant fragments. This might influence the further colonization and spread of the species under field conditions.- We studied the effect of different nutrient concentration on regeneration capacity and regeneration type of eight submerged aquatic plant species.
- Species differed in their regeneration capacity and their regeneration type by new shoot and/or new root production.
- Nutrient effects were found for both regeneration capacity and regeneration type
Species-specific fragmentation rate and colonization potential partly explain the successful spread of aquatic plants in lowland streams
The vegetative spread potential of aquatic plant species is largely based on the quantity of dispersed plant fragments (propagule pressure) and their potential for regrowth and establishment, i.e., fragment regeneration and colonization. In streams, fragment dispersal is of particular significance as the exposure of plants to flow facilitates fragmentation and downstream drift of fragments. We conducted field investigations to quantify the relevance of fragment dispersal and the species-specific propagule pressure due to fragmentation in five small to medium-sized German streams. These field surveys were combined with determination of the potential for regeneration/colonization of fragments collected in the field indicated by relative root formation under standardized conditions. In general, the number of drifting fragments tended to increase with larger stream size. We documented species-specific differences in fragmentation rate, which contributed to weak correlations between the number of drift units and specific plant cover within four streams. The overall likelihood for root formation increased significantly with increasing fragment size and was highest for the invasive Elodea nuttallii (70% of fragments). We conclude that the fragment dispersal capacity in streams is highly species-specific and that propagule pressure alone cannot explain the successful spread of invasive species like Myriophyllum heterophyllum