Andreas Hussner

NRW Ministry of Environment

The study of functional traits is becoming increasingly popular in understanding species ecology, acclimatisation, adaptations and diversity (Funk et al., 2017). Within trait-based ecology, functional traits are often referred to as the morphological, biochemical, physiological, structural, phenological, or behavioural characteristics that are expr...

In Nordrhein-Westfalen sind in den vergangenen Jahren zunehmende Bestände neophytischer Wasser- pflanzen nachgewiesen worden. Einige dieser Arten breiten sich stark aus, bilden in den Gewässern zum Teil große Massenbestände und werden invasiv. Die Massenbestände beeinträchtigen auf vielfältige Weise die betroffenen Ökosysteme und deren menschliche...

• Charophytes are a key group of submerged macrophytes in temperate hardwater lakes, but have declined or been replaced by angiosperms as a result of eutrophication for more than 100 years. At present, this process is continuing in many European lakes despite an overall reduced nutrient loading. In eutrophic lakes, light attenuation by periphyton i...

1. Gravel pit lakes are common across Europe. These novel ecosystems serve as model systems to study human-induced and natural colonisation of isolated lakes by fish. Fisheries-management activities can quickly spread species over large distances, possibly homogenising fish communities across ecosystems, while fostering local fish diversity. 2. Ou...

The parrotfeather (Myriophyllum aquaticum) is an aquatic plant and is included in the list of invasive alien species of Union concern. For such species, Regulation (EU) No 1143/2014 provides for preventive measures to prevent further imports and spread and to control existing stocks. Since several years ago, parrotfeather has been known from two po...

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, em...

Myriophyllum spicatum L. is a widely distributed submerged aquatic plant species, which became a model species for different test systems using either unrooted or sediment-rooted plants. Here, we tested the response of unrooted and sediment-rooted M. spicatum to different combinations of two temperature, light and CO2 conditions, respectively. Over...

a.Aim Provides an overview of selected taxonomic groups of invasive freshwater species: plants, bivalves, crayfish, fish and mammals. b.Main concepts and main methods covered For invasive species in each taxonomic group, major introduction pathways are outlined as well as main impacts and management actions. c.Conclusions Invasive freshwater specie...

I am glad to announce that the special issue “Multiple Roles of Alien Plants in Aquatic Ecosystems: from Processes to Modelling” of Frontiers in Plant Science is now available and freely accessible. A warm thank goes to my co-editors Lorenzo Lastrucci, Giuseppe Brundu and Andreas Hussner that helped me to manage this "editorial enterprise". Thanks...

1. The dispersal of aquatic plant propagules is highly facilitated in streams due to flow. As many aquatic plants predominantly spread through vegetative propagules, the specific retention and thus drift distance of dispersed plant fragments largely contribute to the rapid spread along the course of a stream. 2. We determined fragment retention fo...

The submerged evergreen aquatic plant Myriophyllum heterophyllum is among the worst invasive species in Europe, causing severe problems especially in navigation channels but also lentic systems. This review aims to provide a comprehensive overview and update on the current distribution and risks associated with this species in Europe and elsewhere....

Die aus Südafrika stammende Wechselblattständige Wasserpest, Lagarosiphon major (RIDL.) MOSS gilt als eine der invasivsten Wasserpflanzenarten weltweit. Aufgrund der ökologischen und mitunter wirtschaftlichen Schäden, die große Bestände der Art in den Gewässern verursachen können, wurde Lagarosiphon major als invasive Art von unionsweiter Bedeutung...

The formation and dispersal of viable plant fragments are considered as key determinants for the vegetative spread potential and competitive strength of submerged aquatic macrophytes. Although it is known that the disturbance by flow facilitates fragment dispersal in streams, detailed information on in situ fragmentation rates and the influence of...

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 fragm...

1. Submerged aquatic plant species predominantly spread through vegetative propagules, particularly shoot fragments. While it is known that the successful establishment of fragments in isolated water bodies is largely determined by retention of fragment viability during overland transport (i.e. desiccation resistance), detailed information on speci...

Submerged aquatic plants predominantly disperse via vegetative means, with shoot fragments being the most important propagules. The establishment of new macrophyte stands largely depends on two parameters, (i) the regeneration of plant fragments and (ii) the successful anchorage of these fragments in the sediment (colonization). Here we studied bot...

Freshwater ecosystems are particularly susceptible to invasions by invasive non-native species (INNS) across a range of taxa, largely as a consequence of anthropogenic influences on these systems, with a number of ecological and socio-economic impacts. This chapter reviews freshwater invasive non-native species across the globe, focusing on fishes,...

Hygraula nitens is a New Zealand native moth with aquatic larvae that feed on submerged aquatic plants. The larvae have been mainly observed using native Potamogeton and Myriophyllum species as a food source, although some studies reported larvae feeding on the alien macrophytes Hydrilla verticillata, Lagarosiphon major and Ceratophyllum demersum....

Aquatic plants may face resource constraints or anthropogenic pollution, and effects might be heightened under multiple stress conditions. We investigated if arsenate effects on Myriophyllum spicatum L. would be stronger under CO2 limitation and low phosphorus availability. In a factorial design, we exposed sediment-grown plants to either CO2 (high...

The spatial distribution and species composition of submerged aquatic vegetation is commonly assessed by a combination of methods. Among scuba diving, mechanical detection using rakes and aerial surveys the use of echosounders is an additional approach. Based on technical hard- and software developments the potential of the latter method serves opp...

1. The partial pressure of CO2 in freshwater ecosystems is likely to be affected by climate change but little is known of its potential effects on aquatic plants when interacting with other stressors such as nitrate pollution. 2. We set a laboratory experiment to test the effects of CO2 and nitrate availability on growth, biomass allocation, chloro...

The growth and photosynthesis of submerged aquatic plants is often limited by the CO2 availability in their habitats, but about 50% of all submerged plants are able to use HCO3− as an additional carbon source. This ability to use HCO3− provides a competitive advantage over non-CO2-users under CO2 limiting conditions. Here, we studied the growth and...

Introduced invasive alien aquatic plants (IAAPs) threaten ecosystems due to their excessive growth and have both ecological and economic impacts. To minimize these impacts, effective management of IAAPs is required according to national or international laws and regulations (e.g. the new EU regulation 1143/2014). Prevention of the introduction of I...

Das aus Südamerika stammende Brasilianische Tausendblatt, Myriophyllum aquaticum (VELL.) VERDCOURT, ist eine der invasivsten Pflan-zenarten weltweit. Aufgrund der Schäden, die dichte Bestände der Art in den Gewässern verursachen, wurde Myriophyllum aquaticum in die unionsweite Lis-te invasiver Arten der Europäischen Union aufgenommen, für die gemäß...

Aquatic plants mostly disperse via vegetative means, and plant fragments are the most important vegetative dispersal units. Here we studied the fragment drift in the medium sized River Erft, in which the macrophyte community is dominated by alien aquatic plants. The plant fragments were sampled at six different sites in the drift of the river. We a...

1. The photosynthesis of submerged aquatic plants can be limited by carbon dioxide (CO2) because of the low diffusivity of dissolved gas in water. About half of the species are able to use bicarbonate (HCO3-) as an alternative source of dissolved inorganic carbon (DIC). HCO3- is usually available in several-fold higher concentrations than CO2 at pH...

Ludwigia grandiflora (water primrose), a native to the Americas, is one of the most important invasive alien aquatic plants in Europe. In Germany, a first population was found in an oxbow lake of the River Leda in Lower Saxony, north-western Germany, in 2004. Ludwigia grandiflora formed both dense monospecific patches and mixed stands with native p...

Submerged aquatic plants most commonly spread via a variety of vegetative plant parts, with stem fragments being the most common dispersal units. Such rapid vegetative dispersal poses strong problems in the management of invasive aquatic plant species. Here we tested the fragmentation rate of the three major alien invaders in New Zealand waters, El...

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....

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, B...

Light, temperature and the availability of carbon are three major drivers of submerged plant growth, photosynthesis and competitive strength. A laboratory experiment using a three factorial experimental design (light x temperature x CO2) was used to evaluate growth responses (RGR (relative growth rate), LDMC (leaf dry matter content) and root:shoot...

Elodea nuttallii and Elodea canadensis, two invasive submerged and rooted aquatic macrophyte species, are receiving increasing attention for their rapid and lasting invasion of many freshwater habitats throughout Europe, Asia and Australia. This review summarizes the present scientific knowledge about means of controlling Elodea nuttallii and Elode...

Alien plant species are rapidly spreading in aquatic ecosystems around the world, causing major ecological effects. They are typically introduced by humans, after which natural vectors facilitate their further spread. Migratory waterbirds have long been recognised as important dispersal vectors for native and aquatic plants, yet little is known abo...

Light, temperature and the availability of carbon and nutrients are major factors affecting aquatic plant growth. A three factorial experimental design in a large outdoor mesocosm experiment was used to evaluate the effects of light, temperature and carbon on the growth parameters of RGR (relative growth rate), LDMC (leaf dry matter content) and ro...

Global warming is expected to accelerate the invasive success of non-native plants. Long-term data on aquatic macrophytes confirming this hypothesis, however, are scarce. In this study we analyzed the development of native and neophytic aquatic macrophyte species number and abundance in a geothermally warmed river (Erft, North-western Germany) duri...

Wolffia columbiana is a member of the family Lemnaceae and native to the Americas. In 2013, the first two occurrences of Wolffia columbiana in Europe were found in Germany and the Netherlands. Differentiation between W. columbiana and the rare native W. arrhiza is difficult and a scanning electron microscope (SEM) was used to confirm plant identifi...

Alien aquatic plant species can strongly affect all types of freshwater ecosystems. Their number has more than doubled between 1980 and 2009 in Germany, and currently 27 are known and their number is still increasing. Eleven have been classified as invasive, but only four are managed yet, mainly by weed cutting. Most of the alien aquatic plant spec...

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 fr...

Case histories of non-indigenous and cryptogenic plant species [in German]

Alien aquatic plant species cause serious ecological and economic impacts to European freshwater ecosystems. This study presents a comprehensive overview of all alien aquatic plants in Europe, their places of origin and their distribution within the 46 European countries. In total, 96 aquatic species from 30 families have been reported as aliens fr...

The Holarctic fruticose lichen Stereocaulon paschale is known to be capable of tolerating at least six weeks of constant submersion under natural conditions in a meltwater pool at about 1000 m above sea level in Rondane in eastern Norway. Its adaptations to temporary submergence involve both physiology and anatomy, differing fundamentally from Clad...

An optode device for net-photosynthesis measurements, based on oxygen-depending quenching of fluorescence from O2-specific sensors, and PAM fluorometry have been used to study diurnal courses of net-photosynthesis and the Fv/Fm ratio of the submerged plant Lagarosiphon major. Plants were pre-cultivated and studied in large mesocosm flow-through out...

An optode device for net-photosynthesis measurements, based on oxygen-depending quenching of fluorescence from O2-specific sensors, and PAM fluorometry have been used to study diurnal courses of net-photosynthesis and the Fv/Fm ratio of the submerged plant Lagarosiphon major. Plants were precultivated and studied in large mesocosm flow-through outd...

Hussner A, Van de Weyer K, Gross EM & Hilt S (2010). Comments on increasing number and abundance of non-indigenous aquatic macrophyte species in Germany. Weed Research 50, 519–526. Non-indigenous aquatic plants are a major cause of biodiversity loss in many countries. In this study, our own field data and a literature review have been used to get a...

The high light sensitivity of three submerged aquatic freshwater plant species, Egeria densa, Elodea nuttallii and Myriophyllum heterophyllum, which have been cultivated at a photosynthetically active radiation (PAR, 400–700 nm) of 70 μmol photons m−2 s−1, was studied by means of chlorophyll fluorescence and pigment analyses. Exposure of plants to...

Ludwigia grandiflora and Ludwigia peploides, both native to South America, are aquatic plants, which favourably grow in stagnant or slow flowing waters. Due to their rapid growth both species are considered two of the most important aquatic weeds worldwide. The species have invaded several countries in SW Europe and often cause problems, e.g.in Fra...

Floating Pennywort (Hydrocotyle ranunculoides L.fil.), a native to North America and naturalized in Central and South America, is an invasive aquatic weed in western Europe and several other regions worldwide. H. ranunculoides settles primarily in stagnant to slow-flowing waters (e.g. ditches, canals, rivers, lakes and ponds). The species prefers s...

Crassula helmsii, Hydrocotyle ranunculoides, Ludwigia grandiflora and Myriophyllum aquaticum are four well known invasive aquatic plants in European waters. In this study, plant growth at different nutrient availabilities, regeneration capacity and photosynthesis were investigated. Results show high relative growth rates (RGR) of the species of up...

Myriophyllum aquaticum is an aquatic plant of still or slow flowing waters. The species mostly occurs in its emerged growth form in dense stands, but submerged shoots can also be found. Due to its rapid growth, M. aquaticum is considered one of the most important aquatic weeds worldwide. In southern Europe, M. aquaticum occurs in irrigation and dra...

Biologische Invasionen werden weltweit als ein wesentlicher Bestandteil des „Global Change“ betrachtet. Sie werden neben der Veränderung in der Landnutzung, der zunehmenden Eutrophierung und der globalen Erwärmung als eine der größten Gefahren für die biologische Vielfalt angesehen. Dabei spielen auch aquatische Neophyten eine immer größer werdende...

In 2005 invasive Myriophyllum heterophyllum Michaux was found in shallow urban city lakes Kaiserteich, Schwanenspiegel and Spee’scher Graben in Düsseldorf (TK 4707/4). The evergreen species became rapidly dominant in the lakes and covers more than 90% of the water surface. Thick algae mats laid down on the dense macrophyte stands and became a nuisa...

Crassula helmsii is a neophytic aquatic plant species, which is native to Australia. In Germany the species is known since more than 20 years and is still spreading. Most populations of C. helmsii in Germany are known from North Rhine-Westphalia. The species settles both in terrestric/amphibic and aquatic habitats down to a maximum water depth of 1...

Floating Pennywort (Hydrocotyle ranunculoides L. fil.) is a worldwide distributed aquatic plant. The species is native to North America and quite common also in Central and South America. In Europe, Japan and Australia it is known as an alien plant, sometimes causing serious problems for affected ecosystems and human use of water bodies. Starting f...

A procedure was developed at the Schaalsee, which cheaply provides usable data on species existence and surface distributions of aquatic macrophytes. The procedure can be used for the fulfillment of operative EC-Water Framework Directive (EC-WFD) and Flora-Fauna-Habitat (FFH) monitorings at large lakes.

Am Schaalsee wurde ein Verfahren entwickelt, das mit geringem Aufwand belastbare Daten zum Artenbestand und zu den Flächenanteilen der aquatischen Makrophyten liefert. Das Verfahren kann zur Erfüllung des operativen EG-WRRL-Monitorings und FFH-Monitorings an großen Seen eingesetzt werden.

Floristic 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 d...

Nach dem Erstfund von Hydrocotyle ranunculoides L. fil. in einem mit Erftwasser gespeisten Graben im Sommer 2004 wurden in der Folgezeit weitere Vorkommen der Art in Nordrhein-Westfalen notiert. Neben dem ersten Fundort in dem Graben nahe Grevenbroich/Gustorf konnte Hyrocotyle ranunculoides nun auch in der Erft, der Niers, dem Offelter Bach (nahe d...

In den letzten Jahren ruckten aquatische Neophyten in den Fokus weltweiter Forschung, vor allem aufgrund vermehrt auftretender Probleme mit Massenbestanden neophytischer Feuchtgebiets- und Wasserpflanzenarten. Die ausgelosten Probleme konnen dabei ganz unterschiedlicher Natur sein. So sorgen neophytische Wasserpflanzenvorkommen fur verschiedenartig...