The literature is full of examples detailing ecological impacts of invasive species and predictions of which and where species will invade next. Many fewer examples of effective prevention strategies are known. Prevention of aquatic invasive species (AIS) to inland lakes should be easily established because most AIS are initially introduced into watersheds by recreational boating activities, especially in North America. The Watershed Management Plan for Otsego Lake, a central New York glacial lake, provides for prevention of AIS via a stringent boat inspection and washing program (BIP). All boats entering Otsego Lake at the public launch are visually inspected and those deemed likely to harbor AIS are required to power wash before launching. However, other sites are available to launch boats. BIP expenses average $30,000 per year, much of which has been covered by collecting a launch fee. After implementation of the BIP, only one boat was refused access, and less than 1% required washing before allowed access, however, zebra mussels (Dreissena polymorpha) and water chestnut (Trapa natans) have since been found in the lake. The BIP continues to be supported because other AIS may have been prevented or may be prevented in the future.

Lake Österträsk, a shallow, 25 ha lake in Åland, SW Finland, was invaded by the common watermilfoil, Myriophyllum sibiricumKomarov 1914 (Magnoliophyta: Haloragaceae), in the 1990s. In summer 2006 the dense vegetation, up to 2.5 m tall, richly branching Myriophyllum shoots, caused pH values of about 10 and oxygen supersaturation near the surface. Deeper layers were hypoxic throughout the season. The surface water Chlorophyll a values were about 10 µg L^-1. Shoot formation from the turions was temperature dependent and enhanced by nutrient as well as sediment addition. Decaying plants release nutrients to the water, produce organic sediments, and cause bottom oxygen depletion, changing the chemistry, nutrient dynamics and plant structure of the lake.

Lough Doon is a dual basin lake in the west of Ireland, split into an upper and lower basin that are morphometrically and physiochemically similar. Zebra mussels (Dreissena polymorpha Pallas, 1771) were introduced in the lower basin in 1998 and are now well established there. A survey in July 2007 involving scuba dive transects and dredging revealed a population of 5.5 x 10^8 zebra mussels (4.9 x 10^5 kg) in the lower basin, while just 3 zebra mussels were recorded in the upper basin. To assess the effects of Dreissena infestation on suspended solids, algal production and nutrient concentrations, near-surface water samples from Lough Doon were analysed from January-July 2007 (n = 12) for selected chemical and biological parameters. Sampling revealed marked differences in seston load between the two basins, with the infested lower basin exhibiting significantly reduced concentrations of suspended solids, chlorophyll-a and phytoplankton biovolumes and, conversely, greater Secchi transparency. Total phosphorus concentrations were lower in the lower basin but concentrations of ammonium and, particularly, nitrate were significantly higher. Inter-basin differences in Lough Doon mirror the post-invasion changes observed in other, larger European and North American lakes and reflect the effectiveness of coupled filter feeding-excretion by zebra mussels in reducing seston load and converting particulate nutrients into soluble forms. The data provide initial evidence that modest zebra mussel populations can significantly alter water chemistry in a small well-mixed lough, with implications for water quality management as the zebra mussel continues its rapid range extension in Ireland.

The invasion of freshwater ecosystems in North America by the zebra mussel, Dreissena polymorpha (Pallas, 1769), has repeatedly led to rapid changes in water clarity and phytoplankton abundance. Examining cases where a successful invasion has occurred but where rapid changes do not occur can help us understand the full range of responses of ecosystems to invasions. We re-sampled established sampling locations in Green Bay, Lake Michigan during four years of the post-invasion period. We determined Secchi depths, Chlorophyll-a concentrations, and phytoplankton composition and biovolume at five stations along a previously documented trophic gradient. Our data support the continued existence of a strong trophic gradient between lower and middle bay areas of Green Bay. Secchi depth did not significantly change following invasion at either lower bay or middle bay locations. Responses to invasion were stronger at middle bay than lower bay for both Chlorophyll-a and phytoplankton biovolume. Chlorophyll-a was significantly greater in the post-invasion period at both locations, while phytoplankton biovolume was significantly higher following invasion in middle bay. Along with these increases in abundance there was a significant shift to higher and more frequent dominance of the phytoplankton community by cyanobacteria. The increased phytoplankton abundance during the post-invasion period is likely explained by selective feeding and increased nutrient recycling by zebra mussels under high turbidity conditions in this highly productive embayment of Lake Michigan.

The fishhook water flea (Cercopagis pengoi Ostroumov, 1891) is an invasive zooplankter that can decrease the abundance and diversity of cladocerans and rotifers, which theoretically could release phytoplankton from grazing pressure and increase algal primary productivity. In the last decade, C. pengoi established and primary productivity increased concurrently in Owasco Lake (New York, USA). We studied plankton density, primary productivity, and standard limnological conditions in Owasco Lake during summer 2007 (1) to document summer densities of invertebrate predators, (2) to investigate correlations between C. pengoi and the abiotic environment, and (3) to examine the relationships among C. pengoi, native zooplankton, and productivity. Although the maximum abundance of C. pengoi observed (245 ind./m^3) far exceeded that of any native invertebrate predator, at most locations and dates unimodal density peaks between 35-60 ind./m^3 were typical and comparable to Leptodora kindtii (Focke, 1844), the most common native planktivore. Abiotic conditions were suitable for growth and reproduction throughout the sampling period, but were not linearly correlated with C. pengoi abundance. We observed reciprocal trends between predacious cladoceran density (both C. pengoi and L. kindtii) and herbivorous cladoceran density, and between herbivorous cladoceran density and Chlorophyll a concentration. Although these trends are only corollary, they support the possibility that C. pengoi may affect the trophy of Owasco Lake by reducing grazing zooplankton beyond the level of the native planktivores. Further study is needed to quantify the relative contributions of C. pengoi and L. kindtii to seasonal changes in the herbivorous cladoceran assemblage.

In the last 125 years numerous invasive species have been introduced into Lake Tahoe. In recent years there has been an invasion of warm water fishes including largemouth bass [Micropterus salmoides (Lacepède, 1802)], and bluegill [Lepomis macrochirus (Rafinesque, 1820)]. These species threaten to displace and decrease native fish populations, and reduce nearshore water clarity. It is believed, with the help of climate change increasing lake temperature, these species are spreading to other areas from established populations on the south shore. Our objective was to determine current distribution and the potential impacts of warm water nonnative fishes. Snorkel surveys were conducted bi-weekly from May to November 2006 and electrofishing was conducted four times within the snorkel survey period at locations where warm water species are already established. Snorkel surveys and electro-fishing revealed that 57% of monitored sites contained warm water nonnative fish species. At electro-fish sites, number of native fish decreased with increasing nonnative fish species. Comparing historical and current diet data of natives and nonnatives indicated the latter are consuming the same diet items that native fish consumed historically. As a result, where nonnative and native fish habitats overlap, predation on and competition with native fish is likely. Current distributions of nonnative species found during this study are where the next established populations can be expected if their spread is not controlled.

The recent invasion of water hyacinth Eichhornia crassipes (C. Mart.) Solms (1883) in the Guadiana River Basin (Spain) is described and the distribution of this Amazonian floating plant is analyzed from a geobotanical and chorological perspective. Georeferenced locations of invasion in Spain and Portugal are presented and the relative growth rate (RGR) and doubling time (DT) indexes defined by Gopal (1987) were calculated. The sexual reproductive cycles were determined in order to evaluate the invasive capacity at these latitudes. Predictive models of the plant's potential distribution in the Guadiana River were constructed based on expert knowledge and using a Geographic Information System, on the basis of the water's physico-chemical parameters. Given the size of the potential area of distribution, it seems necessary to make provision for an important increase and subsequent maintenance in the level of the means and logistics targeted at the prevention and control of this weed.

The Asian Clam, Corbicula fluminea (Müller, 1774) invaded British waters in 1998. It remained confined to an isolated network or rivers in Eastern Britain until 2004, when it was discovered in low densities in the River Thames, London. We report that C. fluminea has now been discovered at three more sites on the tidal River Thames. Surveys indicate that the clam has now established dense populations of up to 648±352 m^-2 at Ham on the River Thames, with evidence of annual recruitment. Given the substantial connectedness of the Thames to many of Britain’s other rivers, it is likely that C. fluminea will now continue to spread through Britain’s waterways.

Open-ocean ballast-water exchange (BWE) is currently the most common treatment used to reduce the ballast transfer of organisms and the subsequent risk of invasions among coastal ecosystems. Freshwater or estuarine organisms remaining after BWE often experience high mortality, due to osmotic shock caused by high-salinity exposure. We conducted 70 salinity tolerance experiments on 54 different taxa to measure mortality rates of freshwater and estuarine organisms after exposure to oceanic seawater (34 psu), simulating both flow-through (F-T) and empty-refill (E-R) BWE methods. We focused especially on larval and adult crustaceans from freshwater and mesohaline habitats adjacent to ports of the Baltic Sea, North Sea, Great Lakes, Chesapeake Bay, and San Francisco Bay. Animals from oligohaline habitats (0-2 psu) experienced the highest mortality: all individuals died in 82% of the F-T treatments and 88% of the E-R treatments. The effectiveness of both treatment types decreased with animals from low-salinity (2-5 psu, 100% mortality in 27% of F-T and 46% of E-R treatments) and mesohaline habitats (5-18 psu, 100% mortality in 40% of F-T and 52% of E-R treatments). In 43% of cases among all salinity categories, empty-refill treatments required less exposure time to cause significant mortality than flow-through treatments. Invertebrates that exhibited significant survivorship were most often peracarid crustaceans including widely introduced species of mysid shrimps and amphipods. Although salinity shock does not completely prevent the transfer of all low-salinity biota, BWE provides a useful management tool to reduce species transfers, especially considering the combined effects of removal and mortality.

Barbronia weberi (R. Blanchard, 1897), an Asian leech with records of introductions to South and North America, Australia, New Zealand and Europe, was found in two small-size pedemontane streams in North-West Italy (Regione Lombardia) during macroinvertebrate bioassessment sampling. This is the first record of the species in this country, where the family Salifidae is not represented. The species can be distinguished from common native erpobdellids of similar general habitus by the presence of two accessory ventral pores, three pairs of pharyngeal stylets and the presence of minute papillae covering the body. Current distribution and effects of B. weberi on Italian freshwater ecosystems should be determined through further studies.

The invasive North American gastropod Ferrissia fragilis (Tryon, 1863) has been recorded for the first time in August 2007 at three sites on the Pripyat River basin (the Belarusian part of the inland European “central invasion corridor”). This species occurs in the onshore shallow zone (depth 0.2-0.3 m) with dense aquatic vegetation and temperature from 21.8 to 23.7°C. Maximal abundances of this species have been observed in Mykashevichy port bay. Most likely, this invasive gastropod entered the River Pripyat basin from the Ukrainian territory where it was found early in cooling reservoir of Chernobyl Nuclear Power Station however invasion pathways though the western (Poland) and ornamental ways are also likely.

We report the first results of parasitological study of Dreissena polymorpha (zebra mussels) from Sweden. The samples of Dreissena were collected from Lake Erken in July 2007. The most common endosymbionts found in the mantle cavity of the mussels were the commensal ciliate Conchophthirus acuminatus and free-living nematodes Chromadorina bioculata and Laimydorus sp. Unidentified chironomid larvae and aquatic mites were also occasionally observed in the mantle cavity. The finding of host-specific ciliate C. acuminatus suggests that zebra mussels invaded Lake Erken at the juvenile or adult stage.

The paper presents the first record of Corbicula fluminea (Müller, 1774) in the Guadiana River Basin (Iberian Peninsula). This exotic bivalve was found in June 2006 on the Lacarón and Guadiana rivers with mean density is between 3.3 and 16.9 individuals per squared meter. Population structure and the dates of the first records suggest that the introductions may have occurred between 2003 and 2004. The potential impact of the invasion on native freshwater bivalves is discussed along with the need for monitoring and prevention of further introductions of non-indigenous bivalves in the Iberian Peninsula.

In this paper we have compiled all information on Chinese pond mussel Sinanodonta woodiana (Lea, 1834) in the Czech Republic. This species was found in the Czech Republic for the first time in 1996 and altogether 20 records about its occurrence had been obtained till the beginning of 2008. The species was found in rivers, oxbow lakes and ponds. The expansion is the most intensive in Southern and Central Moravia, which is likely due to the fact that it is the warmest part of the country.

Dikerogammarus villosus (Sowinsky, 1894) has been recorded for the first time in the Vistula River, the biggest river in Poland and in the whole Baltic drainage system. Until now the species has been found in the Bug River that is a tributary of the Vistula. It has migrated there from the Ponto-Caspian basin through the central invasion corridor (namely Pripet-Bug canal). Another population of that species has been found in the Oder River. It came there via the Mittelland Canal from the Rhine River that had been colonised from the Black Sea basin through the southern invasion corridor. In the Vistula River, D. villosus co-occurs only with other Ponto-Caspian gammarids.

The mysid shrimp, Hemimysis anomala G.O. Sars, 1907, has recently colonized the Hungarian reach of the Danube River. It has formed self-sustaining populations. The species has been found in samples collected in September 2004 almost one year earlier than the first record published.

A population of the virile crayfish, Orconectes virilis (Hagen, 1870), has been recorded within the River Lee system of North London in the United Kingdom. First detected in 2004 and thought to be the spiny-cheek crayfish, Orconectes limosus (Rafinesque, 1817), a recent re-examination of the specimens has confirmed that this is the first recorded breeding population of O. virilis in the United Kingdom. A monitoring programme is being established to assess the rate at which the species colonises the catchment and its ecological impact.

In 2005 a new, non-indigenous crayfish species was discovered in the Dessoubre River (eastern France). The species was initially considered as Orconectes rusticus (Girard, 1852). However, an examination of form I males caught in 2007 revealed that the species is in fact Orconectes juvenilis (Hagen, 1870), a closely related congener of O. rusticus. According to our knowledge, this is the first record of O. juvenilis outside the North American continent. The ecological implications as well as the possible impact on the native European crayfish are discussed briefly.

Since the first authorised introductions to Spain in 1921 of the Eastern mosquitofish Gambusia holbrooki (Girard, 1859), this North American freshwater fish species has invaded large parts of several Iberian basins. For the River Ebro basin, we report 24 new records of this exotic species between 2005 and 2007 which represents a considerable expansion. Potential negative implications for aquatic invertebrate and fish communities are discussed.