Research on the ecology and impacts of the zebra mussel (Dreissena polymorpha) has developed in parallel with the long history of their spread across Europe and to North America. There is less scientific knowledge however about the quagga mussel (Dreissena rostriformis bugensis). The recent spread of both zebra and quagga mussels to the Western states of the USA, has spurred on dreissenid research. The 17th International Conference on Aquatic Invasive Species (ICAIS), was held in San Diego, California in September 2010. This special edition of Aquatic Invasions includes topical research presented at ICAIS and also extra subsequent papers on ecology, risk assessment and control of various aquatic invasive species in different parts of the globe.

Settlement and growth of quagga mussels Dreissena rostriformis bugensis were monitored in Lake Mead, NV, USA, where the first dreissenid occurrence was confirmed in the western United States. To measure the settlement rate of these invasive mussels, seven acrylonitrile butadiene styrene (ABS) pipes were attached to a line in shallow water (7.7 m below the surface) since November 23, 2007; eight ABS pipes were placed on another line in deep water (13.4 m below the surface) since January 3, 2008. Quagga mussels were sampled from these pipes on March 19, May 21, July 9, October 20, and December 19, 2008. Active settlement of veligers was recorded in all sampling events. The settlement rates of quagga mussels did not differ among the two lines and the highest settlement rate was found from October 20 to December 19. Three methods were used to estimate the growth of quagga mussels in Lake Mead: caged mussels, size distribution analyses on both natural populations and mussels attached to ABS pipes. Caged mussels were held in Las Vegas Boat Harbor from July 31, 2007 to March 19, 2008, where smaller mussels grew faster than larger ones. Size distribution data on two natural populations of quagga mussels collected from Sentinel Island and Indian Canyon in 2007 also showed that the growth rates decreased significantly as mussel size increased. Shell length data of cohorts collected from the ABS pipes were also used to estimate the growth of quagga mussels. The growth patterns of quagga mussels from the two lines were quite similar with the lowest growth rates detected from late summer to early autumn. The information on settlement and growth of quagga mussels from this study can help understand their population dynamics in the western United States.

A field experiment was conducted in 2009 using Lake Ontario water in a continuous flow through system to determine the impact of low pH on dreissenid mussel settlement and survival in calcium rich waters. Raw water containing veligers was pumped to the field laboratory where the incoming water was divided into four streams. Three of the streams had the pH adjusted using phosphoric acid to pH 7.3, 7.1 and 6.9. The fourth stream was used as a control. Three replicates of each pH resulted in 9 treatment tanks and three control tanks. Three bags of caged adults were placed in each tank. Adult mortality of almost 40% was recorded at a pH of 6.9 after 10 weeks of exposure. Analysis of the weight/length relationship of adult mussels confirmed that for any given length the mussels were significantly lighter at all three pH levels when compared to the controls. Visually, erosion and perforation of the shells was noted, leading to the conclusion that the loss in weight was primarily due to loss of calcium from the shells of the adults. The visual loss of calcium was the greatest at a pH of 6.9. New settlement was essentially prevented at a pH of 7.1. Based on these results, downward adjustment of pH in calcium rich waters may be a viable treatment for prevention of dreissenid fouling in industrial cooling water systems and raw water conveyances.

Ballast water contains organisms which can survive the ship’s journey and become established in the recipient water body when discharged. Phytoplankton species can become invasive and might be harmful by producing toxins or anoxic conditions following their blooms. Different technologies exist to treat ballast water in order to reduce the spread of invasive species. The effectiveness of a UV-based ballast water treatment system was tested in an incubation experiment over 20 days. After an initial decline in cell numbers, re-growth could be observed of certain phytoplankton taxa, namely the diatoms Thalassiosira, Skeletonema, Chaetoceros, Pseudo-nitzschia, and Nitzschia (order represents rank of abundance). The conclusion of this study is that a variety of taxa are able to survive UV-treatment. These may include harmful and potential invasive phytoplankton species. Long-term incubation experiments should be considered when testing the effectiveness of UV-based treatment systems. The dominant re-growing phytoplankton group was Thalassiosira which could be a suitable indicator organism for testing the efficiency of UV-units.

Bighead [Hypophthalmichthys nobilis (Richardson, 1845)] and silver [H. molitrix (Valenciennes, 1844)] carps (collectively, Asian carp) have invaded the Mississippi River Basin and successfully established populations in the Illinois River, where they have negatively influenced native fishes and now pose an imminent threat to invading Lake Michigan through the Chicago Sanitary and Ship Canal. Sound-bubble-strobe light barrier (SBSLB) technologies may have the potential to slow Asian carp range expansions; for example, a sound-bubble barrier was 95% effective at deterring bighead carp passage in a hatchery raceway experiment. In 2009-2010, we tested the effectiveness of a SBSLB at repelling Asian and non-Asian carp species (all other fishes tested) within Quiver Creek, a tributary to the Illinois River. To test barrier effectiveness, Asian carp and non-Asian carp species were removed from upstream of the barrier, marked, and released downstream of the SBSLB. Asian carp were also collected from the mainstem Illinois River and transplanted downstream of the barrier. Trials were conducted with the SBSLB ON and OFF to determine upstream passage rates. Short-term and extended trials were also conducted to test for differences in upstream passage rates using sound, bubbles, and strobe lights (flashing and not flashing) versus sound and bubbles only. Barrier effectiveness was evaluated by upstream recaptures. Two of 575 marked silver carp and 85 of 2,937 marked individuals of other fish species breached the barrier and were recaptured. No marked bighead carp (n=101) made upstream passage. Our results suggest that SBSLB technologies could be used as a deterrent system to repel Asian carp, but should not be used as an absolute barrier to prevent range expansions. Potential negative influences of this technology on non-target fishes must also be evaluated prior to implementation as a management tool.

Non-native species can cause negative impacts when they become invasive. This study entails a comparison of risk classifications for 25 aquatic non-native species using various European risk identification protocols. For 72% of the species assessed, risk classifications were dissimilar between countries. The pair-wise comparison of Freshwater Fish Invasiveness Scoring Kit (FISK) scores of in total 28 fish species from the UK, Flanders (Belgium) and Belarus resulted in a higher correlation for scores of Flanders-Belarus than that of Flanders-UK and Belarus-UK. We conclude that different risk classifications may occur due to differences in (1) national assessment protocols, (2) species-environment matches in various biogeographical regions, and (3) data availability and expert judgement. European standardisation of risk assessment protocols, performance of biogeographical region specific risk classifications and further research on key factors for invasiveness of aquatic ecosystems are recommended.

Aquatic invasive species pose major ecological and economic threats to aquatic ecosystems worldwide via displacement, predation, or hybridization with native species and the alteration of aquatic habitats and hydrologic cycles. Modeling the habitat suitability of alien aquatic species through spatially explicit mapping is an increasingly important risk assessment tool. Habitat modeling also facilitates identification of key environmental variables influencing invasive species distributions. We compared four modeling methods to predict the potential continental United States distributions of northern snakehead Channa argus (Cantor, 1842), round goby Neogobius melanostomus (Pallas, 1814), and silver carp Hypophthalmichthys molitrix (Valenciennes, 1844) using maximum entropy (Maxent), the genetic algorithm for rule set production (GARP), DOMAIN, and support vector machines (SVM). We used inventory records from the USGS Nonindigenous Aquatic Species Database and a geographic information system of 20 climatic and environmental variables to generate individual and ensemble distribution maps for each species. The ensemble maps from our study performed as well as or better than all of the individual models except Maxent. The ensemble and Maxent models produced significantly higher accuracy individual maps than GARP, one-class SVMs, or DOMAIN. The key environmental predictor variables in the individual models were consistent with the tolerances of each species. Results from this study provide insights into which locations and environmental conditions may promote the future spread of invasive fish in the US.

This study documents the spread of the invasive clam Corbicula spp. in Switzerland since its first record in the River Rhine in 1995. Clams were newly recorded in several Swiss lowland lakes whose interconnecting rivers have not yet been colonized. We present evidence for separate introductions of an identical haplotype of Corbicula fluminea into five lakes in Switzerland in the years 2003–2010 based on the mitochondrial DNA-sequence of the COI in specimens sampled. This suggests passive dispersal of the clam by human activities and/or waterfowl. All but one of the 72 genetically analysed individuals were assigned to a single haplotype FW5 and to the species name C. fluminea. Recent records of specimens, which were not genetically analysed, displayed all the shell morphology of C. fluminea, confirming the dominance of this clam in Swiss rivers and lakes.

Similar to the zebra mussel (Dreissena polymorpha) and the quagga mussel (Dreissena bugensis), the Asian clam (Corbicula fluminea) is an invasive bivalve that has colonized many waterbodies in the United States and Europe. So far, low water temperature and ice formation during winter appear to have limited its northern distribution, especially in Eastern North America. This paper documents the recent discovery of a Corbicula fluminea population in the St. Lawrence River, in the thermal plume produced by the Gentilly-2 nuclear power plant (Bécancour, Québec, Canada). Based on a benthic samples obtained during November 2009 from 21 sites, both upstream and downstream of the power plant outlet, average density (± standard error) of this non-indigenous species was 368 ± 176 living individuals/m². Additional samples collected in 2010 showed an increase in density to 3,380 ± 1,315 living individuals/m² downstream the power station, and established the range limit at 4 km downstream. The species was present only downstream of the power plant and its distribution appears to be associated with the warm water plume. The influence of the thermal plume at 4 km from the power station was however fairly limited. The size of individuals varied from < 1 mm to 24 mm in length. These results confirm the establishment of the species in the St. Lawrence River, thereby extending the northern boundary of its distribution in North America.

In order to evaluate the effects of the golden mussel Limnoperna fortunei on phytoplankton density and composition and nutrient recycling we conducted a 24 h filtration experiment in Río Tercero Reservoir (Argentina) using four 400 L mesocosms, two of them stocked with 1700-1800 adult mussels each, and two controls (without mussels). Nutrient concentrations and phytoplankton composition and density were evaluated at 0, 3, 6, 12, and 24 h. Estimated filtration rates were 1.48-3.14 mL mg DW^-1 h^-1. Grazing pressure by the mussel was not associated with algal taxonomy or cell size. After 24 h, L. fortunei removed 84% of the particulate nitrogen, and 49% of the particulate phosphorus. Nutrient regeneration was very significant as well: ammonium was produced at a rate of 3 μM NH₃ g DW^-1 h^-1, whereas production of phosphates was 0.42 μM PO₄ g DW^-1 h^-1. It is concluded that the impact of L. fortunei on phytoplankton and nutrient cycling can be as significant as that reported for another invasive bivalve - the zebra mussel Dreissena polymorpha in Europe and North America, but the overall effect of this impact on the biota may differ strongly under different environmental settings.

As part of a multi-year field study to investigate plankton dynamics in the Lower Columbia River Estuary (LCRE), we conducted monthly sampling of the mesozooplankton (> 73 μm) at a station near Astoria, Oregon. The planktonic copepod community was numerically dominated by three non-indigenous species (NIS), Pseudodiaptomus forbesi, Limnoithona tetraspina, and Sinocalanus doerrii, and two native species, Eurytemora affinis and Diacyclops thomasi. However, seasonal co-occurrence of non-indigenous and native copepods was highly variable between species-pairs. The native E. affinis and the non-indigenous S. doerrii showed the greatest temporal overlap (March-October), but other species-pairs also showed periods of considerable overlap during some seasons (e.g., E. affinis and P. forbesi in June-September). Spatial co-occurrence of native and non-indigenous species was also examined in temperature and salinity “space” (rather than geographic space): all six species-pairs (3 non-indigenous species × 2 native species) showed some degree of overlap, with the greatest (proportional) overlap occurring between the native E. affinis and the two non-indigenous species, S. doerrii and P. forbesi. This suggests the potential for competition to occur between native and non-native copepods in the LCRE, although with variation between seasons and species. Future studies are recommended that explicitly test for and distinguish between the relative importance of biological (e.g., competition and predation) and physico-chemical processes (e.g., freshwater runoff, eutrophication) in regulating the population dynamics of native and invasive copepods in the LCRE.

The Chinese mitten crab is an invasive catadromous species that has populated many European estuaries. However, despite repeated ‘introductions’, the only known established North American population is in the San Francisco Bay Delta, along with recent populations discovered in Chesapeake Bay and the Hudson River. In established populations, adult mitten crab numbers oscillate dramatically, and large numbers of crabs can have severe environmental impacts. Extremely little is known about the biology and ecology of juvenile stages, but understanding the factors behind new cohort survival is crucial for understanding the dynamics of newly-established populations. In this study, we use the only known long-term life-history data set to assess the relative importance of reproductive potential and environmental factors in regulating mitten crab population dynamics in San Francisco Bay. Both exploratory regression tree and bivariate data analyses support the hypotheses that concentrations of planktonic zoeae are strongly influenced by interactions between the number of breeding female crabs, the timing of reproduction, and water temperature. Additional studies are needed in other estuaries invaded by mitten crabs to test the generalities of these relationships and further evaluate the potential of these relationships to inform predictions about the extent and magnitude of mitten crab populations.

New Zealand’s current surveillance programme for marine pests does not include methods for identification of organisms in the water column, therefore dispersive forms go undetected. Molecular methods provide an opportunity to detect dispersive forms thereby contributing to a more robust surveillance programme. Additionally, New Zealand has become a signatory to the IMO Ballast Water Convention and there is scope for developing enumeration methods for detection of viable organisms as well as species-specific molecular probes for indicator bacteria. We describe here the outcome of experiments testing the effects of various matrices (e.g. sediment, biofilms, benthic assemblage, seawater) against a quantitative PCR (QPCR) assay developed for Potamocorbula amurensis. The limit of detection of the assay for sediments and benthic assemblages ranged between one to five larvae per 10 g wet weight. We also report a QPCR assay for Vibrio cholerae, one of the indicator species in the Ballast Water Convention. Quantitative PCR of seawater spiked with different concentrations of culture showed that assay sensitivity was insufficient to detect the regulatory limit of 1 colony forming unit (CFU) per 100 mL. More recent work suggests that sufficient sensitivity can be achieved with cultivation based methods (most probable number-QPCR [MPN-QPCR]). We are currently appraising several multispecies detection methods including micro-arrays and next generation sequencing for their suitability in marine pest detection. The advantages and disadvantages of each are discussed herein. We highlight the need to consider issues relating to sampling design when using molecular methods for surveillance and compliance monitoring.

The Eleven Point River drainage in the Ozarks ecoregion of North America contains the largest known populations of and critical habitat for the globally imperiled coldwater crayfish (Orconectes eupunctus). We present here the discovery of an introduced population of alien ringed crayfish (Orconectes neglectus neglectus) in Jolliff Spring Branch in the upper reaches of the drainage. Sampling was conducted at eight sites throughout the tributary to determine the extent of the alien species’ range in the stream. Orconectes n. neglectus were found at four sites extending along 3.4 km of stream, with reproducing populations confirmed at two upstream sites, and few individuals found at two others. This invasion represents a threat to O. eupunctus, which occurs a few kilometers further downstream in the drainage and has been recorded from only the lower reaches of Barren Fork and throughout the mainstem Eleven Point River. Introduced O. neglectus were previously associated with localized extirpation of O. eupunctus in another drainage. Study results warrant monitoring of the invasion and possible reassessment of the conservation status for O. eupunctus.

Vegetative reproduction promotes human-mediated dispersal of aquatic invasive plants as fragments “hitchhike” between water bodies on boats and trailers. However, desiccation of plant fragments may also reduce fitness, decreasing the likelihood of fragment survival as transport distances increase. Current inter-lake invasive species spread models do not directly consider fitness loss due to desiccation and mechanical damage of the transport pathway. Here, we estimate survival as a function of desiccation exposure for Eurasian watermilfoil (Myriophyllum spicatum). Following desiccation treatments, we monitored survival and root formation of individual fragments and assessed the differences between treatments. Highest survival rates occurred for short (< one hour) air exposures and coiled fragments with root production for the coiled treatment occurring in less than two weeks, irrespective of fragment length. In contrast, fragments that experienced desiccation for more than 24 hours had little risk of surviving. Our results emphasize the threat posed by same-day overland movements of boats from invaded to uninvaded waterways, and provide managers with a surveillance radius to inform delimitation surveys arising from the discovery of a new invasion.

Alligator weed Alternanthera philoxeroides (Mart.) Griseb (Amaranthaceae) is being reported for the first time from Kashmir, India. Alternanthera philoxeroides was collected in 2008 during the vegetation survey of Wular Lake, a wetland of international importance under Ramsar convention. Alternanthera philoxeroides is a noxious invasive weed widespread throughout the world. We suggested that all lakes and wetlands in the Kashmir valley are susceptible to this weed and its growth may assume destructive levels. The morphology and nomenclature of the species is described and illustrated.