Globally, Invasive Alien Species (IAS) are considered to be one of the major threats to native biodiversity, with the World Conservation Union (IUCN) citing their impacts as ‘immense, insidious, and usually irreversible’. It is estimated that 11% of the c. 12,000 alien species in Europe are invasive, causing environmental, economic and social damage; and it is reasonable to expect that the rate of biological invasions into Europe will increase in the coming years. In order to assess the current position regarding IAS in Europe and to determine the issues that were deemed to be most important or critical regarding these damaging species, the international Freshwater Invasives - Networking for Strategy (FINS) conference was convened in Ireland in April 2013. Delegates from throughout Europe and invited speakers from around the world were brought together for the conference. These comprised academics, applied scientists, policy makers, politicians, practitioners and representative stakeholder groups. A horizon scanning and issue prioritization approach was used by in excess of 100 expert delegates in a workshop setting to elucidate the Top 20 IAS issues in Europe. These issues do not focus solely on freshwater habitats and taxa but relate also to marine and terrestrial situations. The Top 20 issues that resulted represent a tool for IAS management and should also be used to support policy makers as they prepare European IAS legislation.

Sea-chests, recesses built into the hull of a vessel, have been recently identified as hotspots for fouling organisms. In this study, we examined the types and abundances of taxa found in sea-chests of commercial vessels, and investigated whether vessel specifications and voyage histories influenced the nature and extent of sea-chest fouling. Eighty-two sea-chests were sampled from 39 commercial vessels while in dry dock on the West or East Coast of Canada. Overall, 80% of the vessels showed evidence of sea-chest fouling, and 46% harboured at least one non-indigenous species. In total, 299 unique taxa were recorded, including a number of non-indigenous and cryptogenic organisms that collectively made up 20.5% and 14.4% of the taxa sampled from West and East Coast vessels, respectively. Additional results suggested that in-service period (i.e., duration since last sea-chest cleaning) and vessel origin (i.e., domestic versus international) may, in part, determine the nature and extent of sea-chest fouling. By contrast, vessel size and port duration were unable to explain taxonomic richness or abundance of fouling organisms in sea-chests. Taken together, these findings highlight the role of sea-chests as an important vector responsible for the introduction and spread of a variety of taxa, including aquatic invasive species, but also suggest that the factors that influence sea-chest fouling in commercial vessels are complex. Further research, aimed at better understanding the determinants of sea-chest fouling and the efficacy of anti-fouling systems, would help further refine management strategies and reduce the risks associated with sea-chest fouling.

The submerged aquatic macrophyte Myriophyllum spicatum L. (Haloragaceae) has been recorded in southern Africa since 1829. It was first considered problematic in 2005 on the Vaal River, which has highlighted the need for an assessment of the invasion status and an appropriate management strategy to be identified. We used a unified invasion framework to categorise M. spicatum in southern Africa and define appropriate management strategies. Historical records and field surveys were used to assess the invasion status. Populations were considered established if collection records from a particular catchment or river system spanned at least 10 years and in some cases several localities. Of the 21 river systems where it has been recorded, it was evaluated as established in 13 and in the D1-E category of invasion. The disjunct populations suggest that it was point source introductions and thus the major barrier that prevents M. spicatum from proceeding along the invasion framework is its inability to naturally disperse the greater distances between catchments. Appropriate management strategies need to be catchment or river system based depending on the stage or state and category of invasion. Where M. spicatum is in the D1-E stage – established and potentially spreading, the appropriate management strategies include containment, and where possible, mitigation.

A mathematical model was used to describe the population of the aquatic invasive species, Ciona intestinalis in the presence of cultured mussel production. A differential equation model was developed to represent the key life stages: egg, larva, recruit, juvenile and adult. Stage transition rates were calculated from time spent in a stage and transition probabilities. Because surface availability for the settlement phase is a key determinant of population growth, dead juvenile and dead adult stages were also modelled, together with their drop-off rates. This model incorporated temperature dependencies and an environmental carrying capacity. Model validation was carried out against field data collected from Georgetown Harbour, in 2008. Relative sensitivity indices were calculated to determine the most influential factors in the model. The results indicated that the modelled outputs were broadly in agreement with the observed data. Under baseline conditions the number of C. intestinalis increased from early September to late October, after which they reached a plateau at an abundance of approximately five individuals per cm2. Sensitivity analyses revealed that a reduction in spawning interval or the development time of larva accelerated C. intestinalis population growth. In contrast, decreasing either carrying capacity or the percentage drop-off of live juvenile and adult stages resulted in a decline in the population. This research provides the first detailed model describing population dynamics of C. intestinalis in mussel farms and will be valuable in exploring effective treatment strategies for this invasive species.

Over the past few decades, the invasive colonial ascidian Didemnum vexillum Kott, 2002 has established in many temperate regions, sometimes bringing detrimental perturbations to native marine ecosystems and local economies. A reliable supply of healthy, genetically defined D. vexillum stocks/strains would greatly assist research into the traits of this species relevant to its invasive success. To this end, here we describe basic methodologies for the growth, maintenance, formation of chimeric colonies and their follow-up observations in ex situ cultures of D. vexillum. Didemnum colonies were collected during the austral late winter/early spring from a marina (Nelson, New Zealand) and were maintained in the laboratory using re-circulated, unfiltered seawater. Ramets (1-10 cm2; >70 fragments) from a variety of colony locations (peripheral/central, flat/lobe/tendril-shaped); were isolated by razor blade and secured to glass slides using cotton thread. The ramets attached to the glass slides within 24 hours, displayed 100% survivorship and could be successfully further sub-cloned for up to 10 weeks, when the study was terminated. Two distinct processes for tunic–substrate attachment were observed: (i) the secretion of growing marginal fronts made of tunic matrix containing spicules but without zooids and (ii) the secretion of thin tunic extensions with clusters of tunic cells at their tips. Allogeneic paired colony fusion assays, using naturally growing edges of colony fragments (i.e. mimicking natural fusion scenarios) resulted in fusions and chimeric colony formation. Zooids from both partners within a chimera appeared to intermingle and the resulting chimeric entities grew vigorously. This brief report provides an outline of simple, low-tech laboratory culture conditions for the maintenance, asexual propagation and chimeric colony formation of D. vexillum. The techniques described present a foundation for the development of genetically defined D. vexillum strains which will facilitate research into the traits of this species that are relevant to its invasive success.

A rapid assessment method to evaluate the relative impact of zebra mussel, Dreissena polymorpha, was undertaken in a 11.5 km2 temperate lake within an Irish drumlin landscape. The lake was divided into three assessment units: the north lake, the south lake and a river section situated downstream of the two lake assessment units. Survey work was conducted as a single survey in September 2011. Following an evaluation of the mussel abundance and distribution range within each assessment unit, the Biological Pollution Level (BPL) was calculated. Additional environmental information was obtained from historical monitoring conducted by the Irish Environmental Protection Agency. The zebra mussel was rated as having a high abundance and distribution range in one lake assessment unit, was absent in the second lake assessment unit, and had a low abundance and distribution range for the river assessment unit. Ninety-three stations were surveyed in two and a half days illustrating a practical approach to monitoring which can meet legislative requirements.

The effect of grazing by large herbivores on grassland communities has been extensively studied, however less is known about changes associated with sites of high-intensity activity, such as dust bowls, tracks, urine patches and dung piles, that might induce disproportionate impacts to the directly affected areas and the surrounding vegetation. This paper explores the changes associated with exotic feral horse dung piles in relicts of natural grasslands in Argentine Pampas. We expected greater changes in the composition of plant communities and a greater facilitation effect on the establishment of invasive alien plants adjacent to the dung piles. Characteristics of the vegetation surrounding dung piles were recorded in 100x25 cm plots located 0–1.5 m from the edge of the piles. We compared the immediate surroundings with reference plots at 5 m. The diversity of plant species increased as distance from the edge increased from 0–1.5 m; however, species richness was significantly higher in the first meter next to dung piles than 5 m away. Percentage cover of bare ground decreased further from the dung piles at both scales. Percentage cover of woody plants was greater at greater distances from the manure, whereas percentage cover of exotic plants was significantly higher next to the dung piles. The reported changes could be related to concentration gradients of nutrients liberated from the manure and/or to behaviour patterns of the horses, which may avoid grazing in the immediate surroundings of dung piles. These changes result in invasion windows facilitating the establishment and subsequent dispersal of exotic plant species in grasslands.