The invasion of the colonial ascidian Didemnum vexillum (Kott, 2002) represents a significant threat to marine ecosystems. In Norway, D. vexillum was recorded for the first time in 2020 and has since continued spreading along the coast. Although the total eradication of this species appears highly unlikely, the implementation of control measures is important to slow down its proliferation and limit the impacts on important species and habitats. In this study, we performed three laboratory experiments, to separately test the effects of lime (fine and coarse quicklime particles and hydrated lime), hydrogen peroxide (H₂O₂; 0, 1000, 2000 and 4000 mg l^-1) and Azamethiphos (0, 50, 100 and 200 µg l^-1), on the biofouling cover of D. vexillum. No significant effect of Azamethiphos was detected on D. vexillum cover after 1 hr of exposure, while exposure to H₂O₂ for 1 hr only reduced its biofouling cover by 50% after exposure to the highest concentration (4000 mg l^-1). Conversely, both fine and coarse quicklime particles appeared as suitable control options, reducing the size of the colonies by 100% and 99%, respectively, after exposure for 20 hrs. Additionally, treatment with hydrated lime induced a significant decline in D. vexillum cover by about 89% after 1 hr of exposure. Our results suggest the importance of considering the seasonal variations in environmental conditions and the biology of D. vexillum, to optimize the efficacy of the treatment. Here, we suggest using quicklime and hydrated lime between October and December in the Northern Hemisphere, to benefit from the natural degeneration of D. vexillum during winter and to more effectively eradicate potential remnants that could serve as a basis for regeneration.

We present a case study using trapping data and species accumulation theory to assess the sampling effort needed to detect species that are rare in habitats sampled as part of the management of invasive European green crab Carcinus maenas on the coast of Washington State and Salish Sea shorelines, such as is desired for early detection of invasive species. In response to detections of green crab on the west coast of North America monitoring efforts, including early detection monitoring, have increased. The goal of invasive species early detection monitoring programs is to detect new infestations soon after introduction so that eradication and quarantine measures can be used to control their spread. However, detection of newly introduced invasive species often occurs after populations are large and well established. The ability to detect newly introduced invasive species is affected by sampling procedures, including how much effort is expended. To assess the level of trapping effort needed to detect green crab and other taxa when they are rare, we calculate sample-based rarefaction curves, total species richness, and estimates of sample completeness. We then use these estimates to describe the relationship between sampling effort and detection at two different spatial scales. Our results suggest that high probability early detection of green crabs or other rare taxa in many coastal waterbodies will require significantly more trapping effort than was expended in 2020. Our analyses further suggest that the effort required to provide for early detection was less at the site-specific spatial scale than at the waterbody scale. However, sample completeness at the site-specific spatial scale was negatively correlated with species richness. Current efforts to look for new green crab populations and to manage existing populations provide an opportunity to look for other invasive organisms that may establish in similar habitats.

A prolific aquatic invasive species, the quagga mussel (Dreissena rostriformis bugensis), broadly impacts freshwater systems by altering ecosystem structure and function, damaging infrastructure, and limiting recreational boating opportunities. Quagga mussel populations have become established in several Western U.S. reservoirs which feed hydroelectric power facilities. Impacted facilities incur increased operational and maintenance costs and are at risk of power generation disruption. Current habitat suitability models suggest additional reservoirs are susceptible to successful invasion should introduction occur. The U.S. Bureau of Reclamation has detected additional quagga mussel introductions to numerous reservoirs, yet these populations appear not to have persisted. To further refine quagga habitat suitability models, we examined how reservoir surface elevation patterns, or storage dynamics, vary across reservoirs of three quagga mussel population statuses: established (i.e., established population confirmed), suspect (i.e., introduction detected without population establishment), and negative (i.e., no introduction detected). For this work, “drawdown events” or periodic water surface elevation declines, were operationally defined based on relevance to quagga desiccation mortality. Our comparisons of reservoir drawdown properties revealed that water-level declines were typically greater in suspect and negative reservoirs than in reservoirs with established quagga populations. Further, suspect reservoirs typically had less frequent, yet in many cases longer duration drawdown events than established reservoirs. Therefore, the magnitude and duration of drawdowns potentially have negative impacts on quagga population establishment in a novel environment. Managed large-magnitude and long-duration drawdowns may serve as a risk-reduction strategy for quagga invasion prevention.

Early detection and rapid response represent cornerstones of effective management of biological invasions, and development of methods that increase the sensitivity and efficiency of species detection directly benefit such efforts. We compared environmental DNA (eDNA) and canine scent detection of Dreissena polymorpha (Pallas, 1771), the Eurasian zebra mussel, in lakes of central Texas, USA. Environmental DNA analysis has become routinely incorporated as a component of D. polymorpha management programs; however, canine scent detection has typically been limited to inspection for adult mussels on watercraft. Thus, our work represents the first attempt to evaluate detection of D. polymorpha veligers (i.e., free-swimming larval stages) and other microscopic traces in environmental samples with canine scent detection. The specific objectives of this study were to: 1) evaluate whether canines can detect D. polymorpha in environmental samples; 2) quantify and compare limits of detection of canine scent detection and eDNA analysis; and 3) assess the performance of detection technologies through blind screening of ten lakes. In order of objective, our major findings include: 1) canines can be trained to detect D. polymorpha veligers in water samples; 2) eDNA detection is 2–100x more sensitive than canine scent detection; and 3) canine scent detection and eDNA both appear to outperform microscopy for D. polymorpha detection in environmental water samples. However, more work is needed to understand the conditions dictating when canine scent detection or eDNA outperforms the other.

Zebra mussels (Dreissena polymorpha) are an invasive bivalve that has spread across much of the central and eastern U.S. since their initial introduction to North America. Eradication efforts have largely relied on chemical control methods, which can be costly and not always effective. In 2014, a highly localized introduction of zebra mussels was discovered in the 35.6 km² Lake Waco in Central Texas, USA. After weighing treatment options, a decision was made to attempt eradication using a novel gas impermeable benthic barrier approach previously only used for bivalves to successfully suppress Asian clam (Corbicula fluminea) populations. A polyvinyl chloride benthic barrier was installed to cover an area of approximately 3,900 m² of the shoreline and lake bottom in the littoral zone and left in place for nearly five months with frequent monitoring and periodic maintenance. Following barrier removal, environmental DNA, plankton sampling for larvae, and shoreline/substrate surveys for settled mussels were implemented to monitor eradication effort success. Although two live mussels were found immediately after barrier removal indicating mortality was not 100%, there were no further detections of zebra mussels suggesting an insufficient number remained post-treatment to develop a population. Following over five years with no detections, the zebra mussel population was declared to be eradicated from the lake in early 2021. This is the first demonstrated use of a benthic barrier approach to successfully eradicate a dreissenid mussel introduction. The use of this technique was facilitated by early detection, the localized nature of the introduction, cooperation in closing the boat ramp in the affected area, the gently sloping bathymetry of the lake’s littoral zone, and partnership efforts and contributions by multiple agencies and other entities. Lake Waco remains at risk for future zebra mussel re-introduction and early detection monitoring is ongoing.

Sporobolus alterniflorus (S. alterniflorus) is a widespread invasive plant that poses significant threats to coastal wetland ecosystems and local economies worldwide. However, most existing management methods for S. alterniflorus are costly and provide only temporary relief due to reoccurrences and reinvasion. Additionally, limited attention has been paid to examining the application of invasion mechanisms in the design of management measures, hindering the development of effective strategies. In this paper, we reviewed the literature on the mechanisms and management of S. alterniflorus invasion. We identified the key factors enabling invasion mechanisms, analyzed how they are targeted in current control methods, and pointed out their implications for future research. We recommend that the invasion mechanisms of S. alterniflorus should be comprehensively considered during the design of management measures. Furthermore, future research on invasion mechanisms could focus on the joint effects and the relative roles of individual factors in successful invasion, the impact of S. alterniflorus invasion on the coupled human and natural systems, and the systematic review of studies at different scales.

Nitellopsis obtusa is a large invasive freshwater macroalgae that forms extensive, monotypic beds which have altered habitat and impacted littoral communities in lakes across North America. N. obtusa is native to Eurasia including the UK but is considered to be cryptogenic and likely introduced in Ireland, where it was first recorded in 2016. Recent evidence of its spread prompted this hydroacoustic survey which investigated the distribution and abundance of N. obtusa in two large interconnected lakes, Loughs Ree and Derg, within the Shannon River system. Using a consumer grade depth finder and a simplistic approach, we propose an accessible method of hydroacoustic surveying for macrophytes such as N. obtusa which form dense, often monotypic beds. Nitellopsis obtusa beds quantified within three bays in Lough Ree covered 254.4 hectares with a total biovolume of ~ 2.7 million m³, indicating that it may be one of the most aggressive macrophytes introduced to Ireland. The hydroacoustic survey methodology proved to be cost and time efficient. Measurements of plant height and lake depth gathered from the hydroacoustic survey were comparable to diver gathered measurements which provides confidence in the methodology. The rapid expansion of N. obtusa within Loughs Ree and Derg is a concern for other alkaline waterbodies in Ireland, especially marl lake systems, and warrants monitoring. There is no feasible method to eliminate the extensive populations of N. obtusa in Lough Ree and therefore management interventions should aim to limit the spread of this species to other waterbodies.

Invasive alien species frequently possess seed related attributes that contribute to invasion success, such as environmental tolerance, numerous seeds, longevity, rapid germination, and high germination rates, among others. These traits can enhance propagule pressure, thus having important implications for management. The genus Kalanchoe contains species widely used in the horticultural trade, but a few have become invasive around the world. We evaluated the performance of Kalanchoe delagoensis seeds of different age to determine the probability of generating a seed bank under dark-light conditions and constant/alternating temperature to assess photoblastic response and seed tolerance to temperature. Seeds were sown following a factorial experiment that comprised four seed ages (5, 8, 11 and 13 months after collection), two temperature conditions (25 °C constant and 16/25 °C alternating), and two light conditions (light and darkness) resulting in 16 experimental treatments with 10 replicates each and 50 seeds per replicate. Seeds were positive photoblastic with no germination under darkness conditions. Final germination percentage ranged from 1.8% to 49.4% among treatments but decreased with seed age and the interaction with temperature. Mean germination time ranged from 4.5 to 10.9 days among treatments. Results suggest that K. delagoensis seeds germinate rapidly, and have a neutral response to the 16/25 °C alternating temperature in germinability. Seed viability rapidly decreases within the first year after the reproductive season, suggesting that this species would only form a transient seed bank. Avoiding inflorescence maturation and covering or burying seeds will contribute to the depletion of the seed bank over the short term and could provide adequate control of invasive K. delagoensis populations.