Hedychium coronarium is an invasive plant widespread in the Brazilian Atlantic forest, especially in riparian areas. However, its distribution along streams is not continuous and the factors that are related to its local occurrence are unknown. We investigated which natural and anthropogenic drivers, particularly concerning dispersal and disturbance, facilitate establishment of H. coronarium. We sampled 148 randomly chosen riparian sites (each containing two plots) in a subtropical basin in southern Brazil and recorded presence/absence of the plant and some environmental variables in situ; other variables were extracted via GIS software. We performed a GLMM with presence/absence as the response variable, sampling site as a random factor and five predictors: intensity of ecosystem degradation, dominant type of terrestrial vegetation, river substrate size class, Strahler stream order and downstream distance to the nearest urban centre. Our results point out that invader presence is favoured by local human disturbance (high riparian degradation and presence of non-native forest), and possibly dispersal, as there is a higher H. coronarium presence probability in proximity to urban centres. Furthermore, a higher presence probability in downstream sections (higher Strahler order) might be explained by hydrologic dispersal of rhizome fragments. Our study illustrates that in the case of riparian invasions it is important to consider terrestrial and aquatic drivers, both natural and anthropogenic.

Fluridone-resistant hydrilla was first suspected in Florida in 1999 and was confirmed using molecular genetics techniques in 2003. Although the vast majority of species that evolve resistance to herbicides or other stressors do so through the genetic mutations that occur during sexual reproduction, all hydrilla in Florida is of the dioecious pistillate (“female”) biotype and all reproduction and spread is via vegetative means. The Hardy-Weinberg principle of constant allele frequencies (i.e., p + q = 1), used to predict allelic frequency shifts within populations due to selection, is based on a number of assumptions that are violated by species that reproduce asexually. In this paper, we address the assumptions of the model in the context of the clonally propagated species hydrilla and compare theoretical model predictions to the likely timeline of actual events that occurred in many bodies of water in Florida. The generational shifts in within-population allele frequencies from almost exclusively fluridone-susceptible to almost exclusively fluridone-resistant track well with the actual development of fluridone-resistant populations of hydrilla in Florida when considering fitness differences among fluridone resistance alleles after fluridone treatments. The present study illustrates how the Hardy-Weinberg principle of constant allele frequencies can be used as an exploratory tool to model resistance evolution in asexually reproducing species such as hydrilla.

The number of organisms that spread and invade new habitats has increased in recent decades as a result of drastic environmental changes such as climate change and anthropogenic activities. Microbial species invasions occur worldwide in terrestrial and aquatic systems and represent an emerging challenge to our understanding of the interplay between biodiversity and ecosystem functioning. Due to the difficulty of detecting and evaluating non-indigenous microorganisms, little is known about them and the processes that drive successful microbial invasions – especially when compared to macroinvasive species. Microalgae are one of the most abundant microorganisms in aquatic systems, and some are able to produce massive proliferations (mats) with significant impact on biodiversity and economic activities. Among microalgae invaders, Didymosphenia geminata is a benthic diatom that constitutes a major global threat for freshwater ecosystem conservation. Despite two decades of research, the cause of mat proliferations remains uncertain. It has been proposed that bacterial biofilm composition may contribute to successful attachment and consequently to proliferation. The aim of this work was to assess the bacterial diversity associated with the mat-forming diatom D. geminata in three aquatic ecosystems of the Chilean Patagonia by implementing genomic-based tools. Using a metabarcoding approach, we determined a core microbiota represented by 4 phyla, 16 families, and 20 genera. Proteobacteria (Alpha and Beta) and Bacteroidetes were the dominant phyla, followed by Cyanobacteria and Planctomycetes. At the lower taxonomic level, unidentified genera from the Comamonadacea family were the most abundant bacteria of the core microbiota. The bacterial composition we found was very similar, with some relative abundance changes, to that reported in a previous study of the bacterial diversity of biofilms from rivers contaminated with D. geminata in New Zealand. This geographical co-occurrence pattern between bacteria and D. geminata in different independent studies suggests that a specific microbiota may be associated with D. geminata distributions, establishment and proliferation. Our work serves as the starting point to design an experimental study that aims to determine whether these specific bacteria facilitate the establishment of the microalgae by creating favorable conditions or are the result of the diatom invasion.

Carijoa riisei is a snowflake coral that has aggressively spread across many coastal habitats in the Atlantic and Pacific oceans, threatening a number of tropical ecosystems worldwide, including coral reefs. The aim of this work was to evaluate the distribution and provide an estimation of abundance of the invasive octocoral C. riisei along the Ecuadorian coast, as well as the relationship between its abundance and different environmental variables. In a field survey, high abundances of C. riisei colonies were reported growing over corals and sessile communities at 5 of 43 sampling sites. The areas with highest relative abundance were found in the Manabí province, at two sites in Jama: Bajo Londres (44.57% coverage) and Vaca Brava 1 (20.25%). Results of ordination and grouping statistical analyses showed no significant differences between invaded and not invaded sites as regards community composition or environmental characteristics, suggesting neither biotic nor abiotic factors could be limiting C. riisei dispersal along the Ecuadorian coast. Results from a bibliographic survey covering occurrence data up to 2020 were in accordance, showing that in that period C. riisei became an established species to the Ecuadorian coast, being present in at least 22 of the 43 sites, including various sites in Marine Protected Areas. Based on these findings, recommendations are made to promote urgent monitoring programs to detect C. riisei in new areas along the coast of Ecuador and in the Galapagos Marine Reserve, in order to develop a mitigation program and to take actions to conserve the ecosystems affected by this invasion.

Sponges are normally considered as living hotels and they have been the most common basebionts (45.5%) for the non-indigenous species Ophiothela mirabilis Verrill, 1867 in the Brazilian coast. This ophiuroid is native to the Pacific Ocean but is spreading out in the Tropical Western Atlantic since 2000. Regarding this invasion, quantitative data is necessary to understand O. mirabilis threat. The aim of this study was to quantify the abundance of O. mirabilis on marine sponges along the Brazilian coast, and to evaluate the relationship of the non-indigenous species with sponge phenotypes, to test the hypothesis that this non-indigenous species prefers erect, irregular and yellowish sponges to facilitate attachment and camouflage. Epibiosis of O. mirabilis on sponges were photographed in 27 sites from Maranhão to Rio de Janeiro States, Brazil, and the abundance of sponges and ophiuroids on each sponge individual was counted. Only Bahia and Rio de Janeiro States presented an association, which was positively correlated (R² = 0.85, F = 36.16, p < 0.001) between sponges and ophiuroid mean abundances. No morphological trait was statistically chosen by O. mirabilis, but the null probabilistic model indicates Mycale (Zygomycale) angulosa (Duchassaing & Michelotti, 1864) may be a preferred sponge basebiont. This first large-scale quantitative study indicates O. mirabilis may become a dangerous invader due to weak host preferences and efficient asexual reproduction strategy. This work can be used as a baseline template for monitoring and eradication programs, especially in Brazilian bays of high diversity and with human impact.

Zebra mussels (Dreissena polymorpha) are one of the most economically and ecologically disruptive aquatic invasive species in North America, where they damage infrastructure and alter ecological processes. Understanding zebra mussel propagule pressure and establishment is essential for predicting expansion into subtropical lakes and reservoirs. Key water quality parameters, such as temperature, water clarity, dissolved oxygen, and primary productivity have been found to play major roles in these processes. To test if environmental variation affected zebra mussel propagule pressure and establishment within a large, subtropical lake, we measured zebra mussel larval (veliger) abundances in the water column and post-veliger abundances on hard surfaces and quantified water quality during 2011–2015 at six sites spanning 32.8 km in Lake Texoma, OK-TX which differed markedly in salinity, water clarity, and algal abundances. We found that densities of both life stages were lower at western sites with lower water clarity, higher salinity, and higher productivity. Additionally, higher numbers of zebra mussel post-veligers accrued on the undersides of deeper surfaces, suggesting preference for lower temperatures and refuge from predators. Our results suggest that in habitats that are particularly stressful for zebra mussels, water quality predicts propagule pressure and establishment of zebra mussels across a lake, emphasizing the need to consider environmental heterogeneity within large lakes when predicting the potential range and impact of this cosmopolitan invader.

Both the quagga mussel (Dreissena bugensis) and the zebra mussel (Dreissena polymorpha) are notorious for dominating hard substrates in freshwater ecosystems throughout most of the Northern hemisphere. Despite widespread observations of a dominance shift favouring D. bugensis, where both Ponto-Caspian dreissenids co-occur, mechanisms driving this shift are still largely unknown. This study assessed whether movement behaviour differs between these two mussel species. That way we aimed at assessing whether mobility might be a contributing driver to the observed dominance shift. The mobility of dreissenids was assessed in an experimental set-up consisting of polyethene tanks marked with squares and concentric circles facilitating location tracking of the dreissenids by time-lapse photography. Specimens were collected at the Haringvliet and Hollands Diep in the Rhine-Meuse river delta. The experiments mimicked unfavourable habitat conditions by drying, cleaning, tagging and placing mussels in a new environment. After these disturbances, the movement rate, duration, distance, pattern and speed of 299 individuals were monitored. For both species, most individuals moved in more or less circular patterns, causing their actual movement distance to be twice as high as their displacement distance. The average movement duration within 24 hours after the start of each experiment was 65 min, with an average speed of 28 cm/h and an average distance of 29 cm. Hereby no significant differences were found between D. polymorpha and D. bugensis. However, a higher top speed was observed for D. bugensis than for D. polymorpha. The fastest individuals of these two species moved at 90 cm/h and 60 cm/h, respectively. Moreover, about twice as many D. bugensis individuals moved during the experiments in comparison to D. polymorpha individuals. Hereby it was recorded that any point in time close to 10% more D. bugensis specimens were moving around. The results support our hypothesis that D. bugensis could have a competitive benefit over D. polymorpha by having a higher top speed and a significantly higher number of individuals moving after a disturbance of their population. Detachment and mobility of sessile mussel species are supposed to be avoidance mechanisms during unfavourable environmental conditions. Therefore, mobility might be one of the contributing drivers of the observed dominance shift between both species.

Dreissenid (zebra and quagga) mussels are spreading across North America and having an impact on freshwater ecosystems, through bottom-up impacts. Lakes in British Columbia are known to be at risk for mussel invasion due to favourable water chemistry and significant cross-border boat movements. This project uses Ecopath with Ecosim (EwE) to model a hypothetical mussel invasion into Shuswap Lake: one of the most popular lakes for recreation and one of the most productive sockeye lakes in the province. A model of the ecosystem was fit to available data and then projected forward to examine the effects from three different scenarios: no invasion, a base mussel invasion scenario resulting in a carrying capacity of 5 g∙m^-2 and 15 g∙m^-2 of zebra and quagga mussels, respectively, and a high density invasion scenario resulting in a combined carrying capacity of 40 g∙m^-2 of Dreissenid mussels. The greatest ecosystem impacts resulted in declines in large piscivorous rainbow trout and lake trout, followed by non-anadromous kokanee salmon, with little effect observed on anadromous sockeye salmon. Two mechanisms limit the predicted impact of mussels in the study system: (1) paucity of shallow water habitat, limiting the scope for invasion; and (2) movements by fish in and out of the system. This second mechanism includes some resident species that rear for up to three years upstream of the lake, as well as anadromous species, which spend most of their life in the marine environment. While most of the effects are observed on recreationally important species, there is also the possibility of mussels spreading from this system into others within the same watershed, reiterating the importance of preventing the invasion and spread of Dreissenid mussels.

Genetic compositions and comparative diversity of zebra (Dreissena polymorpha) and quagga (D. rostriformis) mussel populations are compared across their three decade-long histories as invasive species in the Hudson River and Lake Erie of North America. We analyze 15 nuclear DNA microsatellite loci for the zebra mussel and 10 for the quagga mussel. Results indicate that the Hudson River and Lake Erie zebra mussel populations slightly diverge in genetic compositions, and possess similar overall genetic diversity levels. The allelic composition of the Hudson River zebra mussel population significantly changed during the middle time period (2003) analyzed, suggesting genetic replacement. Yet, its overall levels of genetic diversity levels have stayed similar. In contrast, the Hudson River’s quagga mussel population has remained genetically consistent over time in both composition and diversity. Lake Erie’s zebra mussel population underwent slight change in allelic composition and increased in genetic diversity from the earliest timepoint, suggesting allelic supplementation from newly arriving propagules. In contrast, Lake Erie’s quagga mussel population has remained genetically consistent over time. The genetic composition of Lake Erie zebra mussel veliger larvae sampled in 2016 differed from its adult samples, attributable to gene flow from other areas and genetic admixture. Overall findings indicate that invasive populations may undergo significant genetic divergence or remain consistent over time, whose patterns may differ across their ranges and between related species. The population dynamics underlying their invasional successes thus may be complex.

Non-native species that become invasive threaten natural biodiversity and can lead to socioeconomic impacts. Prediction of invasive species distributions is important to prevent further spread and protect vulnerable habitats and species at risk (SAR) from future invasions. The Chinese mystery snail, chinensis, native to Eastern Asia, is a non-native, potentially invasive, freshwater snail now widely established across North America, Belgium, and the Netherlands. This species was first reported in Nova Scotia, eastern Canada in 1955, but was not found to be established until the 1990’s and now exists at high densities in several urban lakes. Nonetheless, the presence and potential distribution of this species in Nova Scotia remains unknown. Limited resources make it difficult to do a broad survey of freshwater lakes in Nova Scotia, however a species distribution probability model has the potential to direct focus to priority areas. We apply a random forest model in tandem with a combination of water quality, fish community, anthropogenic water use, and geomorphological data to predict C. chinensis habitat in Nova Scotia (NS), Canada. All predicted probabilities of suitable C. chinensisi habitats in Nova Scotia were > 50% and include Cape Breton Island, the Nova Scotia-New Brunswick border, and the Halifax Regional Municipality. Suitable habitats predicted for C. chinensis overlap with many SAR habitats, most notably brook floater mussel, Alasmidonta varicosa, and yellow lampmussel, Lampsila cariosa. Our results indicate that C. chinensis could become widespread throughout NS, appearing first in the aforementioned areas of highest probability. Further research is required to test C. chinensis ecological thresholds in order to improve the accuracy of future species distribution and habitat models, and to determine C. chinensis impacts on native freshwater mussel populations of conservation concern.