Marine bioinvasions are one of the main threats to biodiversity. According to assumptions based on ecological niche models, the conservatism and equilibrium of species with the environment are vital to understanding the bioinvasion process. However, these assumptions have been evaluated primarily for terrestrial species, with few examples in marine environments. We tested the niche conservatism and niche shift hypotheses in native and invaded environments and evaluated the niche dynamics and invasion stages on three invasive marine species: the algae Asparagopsis armata and Codium fragile, and the ascidian Asterocarpa humilis. We applied the identity and background similarity tests to assess the conservatism, the principal component analysis to evaluate the niche dynamics, the Gallien et al. approach to evaluate the invasion stages, and an ensemble of model to estimate potential distribution. Findings showed that the niche equivalence hypothesis was not rejected for any of the species, indicating equivalent ecological niches. Niche similarity demonstrated that niches in native and invaded ranges were not similar as expected by chance for A. humilis and C. fragile. However, for A. armata, the populations in the native and invaded areas had a very similar environmental niche. In addition, high niche stability is evident in the niche dynamics, and so as the stabilization phase of the invasion phases of the three species; thus, studying the three species supported the hypothesis of niche conservatism. These results indicated that all three species have dispersed and are in biogeographic equilibrium within their invaded regions.

Tubastraea coccinea is a coral species originally described for the Pacific Ocean. It is widely distributed throughout the Brazilian coast and in several other Atlantic areas. Its widespread occurrence is presumably facilitated by its production of secondary metabolites with defensive action against predators and competitors. This study evaluated the spatial and temporal variability in the chemical profile of T. coccinea in Arraial do Cabo Bay, Southeastern Brazil, using GC/MS analysis. We also compared the profiles between sites/seasons with non-Metric Multidimensional Scaling (n-MDS) and Principal Component Analysis (PCA). Our results showed that the total metabolite (extract yield) decreased in winter and increased significantly in spring. Sterols and fatty acid esters were the main compounds identified in the four T. coccinea populations. The extracts differed qualitatively and quantitatively between the four T. coccinea populations. Winter samples had the highest lipid contents, although they showed the lowest contents of total metabolites. The highest values of extract yields were obtained for the spring samples, while in fall it did not show significant diferences. The n-MDS and PCA also revealed differences in the chemical profiles between fall, winter, and spring samples. However, the observed chemical variability did not allow a clear distinction between the T. coccinea populations. It did reflect similar environmental conditions at sites close to the ocean and sheltered areas. This invasive coral has already adapted itself to the presumed dynamics of interactions with competitors and consumers.

As the impact of coastal development impinge on our natural ecosystem, we are increasingly compelled to study the effects of artificial habitats on the distribution and abundance of marine species. In particular, understanding how physical factors can influence distributional patterns of benthic communities along artificial structures built in ports that create possibilities for a variety of non-indigenous species (NIS) occur. This paper aims to compare the distribution of mollusc’s assemblage along environmental factors known to influence the distribution of epibenthic species: depth, shading and locality features such as distance from shore and period of submersion of artificial structures. Molluscan assemblages were examined over a depth gradient extending from middle intertidal (0 m) to shallow subtidal (5 m). We also assessed and compared the distribution of Eualetes tulipa (established) and Isognomon bicolor (invasive) in two port locations at Northeast coast of Brazil. A total of 33 native species, 7 cryptogenic and two NIS were found. The most abundant was a native species, Crassostrea brasiliana, followed by the NIS I. bicolor and E. tulipa, respectively. Using PERMANOVA: depth gradient, locality and interaction between these fixed factors showed significant effects on the vertical distribution along the artificial structures sampled. Results suggest that recent substrata availability supports the colonization of NIS species and that these, in areas with more stable communities, cohabit with and are regulated by native species. Furthermore, this is the first study discussing the distribution of the established NIS vermetid E. tulipa in Northeast Brazilian coast.

Nuttall’s waterweed (Elodea nuttallii) is an aquatic plant native to North America. In Poland, the species was first identified in the early 1990s and since then it has started to spread in surface waters. We investigated one of the six lakes in Poland (Probarskie Lake), which were reported to be invaded by E. nuttallii among all the lakes monitored in the period 2005–2016. Based on our field survey data (2019 and 2020) and historical monitoring data (2011 and 2017), we explored the rate of invasion, the effects on taxonomic composition, spatial structure, and abundance of biological assemblages, and the ecological status assessment of this new incomer. We surveyed the lake for macrophytes, phytoplankton and macrozoobenthos for two subsequent years using the field protocols applied in lake monitoring in Poland. Water physicochemistry, planktonic algae and benthic invertebrates were sampled at the sites that were invaded and uninvaded by E. nuttallii, and phytoplankton and physicochemistry also in pelagic sites. Nuttall’s waterweed was identified in Probarskie Lake in 2017 for the first time, occupying about 30% of the phytolittoral area, while in 2019 and 2020, it dominated the macrophyte community, occupying over 80% of the total hydrophyte area. The appearance of the alien invader and its relatively fast taking over of the dominance in the macrophyte community were not reflected in the bioassessment results. None of the analysed biological assemblages truly mirrored the severe changes in macrophyte taxonomic composition among the sampling sites as well as over the subsequent years. As the spread of E. nuttallii is anticipated to increase in Polish waters, there is an urgent need for verification of ecological status assessment methods to improve their diagnostic capacity to capture the problem of ecological invasions.

The freshwater crayfish Pacifastacus leniusculus is among the most widespread invasive crayfish species in Europe. Pacifastacus leniusculus invaded Hungary around 1998 and here we investigated the recent expansion of this species and its impact on other aquatic macroinvertebrates. The colonization of watercourses throughout Europe by the signal crayfish resulted in negative impacts on the present aquatic communities. Our investigation (i.e. in Rába, Pinka, Gyöngyös-stream, Répce, Arany-stream and Strém systems) revealed that the distribution range of signal crayfish is still in expansion in the western part of Hungary and in all likelihood impacting the aquatic communities in these watercourses. Our results obviously demonstrated that signal crayfish densities were highest in habitats with gravel or coarse particulate organic matter, which seems to reflect a species-specific habitat preference. Our investigation proved that the presence of P. leniusculus had negative effects on a number of protected species such as Calopteryx virgo and Onychogomphus forcipatus next to a significant negative effect on the Odonata and Trichoptera species richness as well as on the abundances of Ephemeroptera, Odonata and Trichoptera. Our study in Hungary supports the notion of the significant negative impact of signal crayfish on native freshwater invertebrate communities throughout Europe. In order to assess whether these impacts are restricted to fast flowing waters only, an adequate monitoring plan providing more knowledge on this species with respect to biotic and abiotic preferences and aquatic macroinvertebrate composition is required.

Originating from South East Asia the catadromous Chinese mitten crab (Eriocheir sinensis H. Milne Edwards, 1853) is listed as one of the 100 world’s worst invasive species. In 1912 E. sinensis was first recorded in Central Europe. Nowadays the species is common in various European rivers and widespread in large rivers of the northern hemisphere. High densities of the crab can cause serious economic damage in water management and to the fishing industry. During their natural migration from the estuary upstream, subadult individuals are able to reach river sections several hundred kilometers away from the delta. The ecological impacts on community and food web structures of the Chinese mitten crab (CMC) are less often considered in scientific studies than their economic effects. The diet of CMC under natural conditions is rarely studied, but macrophytes are known to be an important food source of the crab. However, in the main stretch of the Lower Rhine macrophytes are broadly missing. Initial stable isotope analyses showed that CMC occupies a trophic level comparable to carnivorous fish in this system. Thus, a strong predatory impact of CMC on the fauna is likely. Here we use qualitative and quantitative approaches to investigate the diet of Chinese mitten crab to estimate their impact on the food web. Bulk stable isotope analyses of δ¹³C and δ¹⁵N of E. sinensis and potential food resources were conducted and genetic gut content analyses (GGCA) via group-specific primers for common macroinvertebrates of the River Rhine were used to determine prey organisms. While GGCA only rarely detected invertebrate prey and many plant fibres were visible in the stomachs and guts of the CMCs, stable isotope mixing model (simmr) analyses revealed a high contribution of some easily accessible macroinvertebrate species to the CMCs diet. This contradiction between the gut content findings and the simmr mixing model results indicate not only that animal material is more easily assimilated, but also that the CMC may have a strong impact on the benthic fauna of the Lower Rhine, which would have been underestimated if solely gut content analyses were used.

We report on the discovery of a wild, reproducing population of Channa aurolineata (Pisces: Channidae) in west-central Florida (USA), and first documented occurrence of snakeheads in the Gulf Coast region. Channa aurolineata is a large, predatory fish of the bullseye snakehead “Marulius group” species complex from Asia. Adult and juvenile specimens were captured in June 2020 in a 1.8-hectare pond that connects during high water to a small stream within the Manatee River-Tampa Bay Basin. The pond site is 250-km from the only other wild C. aurolineata population in the USA (present in southeast Florida since ca. 2000) and is considered a separate introduction and not the result of natural dispersal. Morphological and molecular comparisons revealed high overlap between the two Florida populations, evidence humans may have transported fish between sites. To verify identification, we compared Florida samples to C. aurolineata from Thailand and found mtDNA-COI barcode sequences to be identical or to differ by only a single base pair. Life body coloration of Florida samples matched their Asian counterparts, but Florida specimens averaged fewer dorsal fin rays (53.6 vs. 56.0), anal fin rays (34.2 vs 36.1), lateral line scales (65.3 vs. 67.4), and vertebrae (62.1 vs. 64.3), differences implying possible founder effect or sampling bias. Existence of this invasive predator is a concern because of the risk of spread and negative ecological effects, including an observation of terrestrial hunting behavior. In 2020–2021, several hundred C. aurolineata were removed from the pond by nets and electrofishing, and surveys suggested the population had not spread to nearby waters. In May 2021 the pond was treated with rotenone and 48 more specimens were recovered. No additional snakeheads have been sighted since the piscicide operation, although verification of eradication will require monitoring of the watershed.