Ponto-Caspian gammarids comprise dozens of endemic taxa. Many are invasive throughout the world, being exceptionally adaptable thanks to the dynamic geological history of the region where they have evolved. Many species described from the Caspian basin were found in the Pontic (Black Sea) basin only in the last century. It remains unclear whether they are native or non-native in this region. Herein, we investigate whether Amathillina cristata, originally described from the Caspian Sea and occasionally listed as an invasive species in the Black Sea, is in fact native to the Black Sea basin. To achieve this goal, we analyse molecular data from Ukraine and – for the first time ever – from Turkey; we also review the entire geographical distribution of the species. For descriptive purposes, we document for the first time the cuticle ultrastructure throughout the body, appendages and mouthparts using scanning electron microscopy. Our results show that A. cristata is distributed in the NW-W part of the Black Sea basin and all investigated Black Sea drainages contain unique haplotypes that appear to have been isolated since the Late Pleistocene, demonstrating that this species is native throughout this basin. Ultrastructure investigation revealed a uniform pattern of pores and sensilla throughout all body regions except the urosome. At least two colour morphs were observed in living specimens. We consider that this species is vulnerable, in particular the Ukrainian populations, due to the high anthropogenic pressure in the region. The destruction of the Kakhovka reservoir in June 2023 most likely affected the known populations in the lower reaches of the Dnieper and Southern Bug rivers.

We report two new for science genetically distinct Molecular Operational Taxonomic Units (MOTUs) of Lepidochitona molluscs from the Ukrainian and Romanian North-Western part of the Black Sea, assess their conservation status using IUCN ratings and evaluated their habitats according to the European Red List of Habitats. The genetic analysis was done based on DNA-barcoding analysis of the cox1 gene region. This is the first molecular data for this genus from the Black Sea region. Although previous morphological studies suggested the presence of two species in this area: mediterranean Lepidochitona cinerea and the recently described local species L. bondarevi, genetically they remained unstudied. Our DNA-barcoding analysis confirmed the presence of two species; moreover, analysis showed that the Ukrainian MOTU of Lepidochitona aff. cinerea is genetically different from those two European L. cinerea. Considering the uniqueness of Lepidochitona genus in the Black Sea basin, we assessed IUCN conservation status of species. Chitons L. bondarevi was classified as Vulnerable under IUCN criteria B2a,c(ii,iii) due to their Area Of Occurrence (AOO) criteria and fragmented locations which exacerbated by the ongoing from 2022 military conflict in the Black Sea. Chitons Lepidochitona aff. cinerea, the Black Sea MOTU, is more adaptable than L. bondarevi and is not limited to a narrow strip of coastal habitats, thus have not a high level of protection according to any of the IUCN criteria measured as they do not require it since they are less limited in terms of their habitat requirements. Our study underscores the endemicity of chitons in the Black Sea and needs in conservation efforts of Lepidochitona.

Freshwater bivalves (FWB) are attracting scientific and societal attention given their essential ecosystem services, ecological functions, and poor conservation status. Current knowledge of the spatial distribution of West Palearctic FWB is poor preventing the understanding of biogeography and conservation planning. One of the priorities of the pan-European networking project "CONFREMU - Conservation of freshwater mussels: a pan-European approach" funded by the European Union, was to fill the knowledge gap on the distribution of FWB in Europe and adjacent regions. Based on the efforts of this network of scientists, we provide the most complete, taxonomically, and geographically accurate distribution of FWB species for the entire West Palearctic. The dataset contains 270,287 geo-referenced records of 93 native and 8 non-native FWB from 1674 to 2023. The dataset compiles information from private records from 82 specialists and multiple sources (e.g., published articles, grey literature, biodiversity databases, and scientific collections). This dataset, available online, represents an important data source for future studies on the biodiversity, biogeography, and conservation of these important organisms.

Shellfish mariculture, particularly of oysters, poses a significant risk for the introduction of non-native species into marine ecosystems. This study investigates the diversity of invertebrate species colonizing live and discarded oyster shells originating from a farm and oyster bar in the Tylihul Estuary, a region with active oyster farming. Advanced molecular techniques identified several invasive species associated with the discarded shells, including Semibalanus balanoides, Austrominius modestus and Monocorophium insidiosum. These taxa have not been previously documented in the region. Our findings indicate that macrofaunal composition differs between live and discarded oyster shells, and that the richness of invasive invertebrates associated with oyster shells is higher than expected. The discarded shells not only act as a substrate for colonization but also serve as potential vectors for biological invasions. We performed a Species-related Risk Assessment to identify the potential ecological impacts on local biodiversity and ecosystems of the invasive species associated with oysters. Our study proposes management strategies aimed at mitigating the risks associated with shells discarded by oyster bars. Our recommendations include informing recreational travellers and retailers about the implications of discarding shells into the water and advocating for the control of risks related to the use of shells as a construction material.

Biological invasions pose a significant threat to aquatic ecosystems, and the spread of uncontrolled non-indigenous species can have detrimental effects on biodiversity, ecosystem processes, and economic activities. The Chesapeake blue crab, Callinectes sapidus, native to the western Atlantic Ocean, is non-indigenous in the Black Sea region. This study presents novel findings on its presence and breeding in the Black Sea, particularly in North-Western part within the territorial confines of Ukraine. The study provides evidence of successful reproduction by a female blue crab with eggs in this non-native habitat, i.e. off the coast of Ukraine. Furthermore, molecular DNA barcoding analysis revealed the Ukrainian crab to be of a haplotype found in Italy and the United States, indicating potential connectivity between the Black Sea population and other established populations. Additionally, other haplotypes were detected in the Black Sea region, suggesting the possibility of multiple introductions and admixture between non-indigenous populations of different origins. The successful establishment and spread of C. sapidus in the Black Sea region may be attributed to its adaptability to a wide range of environmental conditions and the lack of natural predators or competitors in the invaded regions. This crab is commercialized in the USA, which may have implications for fisheries and aquaculture activities in Ukraine.

The Marine Strategy Framework Directive (MSFD, 2008/56/EC) sets the foundation for community actions in the field of marine environmental protection and a robust and collaborative assessment of the implementation of measures by Member States (MS) of the European Union. In particular, the Commission Decision (EU) 2017/848 lays down criteria and methodological standards on good environmental status (GES) for assessing non-indigenous species (NIS) pressure in marine waters. One of these criteria (i.e. D2C1) aims to minimise and where possible reduce to zero, the number of NIS newly introduced into Europe’s marine waters. To this end, the need for up-to-date data on newly introduced NIS is paramount to enable a quantitative assessment of D2C1. This paper provides a summary of the latest developments on the methodologies for assessing D2C1 and their application on the Black Sea dataset. The analysis identifies common practices and needs; strengthening NIS monitoring would improve the confidence of NIS assessment and allow for investigation of changes in NIS spread, ecological impact and effectiveness of management action. Additional efforts should also be made to ensure access to the monitoring results.

Mass mortality events (MMEs) are decimating populations and compromising key ecosystem functions around the globe. One taxon particularly vulnerable to MMEs is freshwater bivalve mollusks. This group has important ecosystem engineering capacities and includes highly threatened and highly invasive taxa. Thus, MMEs of freshwater bivalves have important implications for conservation and ecosystems. Despite this, little is known about the magnitude, frequency, duration, distribution, and causes of freshwater bivalve MMEs. Using a questionnaire, we compiled data from 239 reports describing freshwater bivalve MMEs across 22 European countries since 1960. With these data, we analyzed trends in MME timing, location, and magnitude; identified the species affected; and evaluated the suggested causes (including reporter certainty). We found that the frequency of reports of MMEs increased each year, MMEs affected a broad range of species, clear geographical patterns linking certain causes to specific locations were lacking, factors related to drying and habitat destruction predominated suggested causes, and considerable uncertainty surrounded the causes of many MMEs, particularly those associated with potential pollutants and disease agents. Based on our findings, we recommend the standardization of many aspects of MME research (e.g., reporting and recovery assessment protocols), increased surveying for MMEs, further investigation into the causes of MMEs, especially those with significant uncertainty, and immediate actions to improve waterbody management, mitigate the effects of high temperatures, and further protect freshwater bivalves through the development and implementation of appropriate management actions and legislation.

The taxonomy of the notostracan Lepidurus is complicated by a large number of synonymised species and extensive intraspecific variability in many relevant characters. We demonstrate, based on an integrative taxonomic approach, that the Ukrainian populations of Lepidurus are not conspecific with any currently accepted Lepidurus species and assign them to the previously synonymised species Lepidurus middendorffiicomp. nov. (). This species exemplarily highlights the problems in the taxonomy of Lepidurus. The species was originally described as Apus extensus var. middendorffii (), but L. extensus is a junior synonym of Lepidurus lubbocki (), which is currently treated as a subspecies of Lepidurus apus (). Our molecular genetic analyses based on mitochondrial COI, 12S, 16S, and nuclear 28S, which included published data, suggest the presence of further, possibly cryptic species that await formal recognition and stress the importance for a more extensive revision of Lepidurus. The original type specimens of L. middendorffii, previously stored at the Museum of Natural History (Wroc & lstrok;aw University, Wroc & lstrok;aw, Poland), are lost and a neotype is designated. Lepidurus middendorffii is characterised by the dorsal organ position between the ocular tubercle margins, the sharp carapace sulcus spines, the long supra-anal plate with many median spines, a telson length to carapace length ratio 0.18-0.35, and differs by > 9% uncorrected COI p-distances from all other Lepidurus species.

At this time East Asian river prawn Macrobrachium nipponense is present almost everywhere in the lower reaches of the Danube and Dniester basins, in the Danube-Dniester interfluves and water bodies to the east of the Dniester. Successful adaptation and favorable climatic conditions in recent years have provided a significant increase in the East Asian river prawn populations in the Danube and Dniester. High growth rates of M. nipponense have been observed in the Danube and Dniester. In these river basins, higher values of maximum body length of the prawn (males 115 mm, females 87 mm) than those recorded in the native range water bodies and the cooler water bodies of thermal power plants during introduction were recorded. In small shallow brackish-water reservoirs of the region (PSU 1.5–6.0) the growth rate of M. nipponense is significantly lower than in the freshwater Danube and Dniester deltaic zones. Female East Asian river prawn in such water bodies mature at a much smaller size. The egg-laying period of female M. nipponense in the Danube lasts from June to October. The peak of egg laying is observed in July and August. There have been reported cases of M. nipponense being affected by crustacean burn-spot disease. The prospect of organizing the fishing of M. nipponense in the Danube River has been determined. It is necessary to continue research to increase selectivity of fishing gears, determination of optimal terms of fishing, and places of installation of fishing gears.

Two new fish species were recorded while monitoring the fish fauna of Sukhyi Lyman (or Sukhyi Estuary), an estuary in the northwestern Black Sea (Ukraine) close to the marine port of Chornomorsk. A single pumpkinseed, Lepomis gibbosus (Linnaeus, 1758), was observed in May 1999, followed by numerous observations in May 2021, while a single peacock blenny, Salaria pavo (Risso, 1810), was photographed during snorkeling observations in September 2021. The estuary is a known hub for invasive alien species and other neobionts due to the presence of the marine port. The new population of pumpkinseed, a North American invasive species, in the estuary represents the next stage in the species’ ongoing expansion along the Ukrainian Black Sea coast. Likewise, the appearance of the peacock blenny represents the latest stage in the “Mediterranization” of the Black Sea, a process that has been ongoing over the last several thousand years.

The SE Baltic region harbors a diverse assemblage of alien amphipods of Ponto-Caspian origin. The composition of this fauna was shaped by three invasion waves: (1) pre-twentieth century dispersals via watershed-connecting canals, (2) deliberate introductions in the 1960s, and (3) last decade dispersals via shipping and existing canals. Given this complex history, we test whether genetic diversity (mitochondrial COI and nuclear OPS) differs between the native and invaded ranges and between the deliberately introduced species and the ones that dispersed on their own. We find that in the native range the two species groups exhibited similar COI diversity, while OPS diversity was higher in the deliberately introduced species. In the invaded range, COI diversity significantly decreased in all species, but more so in the self-dispersed group. No change in OPS diversity was detected among ranges. Mitochondrial diversity was more structured geographically in the native range, and the dominant invasive haplotypes were detected in the native populations of all but one species, further highlighting the utility of this marker in tracing invasion sources. Our comparative approach provides important insight into the inter-range genetic diversity of Ponto-Caspian invaders, highlighting the role of introduction mode.

The invasive Asian date mussel Arcuatula senhousia has now been recorded from the Shatt Al-Basrah Canal in the south of Iraq.High densities of up to 102 ind.m -2 were found on rocky substrates in the intertidal zone during March 2020.The species was confirmed based on morphological characters of the shell.We hypothesize that the initial introduction was associated with shipping, with secondary dispersion into the Shatt Al-Basrah canal.It is possible that the species could extend its distribution into the Shatt Al-Arab and northern Arabian Gulf naturally or by additional anthropogenic means.

Studies of alien aquatic invertebrates in 2021-2022 covered fresh marine and transitional waters mostly within the boundaries of the Danube Biosphere Reserve. As a result of these studies, important new findings of six species of aquatic macroinvertebrates were obtained: Menetus dilatatus (Gould, 1841) is first indicated for the Danube Basin, and three marine species (Arcuatula senhousia (Benson, 1842), Polydora cornuta Bosc, 1802 and Streblospio gynobranchiata Rice & Levin, 1998) for the first time for Ukrainian Danube Delta. For two species (Pectinatella magnifica (Leidy, 1851) and Ferrissia californica (Rowell, 1863)), new localities were found within the delta. In the case of M. dilatatus, the pathway of entry into the Danube Delta is an absolute mystery. The most likely pathway of dispersal of this species is natural dispersion, both along the river network and associated with waterfowl, however, the large distance between the Danube Delta and the nearest locations in Western Ukraine makes direct transportation unlikely. In all probability, the similarity of this species with local species leads to the formation of cryptic populations, not identified by researchers, which may be intermediate stages of species expansion towards the Northrn Black Sea area.

The Ponto-Caspian amphipod Dikerogammarus bispinosus was originally described from the Black Sea basin. Its recent discovery in the Caspian Sea basin was puzzling because it was unknown whether it was an invasive or an overlooked native species in this area. Here, we examined specimens collected from both the Black and Caspian Sea basins by means of molecular species delimitation based on nuclear (28S) and mitochondrial (COI) DNA sequences, as well as scanning electron microscopy (SEM). Our analyses reveal that D. bispinosus comprises three evolutionary independent lineages that are molecularly and morphologically distinct. One lineage occurs throughout rivers in the Black Sea basin, while the other two inhabit the Caspian Sea and were found in sympatry, further reinforcing that they are distinct species. Our time-calibrated phylogeny indicates that these lineages split during the Late Miocene-Pliocene, a period corresponding with the separation of the Black and Caspian basins via the Caucasus mountain uplift. SEM imaging revealed morphological differences with respect to setal patterns on the gnathopod propodi among all three lineages. Therefore, our results clearly indicate not only that D. bispinosus is native in the Caspian region, but that it has been overlooked for a long time. Additional populations covering the entire range of this species complex need to be further studied in order to gain a more complete picture of its evolutionary history and resolve its taxonomy.

ABSTRACT Here, we investigate the shell shape variation of some closely related freshwater species of the bivalve genus Corbicula using descriptive (qualitative), geometric morphometric and traditional conchometric approaches. The combination of these different approaches allows for an effective discrimination between the species C. fluminalis, C. fluminea and C. leana, as well as an unidentified Corbicula sp. The roundness of the shell hinge is an important diagnostic feature, as are shell sculpture (ribs), symmetry of the apertural margin, and both position and extension of the umbo. We also identify possible hybrids between C. fluminalis and C. leana, with these showing features intermediate to those of the parent species. We examine variability of shell features of C. leana in selected areas in Europe and compare these results with material from the native range of Japan and Korea. For C. leana, we identify two geographic morphotypes from the native area; within Europe, there is a high morphological diversity of this species with several new forms arising, most probably as a result of hybridization.

The declining biodiversity has upsetting consequences for social and economic development and represents a major concern for humanity. Legal and political framework plays an important role in biodiversity conservation planning, implementation, and coordination of actions. Legal provisions are complex and operate on different levels of governance (from supranational to national), which means that the status of single species or populations may be governed by a set of interacting or even conflicting regulations, with increasing complexity for species that occur across national borders. Romania (EU member state) and Ukraine (non-EU member state) exemplify neighboring countries with different governance systems, which share the same endemic aquatic communities inhabiting the transitional zones between freshwater and marine ecosystems, known regionally as Pontocaspian (PC) biota. These communities include flagship species such as sturgeons and less-known crustaceans and mollusks and are severely threatened as a result of human activities. We assessed the legal basis for the protection of PC biota in the Danube Delta and the effectiveness of current conservation approaches based on a review of legal documents and literature, expert opinion, and practitioner reflections regarding PC biodiversity conservation. We found that PC invertebrate species are not adequately addressed in the current legal documents and that the surrogate approach (where protection of umbrella species results in protection of background species) does not work as there is little overlap between the habitats of sturgeons and PC invertebrate communities. Furthermore, the habitat definitions currently used in legal documents lack the level of detail needed to protect PC habitats that are characterized by specific salinity (brackish) conditions. We finish by sketching out recommendations toward improved legal and political frameworks for effective and efficient conservation of PC invertebrate biota.

Europe has a long history of human pressure on freshwater ecosystems. As pressure continues to grow and new threats emerge, there is an urgent need for conservation of freshwater biodiversity and its ecosystem services. However, whilst some taxonomic groups, mainly vertebrates, have received a disproportionate amount of attention and funds, other groups remain largely off the public and scientific radar. Freshwater mussels (Bivalvia, Unionida) are an alarming example of this conservation bias and here we point out six conceptual areas that need immediate and long-term attention: knowledge, threats, socioeconomics, conservation, governance and education. The proposed roadmap aims to advance research, policy and education by identifying the most pressing priorities for the short- and long-term conservation of freshwater mussels across Europe.

Niphargus comprises hundreds of narrowly-endemic West Palaearctic subterranean taxa. However, a few exceptional species inhabit surface waters and have remarkably large ranges. Herein, based on morphological and molecular analyses, we provide important new records for two of these species. N. potamophilus, previously known from the eastern Azov Sea lowlands, is reported for the first time from Ukraine and Bulgaria from localities adjacent to the Black Sea. These findings expand its range westward by more than 1000 km along the coastline. From Bulgaria, we also report for the first time N. hrabei, a species previously known to occur along the middle and lower Danube lowlands and in isolated populations at the foothills of the Northern Caucasus. Our new record thus extends its range southwards by more than 150 km. Both species contained unique haplotypes at all of the sampled localities. These were, nevertheless, not very divergent from more distant populations, emphasizing their good dispersal ability. Ecologically, the sampling localities were generally characterized by stagnant to low running water, dense vegetation, and muddy substrate. Overall, our results bring important insights, shedding more light on the biogeography and ecology of Niphargus.