The scale of the dataset reflects years of patient compilation. The researchers searched scientific literature stretching back to the mid-nineteenth century, identifying nearly five hundred relevant publications that together span more than 150 years of documentation. To this historical record they added a systematic nationwide field campaign conducted between 2020 and 2022, in which surveyors visited sites across the country using sampling methods tailored to each environment. A third stream came from citizen science, specifically research-grade observations uploaded to the iNaturalist platform through the end of 2023. By merging these three sources into a single standardized, openly accessible dataset, the team created a resource that meets FAIR principles, meaning the data are findable, accessible, interoperable, and reusable, which makes them usable not only for national reporting but also for continental-scale analyses of invasion patterns.

The taxonomic breakdown of the 297 species is telling. Terrestrial species dominate the list, accounting for roughly seven in ten of all alien invertebrates recorded in the country. Marine species make up nearly a fifth, a reflection of Romania’s Black Sea coastline and the intense shipping traffic that connects the region to global trade routes. Freshwater species, while the smallest group numerically, include some of the most ecologically consequential invaders, particularly crustaceans and mollusks that have moved along inland water corridors. This distribution mirrors patterns seen elsewhere in Europe, where terrestrial arthropods tend to accumulate the largest numbers of introductions while aquatic species often generate the most dramatic ecological disruptions.

One of the most striking findings concerns how little overlap exists between data sources. More than half of the species in the dataset, 170 in total, were documented by only one of the three sources consulted. Scientific literature proved the richest single source, yielding 241 species, yet 119 of those had not been confirmed by recent fieldwork or citizen science observations. This gap could reflect genuine local extinctions, misidentifications in older publications, or simply the fact that many species are so inconspicuous that modern surveys have not yet targeted them. Conversely, citizen scientists contributed records for 60 species, and eight of those were documented exclusively through public participation, demonstrating that volunteer observers can detect species that professional researchers and historical records have missed entirely.

The complementarity of these sources carries practical implications. Historical literature captures species that arrived decades ago and may no longer be present, but it also establishes baselines against which current distributions can be measured. Systematic fieldwork provides standardized, verifiable records with precise locations and collection dates, which are essential for tracking population trends over time. Citizen science offers vast spatial coverage at low cost, with thousands of volunteer observers effectively extending the reach of professional ecologists into private gardens, urban parks, and remote areas that would otherwise go unsampled. The challenge, as the study makes clear, is that each source carries its own biases, and treating any single source as definitive risks either overestimating or underestimating the true extent of biological invasions.

Geographically, the records cluster strongly around Romania’s major urban centers and along its waterways. This pattern is consistent with what invasion biologists have documented across Europe and beyond: cities act as gateways for introductions because they concentrate trade, transport infrastructure, horticulture, and the pet and aquarium trades, all of which are well-established pathways for moving species across continents. Rivers and canals serve as dispersal corridors once species become established, allowing them to spread from initial introduction points into surrounding landscapes. The Danube River, which flows through Romania and connects the country to a vast catchment spanning much of central Europe, is particularly significant in this respect. The river system has historically functioned as a conduit for Ponto-Caspian species moving westward into the rest of Europe, and it continues to channel new arrivals into Romanian waters.

The Ponto-Caspian region, encompassing the Black, Caspian, and Azov Seas and their tributaries, deserves particular attention as a source of freshwater invaders. Research on other major European rivers has shown that a substantial proportion of alien macroinvertebrates established in western European waterways originated from this region. Species that evolved in the brackish and variable conditions of Ponto-Caspian basins appear pre-adapted to survive transport in ship ballast tanks and to tolerate the salinity and temperature fluctuations they encounter in canal systems. Romania sits at the downstream end of this corridor, which means the country both receives invaders from upstream and, historically, has served as a donor region for species spreading elsewhere in Europe.

Among the species flagged as management priorities in the study are three listed as invasive alien species of concern under EU Regulation 1143/2014: the spinycheek crayfish, the marbled crayfish, and the Chinese mitten crab. The spinycheek crayfish, native to North America, has been spreading through Danube tributaries for years and is known to outcompete native crayfish species while also acting as a vector for the crayfish plague, a fungal disease lethal to European crayfish. The marbled crayfish is remarkable because it reproduces entirely without males, through a form of cloning, meaning a single individual released into the wild can found a new population. The Chinese mitten crab, a catadromous species that migrates between fresh and salt water, has invaded waterways across Europe and causes damage through its burrowing behavior and mass migrations. Despite their documented invasive potential, all three species show sparse occurrence records in the Romanian dataset, suggesting that current monitoring may be insufficient to track their actual distributions.

This gap between known and actual distributions is a recurring theme in invasion biology and has direct consequences for policy implementation. EU Regulation 1143/2014 requires Member States to establish early detection and rapid response systems, which depend on timely and accurate information about where invasive species are present. If a species is spreading undetected because no one is looking in the right places, the window for cost-effective eradication closes before authorities even realize it is open. The study’s authors argue that closing this gap requires not just more surveys but better integration of the data streams that already exist, connecting researchers, citizen scientists, and policymakers through interoperable information systems that allow records to flow quickly from observation to database to decision-making.

The economic stakes of invertebrate invasions are substantial. Global estimates suggest that terrestrial invertebrates alone have cost the world economy hundreds of billions of dollars, with invasive insects responsible for the overwhelming majority of documented expenses. These costs arise from crop damage, infrastructure degradation, disease transmission, and the expense of control programs. Romania’s agricultural sector, which occupies a large share of the national territory, is particularly exposed to crop-damaging pests such as the brown marmorated stink bug, an Asian species that has caused significant losses in fruit and vegetable production across Europe and North America. The Asian hornet, another arrival from Asia, threatens both native pollinators and the beekeeping industry, which has economic and ecological importance well beyond honey production.

In the marine realm, Romania’s Black Sea coast has experienced some of the most dramatic invasion-driven ecosystem changes in Europe. The veined rapa whelk, a predatory sea snail introduced from the Pacific, and the warty comb jelly, a gelatinous zooplankton consumer native to the Americas, both arrived in the Black Sea in the twentieth century and fundamentally altered food webs. The comb jelly in particular contributed to collapses in fish stocks during the 1990s, with consequences that rippled through the fishing economies of all Black Sea littoral states. These historical examples illustrate how a single introduction can cascade through an entire ecosystem, and they underscore why prevention and early detection remain the most cost-effective strategies for managing marine invasions.

The study also highlights a broader challenge facing Central and Eastern Europe. Countries in this region have historically published invasion research in local journals with limited international visibility, meaning that data exist but are not discoverable through major global databases. This fragmentation hampers not only national management efforts but also continental-scale analyses that depend on comparable data from all Member States. By compiling Romanian records into a FAIR-compliant dataset and making it openly accessible, the researchers have taken a concrete step toward addressing this problem, and their approach could serve as a model for other countries in the region facing similar data fragmentation.

Looking ahead, the authors emphasize that biological invasions are accelerating globally, with projections suggesting a substantial increase in the number of alien species established worldwide by mid-century, driven by expanding trade, climate change, and land-use intensification. Arthropods, particularly insects, are expected to dominate this expansion. For Romania and other countries at the crossroads of major trade corridors, the message of this study is clear: the window for understanding and managing alien invertebrate invasions depends on sustained investment in monitoring, data integration, and the collaborative networks that connect professional researchers with the growing community of citizen observers whose contributions are increasingly indispensable to invasion science.

Subject of Research: Alien invertebrate species diversity and distribution in Romania

Article Title: From soil to stream and sea: species richness and distribution of alien invertebrates in Romania

Article References: Preda, C., Adam, C., Constantinescu, I. C., Popa, O. P., Popa, L. O., Bâlcu, M.-J., Brezeanu, A. M., Dascălu, M.-M., Drăghici, A.-C., Gavrilescu, C. F., Gavrilidis, A. A., Gheoca, V., Iorgu, E. I., Iorgu, I. Ș., Krapal, A. M., Maican, S., Manci, C.-O., Manta, N., Manu, M., … Skolka, M. (2026). From soil to stream and sea: species richness and distribution of alien invertebrates in Romania. NeoBiota, 108, 21-52. https://doi.org/10.3897/neobiota.108.175337

Image Credits: AI Generated

DOI: 10.3897/neobiota.108.175337

Keywords: alien species, invertebrates, Romania, biodiversity, invasive species, biosecurity, checklist, entomology, freshwater ecology, marine ecology, data gaps, NeoBiota