Long-term marine monitoring programmes have provided numerous quantitative data on the composition of North Sea benthic communities and their changes over time, including species introductions. Particularly in the German Bight, the rapid environmental and hydrographical changes are promoting the spreading (usually anthropogenically mediated) of neobiota, with more than 150 species being registered to date. During routine seafloor monitoring, grab samples taken on the subtidal sandbank of the Borkum Reef Ground revealed the presence of the polychaete Streptosyllis nunezi in different years, a species previously unreported in the southern North Sea. In this paper, these individuals are described morphologically and the population status is discussed. Our finding demonstrates the importance of intensive and regular environmental monitoring programmes for the assessment of regional biodiversity and its potential changes.

This study describes the presence of the royal cucumber Parastichopus regalis (Cuvier, 1817) in The Natural Park of Ria Formosa (NPRF), Portugal. A single individual was observed during a monitoring scuba dive at a depth of 3 m inside this shallow mesotidal lagoon. The most plausible explanation for this occurrence is attributed to the rejection by trawlers when returning to their home port from their fishing grounds. This marine species has a deeper distribution outside the lagoon and is commonly captured as by-catch and subsequently discarded. This study also alerts us to the growing presence of non-indigenous species and the emergent threat of new invasions, highlighting the need to adopt biosecurity measures, like good practices for fishers when dealing with discards to avoid new species introductions in this fragile coastal marine habitat.

Egg masses from an unknown mollusc have been found in South-West Iceland since 2020, but it was not until September 2023 that the adult organism was collected. Morphological analysis of both adults and egg masses pointed towards the identification of the species as Melanochlamys diomedea. This was further confirmed through DNA analyses using COI, H3, and 16S rRNA markers, which established the presence of a new non-indigenous species in the North Atlantic. Members of the genus Melanochlamys have predominantly been found in the Indo-Pacific basin and the Pacific Ocean, with only one species known to exist across the Madeira Islands, Canary Islands, and Cape Verde in the Atlantic. The known distribution range of M. diomedea extends from Alaska to California on the Pacific side of North America, where it typically inhabits sandy-muddy areas of the littoral in the tidal zone and below. It is not known how the species arrived in Iceland. However, maritime transport through either ballast water or biofouling is being considered as the most likely mode of dispersal.

This study provides the first record of the beaded sea cucumber Euapta lappa at Madeira Island. A single individual was observed during a nocturnal scuba dive at 17 m depth, presumably feeding. After having its previous northern limit in the North-east Atlantic at the Selvagens Islands, this record expands the known distribution and northern limit of this tropical species by about 300 km. This new record of yet another tropical species expanding its range northwards can be seen as another indication of the ongoing tropicalization in the marine environment of Macaronesia in the North-east Atlantic.

Monitoring the spread of non-indigenous species is fundamental to study global warming effects on marine biodiversity. A valuable tool is represented by the continuous updating of the geographic range expansion of non-indigenous species. Lamprohaminoea ovalis is a Lessepsian mollusc initially recorded in the Mediterranean Sea in 2001. This paper reports its range expansion over the last 20 years related to water warming. The first record of Lamprohaminoea ovalis from the Ligurian Sea (NW Mediterranean) is also reported. Two individuals (about 10 mm length) were observed on a sub-vertical rocky bottom at 26 m depth displaying potential trailing behaviour. This recent finding extends the currently known distributional range of Lamprohaminoea ovalis, representing the northernmost occurrence of this non-indigenous species in the western Mediterranean Sea.

The upside-down jellyfish Cassiopea is a benthic scyphozoan, considered a non-indigenous invasive species in the Mediterranean, forming large blooms in eutrophic areas. Taxonomy of the genus Cassiopea is extremely difficult because morphological/meristic characters used are variable within the same species, overlapping among different species, and cryptic species have been identified by molecular markers; nine Cassiopea species are recognized on the basis of molecular study. Mediterranean records of Cassiopea have been ascribed to andromeda species on the basis of a hypothesized invasion pathway from the Suez Canal. In the current study, an analysis of the main morphological characters of the sampled Cassiopea jellyfish from Palermo (Tyrrhenian Sea) was carried out and subsequently, molecular analyses were performed by using COI barcode in order to identify the species. Molecular data were compared with published information in GenBank. Morphological characters were highly variable, but molecular analyses confirmed that Mediterranean Cassiopea specimens belong to andromeda species. Moreover, high values of sequence divergence were found between Mediterranean Cassiopea and the other C. andromeda from the Red Sea, Hawaii and Florida. These results lead to a discussion of possible explanations linked to life history features of the species. Two different explanations are proposed; the first is that Mediterranean C. andromeda, finding a suitable ecological niche good for colonization and proliferation, could have been isolated in Palermo Harbour. The second considers the possibility of multiple introduction events by human transport as demonstrated for other non-indigenous jellyfish; in this case Cassiopea genetic differences increased in the invaded area.

Four species of Pinnotheridae inhabit European marine waters, Afropinnotheres monodi, Nepinnotheres pinnotheres, Pinnotheres pectunculi and Pinnotheres pisum. For these four species there are data available on the morphology of their larval stages as well as DNA markers. This information has allowed us to detect some larvae in plankton samples from the Gulf of Cadiz (SW Iberian Peninsula) that do not belong to any of these European pinnotherid species and to be confirmed by DNA barcoding. In this study these findings are shown as a case of early detection of a newly introduced and unknown species in European marine waters.

Life history accounts for the chance of survival and reproductive success of a species, considering, for example, when, how often and how much a species reproduces. Consequently, it is directly related to the success or failure of bioinvasions. Here, we investigated some aspects of the life history of the cryptogenic calcareous sponge Sycettusa hastifera. A population from Arraial do Cabo, Brazil (south-western Atlantic) was investigated from September 2008 to December 2009 by monthly collections and histological analyses. We observed that S. hastifera reproduced continuously throughout the year without seasonality and presented high fecundity. The fecundity was not different depending on the sponge body part (top or base), but it was related to the wet weight of the sponge (although a minimum size was not required for reproduction). Reproduction could not be predicted by the seawater temperature. The reproductive characteristics of S. hastifera were similar to those of other previously studied calcareous sponges. Sycettusa hastifera shows traits of an invasive species, such as high fecundity, short life cycle, early sexual maturity and the ability to use pioneer habitats. Consequently, it possesses several characteristics that would allow it to invade new areas.

The study analyses the role of non-indigenous invertebrates in the food webs of two eutrophic brackish estuarine ecosystems of the Baltic Sea: the Neva River estuary and the Curonian Lagoon, with the aim of clarifying several questions such as what trophic levels were occupied by newly established species (mainly amphipods and mysids) and whether they can affect the native benthic invertebrates as a result of their possible carnivorous nature. Stable isotope analysis (δ15N values) and gut contents analysis of field-collected specimens were used to estimate trophic level and trophic links of the newly established malacostracan crustaceans, while their consumption rates when feeding as carnivores were measured experimentally. The δ15N analysis allocated four trophic levels (TL) in the coastal food webs of both studied ecosystems with the lowest δ15N (2–4‰) for detritus and algae and the highest for fish (12–14‰). Through their high abundance, non-indigenous crustaceans (Pontogammarus robustoides, Gmelinoides fasciatus, Obessogammarus crassus, Gammarus tigrinus, Limnomysis benedeni and Paramysis lacustris) have become important members of food chains of the studied ecosystems. Their trophic position varied significantly within species during ontogenesis. This suggests that they turned from being typically detritivores/plantivorous (TL 2–2.4) at juvenile stages to omnivores (2.5–3) or to carnivores (>3) as adults. Assessment of the predation pressure by the adult amphipods on other coexisting invertebrates (in the example of the Neva Estuary) showed a low or medium impact, depending on species of predator and productivity of its potential prey organisms.

The cirratulid species Chaetozone corona is reported for the first time from the North-east Atlantic waters. Several specimens were collected during oceanographic surveys between 1996 and 2015 from soft bottom habitats along the coasts of Brittany (Western France). This species, originally described from the coast of California, was recently recorded for the first time from the Mediterranean Sea. We hypothesize that this species could have been recently introduced to the Atlantic coasts of Europe and colonized the northern coast of Bay of Biscay from the Loire estuary to the Iroise Sea. We discuss the potential vectors of introduction and the main environmental factors that could explain its current distribution. An identification key to all the known North-east Atlantic species of Chaetozone is given.

The ascidian Ecteinascidia turbinata is reported from Maltese waters for the first time. Mature colonies were recorded on artificial substrata at two different sites (and on natural substrata at one of these), 4 km apart, during the summer months. The appearance of this ascidian is expected to be seasonal as the winter temperature in Malta may fall below that required for the maintenance of zooid growth. A second species, E. moorei, which was described in 1890 is here confirmed to be the same as E. turbinata, meaning that the species has existed in the Mediterranean since at least ~1880. The possibility that the Mediterranean population is a relic one from warmer periods cannot yet be excluded, so it is best described as being cryptogenic. The species appears to be spreading slowly, perhaps as a result of the rise in surface sea temperature. The Maltese sites offer an opportunity to monitor the species as they are accessible dive sites. This will allow assessment of whether this species remains restricted to these sites, or if it spreads perhaps to impact other species.

The amphipod genus Aoroides is reported for the first time in European marine waters. Specimens of Aoroides semicurvatus and Aoroides curvipes were collected in oyster reefs in Arcachon Bay between 2009 and 2014 and in Hossegor Lake in 2014 (SW France). Specimens of Aoroides longimerus were collected in 2013 and 2014 in subtidal slipper limpet beds and Zostera marina meadows in Arcachon Bay and in 2014 on floating pontoons in the Bay of Brest (W France). These species, native to Asia, may have been accidentally introduced in Arcachon Bay and Hossegor Lake with oyster transfers and in the Bay of Brest through both oyster transfers and shipping.

The introduction of the Manila clam into British coastal waters in the 1980s was contested by conservation agencies. While recognizing the value of the clam for aquaculture, the government decided that it posed no invasive risk, as British sea temperatures would prevent naturalization. This proved incorrect. Here we establish the pattern of introduction and spread of the species over the first 30 years of its presence in Britain. We report archival research on the sequence of licensed introductions and examine their relationship in time and space to the appearance of wild populations as revealed in the literature and by field surveys. By 2010 the species had naturalized in at least 11 estuaries in southern England. These included estuaries with no history of licensed introduction. In these cases activities such as storage of catch before market or deliberate unlicensed introduction represent the probable mechanisms of dispersal. In any event naturalization is not an inevitable consequence of introduction and the chances of establishment over the period in question were finely balanced. Consequently in Britain the species is not currently aggressively invasive and appears not to present significant risk to indigenous diversity or ecosystem function. However it is likely to gradually continue its spread should sea surface temperatures rise as predicted.

Ten alien species were recorded in a first-time survey of the benthic biodiversity of the upper sublittoral at Sigri Bay (Lesvos Island, north-eastern Aegean Sea). The record of the mollusc Syrnola fasciata is the first in Hellenic territorial waters. The records of the brown alga Stypopodium schimperi, the bivalve Septifer cumingii, the gastropods Syrnola fasciata and Smaragdia souverbiana and the bony fish Siganus luridus constitute evidence for a further northwards extension of their geographic ranges in the Aegean Sea. The record of Cerithium scabridum is the first in Lesvos Island and partially fills the gap in the distribution of the species in the eastern Aegean Sea. We also recorded the green alga Caulerpa cylindracea, the angiosperm Halophila stipulacea and the bivalve Pinctada imbricata radiata, which are widely distributed in the eastern Mediterranean. The polychaete Marphysa adenensis, which was also found at Sigri Bay, has recently been reported for the first time from the Mediterranean as a cryptogenic species.

The ichthyofauna of the River Minho tidal freshwater wetlands (TFWs) was studied in a semi-enclosed area, between June 2007 and May 2010, to determine temporal patterns of abundance, biomass and species composition. Fish catches, standardized by the number of fyke nets and by the fishing effort, were analysed and related to river flow, water temperature and precipitation. In total, 21 fish species were identified including six non-indigenous species (NIS) which represented 15% of the total captures (yet 43% of the biomass). Regarding ecological guilds, 82% were freshwater species (61% of the biomass) which included all NIS, whereas 13% of the catches were catadromous species (31% biomass) corresponding to eels. Only 4% were estuarine species (1% biomass) and together marine estuarine opportunists and anadromous species accomplished 1% (2 and 6% biomass, respectively). The fish assemblage showed seasonal patterns with a clear distinction between autumn/winter and spring/summer periods. Significant differences in abundance and biomass were also detected between autumn/winter of 2007/2008 and 2008/2009, i.e., inter-annual variations, with the latter period with lower catches yet higher dominance of NIS. Besides, higher water temperature had a significant negative effect on the observed number of species, but a positive effect on the abundance and biomass of NIS. More attention has to be given to TFWs and their role in structuring fish assemblages, because this information is vital for a sound management, conservation and restoration of estuarine areas.

The shrimp scad, Alepes djedaba is known to be established in the eastern Levant. The present study describes a case of a school (100 specimens) caught with purse seine on 14 June 2012 in Tunisia (Gulf of Gabès: 34°10′240 10°58′180) that constitutes the first record of its westernmost appearance.

Although both Siganus luridus and Siganus rivulatus have been reported from the Maltese Islands in the literature, and on internet sites and databases, there do not seem to be any specific records of S. rivulatus from these islands. In order to address the question whether both or only one of these alien siganids occur in the Maltese Islands, all records of siganids collected or photographed in Maltese waters were evaluated. Thirteen records comprising at least 33 specimens supported by photographs or specimens and 25 records of 48 individual rabbitfish identified in the field were all S. luridus. This suggests that S. rivulatus does not occur in Maltese waters.

The surroundings of the rocky island of Helgoland (German Bight, south-western North Sea) are one of the best-studied sites in European seas with species occurrence data available for nearly 150 years. As the area is strongly affected by global change (e.g. increase in mean sea surface temperature at Helgoland by 1.67°C since 1962), ecosystem structure and function are expected to change more than those of average marine systems. The paper presents a supplement to the local amphipod species inventory (5 nautical miles around the island). At least seven species of this ecologically important taxon seem to have newly established themselves at Helgoland since the late 1980s: Ampelisca typica, Amphilochus brunneus, Caprella mutica, Cheirocratus assimilis, Monocorophium acherusicum, Orchestia mediterranea and Orchomenella crenata. Most of them are not only new for the Helgoland area, but also for the German Bight; and two species (Amphilochus brunneus and Orchomenella crenata) are even new to the North Sea as a whole. Out of the seven new species, one (Caprella mutica) is a neozoon from the north-western Pacific. The other six species show clear warm water affinities (oceanic–Lusitanian species) which suggest a recent range expansion in the context of climate warming. The establishment of an increasing number of species formerly probably absent from the area does not seem to be compensated by losses of species, so that local species diversity is expected to increase.

Management of non-native species introductions is a conservation priority in the Antarctic region. However, despite the recognised importance of intra-regional propagule transfer, the majority of studies have focused on inter-regional pathways (i.e. from outside of the Antarctic region). Here we quantify the number of seeds carried by expeditioners who have visited sub-Antarctic Marion Island. We recorded 420 seeds from 225 items of clothing, with seeds found on 52% of the items and soil on 45% of them. The median number of seeds for field-based and station-based personnel was 20.5 and 3 per person, respectively. Waterproof trousers and socks, particularly those of field workers, carry the greatest number of propagules (for field workers, medians of 5 and 6.5, respectively) and therefore should be the focus of intra-regional management interventions. Amongst the seeds found entrained within clothing several were from species which are widespread aliens in the Antarctic region including Agrostis stolonifera, Poa annua and Sagina procumbens, and indigenous zoochorous species (Acaena magellanica, Uncinia compacta) were also well represented. The present data provide quantitative evidence in support of previous, largely hypothetical concerns about the risks of intra-regional propagule transfer in the Antarctic.

In 1996 a sponge was found in a well studied area in the Ria of Etel, Brittany, France, that had never been recorded there before. This sponge was later described as a new species and genus, Celtodoryx girardae by Perez et al. (2006), who concluded that it is probably an invasive species. Over several years C. girardae was found to occur successively in the Gulf of Morbihan, France, and Oosterschelde estuary, Netherlands. This sponge is characterized by an extensive spatial broading and therewith it rates today among the dominant benthic megafauna in the shallow waters of the Gulf of Morbihan and Dutch inshore waters. During our recent survey of the Chinese Yellow Sea sponge fauna, we found an abundant species with close morphological similarities to C. girardae. Further taxonomic studies have revealed that both the Chinese and European sponges are in fact conspecific with Cornulum ciocalyptoides described by Burton (1935) from Posiet Bay, Sea of Japan and later recorded from other localities of the North West Pacific (e.g. Koltun, 1971; Sim & Byeon, 1989). In this paper we transfer the species of Burton from Cornulum to Celtodoryx and consequently it becomes the senior synonym of C. girardae. Furthermore, we conclude that Celtodoryx ciocalyptoides was introduced to the North East Atlantic from the North West Pacific with aquaculture of the Pacific oyster Crassostrea gigas as the probable vector. This is probably the first case recorded so far of a sponge species being transferred from one ocean to another by human activity.