Globally, the number of invasive non-indigenous species is continually rising, representing a major driver of biodiversity declines and a growing socio-economic burden. Hemigrapsus takanoi, the ...Japanese brush-clawed shore crab, is a highly successful invader in European seas. However, the ecological consequences of this invasion have remained unexamined under environmental changes-such as climatic warming and desalination, which are projected in the Baltic Sea-impeding impact prediction and management. Recently, the comparative functional response (resource use across resource densities) has been pioneered as a reliable approach to quantify and predict the ecological impacts of invasive non-indigenous species under environmental contexts. This study investigated the functional response of H. takanoi factorially between different crab sexes and under environmental conditions predicted for the Baltic Sea in the contexts of climate warming (16 and 22 °C) and desalination (15 and 10), towards blue mussel Mytilus edulis prey provided at different densities. Hemigrapsus takanoi displayed a potentially population-destabilising Type II functional response (i.e. inversely-density dependent) towards mussel prey under all environmental conditions, characterised by high feeding rates at low prey densities that could extirpate prey populations-notwithstanding high in-field abundances of M. edulis. Males exhibited higher feeding rates than females under all environmental conditions. Higher temperatures reduced the feeding rate of male H. takanoi, but did not affect the feeding rate of females. Salinity did not have a clear effect on feeding rates for either sex. These results provide insights into interactions between biological invasions and climate change, with future warming potentially lessening the impacts of this rapidly spreading marine invader, depending on the underlying population demographics and abundances.
Invasive alien species impacts might be mediated by environmental factors such as climatic warming. For invasive predators, multiple predator interactions could also exacerbate or dampen ecological ...impacts. These effects may be especially pronounced in highly diverse coastal ecosystems that are prone to profound and rapid regime shifts. We examine emergent effects of warming on the strength of intraspecific multiple predator effects from a highly successful invasive gammarid
Gammarus tigrinus
, using a functional response approach towards larval chironomids (feeding rates under different prey densities). Single predator maximum feeding rates were three-times higher at 24 °C compared to 18 °C overall, with potentially prey destabilising type II functional responses exhibited. However, pairs of gammarids exhibited intraspecific multiple predator effects that were in turn mediated by temperature regime, whereby synergisms were found at the lower temperature (i.e. positive non-trophic interactions) and antagonisms detected at the higher temperature (i.e. negative non-trophic interactions) under high prey densities. Accordingly, warming scenarios may worsen the impact of this invasive alien species, yet implications of temperature change are dependent on predator–predator interactions. Emergent effects between abiotic and biotic factors should be considered in ecological impact predictions across habitat types for invasive alien species.
The zebra mussel Dreissena polymorpha is one of the most successful, notorious, and detrimental aquatic invasive non‐native species worldwide, having invaded Europe and North America while causing ...substantial ecological and socio‐economic impacts. Here, we investigated the spatiotemporal trends in this species' invasion success using 178 macroinvertebrate abundance time series, containing 1451 records of D. polymorpha collected across nine European countries between 1972–2019. Using these raw (absolute) abundance data, we examined trends and drivers of occurrences and relative abundances of D. polymorpha within invaded communities. Meta‐regression models revealed non‐significant trends both at the European level and for the majority of the invaded countries, except for France (significant decreasing trend) and Hungary (marginally positive trend). At the European level, the number of D. polymorpha occurrences over time followed a flat‐top bell‐shaped distribution, with a steep increase between 1973–1989 followed by a plateau phase prior to significantly declining post‐1998. Using a series of climatic and hydromorphological site‐specific characteristics of invaded and uninvaded sites from two periods (1998–2002; 2011–2015), we found that native richness, non‐native abundance, distance to the next barrier, and elevation were associated with the occurrence of D. polymorpha. We also found that higher native richness and lower latitude were related to lower relative abundances. Using Cohen's D as a measure of D. polymorpha impact, we found that biodiversity within the invaded sites was initially higher than in uninvaded ones, but then declined, suggesting differences in biodiversity trends across invaded and uninvaded sites. While our results emphasise the high invasion success of D. polymorpha, increasing stressors within the context of global change – particularly ongoing climate change – are likely to enhance invasion rates and the impact of D. polymorpha in the near future, exacerbated by the lack of timely and effective management actions.
•Effect of sea freshening on keystone predator impact, Asterias rubens, assessed.•Three ecologically relevant salinity treatments (18, 15, 12ppt).•Zero consumption occurred at the lowest, “future” ...treatment.•Consumption found to mirror larval recruitment results.•Likely implications for the structuring and functioning of ecological communities.
Predicting the myriad effects of climate change on ecological communities is a major challenge for scientists, and to date relatively few studies have focused on the effects of sea freshening on species interactions. In particular, changes in keystone species predatory effects could be pervasive. Here, we assess the consequences of decreasing salinity on the ecological impact exerted by a keystone predatory sea star, Asterias rubens. We quantified sea star functional responses (FRs; per capita predation as a function of prey density) under decreasing salinity treatments aligned with climate change projections (18ppt, 15ppt, 12ppt). Furthermore, we combined FRs with larval recruitment estimates, i.e. ecological “Impact Potential”, to act as an ecological indicator of predator population-level responses under this environmental change. Attack and maximum feeding rates of sea stars were reduced by decreasing salinities, with no instances of predation found at 12ppt. Given that decreasing salinities also reduced larval sea star recruitment, the overall Impact Potential of this keystone predator species was lessened by decreased salinity. Sea freshening projections by the end of this century could thus drive significant decreases in the effects of this keystone predator, with serious implications for the structuring and functioning of ecological communities.
•Native flat and non-native Pacific oysters coexist in the Northern Adriatic Sea.•Flat oyster populations are sparse, while Pacific oysters locally form dense reefs.•Two oyster species inhabit ...different water depths.•Currently interspecific competitive displacement is unlikely.
The Pacific oyster Magallana gigas, globally one of the most translocated marine species, has never been commercially farmed in any part of the Croatian eastern Adriatic Sea, where the native flat oyster Ostrea edulis is the only cultured oyster species. The Pacific oyster has, however, established populations on the west coast of the Istria peninsula, in the northeast Adriatic Sea. Current distribution, abundance and size structure of the flat and Pacific oysters were studied there along spatial and depth gradients in natural and artificial habitats to assess their potential for coexistence. This is the first quantitative assessment of native and non-native oyster populations on a Mediterranean-wide scale providing a baseline for determining future changes in their distribution. Both species were omnipresent, with the Pacific oyster displaying a more pronounced variability in abundance and size in relation to survey regions and depths. The population density of flat oysters was low, generally less than 1 individual/m2, with no difference among regions. The density of the Pacific oyster was significantly higher, being on average 5 individuals/m2. Dense, reef-forming aggregations of Pacific oysters were contained in Lim Bay, a nationally-important shellfish aquaculture area, where its mean density was 107 individuals/m2. Along the open coastline its densities were considerably lower and followed a latitudinal gradient. The observed abundance and size distribution patterns of the Pacific oyster suggest that Lim Bay was the introduction point, with feral settlement likely originating from short-lived experimental aquaculture trials and subsequently dispersing by prevailing local currents. The flat oysters were larger in size and settled at different depths compared to the Pacific oysters. The vertical range of Pacific oysters was mostly contained in the tidal zone, while flat oysters were present in the subtidal exclusively. Such spatial partitioning likely resulted from introduced oysters occupying a vacant ecological niche and not due to interspecific competitive exclusion. Habitat type had a strong effect on proliferation of Pacific oysters. Artificial hard substrata harboured more abundant and larger Pacific oysters than the natural rocky shore habitat. The possibility of multiple local introduction pathways in ports and marinas is also discussed. Currently, there seems to be no spatial competition between the two oyster species, but as it is hard to predict future possible impacts of non-native species, we strongly suggest regular monitoring of the Pacific oyster, prioritising sensitive and protected areas as well as areas at the edge of its distribution.
Background
Biological invasions threaten the functioning of ecosystems, biodiversity, and human well-being by degrading ecosystem services and eliciting massive economic costs. The European Union has ...historically been a hub for cultural development and global trade, and thus, has extensive opportunities for the introduction and spread of alien species. While reported costs of biological invasions to some member states have been recently assessed, ongoing knowledge gaps in taxonomic and spatio-temporal data suggest that these costs were considerably underestimated.
Results
We used the latest available cost data in
InvaCost
(v4.1)—the most comprehensive database on the costs of biological invasions—to assess the magnitude of this underestimation within the European Union via projections of current and future invasion costs. We used macroeconomic scaling and temporal modelling approaches to project available cost information over gaps in taxa, space, and time, thereby producing a more complete estimate for the European Union economy. We identified that only 259 out of 13,331 (~ 1%) known invasive alien species have reported costs in the European Union. Using a conservative subset of highly reliable, observed, country-level cost entries from 49 species (totalling US$4.7 billion; 2017 value), combined with the establishment data of alien species within European Union member states, we projected unreported cost data for all member states.
Conclusions
Our corrected estimate of observed costs was potentially 501% higher (US$28.0 billion) than currently recorded. Using future projections of current estimates, we also identified a substantial increase in costs and costly species (US$148.2 billion) by 2040. We urge that cost reporting be improved to clarify the economic impacts of greatest concern, concomitant with coordinated international action to prevent and mitigate the impacts of invasive alien species in the European Union and globally.
The global transhipment of ballast water and associated flora and fauna by cargo vessels has increased dramatically in recent decades. Invertebrate species are frequently carried in ballast water and ...sediment, although identification of diapausing eggs can be extremely problematic. Here we test the application of DNA barcoding using mitochondrial cytochrome
c
oxidase subunit I and 16S rDNA to identify species from diapausing eggs collected in ballast sediment of ships. The accuracy of DNA barcoding identification was tested by comparing results from the molecular markers against each other, and by comparing barcoding results to traditional morphological identification of individuals hatched from diapausing eggs. Further, we explored two public genetic databases to determine the broader applicability of DNA barcodes. Of 289 diapausing eggs surveyed, sufficient DNA for barcoding was obtained from 96 individuals (33%). Unsuccessful DNA extractions from 67% of eggs in our study were most likely due to degraded condition of eggs. Of 96 eggs with successful DNA extraction, 61 (64%) were identified to species level, while 36% were identified to possible family/order level. Species level identifications were always consistent between methodologies. DNA barcoding was suitable for a wide range of taxa, including Branchiopoda, Copepoda, Rotifera, Bryozoa and Ascidia. Branchiopoda and Copepoda were respectively the best and worst represented groups in genetic databases. Though genetic databases remain incomplete, DNA barcoding resolved nearly double the number of species identified by traditional taxonomy (19 vs. 10). Notorious invaders are well represented in existing databases, rendering these NIS detectable using molecular methods. DNA barcoding provides a rapid and accurate approach to identification of invertebrate diapausing eggs that otherwise would be very difficult to identify.
Gelatinous zooplankton outbreaks have increased globally owing to a number of human-mediated factors, including food web alterations and species introductions. The invasive ctenophore Mnemiopsis ...leidyi entered the Black Sea in the early 1980s. The invasion was followed by the Azov, Caspian, Baltic and North Seas, and, most recently, the Mediterranean Sea. Previous studies identified two distinct invasion pathways of M. leidyi from its native range in the western Atlantic Ocean to Eurasia. However, the source of newly established populations in the Mediterranean Sea remains unclear. Here we build upon our previous study and investigate sequence variation in both mitochondrial (Cytochrome c Oxidase subunit I) and nuclear (Internal Transcribed Spacer) markers in M. leidyi, encompassing five native and 11 introduced populations, including four from the Mediterranean Sea. Extant genetic diversity in Mediterranean populations (n = 8, N a = 10) preclude the occurrence of a severe genetic bottleneck or founder effects in the initial colonizing population. Our mitochondrial and nuclear marker surveys revealed two possible pathways of introduction into Mediterranean Sea. In total, 17 haplotypes and 18 alleles were recovered from all surveyed populations. Haplotype and allelic diversity of Mediterranean populations were comparable to populations from which they were likely drawn. The distribution of genetic diversity and pattern of genetic differentiation suggest initial colonization of the Mediterranean from the Black-Azov Seas (pairwise F ST = 0.001-0.028). However, some haplotypes and alleles from the Mediterranean Sea were not detected from the well-sampled Black Sea, although they were found in Gulf of Mexico populations that were also genetically similar to those in the Mediterranean Sea (pairwise F ST = 0.010-0.032), raising the possibility of multiple invasion sources. Multiple introductions from a combination of Black Sea and native region sources could be facilitated by intense local and transcontinental shipping activity, respectively.
Increasing rates of biological invasions pose major ecological and economic threats globally. The pet trade is one major invasion pathway, and environmental change could mediate the successful ...establishment and impact of these released or escaped non-native species (NNS). Salinity regime shifts are a pervasive but often overlooked environmental change in aquatic ecosystems. This study investigates the establishment and impact risks posed by three readily available, traded snail species – Melanoides tuberculata , Tarebia granifera and Anentome helena – by assessing their survival and feeding responses across a spectrum of salinity levels (0.2–16 g/kg). Survival differed among the species, with M. tuberculata showing close to 100% survival across the salinity range, T. granifera exhibiting heightened mortality at 16 g/kg, and A. helena displaying no survival at salinities above 12 g/kg. In feeding experiments assessing the more resilient M. tuberculata and T. granifera , the former had greater consumption rates towards both plant- (spinach) and animal-based (daphniid) resources. While salinity and density effects did not affect animal consumption, they both had significant effects on plant consumption, with feeding suppressed for both consumers under a salinity of 8 g/kg relative to freshwater conditions. When combining proportional survival and resource consumption for M. tuberculata and T. granifera , M. tuberculata demonstrated higher impact potential towards both plant and animal resources, highlighting its potential to exert higher ecological impacts. Studies have overlooked the importance of salinity for invasion success and the impact of pet trade species. We therefore propose that these methods provide a screening tool to assess the potential risks of traded species establishing and exerting impacts, and we encourage future studies to account for a broader range of abiotic stressors.
An increasingly globalised world has facilitated the movement of non‐native species (NNS) via the poorly regulated international pet trade. While focus is increasingly being placed on preventative ...action to combat invasive NNS—often cheaper and less difficult than the management of established populations—successful prevention requires controlling potential pathways and obtaining baseline knowledge of species' availability.
Here we performed an in‐depth analysis of the freshwater pet trade as one major vector of NNS, compiling its species inventory and deriving threats of NNS release and establishment in the wild. With Germany as our study region, we surveyed pet stores, websites and the country's largest online classified portal, eBay Kleinanzeigen, recording the taxa encountered. For each species, we determined the likelihood of release based on availability and price (cheaper and/or more readily available species have been shown to be of greater risk), and the likelihood of establishment based on ecological niche breadth and niche overlap with environmental conditions in Germany.
The survey revealed 669 species, of which 651 were non‐native to Germany. Looking at release likelihood, more readily available species in pet stores and on websites proved to be cheaper. For websites, there was a significant effect of occurrence status (i.e. released, not released, native) on price, with released and native species being significantly cheaper. Species previously released in Germany and elsewhere demonstrated greater niche breadths and greater niche overlaps between their source regions and Germany; and for species released in Germany, there was a significantly positive relationship between the magnitude of niche overlap and the number of documented occurrences.
Finally, we combined our release and establishment likelihood findings under ‘Release Risk’ metrics to highlight the species most worthy of prioritisation. We propose these metrics as proactive methods for screening species in the trade, which can inform future policy direction and intervention.
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Zusammenfassung
Die zunehmende Globalisierung fördert den Transport gebietsfremder Arten über den wenig regulierten internationalen Haustierhandel. Während Präventivmaßnahmen zur Bekämpfung invasiver Arten immer mehr in den Vordergrund rücken, insbesondere weil sie kostengünstiger und einfacher sind als das Management bereits etablierter Populationen, erfordert eine erfolgreiche Prävention die Kontrolle potenzieller Einführungswege sowie Kenntnisse zur Verfügbarkeit gebietsfremder Arten.
In dieser Studie führten wir eine intensive Analyse des Süßwasser‐Tierhandels als einem der wichtigsten Vektoren für die Einfuhr gebietsfremder Arten durch. Insbesondere analysierten wir die gehandelten Arten und leiteten daraus Risiken durch die Freisetzung und Etablierung der Arten ab. Wir konzentrierten uns dabei auf Deutschland und untersuchten Zoohandlungen, Websites und das große Onlineportal eBay‐Kleinanzeigen. Für jede angebotene Art ermittelten wir die Wahrscheinlichkeit der Freisetzung anhand von Verfügbarkeit und Preis (preisgünstigere und/oder leichter verfügbare Arten sind nachweislich mit einem größeren Risiko verbunden) und die Wahrscheinlichkeit der Etablierung anhand der Breite der ökologischen Nische und der Nischenüberschneidung mit den Umweltbedingungen in Deutschland.
Wir fanden 669 angebotene Arten, von denen 651 in Deutschland gebietsfremd sind. Was die Wahrscheinlichkeit der Freisetzung betrifft, so erwiesen sich in Zoohandlungen und auf Websites leichter erhältliche Arten als preisgünstiger. Bei Websites zeigte sich ein signifikanter Zusammenhang zwischen dem Status (freigelassen, nicht freigelassen oder heimisch) auf den Preis, wobei freigelassene und heimische Arten signifikant preisgünstiger waren. Arten, die zuvor in Deutschland und anderswo freigelassen wurden, wiesen eine größere Nischenbreite und größere Nischenüberschneidung zwischen ihren Herkunftsregionen und Deutschland auf; und für in Deutschland freigelassene Arten gab es eine signifikant positive Beziehung zwischen dem Ausmaß der Nischenüberschneidung und der Anzahl der dokumentierten Vorkommen.
Schließlich fassten wir unsere Ergebnisse zur Freisetzungs‐ und Etablierungswahrscheinlichkeit mittels Metriken zum Freisetzungsrisiko zusammen, um gebietsfremde Arten hervorzuheben, die priorisiert werden sollten. Wir schlagen diese Metriken als proaktive Methoden für das Screening gehandelter Arten vor, die als Grundlage für politische Maßnahmen und Interventionen dienen können.
Read the free Plain Language Summary for this article on the Journal blog.
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