Salinity tolerance and geographical origin predict global alien amphipod invasions

Invasive alien species are driving global biodiversity loss, compromising ecosystem function and service provision, and human, animal and plant health. Habitat characteristics and geographical origin may predict invasion success, and in aquatic environments could be mediated principally by salinity tolerance. Crustacean invaders are causing global problems and we urgently require better predictive power of their invasiveness. Here, we compiled global aquatic gammarid (Crustacea: Amphipoda: Gammaroidea) diversity and examined their salinity tolerances and regions of origin to test whether these factors predict invasion success. Across 918 aquatic species within this superfamily, relatively few gammarids (n = 27, 3%) were reported as aliens, despite extensive invasion opportunities and high numbers of published studies on amphipod invasions. However, reported alien species were disproportionately salt-tolerant (i.e. 32% of brackish-water species), with significantly lower proportions of aliens originating from freshwater and marine environments (both 1%). Alien gammarids also significantly disproportionally originated from the Ponto-Caspian (20% of these taxa) when compared with all ‘other' grouped regions (1%), and principally invaded Eurasian waters, with translocations of salt-tolerant taxa to freshwaters being pervasive. This suggests habitat characteristics, alongside regional contexts, help predict invasibility. In particular, broad environmental tolerances to harsh environments and associated evolutionary history probably promote success of aliens globally

Do alternative resources dampen functional responses of native but not alien gammarids?

While aquatic invasive predators are among the most impactful trophic groups, we lack the understanding of whether alternative food resources mediate adverse predatory effects and stabilize native prey communities. Here, we use comparative functional responses to examine the influence of alternative food resources (Fucus sp.) on predator–prey interaction strengths from three gammarid crustaceans, with one native (Gammarus locusta) and two existing and emerging invasive (Gammarus tigrinus, Pontogammarus maeoticus, respectively) species, towards larval chironomid prey. All gammarids exhibited Type II functional responses, irrespective of the presence of alternative seaweed disks. Fucus sp. disks significantly reduced predation rates overall; however, significant reductions in maximum feeding rates (i.e., functional response magnitudes) were only evident in the native species and not for the two invaders. Our results thus may suggest that alternative resources dampen the predatory interaction strength of native but not invasive alien species, concerning these three study organisms. This potentially exacerbates the impacts of invasive predators relative to natives in diverse communities. Studies should increasingly consider alternative resources when quantifying ecological impacts of current and future invasive alien species compared with natives

Emergent effects of temperature and salinity on mortality of a key herbivore

Highlights: • Warming and desalination cause mortality of sea urchin Paracentrotus lividus. • Total mortality displayed at 27 °C and 25 salinity in one population. • Salinity effects were strongest at the highest temperature. • Multiple stressors associated with environmental change threaten keystone species. Abstract: Aquatic ecosystems are threatened by multiple stressors which might interact in non-additive ways. Two key stressors in marine systems that are likely to be mediated by ongoing climate change are temperature and salinity. Here, we experimentally examine the influence of warming and desalination on mortality rates of a key herbivorous sea urchin, Paracentrotus lividus, between two populations over time. Mortality rates were significantly increased by warming and desalination as individual stressors, with up to total mortality exhibited at the highest water temperature (27 °C) and lowest salinity (25). However, these stressors interacted, with desalination significantly exacerbating mortality rates at the highest temperature, but not under lower thermal regimes (21 °C and 25 °C). Mortality rates were relatively consistent between two sea urchin populations. Overall, temperature and salinity stressors can significantly interact to mediate mortality rates of key aquatic species, in ways that cannot be predicted by considering individual stressors in isolation. Future research should incorporate multiple environmental contexts to better understand and predict species responses to changing climate

Alien species lists for regions: Great Lakes-St. Lawrence River, North and Baltic Seas, and Chesapeake Bay

Underlying established alien species lists for three recipeint regions: Great Lakes-St. Lawrence River (GLSL), North and Baltic Seas (NBS), and Chesapeake Bay (CB). Each species entry is recorded against its taxonomic grouping and geographic origin

Aquatic invasion patterns across the North Atlantic

Biological invasions are a major driver of biodiversity loss and socioeconomic burden globally. As invasion rates accelerate worldwide, understanding past invasion dynamics is essential to inform predictions of future invaders and impacts. Owing to a high diversity of pathways and current biosecurity gaps, aquatic systems near urban centres are especially susceptible to alien species establishments. Here, we compiled and compared alien species lists for three different aquatic recipient regions spanning the North Atlantic: Chesapeake Bay, Great Lakes-St. Lawrence River and North and Baltic Seas. Each system is a major trade centre, with a history of invasions, and characterised by a strong natural salinity gradient. Our goal was to compare the alien species across systems, to test for similarities in the taxonomic composition and geographic origin as well as species overlap among the three regions. We selected specific macroinvertebrate, algae and fish taxa for analysis, to control for uneven taxonomic and biogeographic resolution across regions. Cumulatively, we identified 326 individual alien species established in these aquatic systems, with the North and Baltic Seas most invaded overall (163), followed by Great Lakes-St. Lawrence River (84) and Chesapeake Bay (79). Most invasions were from Ponto-Caspian, Eurasian, Northwest Pacific, Northwest Atlantic and North American origins, and mostly comprised Arthropoda, Chordata, Mollusca and Annelida. However, origins and taxonomies differed significantly among destinations, with Ponto-Caspian species particularly successful invaders to the North and Baltic Seas then Great Lakes-St. Lawrence River, but less so to Chesapeake Bay. Nevertheless, approximately eight tenths of invaders established in only one region, indicating disparate invasion patterns and a high potential for future aliens to accrue from increasingly diverse source pools and pathways. These results support biosecurity strategies that consider a broad range of geographic origins and taxonomic groups to limit the translocation, arrival and spread of alien species worldwide

Unevenly distributed biological invasion costs among origin and recipient regions

Globalization challenges sustainability by intensifying the ecological and economic impacts of biological invasions. These impacts may be unevenly distributed worldwide, with costs disproportionately incurred by a few regions. We identify economic cost distributions of invasions among origin and recipient countries and continents, and determine socio-economic and biodiversity-related predictors of cost dynamics. Using data filtered from the InvaCost database, which inevitably includes geographic biases in cost reporting, we found that recorded costly invasive alien species have originated from almost all regions, most frequently causing impacts to Europe. In terms of cost magnitude, reported monetary costs predominantly resulted from species with origins in Asia impacting North America. High reported cost linkages (flows) between species' native countries and their invaded countries were related to proxies of shared environments and shared trade history. This pattern can be partly attributed to the legacy of colonial expansion and trade patterns. The characterization of 'sender' and 'receiver' regions of invasive alien species and their associated cost can contribute to more sustainable economies and societies while protecting biodiversity by informing biosecurity planning and the prioritization of control efforts across invasion routes

Does non-native diversity mirror Earth's biodiversity?

Aim: Human activities have introduced numerous non-native species (NNS) worldwide. Understanding and predicting large-scale NNS establishment patterns remain fundamental scientific challenges. Here, we evaluate if NNS composition represents a proportional subset of the total species pool available to invade (i.e. total global biodiversity), or, conversely, certain taxa are disproportionately pre-disposed to establish in non-native areas. Location: Global. Time period: Present day. Major taxa studied: Global diversity. Methods: We compiled one of the most comprehensive global databases of NNS (36,822 established species) to determine if NNS diversity is a representative proportional subset of global biodiversity. Results: Our study revealed that, while NNS diversity mirrors global biodiversity to a certain extent, due to significant deviance from the null model it is not always a representative proportional subset of global biodiversity. The strength of global biodiversity as a predictor depended on the taxonomic scale, with successive lower taxonomic levels less predictive than the one above it. Consequently, on average, 58%, 42% and 28% of variability in NNS numbers were explained by global biodiversity for phylum, class and family respectively. Moreover, global biodiversity was a similarly strong explanatory variable for NNS diversity among regions, but not habitats (i.e. terrestrial, freshwater and marine), where it better predicted NNS diversity for terrestrial than for freshwater and marine habitats. Freshwater and marine habitats were also greatly understudied relative to invasions in the terrestrial habitats. Over-represented NNS relative to global biodiversity tended to be those intentionally introduced and/or ‘hitchhikers’ associated with deliberate introductions. Finally, randomness is likely an important factor in the establishment success of NNS. Main conclusions: Besides global biodiversity, other important explanatory variables for large-scale patterns of NNS diversity likely include propagule and colonization pressures, environmental similarity between native and non-native regions, biased selection of intentionally introduced species and disparate research efforts of habitats and taxa

Non-native species list to examine non-native species diversity globally

Fifteen independent lists of non-native species (NNS) were used to examine NNS diversity globally. The lists were chosen opportunistically as the majority of them were publicly available; a few additional ones were assembled by authors of this study. Furthermore, to examine NNS diversity in different biological systems (i.e. terrestrial, aquatic, freshwater, and marine), the global list (Briski et al. 2016) was further divided into aquatic and terrestrial lists, while the European list (DAISIE 2016) was split into marine, freshwater, and terrestrial; the way these two lists were divided was based on available habitat classifications in the lists. Aquatic taxa were defined as freshwater and marine combined. Overlapping regions were defined as those that geographically cover one or more smaller listed regions. For example, if a species was listed in the European marine list, it may be listed there because it was included in the Mediterranean Sea list. The lists were not standardised to each other, but were kept in their original state (i.e. including all listed species), incorporating their independency due to taxonomic and scientific expertise and interests of scientists assembling them. We took this approach because we do not compare the lists to each other explicitly, but consider them independently to estimate global NNS biodiversity obtained from the Global Biodiversity Information Facility (GBIF). Therefore, each coefficient of determination (r2) obtained from our regression analyses was unique and independent from one another, representing an independent data point for further statistical analyses (see below). In August and September 2019, species in each list were assigned to phylum, class, and family levels based on the GBIF (2019). Global estimated biodiversity (i.e. numbers of species per taxonomic group) of each particular phylum, class, and family was obtained from the GBIF in June 2020 (GBIF 2020)