DOI: 10.3897/neobiota.108.183096

Authors: Rotem Mor, Oren Kolodny, Tamar Guy-Haim

Abstract: The marbled crayfish (Procambarus virginalis) is an invasive, parthenogenetically reproducing species that has spread to freshwater ecosystems in more than 24 countries across North America, Europe, Africa, and the Middle East. To date, the trophic ecology of the marbled crayfish has been studied only in European lentic and lotic perennial ecosystems. This study aimed to shed light on the trophic ecology of the marbled crayfish in ephemeral streams of semi-arid environments in the Middle East. Three distinct habitats were compared using δ13C and δ15N stable isotope analysis to evaluate spatial variation in trophic position and resource use. A diet regime experiment was also conducted to test the impact of herbivorous and omnivorous diets on crayfish survival. In agreement with studies elsewhere, the analysis confirmed that P. virginalis functions as a flexible omnivore, occupying an intermediate trophic level (trophic position: 2.3–2.9), with the highest values observed during summer. The diet regime experiment indicated that juveniles can survive on various diets, with only small differences in survival rates among the three diets tested. The highest survival rate was observed under the poor plant-based diet. Adults and sub-adults also showed high survival rates under all tested diets, as well as some extent of cannibalism, which was amplified when they were fed purely plant-based diets. Cannibalism was primarily directed at small-sized juveniles (0–2 months old). In contrast, cannibalism among adults and sub-adults was very limited, even when they were reared at high densities.

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DOI: 10.3897/neobiota.107.176248

Authors: Daniel Szarmach, Katarzyna Lichocka, Jarosław Kobak, Aleksandra Bomba, Alicja Krzeszowiak, Sebastian Terebiński, Kamil Wiśniewski, Małgorzata Poznańska-Kakareko

Abstract: Hydrological droughts driven by climate change threaten freshwater biodiversity, including relatively immobile bivalve fauna, unable to escape from air-exposed areas. Furthermore, they may exacerbate biological invasions by more resistant alien species. We measured survival and behavioural responses (migration following receding water line and burrowing) of the vulnerable native fingernail clam Sphaerium rivicola and the invasive Asian clam (Corbicula complex) to water level reduction and sandy substratum drying in a laboratory setting, to assess their susceptibility to a hydrological drought. Corbicula exhibited higher drought resistance with all clams surviving 15 days of air exposure, whereas S. rivicola reached LT50 (time at which 50% mortality occurred) in 5 days and LT90 (time at 90% mortality) in 8 days. During water level reduction, S. rivicola migrated by crawling downwards to wetter areas and reduced their burrowing depth, whereas Corbicula clams remained in place, burrowing deeper into the sediments. We demonstrate that the invasive Corbicula clams are superior to S. rivicola in surviving air exposure, and their burrowing confers an advantage in drought-prone habitats. In the context of climate change, increased drought frequency and duration may facilitate Corbicula’s dominance and replacement of less drought-resilient native bivalves, such as S. rivicola.

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DOI: 10.3897/neobiota.107.181767

Authors: Péter Borza, Bart Achterkamp, Ton van Haaren

Abstract: After Chelicorophium curvispinum, C. sowinskyi, and C. robustum, recently the fourth Ponto-Caspian filter feeding corophiid (C. maeoticum) has colonized the lower section of the River Rhine in the Netherlands. To test for niche differentiation among the four species along the food particle size spectrum, we measured their filter mesh sizes (i.e., the distance between bristles on the filtering setae). For comparison, we also analyzed a historic sample from the River Tisza in Hungary in which C. maeoticum co-occurred only with C. sowinskyi. We also compared the relative lengths and widths of the second antennae among the species, considering the potential involvement of this appendage in interference competition and deposit feeding. Despite significant interspecific differences in filter mesh sizes in most comparisons, there was a partial overlap between C. maeoticum and C. sowinskyi in the River Rhine but not in the River Tisza. In addition, there was an almost complete overlap between C. curvispinum and C. robustum. Marked interspecific differences could be observed in the relative widths of the second antennae in both sexes, potentially related to performance in competition for microhabitats. Remarkably, the earlier colonists C. curvispinum and C. sowinskyi have thinner second antennae while C. robustum and C. maeoticum with more robust appendages could establish in habitats already occupied by their congeners. Our results suggest that competition for both food and space can shape the coexistence and invasion patterns of Ponto-Caspian corophiids. Nevertheless, more studies are needed to reveal the range of behaviors second antennae are involved in and how their morphological features determine their functionality. The observed differentiation in the measured traits along with differences in body sizes close to the 1.3 ratio are likely to allow the coexistence of the four species and portend the continued spread of C. maeoticum.

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DOI: 10.3897/neobiota.105.170980

Authors: Michael Butler-Margalef, Francesc Rubio-Gracia, Emili García-Berthou, Jolle W. Jolles, Anna Vila-Gispert

Abstract: The success and impact of invasive non-native species depend on how they cope with local abiotic conditions, especially in comparison to co-occurring native taxa. In aquatic systems, salinity serves as a key environmental filter, mediating the establishment of invasive species and influencing biotic interactions. However, the mechanistic basis behind these context-dependent responses remains poorly understood. In this study, we examined interspecific differences in metabolic rate, movement behaviour, and their relationship between the worldwide invasive Gambusia holbrooki and a threatened Spanish endemic fish Aphanius iberus across an experimentally-manipulated salinity gradient. Using intermittent-flow respirometry and automated tracking of movement patterns, we compared aerobic metabolic traits and movement behaviours under various salinities. Toothcarp maintained a stable aerobic scope across salinity treatments, whereas invasive mosquitofish exhibited a markedly lower aerobic scope with higher salinity, primarily due to a decline in maximum metabolic rate. This stress response was not linked to increased osmoregulatory costs, as baseline metabolism decreased. Behavioural tests demonstrated consistent species differences in routine locomotion, with mosquitofish showing more exploratory behaviour and toothcarp showing more stop-go behaviour and remaining more stationary overall. Notably, in toothcarps, we found a negative link between standard metabolic rate and space use, suggesting that individuals with higher baseline metabolism may be constrained in their movement. Conversely, in mosquitofish, although salinity affected metabolic capacities, this effect was not reflected in their movement, indicating a weak relationship between metabolism and behaviour, likely supported by trait flexibility. By integrating metabolic traits with behavioural data, our results reveal mechanisms underlying invasive species responses and strengthen predictions of their performance relative to native fishes under changing conditions, such as salinity in inland waters. This highlights the importance of trait-based approaches for predicting responses to abiotic stressors and for evaluating the ecological impacts of invasive taxa.

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DOI: 10.3897/neobiota.103.157105

Authors: Fernanda Araujo Casares, Vithória Rodrigues de Melo, Marcio Loureiro, Larissa Marques Pires-Teixeira, Simone Siag Oigman-Pszczol, Eduardo Pszczol, Joel Christopher Creed

Abstract: Considering the potential ecological, socioeconomic, and human health threats related to non-native species introduction, the management of biological invasions is a priority for biodiversity conservation and human welfare. Science-based databases that provide lists and records of non-native species are fundamental to supporting regional and local management actions and decision-making processes. When easily available and disseminated, they can also reach the broader public and foster societal engagement. Here, we describe our experience with the Brazilian Biological Invasion Platform, a portal launched in 2019 that compiles and reports records of estuarine and marine non-native species in Brazil. The system was developed by integrating the Application Programming Interface (API) from Google Maps. Data collation involves four steps: (i) taxon selection; (ii) searches for non-native species reported for Brazil in the scientific literature (including gray literature); (iii) data filtration and extraction to spreadsheets for each species—date, type of record, spatial coordinates, habitat, ecosystem, and source of information; and (iv) careful revision and data transfer to a general database. Finally, the records are uploaded to the platform. The website allows searches by species and by record, with different filters, which are displayed on a map. People and institutions can contribute recommendations, comments, and new records through an online form. The portal encompasses more than 188 non-native and 151 cryptogenic species, with over 6,200 georeferenced records of zoo- and phytoplankton, zoo- and phytobenthos, nekton, and bacteria. We discuss the decision-making process and lessons learned during the first years of the platform, highlighting its impact on management and science outreach, gaps, needs, and challenges, in addition to perspectives for the coming years. Sharing these experiences will contribute to other initiatives already in progress or under development, which constitute important tools to connect biological invasion science, policy, and social awareness.

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DOI: 10.3897/neobiota.102.148326

Authors: Sara Cabral, Frederico Carvalho, Joana P. C. Cruz, Joshua Heumüller, Jose M. F. Babarro, Luc A. Comeau, Paula Chainho, Ana C. Brito

Abstract: Despite the burgeoning number of non-indigenous species (NIS) in worldwide coastal ecosystems, the quantification of their direct impacts on native communities remains largely unexplored. This is particularly true concerning feeding competition in sympatric filter-feeding bivalves. In this study, our aim was to fill a gap of knowledge on the potential trophic competition between native and non-indigenous bivalves, namely by focusing on three species that co-occur in Portuguese estuarine systems: the native cockle (Cerastoderma edule) and Portuguese oyster (Magallana angulata) and the non-indigenous Manila clam (Ruditapes philippinarum). The specific objectives were to i) estimate their capture efficiency (≈ particle retention efficiency; CE); ii) assess their clearance rates (CR); and iii) provide a science-based support for suitable management measures regarding NIS. Experiments were conducted in both field and laboratory conditions using the natural seston present in the seawater. The CE was higher for the larger size classes (8–14 μm) of particles measured (ranging from 4–14 µm), regardless of the species. While the individual CRs were not significantly different among species, the CR per gram of ash-free dry body tissue weight was significantly higher for the native cockle, suggesting that the NIS does not hold a competitive advantage in clearing suspended particles. However, the Manila clam might be limiting food sources availability to the native species since there is an overlap of their ecological niches.

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DOI: 10.3897/neobiota.100.149248

Authors: Mathieu Toutain, Ismael Soto, Francisco J. Oficialdegui, Paride Balzani, Ross N. Cuthbert, Augusto Frederico Huber, Phillip J. Haubrock, Antonín Kouba

Abstract: Predator-prey relationships underpin the stability of ecosystems but can be perturbed by numerous factors, such as biological invasions. Crayfish readily colonize new ecosystems and their impacts can modify food webs or ecosystem functioning. However, while crayfish exert high levels of predation pressure handling prey with their claws, claw loss is also common in their populations, which could mediate prey selection pressures. Here, we investigate how the number of claws in the marbled crayfish Procambarus virginalis modulates its preferences for two different available prey: Chironomus plumosus and Gammarus fossarum. We showed that the food preference of P. virginalis was mainly for soft, less mobile prey, such as C. plumosus, with significantly fewer G. fossarum (harder, more mobile prey) being killed. This preference was largely independent of claw presence but depended on the availability of prey, with fewer G. fossarum being targeted as the number of claws decreased. Our results highlight the complexity of predator-prey ecological relationships in invaded freshwater ecosystems and show that some biotic factors, such as the quantity and type of prey available, need to be taken into account in order to better understand their role in ecosystem dynamics.

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DOI: 10.3897/neobiota.100.158545

Authors: Irene Gil-Luna, Lluís Zamora, Pilar Risueño, Ignacio Doadrio, Carlos Fernández-Delgado, Anne E. Magurran, Emili García-Berthou

Abstract: Invasive non-native species are an important cause of biodiversity loss, particularly in fresh waters. The mosquitofish Gambusia holbrooki are among the world’s worst invasive species: they have caused extirpations of native species and are known to sometimes cause trophic cascades and ecosystem effects. This invasive species is also known to impact threatened fishes such as the Spanish toothcarp (Aphanius iberus), which is endemic to Mediterranean Spain. However, it is unclear if the impact of mosquitofish on many fishes is more through resource competition, agonistic interactions or predation, and how often mosquitofish cause trophic cascades. To clarify these questions, we performed a 48-day mesocosm experiment in eutrophic conditions to test for interspecific effects and clarify the impact mechanism using six treatments: the two fish species alone each at two densities, and the two fish species mixed or separated with a net that prevented direct interactions among them. We observed clear fish treatment effects on several variables. At low initial fish densities, the population growth rate of mosquitofish was orders of magnitude greater than that of the Spanish toothcarp, likely contributing to its invasive success and ecological impact. At high fish densities, turbidity, chlorophyll a concentration and daytime dissolved oxygen percentage increased, whereas total phosphorus decreased; crucially, the trophic cascade caused by mosquitofish was stronger than that by toothcarp. The experiment also demonstrated that the interspecific effects of mosquitofish on toothcarp were more important than those of intraspecific competition. The invasive species produced effects on population growth rate, size structure, and fish condition (mass-length relationship) of toothcarp. Effects on population growth rate of toothcarp seem more caused by resource competition, whereas impacts on size structure and condition seem also caused by more direct interactions. The diversity of effects of mosquitofish underscores the difficulty of predicting the impact of invasive species. Our study further provides an approach to differentiate the effects of resource competition from other more direct ecological interactions and so to clarify the impact mechanism of aquatic invasive species.

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DOI: 10.3897/neobiota.99.143667

Authors: Bert Van Bocxlaer, Julie Offerle, Claudia M. Ortiz Sepulveda, Rémi Habert, Anne-Catherine Holl, Nicolas Denize-Proust, Alexis Y. Dollion, Grant Pawindo, Fred D. Chibwana, Virginie Cuvillier-Hot

Abstract: Invasive species cause major losses in biodiversity worldwide and alter ecosystem functioning. Once established, invaders are often impossible to remove from ecosystems, especially in eco-insular systems such as the African Great Lakes. How intrinsic biological properties of invasive taxa interact with human-induced ecosystem modifications is a crucial factor determining invasiveness and our ability to anticipate, prevent and manage bioinvasions. Here we investigate the influence of temperature on key life-history traits, including fecundity, growth, offspring size, survival and parental immune investments, of invasive Asian Melanoides tuberculata (Müller, 1774) from Lake Malawi/Nyassa (morph LMI). We subjected populations of this parthenogenetic (clonal) lineage to uniform temperature treatments of 20 °C, 26 °C and 32 °C and monitored adult and juvenile life-history traits. Constitutive (preventative) and infection-induced immune investments of adults were estimated via antibacterial responses to a natural pathogen. Fecundity was low during our experiment and did not differ amongst temperature treatments, but a burst of offspring release occurred in the first two weeks of the experiment. Juvenile size and growth increased with temperature, which resulted in decreasing generation times. Juvenile mortality was, however, elevated at 32 °C. Temperature differences prompted a shift in immune investments. Under cold temperatures, adults invested in costly constitutive immunity, but they did not in warm environments, where strong investments in infection-induced immune responses occurred. This strategy may enable adults in warm environments to redirect energy from immunity to growth and reproduction, therewith, enhancing competitiveness at the cost of reduced offspring survival. We observed contrasting responses in various studied traits, suggesting that Melanoides tuberculata adopts compensatory mechanisms to cope with environmental changes. This versatility favours invasiveness and contributes to the competitive pressure which invasive Melanoides exerts on native taxa amid global warming and ecosystem change. Understanding the intricate interactions between bioinvasions and environmental change is essential for effective conservation of native species, the stability of their ecosystems and for policy development. Species-specific versatility of invasive species and associated competitive advantages remain understudied, but are critical to predict invasion dynamics in the context of multidimensional anthropogenic stressors, for informed risk assessment and decision-making.

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DOI: 10.3897/neobiota.98.131103

Authors: Brad Martin, Charlie Huveneers, Simon Reeves, Ryan Baring

Abstract: Estuarine ecosystems are often characterised by endemic foundation organisms which facilitate ecosystem interactions and processes established over millennia. Introduction of non-native foundation species can significantly alter ecological communities and functions. Here, we assessed the effects of introduced, reef-forming Pacific oyster Magallana gigas, within a temperate Australian mangrove-dominated estuary. Specifically, we investigated whether mangrove-attached M. gigas oyster reefs influenced intertidal fish and invertebrate communities, and fish foraging behaviour. We measured and contrasted the benthic structure and faunal communities of fringing bare sediment, Avicennia marina mangrove and Pacific oyster M. gigas reef habitats using a combination of quadrats, fyke nets and remote unbaited video (RUV) surveys. Pacific oyster reefs showed no impacts on pneumatophore density or morphology, but were positively associated with higher seedling densities. Furthermore, invertebrate and fish community metrics (e.g. richness, biomass, length) were typically higher in M. gigas reefs compared to the other habitats. However, several mobile, non-native species were predominantly detected in M. gigas reefs, including exotic gobies and European shore crabs Carcinus maenas, a declared marine pest. Overall, we found that M. gigas reefs in fringing mangrove forests were associated with biodiverse faunal communities, including fisheries-targeted species, but also facilitated other non-native species. These outcomes highlight some of the ecological pros and cons of non-native oyster reefs and the complexity of managing estuaries globally where Pacific oysters increasingly co-occur with endemic habitat-forming species.

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DOI: 10.3897/neobiota.97.141901

Authors: James W. E. Dickey, Julian W. Zeller, Elizabeta Briski, Jonathan M. Jeschke, Gareth Arnott

Abstract: Introductions of non-native species (NNS) are major drivers of biodiversity loss. Gammarids (Crustacea, Gammaroidea) have been particularly successful in establishing and spreading in their non-native range, especially in Europe. While their impacts are wide-ranging, interference competition with native species has received limited study to date. Here, we assessed the competitive abilities of the successful North American NNS Gammarus tigrinus relative to the European native Gammarus duebeni, over a chironomid larva as a single food resource. We staged four types of dyadic contest encounters, with individuals of the native or NNS added to the experimental arena containing the food resource, and inter- or intraspecific competitor individuals added upon the first individual taking possession of the resource, or after 20 minutes. Gammarus tigrinus were more likely to take hold of the bloodworm in the opening 20 minutes, and did so more quickly than G. duebeni. During this period, they were also less thigmotactic than the native, being more explorative and spending a smaller proportion of time in the outer zone of the arena. They exhibited more aggressive interactions and activity with increasing size and mass, whereas larger G. duebeni were shown to be less aggressive and less active. Gammarus tigrinus were found to be significantly less likely to lose possession to G. duebeni than they were to conspecifics, whereas G. duebeni were similarly likely to lose possession to G. tigrinus as to conspecifics. Overall, our findings indicate that the behaviour and competitive ability of G. tigrinus demonstrated here add to a list of traits that facilitate its invasion success. In addition, our method offers potential as an effective, standardisable means of assessing the competitive abilities of gammarid NNS. We encourage future studies to develop it further, incorporating alternative resources, such as habitat, and to assess the role of ecologically relevant abiotic stressors in determining contest outcomes.

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DOI: 10.3897/neobiota.97.132365

Authors: Theresa Henke, Hlynur Bárðarson, Magnús Thorlacius, Guðbjörg Asta Ólafsdóttir

Abstract: To address the increasing global issue of biological invasions adequate long-term monitoring data is crucial. Due to substantial resource requirements such continuous monitoring remains largely underdeveloped across many countries. In recent years, experiential knowledge of the public, or specific stakeholder groups, has become increasingly popular to gather species’ occurrence data. In the context of aquatic alien species recreational fishermen often represent a valuable stakeholder group. Using the case study of alien European flounder (Platichthys flesus, Linneaus, 1758) in Iceland, we explore the benefits of incorporating stakeholder observation-based information with traditionally obtained data on the occurrence and distribution of an alien fish. We compiled records of European flounder reported by the recreational fishing community both when directly approached with an anonymous online survey as well as via social media conversations applying the approach of iEcology. We then contrasted this data with a compilation of European flounder records from databases at the Icelandic Marine and Freshwater Research Institute (MFRI). Our results show that including stakeholder-observation based distribution data in the monitoring of alien species offers significant advantage. While all data sources indicated similar patterns in the spread and distribution of European flounder in Iceland, they differed in the number of unique sites provided as well as their geographic distribution. Combining sources therefore allows to counteract inherent biases present across diverse sources. Our study furthermore indicates that interest in voluntarily reporting European flounder sightings decreased over time, but reemerged when stakeholders and/or the public were presented with an easily accessible opportunity to share information in the form of an online survey. We recommend implementing a monitoring approach for alien species that incorporates diverse sources of information and provides clear venues to report information for the public, and where possible involve stakeholders throughout the entire research process to holistically address biological invasions.

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DOI: 10.3897/neobiota.97.121188

Authors: Thomas I. Gibson, Rebecca S. Millard, Isla MacMillan, Nick Taylor, Mark Thrush, Hannah Tidbury

Abstract: Early detection and rapid response are critical to the successful management of non-indigenous species (NIS) and rely on effective surveillance programmes. Risk-based surveillance, where surveillance targets high risk locations, is the most efficient form of NIS surveillance. However, further research is required on the impact of different levels of emphasis on risk, in sampling designs and on surveillance efficacy. This study implements a theoretical surveillance simulator to model the relative merit of different surveillance strategies with different levels of focus on NIS risk for NIS detection at one or more sites. Three potential surveillance scenarios were modelled: random, risk-based and heavy risk-based surveillance, each with three distributions of combined NIS risks of introduction and establishment: exponential, random and uniform. An example analysis using model derived NIS risk data is also provided. Sensitivity and elasticity analyses were conducted to identify variables which influence model outputs. The interaction between sampling method detection probability and changes in NIS abundance was modelled. It was found that NIS risk distribution influences the relative performance of different surveillance strategies and that risk- and heavy risk-based surveillance have lower times to detections and, generally, higher surveillance probabilities of detection compared to random surveillance at more skewed NIS risk distributions. However, there was a trade-off between short detection time and detection failure in risk-based and particularly heavy risk-based surveillance. Therefore, an over-emphasis on risk-based surveillance could provide suboptimal NIS detection. Sensitivity and elasticity analysis showed that the number of NIS seed sites, mean site visit rate and method detection probability had the largest effects on detection time, highlighting the complexity of designing surveillance programmes. In conclusion, the optimal surveillance strategy is conditional on the risk distribution and this study highlights the value of model-based simulators to guide decision-making in the design of NIS surveillance programmes.

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DOI: 10.3897/neobiota.96.129121

Authors: Hui Wei, Lorenzo Vilizzi, Mingsi Zhang, Ying Jiang, Meng Xu, Miao Fang, Fandong Yu, Lu Shu, Xuejie Wang, Dangen Gu

Abstract: Aquatic ecosystems can harbour more than one non-native fish species and this can represent a threat due to trophic interactions with native fishes. However, research on interactions amongst multiple co-occurring native and non-native fish remains scarce. In this study, 551 organisms from 44 native fish, 11 non-native fish, 35 macroinvertebrates (of which one was non-native), together with 162 samples of basal resources were collected from six rivers of the Lower Pearl River Basin of China. Nitrogen and carbon stable isotope analysis was used to calculate community-wide trophic metrics and the degree of trophic overlap between native and non-native fish at both the community and functional feeding group level, together with diet composition. At the community level, there was a high degree of trophic niche overlap between native and non-native fish as a result of similarities in trophic characteristics. At the functional feeding group level, both native and non-native functional feeding groups demonstrated the capacity to occupy the niche space of each other. A significant trophic niche overlap, exceeding 50%, was found between non-native detritivorous and omnivorous fish, suggesting competition. The difference in diet composition between some native and non-native fish depended on the category of diet source across the rivers, suggesting dietary segregation. Albeit limited, the present findings suggest that trophic interaction between native and non-native fish is likely to reach a dynamic equilibrium status in the community owing to trophic segregation of fish species and the antagonistic effects amongst non-native fish.

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DOI: 10.3897/neobiota.96.130198

Authors: Kamil Wiśniewski, Csilla Balogh, Jarosław Kobak, Daniel Szarmach, Łukasz Jermacz, Małgorzata Poznańska-Kakareko

Abstract: Unionid mussels are globally threatened by several human disturbances, including the introduction of non-native species. Among these, biofouling zebra and quagga mussels of Ponto-Caspian origin are considered to be especially detrimental to unionid locomotion, filtration and physical condition. The aim of our study was to determine and compare the impact of dreissenid fouling and/or presence on locomotion and burrowing of the native Unio tumidus and invasive Sinanodonta woodiana, a novel invader expanding its range in Europe in recent decades. We tested unionids collected from Lake Balaton (central Europe) that were fouled by dreissenids (zebra and quagga mussels mixed), cleaned of fouling or non-fouled (collected without any signs of dreissenid fouling). Moreover, unionids were tested in the presence or absence of other fouled individuals and dreissenids isolated in mesh bags to determine the influence of direct fouling and presence of dreissenids in the environment on unionid behaviour. Movement initiation time, locomotion distance and burrowing level were retrieved from videos recorded for 24 hours. Direct fouling affected only the behaviour of U. tumidus, limiting their burrowing and delaying movements. After removal of fouling, movement timing returned back to normal, but mussels still burrowed less than the control non-fouled individuals, indicating persisting effects of fouling on physical condition. Moreover, U. tumidus reduced their locomotion in the presence of fouled unionids. Sinanodonta woodiana responded to the presence of dreissenids (especially quagga mussels) with increased burrowing. These different responses of the two unionid species to Dreissena spp. indicate that biofoulers may influence biotic interactions between the unionids by promoting the invasive species (less susceptible to negative effects of fouling). Moreover, S. woodiana may indirectly affect U. tumidus through apparent competition, constituting an environmental reservoir of biofoulers exerting a stronger impact on the native species.

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DOI: 10.3897/neobiota.94.122939

Authors: Calum MacNeil, Robin Holmes, Edward Challies, Kiely McFarlane, Jason Arnold

Abstract: Invasive non-native species (INNS) are key drivers of global biodiversity loss. This is particularly evident in freshwater ecosystems, where the rates of both vertebrate biodiversity loss and biological invasion exceed those of marine and terrestrial systems. Aotearoa New Zealand (henceforth Aotearoa) like many other island nations, has a troubled history with NNS. However, it is also unique, as the main islands were the last major landmasses on Earth to remain uninhabited by humans. The endemic fauna had evolved in isolation from any anthropogenic influence or introduced NNS, until the mid-thirteenth century with the arrival of Māori, the first people to inhabit Aotearoa. Centuries later, following European colonisation, many non-native freshwater fish were deliberately introduced by acclimatisation societies. Currently, most of the native freshwater fish species of Aotearoa are at risk of extinction, despite almost 90% of these being found nowhere else on earth. Many of these species are highly valued by the indigenous people of Aotearoa, who have repeatedly highlighted biases towards NNS in freshwater fish management. With the rate of biological invasions increasing, it is timely to address interconnected issues concerning the history, impacts, management and current / future policy directions, including those involving biosecurity, for non-native freshwater fish in Aotearoa. We do this by applying a social-ecological systems (SES) lens, with a focus on causal-loop relationships and feedbacks to improve understanding of the dynamics of drivers, mechanisms and impacts of such invasions. We highlight the tensions that have resulted from managing some NNS as ‘pests’ threatening native biodiversity, while simultaneously promoting a tourism and recreational fishery resource for specific NNS. This has generated extremely polarized views on the ‘status’ of non-native freshwater fish species and given rise to contradictory and divergent goals for their management. We show how a disjointed and often incoherent policy landscape has contributed to legal ‘anomalies’ for NNS, including policy misalignments and gaps, hampering effective use of resources, while also entrenching contradictory management programmes for different stakeholders. Our study shows how these interconnected issues have been manifested in social-ecological feedback loops on core aspects of NNS policy and management, past and present. Consequently, there is a need for increased comprehension of the diverse array of potential impacts of NNS for different environments, stakeholders and Māori while developing coherent and practical management methods to reduce such impacts and improve social-ecological resilience. We conclude that adopting a SES approach will aid this endeavour.

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DOI: 10.3897/neobiota.94.125227

Authors: Elisabeth Renk, James W. E. Dickey, Ross N. Cuthbert, Elžbieta Kazanavičiūtė, Elizabeta Briski

Abstract: 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.

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DOI: 10.3897/neobiota.92.110442

Authors: Davide Bottacini, Bart J. A. Pollux, Reindert Nijland, Patrick A. Jansen, Marc Naguib, Alexander Kotrschal

Abstract: Invasive species often severely impact ecosystems and human activities in the areas that they invade. The lionfishes Pterois miles and P. volitans are regarded as the most successful invasive fishes in marine ecosystems. In the last 40 years, these Indo-Pacific predators have established in the tropical western Atlantic Ocean, with well-documented detrimental effects on the local fish communities. Around 10 years ago, a second invasion began in the Mediterranean Sea, which is being colonised by P. miles. Given the invasive potential of P. miles and the fact that the ecology and biodiversity of the temperate/sub-tropical Mediterranean Sea offer a different setting from the tropical western Atlantic, specific knowledge on this second invasion is needed. Here, we: (i) review the scientific knowledge available on the ecology of invasive lionfishes, (ii) discuss such knowledge in the context of invasion ecology and (iii) suggest future research avenues on the P. miles invasion in the Mediterranean Sea. In addition, we offer an update on the spread of P. miles in the Mediterranean Sea. While the history and development of the Mediterranean invasion are resolved and some mitigation plans have been implemented locally, the study of the interactions of P. miles with Mediterranean species and their impact on the local biodiversity is in its infancy. Closing this gap will lead to important fundamental insights in invasion ecology and will result in predictions on the impact of P. miles on the ecology and ecosystem services of the Mediterranean Sea. Such information will have practical implications for policy-makers aiming to devise sound and efficient mitigation plans.

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DOI: 10.3897/neobiota.85.99296

Authors: Bingguo Dai, Junjiro N. Negishi, Kazuya Fujii, Md. Khorshed Alam, Zhongguan Jiang

Abstract: The introduction of non-native fish species poses a threat to native assemblages in floodplain systems. Establishing oxbow lake-based conservation areas has been proposed as a practical approach to mitigate this threat. Previous studies have extensively discussed the effects of lateral connectivity between oxbow lakes and main channels on fish communities but overlooked the spatial longitudinal gradients of oxbow lakes on a broader spatial scale. Over the course of about ten years, the temporal changes in fish community diversity were estimated in 28 oxbow lakes along the Ishikari River in Hokkaido, Japan. The associations between these temporal variations and the locations of the lakes were then explored along a longitudinal spatial gradient. The results showed that upstream oxbow lakes underwent mild alterations to their species composition and maintained a high level of native uniqueness. In contrast, downstream oxbow lakes experienced intense species turnover and increased non-native fish diversity. Additionally, the dominance of non-native fish in downstream areas rapidly expanded upstream to a location 110 km from the source of the Ishikari River over the decade. It is emphasized that the lakes in the upper reaches were the only remaining refuges for native fish and should be prioritized in conservation efforts. Our study proposes the application of location and species contributions to regional community heterogeneity as indicators for highlighting native fish conservation areas.

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DOI: 10.3897/neobiota.75.86528

Authors: Tobias Backström, Carola Winkelmann

Abstract: Salinity is an influential abiotic environmental factor in aquatic species, specifically in freshwater, where salinization causes ecosystem degradation. Secondary salinization, that is increases in salinity due to anthropogenic activities, can affect both osmoregulation and behaviour in freshwater fishes. It is generally believed that invasive species handle climatic change and environmental degradation better than native species, which is one reason for their invasion success. However, how invasive and native species cope with salinity changes remains little understood. Therefore, we investigated how low (500 µS/cm) and high salinity (2000 µS/cm) conditions affected oxygen consumption and behaviour in the invasive round goby (Neogobius melanostomus) and the native European perch (Perca fluviatilis). Our results showed that in round goby oxygen consumption increased and swimming and non-swimming movements changed in response to salinity increments, whereas European perch was not affected by salinity. Thus, it seems as if the invasive round goby is more sensitive to changes in salinity than the native European perch. Our results fit with the minority of studies indicating invasive species being less tolerant than some native species to environmental changes. This finding could be explained by the adaptation of round goby to low salinity due to its long establishment in River Rhine. Further, our results are also confirming that the effect of salinity is species-specific. In addition, European perch and round goby show diametrically different behavioural response to disturbance which could be an effect of holding different ecological niches as well as their anatomical differences.

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DOI: 10.3897/neobiota.73.82636

Authors: Łukasz Wejnerowski, Tümer Orhun Aykut, Aleksandra Pełechata, Michał Rybak, Tamara Dulić, Jussi Meriluoto, Marcin Krzysztof Dziuba

Abstract: Organism dispersal is nowadays highly driven by human vectors. This also refers to the aquatic organisms that can often silently spread in and invade new waters, especially when human vectors of dispersal act without brakes. Thus, it is mandatory to continuously identify human-mediated mechanisms of organism dispersal and implement proper biosecurity treatments. In this study, we demonstrate how the plankton net – one of the basic instruments in the equipment of every plankton sampling person is a good vector for plankton dispersal and invasions. We also demonstrate whether keeping the net in an ethanol solution after sampling is a proper biosecurity treatment, and what kind of treatments are implemented by people worldwide. The first simulation shows that bloom-forming cyanobacteria can easily infiltrate into the new environment thanks to the nets, and can prosper there. However, ethanol-based biosecurity treatment efficiently prevented their spread and proliferation in the new environment. The second simulation, based on wild plankton from an eutrophic lake, indicates that a plethora of phyto- and zooplankton taxa can infiltrate into the new waterbody through the net and sustain themselves there if the net is only flushed in the waterbody and left to dry after sampling (an approach that is commonly used by naturalists). Here, we also show that native plankton residents strongly shape the fate of hitch-hikers, but some of them like cyanobacteria can successfully compete with residents. Survey data alert us to the fact that the vast majority of biologists use either ineffective or questionable biosecurity treatments and only less than a tenth of samplers implement treatments based on disinfectant liquids. Our results emphasize that the lack of proper biosecurity methods implemented by the biologists facilitates the spread and invasions of plankton including also invasive species of a great nuisance to native ecosystems. Considering that naturalists usually use different instruments that might also be good vectors of plankton dispersal, it is necessary to develop proper uniform biosecurity treatments. No longer facilitating the plankton spread through hydrobiological instruments is the milestone that we, plankton samplers worldwide, should achieve together in the nearest future if we want to continue our desire to explore, understand, protect and save nature.

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DOI: 10.3897/neobiota.73.80542

Authors: James W. E. Dickey, Gareth Arnott, Ciara L. O. McGlade, Andrew Moore, Gillian E. Riddell, Jaimie T. A. Dick

Abstract: Invasive alien species (IAS) are major drivers of global biodiversity loss, and the poorly regulated international pet trade is a source of emerging and future invaders. Predictions of the likely ecological impacts and risks of such IAS have been significantly enhanced in recent years with new metrics, which require application to many more actual and potential IAS. Hence, this study assesses the potential ecological impacts and risks of two readily available pet trade species: goldfish, Carassius auratus, a species with non-native populations worldwide; and white cloud mountain minnow, Tanichthys albonubes, a species with a limited invasion history to date. First, we compared the per capita feeding rates of these non-native species with two European trophically analogous natives – the stone loach, Barbatula barbatula, and the common minnow, Phoxinus phoxinus – using the Comparative Functional Response method. Second, we used foraging experiments in conspecific pairs to determine synergistic, neutral or antagonistic intraspecific interactions. Third, we performed novel object experiments using the two pet trade species to assess boldness, a known “dispersal enhancing trait”. Goldfish had the highest maximum feeding rates of the four species, while white cloud mountain minnows had the lowest. Neutral interactions were observed for all four species in the paired foraging experiments, with goldfish having the highest consumption and white cloud mountain minnows having the lowest. Goldfish demonstrated greater boldness, being more active during the experimental trials and more likely to approach a novel object than white cloud mountain minnows. Further, combining maximum feeding rates, boldness and species availabilities from our survey of pet shops, we assessed the relative invasion risks (RIR) of the two non-natives. This highlighted goldfish as the higher risk and most worthy of management prioritisation, mirroring its more extensive invasion history. We propose that such metrics have potential to direct future IAS policy decisions and management towards the ever-increasing rates of biological invasions worldwide.

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DOI: 10.3897/neobiota.72.80500

Authors: Marco Milardi, Andy J. Green, Marco Mancini, Paolo Trotti, Mikko Kiljunen, Jyrki Torniainen, Giuseppe Castaldelli

Abstract: Predatory fish have occasionally been observed preying on birds, sometimes repeatedly, but few studies were able to unravel the overall significance of avian prey in fish diet and the predation impacts on bird populations. We used a control/impact study setup, using a Nature Reserve in northern Italy and a nearby control area, to determine: 1) the contribution of waterbirds to wels catfish diet in the Reserve, 2) the population density of wels catfish in the Reserve and control area and 3) the potential impacts of waterbird depredation by wels catfish on waterbird population trends. Our stable isotope Bayesian mixing model indicated that birds contributed 12.2% (5–27.9%, 50% confidence interval) of the diet of large wels catfish (> 98 cm in total length). Large individuals constituted the majority of the population in the shoreline areas of the reserve in 2013–2019, where the population was stable despite control efforts. Numbers were below detectable levels in the control area. Large wels catfish consumed an average of 224, 148 and 187 kg of birds during the 2019 chick growing period, as estimated through three different bioenergetic models. Compared to the control area, mallard reproductive success was diminished in the Reserve, likely due to higher rates of fish predation, although effects were variable in different years. Overall, our data suggest that high densities of invasive wels catfish might impact waterbird reproductive success through predation on bird chicks, but further studies would be needed to reduce uncertainties related to the intrinsic variability of field ecology data. Our study constitutes a preliminary attempt to assess the potential of introduced wels catfish to affect the conservation value of waterbird protection areas, and should be repeated at broader spatial and temporal scales.

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DOI: 10.3897/neobiota.71.75711

Authors: Emma M. DeRoy, Steven Crookes, Kyle Matheson, Ryan Scott, Cynthia H. McKenzie, Mhairi E. Alexander, Jaimie T. A. Dick, Hugh J. MacIsaac

Abstract: Characterising interspecific interaction strengths, combined with population abundances of prey and their novel predators, is critical to develop predictive invasion ecology. This is especially true of aquatic invasive species, which can pose a significant threat to the structure and stability of the ecosystems to which they are introduced. Here, we investigated consumer-resource dynamics of two globally-established aquatic invasive species, European green crab (Carcinus maenas) and brown trout (Salmo trutta). We explored the mediating effect of prey density on predatory impact in these invaders relative to functionally analogous native rock crab (Cancer irroratus) and Atlantic salmon (Salmo salar), respectively, feeding on shared prey (Mytilus sp. and Tenebrio molitor, respectively). We subsequently combined feeding rates with each predator’s regional abundance to forecast relative ecological impacts. All predators demonstrated potentially destabilising Type II functional responses towards prey, with native rock crab and invasive brown trout exhibiting greater per capita impacts relative to their trophic analogues. Functional Response Ratios (attack rates divided by handling times) were higher for both invasive species, reflecting greater overall per capita effects compared to natives. Impact projections that incorporated predator abundances with per capita effects predicted severe impacts by European green crabs. However, brown trout, despite possessing higher per capita effects than Atlantic salmon, are projected to have low impact owing to currently low abundances in the sampled watershed. Should brown trout density increase sixfold, we predict it would exert higher impact than Atlantic salmon. Such impact-forecasting metrics and methods are thus vital tools to assist in the determination of current and future adverse impacts associated with aquatic invasive species.

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DOI: 10.3897/neobiota.70.68202

Authors: Rafael Muñoz-Mas, Martina Carrete, Pilar Castro-Díez, Miguel Delibes-Mateos, Josep A. Jaques, Marta López-Darias, Manuel Nogales, Joan Pino, Anna Traveset, Xavier Turon, Montserrat Vilà, Emili García-Berthou

Abstract: Scientific and grey literature on invasive alien species (IAS) is conditioned by social, economic and political priorities, editorial preferences and species and ecosystem characteristics. This leads to knowledge gaps and mismatches between scientific research interests and management needs. We reviewed the literature on IAS management in Spain found in Scopus, Web of Science, Google Scholar and Dialnet to identify key deficiencies and priority research areas. The collected literature was classified, employing features describing formal aspects and content. We used bibliometric and keyword co-occurrence network analyses to assess the relationship between features and reveal the existence of additional topics. Most of the compiled documents (n = 388) were focused on terrestrial ecosystems and inland waters, whereas marine and urban ecosystems were under-represented. The literature was largely generic and not species-specific, focusing on raising awareness and proposing changes on current regulation as prominent approaches to prevent further introductions. The compiled authors exhibited many clear publishing preferences (e.g. language or document type), but less regarding target taxa. In addition, there was a strong association between species and the different features considered, especially between the methodological approach (e.g. review, field experiment) and the primary emphasis of study (i.e. basic/theoretical, applied or interdisciplinary). This indicates that research on IAS has had a strong species-specific focus. References about terrestrial species focused mainly on vascular plants, whereas references about inland waters were mostly on fishes and the giant reed (Arundo donax), which has been managed with partial success. Animal culling and plant removal were the most frequent eradication and small-scale control treatments, whereas the documents addressing wider spatial scales were largely theoretical. Consequently, the success of described treatments was largely uncertain. Spanish invasion science research has been occasionally innovative, incorporating novel technologies (e.g. species distribution modelling) and engaging society with citizen-science approaches. However, the ratio between basic/theoretical and applied studies indicates that more applied research/management is needed, especially in inland waters and marine ecosystems. We call for increasing effort in the effective dissemination of experience in IAS management to enhance current practical knowledge, including that of schemes undertaken by public agencies.

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DOI: 10.3897/neobiota.69.73734

Authors: Jarosław Kobak, Michał Rachalewski, Karolina Bącela-Spychalska

Abstract: We used a freshwater amphipod-microsporidian model (Ponto-Caspian hosts: Dikerogammarus villosus and D. haemobaphes, parasite: Cucumispora dikerogammari) to check whether parasites affect biological invasions by modulating behaviour and intra- and interspecific interactions between the invaders. We tested competition for shelter in conspecific and heterospecific male pairs (one or both individuals infected or non-infected). In general, amphipods of both species increased their shelter occupancy time when accompanied by infected rather than non-infected conspecifics and heterospecifics. Infected amphipods faced lower aggression from non-infected conspecifics. Moreover, D. villosus was more aggressive than D. haemobaphes and more aggressive towards conspecifics vs. heterospecifics. In summary, infection reduced the intra- and interspecific competitivity of amphipods, which became less capable of defending their shelters, despite their unchanged need for shelter occupancy. Dikerogammarus haemobaphes, commonly considered as a weaker competitor, displaced by D. villosus from co-occupied locations, was able to compete efficiently for the shelter with D. villosus when microsporidian infections appeared on the scene. This suggests that parasites may be important mediators of biological invasions, facilitating the existence of large intra- and interspecific assemblages of invasive alien amphipods.

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DOI: 10.3897/neobiota.66.63847

Authors: Sergey Golubkov, Alexei Tiunov, Mikhail Golubkov

Abstract: The paucity of data on non-indigenous marine species is a particular challenge for understanding the ecology of invasions and prioritising conservation and research efforts in marine ecosystems. Marenzelleria spp. are amongst the most successful non-native benthic species in the Baltic Sea during recent decades. We used stable isotope analysis (SIA) to test the hypothesis that the dominance of polychaete worm Marenzelleria arctia in the zoobenthos of the Neva Estuary after its invasion in the late 2000s is related to the position of this species in the benthic food webs. The trend towards a gradual decrease in the biomass of Marenzelleria worms was observed during 2014–2020, probably due to significant negative relationships between the biomass of oligochaetes and polychaetes, both of which, according to SIA, primarily use allochthonous organic carbon for their production. The biomass of benthic crustaceans practically did not change and remained very low. The SIA showed that, in contrast to the native crustacean Monoporeia affinis, polychates are practically not consumed either by the main invertebrate predator Saduria entomon, which preys on M. affinis, oligochaetes and larvae of chironomids or by benthivorous fish that prefer native benthic crustaceans. A hypothetical model for the position and functional role of M. arctia in the bottom food web is presented and discussed. According the model, the invasion of M. arctia has created an offshoot food chain in the Estuary food webs. The former dominant food webs, associated with native crustaceans, are now poorly developed. The lack of top-down control obviously contributes to the significant development of the Marenzelleria food chain, which, unlike native food chains, does not provide energy transfer from autochthonous and allochthonous organic matter to the upper trophic levels. The study showed that an alien species, without displacing native species, can significantly change the structure of food webs, creating blind offshoots of the food chain.

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DOI: 10.3897/neobiota.58.49358

Authors: Johannes C. Rusch, Michaela Mojžišová, David A. Strand, Jitka Svobodová, Trude Vrålstad, Adam Petrusek

Abstract: Crayfish of North American origin are amongst the most prominent high-impact invasive invertebrates in European freshwaters. They contribute to the decline of European native crayfish species by spreading the pathogen causing crayfish plague, the oomycete Aphanomyces astaci. In this study we validated the specificity of four quantitative PCR (qPCR) assays, either published or newly developed, usable for environmental DNA (eDNA) screening for widely distributed native and non-native crayfish present in Central Europe: Astacus astacus, Pacifastacus leniusculus, Faxonius limosus and Procambarus virginalis. We then conducted an eDNA monitoring survey of these crayfish as well as the crayfish plague pathogen in a wide variety of habitat types representative for Central and Western Europe. The specificity of qPCR assays was validated against an extensive collection of crayfish DNA isolates, containing most crayfish species documented from European waters. The three assays developed in this study were sufficiently species-specific, but the published assay for F. limosus displayed a weak cross-reaction with multiple other crayfish species of the family Cambaridae. In the field study, we infrequently detected eDNA of A. astaci together with the three non-native crayfish species under examination. We never detected eDNA from A. astaci together with native crayfish, but in a few locations eDNA from both native and non-native crayfish was captured, due either to passive transport of eDNA from upstream populations or co-existence in the absence of infected crayfish carriers of A. astaci. In the study, we evaluated a robust, easy-to-use and low-cost version of the eDNA sampling equipment, based mostly on items readily available in garden stores and hobby markets, for filtering relatively large (~5 l) water samples. It performed just as well as the far more expensive equipment industrially designed for eDNA water sampling, thus opening the possibility of collecting suitable eDNA samples to a wide range of stakeholders. Overall, our study confirms that eDNA-based screening for crayfish and their associated pathogen is a feasible alternative to traditional monitoring.

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DOI: 10.3897/neobiota.57.49196

Authors: Alexandra Markert

Abstract: Pacific oysters Crassostrea (Magallana) gigas have been successfully invading ecosystems worldwide. As an ecosystem engineer, they have the potential to substantially impact on other species and on functional processes of invaded ecosystems. Engineering strength depends on oyster density in space and time. Density has not yet been studied on the extent of reef structural dynamics. This study assessed abundance of naturalized Pacific oysters by shell length (SL) of live individuals and post-mortem shells at six sites over six consecutive years during post-establishment. Individual biomass, i.e. live wet mass (LWM), flesh mass (FM) and live shell mass (SM LIVE), were determined from a total of 1.935 live oysters in order to estimate areal biomass. The generic term density attribute was used for SL-related population categories and the biomass variables LWM, FM, SM LIVE and SM. As the oyster invasion modulated resident Mytilus edulis beds, the study was supplemented by contemporaneously assessed data of mussels and corresponding analyses. Interrelations of abundance and areal biomass revealed distinct linkages between specific density attributes. Most importantly, large individuals were identified as intrinsic drivers for the determination of areal biomass. Additionally, allometry of large oysters differed from small oysters by attenuated scaling relations. This effect was enhanced by oyster density as results showed that crowding forced large individuals into an increasing slender shape. The significant relationship between the density attributes large oyster and biomass enabled a classification of reef types by large oyster abundance. Reef type (simple or complex reef) and oyster size (small or large) were considered by implementing a novel concept of weighted twin functions (TF) for the relationship between SL and individual biomass. This study demonstrates that the interplay of scaling parameters (scalar, exponent) is highly sensitive to the estimation of individual biomass (shape) and that putative similar scaling parameters can exceedingly affect the estimation of areal biomass. For the first time, this study documents the crucial relevance of areal reference, i.e. cluster density (CD) or reef density (RD), when comparing density. RD considers reef areas devoid of oysters and results from CD reduced by reef coverage (RC) as the relative reef area occupied by oysters. A compilation of density attributes at simple and complex reefs shall serve as a density guide. Irrespective of areal reference, oyster structural density attributes were significantly higher at complex than at simple reefs. In contrast, areal reference was of vital importance when evaluating the impact of engineering strength at ecosystem-level. While mussel CD was similar at both reef types, RD at complex reefs supported significantly more large mussels and higher mussel biomass than at simple reefs. Although mussels dominated both reef types by abundance of large individuals, oysters were the keystone engineers by dominating biomass. The prominent status of large oysters for both allometric scaling and density, presumably characteristic for Pacific oyster populations worldwide, should be considered when conducting future investigations. The effort of monitoring will substantially be reduced as only large oysters have to be counted for an empirical characterization of Pacific oyster reefs. The large oyster concept is independent of sampling season, assessment method or ecosystem, and is also applicable to old data sets. Harmonization on the proposed density attributes with a clear specification of areal reference will allow trans-regional comparisons of Pacific oyster reefs and will facilitate evaluations of engineering strength, reef performance and invasional impacts at ecosystem-level.

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DOI: 10.3897/neobiota.45.33116

Authors: Patrick W.S. Joyce, Louise Kregting, Jaimie T.A. Dick

Abstract: The ecological impacts of invasive species can be severe, but are generally viewed as highly unpredictable. Recent methods combining per capita feeding rates, population abundances and environmental contexts have shown great utility in predicting invader impacts. Here, clearance rates of the invasive Pacific oyster, Crassostrea gigas, and native mussel, Mytilus edulis, were investigated in a laboratory experiment where oscillatory water flow and algal food concentrations were manipulated. Invasive oysters had lower clearance rates than native mussels in all experimental groups and did not differ among flow velocities or food concentrations. Native mussel clearance rates were higher at 5 cm s-1 compared to 0 and 15 cm s-1 flow velocities and increased with increasing food concentration. The Relative Impact Potential (RIP) metric was used to assess (i) the influence of flow velocity and food concentration on potential impacts of C. gigas on plankton resources and, (ii) the impacts of coexisting reefs, containing both species, on resources compared to monospecific native mussel beds. Greatest Relative Impact Potential of invasive oysters was seen at the lowest flow velocity, but became reduced with increasing flow velocity and food concentration. Relative Impact Potentials of coexisting reefs were generally greater than monospecific native mussel beds, with greatest impacts predicted at lowest flow velocity. We suggest that the greatest ecological impacts and competition potential of C. gigas will occur in areas with low flow velocity, but that increased flow will mediate co-existence between the two species.

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DOI: 10.3897/neobiota.22.6224

Authors: Mads Thomsen, Thomas Wernberg, Julian Olden, James E. Byers, John Bruno, Brian Silliman, David Schiel

Abstract: Invasions by non-native species are a threat to biodiversity because invaders can impact native populations, communities and entire ecosystems. To manage this threat, it is necessary to have a strong mechanistic understanding of how non-native species affect local species and communities. We reviewed 259 published papers (1972–2012) that described field experiments quantifying the impact of aquatic non-native species, to examine whether various types of study biases are limiting this understanding. Our review revealed that invasion impacts had been experimentally quantified for 101 aquatic non-native species, in all major freshwater and marine habitats, on all continents except Antarctica and for most higher taxonomic groupings. Over one-quarter (26%) of studies included tests for impacts on local biodiversity. However, despite this extensive research effort, certain taxa, habitats and regions remain poorly studied. For example, of the over one hundred species examined in previous studies, only one was a marine fish and only six were herbivores. Furthermore, over half (53%) the studies were from the USA and two-thirds (66%) were from experiments conducted in temperate latitudes. By contrast, only 3% of studies were from Africa and <2% from high latitudes. We also found that one-fifth (20%) of studies were conducted in estuaries, but only 1% from coral reefs. Finally, we note that the standard procedure of pooling or not reporting non-significant treatments and responses is likely to limit future synthetic advancement by biasing meta-analysis and severely limiting our ability to identify non-native species with none or negligible ecological impacts. In conclusion, a future focus on poorly-studied taxa, habitats and regions, and enhanced reporting of results, should improve our understanding and management of impacts associated with aquatic non-native species.

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DOI: 10.3897/neobiota.20.5062

Authors: Otto Lorenz, Patrick Smith, Lyndon Coghill

Abstract: A hybrid form of tilapia was introduced into Port Sulphur, Louisiana and was subsequently managed by treatment with rotenone and stocking of native predatory fishes. Measurements of tilapia from before this management event were compared to measurements of tilapia in the two years after the treatment. Post-management tilapia were consistently deeper in body and had greater weight per unit length (condition) when compared to pre-management fish. Procrustes generalized least squares data supported this by consistently finding post-management tilapia to be consistently deeper in body and head shape than pre-management fish. Although this could indicate the effectiveness of stocking native predators, several other factors, including two cold winters, seasonal effects, and less competition, may have contributed to this result.

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DOI: 10.3897/neobiota.19.4839

Authors: Calum MacNeil, Jaimie Dick, Mhairi Alexander, Jennifer Dodd, Anthony Ricciardi

Abstract: The success of invading species can be restricted by interspecific interactions such as competition and predation (i.e. biotic resistance) from resident species, which may be natives or previous invaders. Whilst there are myriad examples of resident species preying on invaders, simply showing that such an interaction exists does not demonstrate that predation limits invader establishment, abundance or spread. Support for this conclusion requires evidence of negative associations between invaders and resident predators in the field and, further, that the predator-prey interaction is likely to strongly regulate or potentially de-stabilise the introduced prey population. Moreover, it must be considered that different resident predator species may have different abilities to restrict invaders. In this study, we show from analysis of field data that two European predatory freshwater amphipods, Gammarus pulex and G. duebeni celticus, have strong negative field associations with their prey, the invasive North American amphipod Crangonyx pseudogracilis. This negative field association is significantly stronger with G. pulex, a previous and now resident invader in the study sites, than with the native G. d. celticus. These field patterns were consistent with our experimental findings that both resident predators display potentially population de-stabilising Type II functional responses towards the invasive prey, with a significantly greater magnitude of response exhibited by G. pulex than by G. d. celticus. Further, these Type II functional responses were consistent across homo- and heterogeneous environments, contrary to the expectation that heterogeneity facilitates more stabilising Type III functional responses through the provision of prey refugia. Our experimental approach confirms correlative field surveys and thus supports the hypothesis that resident predatory invertebrates are differentially limiting the distribution and abundance of an introduced invertebrate. We discuss how the comparative functional response approach not only enhances understanding of the success or failure of invasions in the face of various resident predators, but potentially also allows prediction of population- and community-level outcomes of species introductions.

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