Zoochorous dispersal of freshwater bivalves: an overlooked vector in biological invasions?

Vectors that underpin the natural dispersal of invasive alien species are frequently unknown. In particular, the passive dispersal (zoochory) of one organism (or propagule) by another, usually more mobile animal, remains poorly understood. Field observations of the adherence of invasive freshwater bivalves to other organisms have prompted us to assess the importance of zoochory in the spread of three prolific invaders: zebra mussel Dreissena polymorpha; quagga mussel Dreissena bugensis; and Asian clam Corbicula fluminea. An extensive, systematic search of the literature was conducted across multiple on-line scientific databases using various search terms and associated synonyms. In total, only five publications fully satisfied the search criteria. It appears that some fish species can internally transport viable adult D. polymorpha and C. fluminea specimens. Additionally, literature indicates that veligers and juvenile D. polymorpha can adhere to the external surfaces of waterbirds. Overall, literature suggests that zoochorous dispersal of invasive bivalves is possible, but likely a rare occurrence. However, even the establishment of a few individuals (or a single self-fertilising C. fluminea specimen) can, over-time, result in a substantial population. Here, we highlight knowledge gaps, identify realistic opportunities for data collection, and suggest management protocols to mitigate the spread of invasive alien species

Comparative feeding rates of native and invasive ascidians

Ascidians have a recent history of species introductions globally, often with strong ecological impacts. Comparisons of per capita effects of invaders and comparable natives are useful to assess such impacts. Here, we explore ingestion rates (IR) and clearance rates (CR) of Ciona intestinalis and Ciona robusta, co-occurring native and non-native ascidians, respectively, from Brittany, France. IR was positively related to food concentration, with the invader responding more strongly to increasing food concentration. CR also differed by species, with the invader demonstrating higher values. C. robusta exhibited a higher functional response (Type I) than did C. intestinalis (Type II). Relative impact measured using seasonal abundance and IR revealed that C. robusta has a much greater impact than C. intestinalis at all food concentrations tested, though the former has a constrained distribution which limits its regional impact. Nevertheless, when abundant, we expect C. robusta to exert a greater impact on algal foods

No time to dye: dye-induced light differences mediate growth rates among invasive macrophytes

Invasive, submerged macrophytes negatively alter aquatic ecosystems and biodiversity through disruption of ecological structure and functioning. These plants are especially challenging and costly to control, with relatively few successful eradications. We examine the efficacy of dye treatments to control three invasive, submerged macrophyte species: Elodea canadensis Michx., Elodea nuttallii (Planchon) H. St. John and Lagarosiphon major (Ridley). Using an experimental mesocosm approach, growth rates of each species were monitored in relation to five light treatment groups: light, 1×, 2×, 3× dye dosage, and complete darkness (range: 270 to 0 μmol·m-2·s-1). Dye presence did not negate growth in any of the tested species, but the effects of treatments on invasive macrophyte growth rates differed across species. In dyed conditions, E. canadensis exhibited significantly greater increases in length compared to E. nuttallii and L. major, whilst E. nuttallii and L. major were lower and statistically similar. However, L. major significantly increased length relative to Elodea spp. in dark conditions. Similarly, for biomass changes, Elodea spp. gained significantly more biomass than L. major under light and dyed conditions, but not in the dark. Our findings suggest that the tested dye concentrations are not sufficient to halt the growth of these plants. However, under certain conditions, they could potentially help to reduce densities of invasive macrophytes by slowing growth rates and reducing biomass in select species. Differential responses to light could also help explain species replacement dynamics under varying environmental contexts. Overall, while further empirical research is required, management actions that reduce light could help control aquatic macrophytes in combination with other actions, but could also simultaneously mediate shifts in community assembly

The accumulation of microplastic pollution in a commercially important fishing ground.

Publication history: Accepted - 3 March 2022; Published online - 10 March 2022The Irish Sea is an important area for Norway Lobster Nephrops norvegicus fisheries, which are the most valuable fishing resource in the UK. Norway lobster are known to ingest microplastic pollution present in the sediment and have displayed reduced body mass when exposed to microplastic pollution. Here, we identified microplastic pollution in the Irish Sea fishing grounds through analysis of 24 sediment samples from four sites of differing proximity to the Western Irish Sea Gyre in both 2016 and 2019. We used µFTIR spectroscopy to identify seven polymer types, and a total of 77 microplastics consisting of fibres and fragments. The mean microplastics per gram of sediment ranged from 0.13 to 0.49 and 0 to 1.17 MP/g in 2016 and 2019, respectively. There were no differences in the microplastic counts across years, and there was no correlation of microplastic counts with proximity to the Western Irish Sea Gyre. Considering the consistently high microplastic abundance found in the Irish Sea, and the propensity of N. norvegicus to ingest and be negatively impacted by them, we suggest microplastic pollution levels in the Irish Sea may have adverse impacts on N. norvegicus and negative implications for fishery sustainability in the future.EMC is supported by the Department for Agriculture, Environment and Rural Affairs Northern Ireland. NHJ is supported by an Envision Doctoral Training Programme Scholarship funded by the UK National Environment Research Council (NERC). EMC gratefully thanks Dave Williams and Hazel Clark for their technical assistance, Prof Jochen H. E. Koop for facilitating the µFTIR analysis at the Federal Institute of Hydrology, BfG, Koblenz, Germany, and Dr Jason Kirby for facilitating the microplastic analysis at Liverpool John Moores University

Ecological Impacts of Alien Species: Quantification, Scope, Caveats, and Recommendations

Despite intensive research during the past decade on the effects of alien species, invasion science still lacks the capacity to accurately predict the impacts of those species and, therefore, to provide timely advice to managers on where limited resources should be allocated. This capacity has been limited partly by the context-dependent nature of ecological impacts, research highly skewed toward certain taxa and habitat types, and the lack of standardized methods for detecting and quantifying impacts. We review different strategies, including specific experimental and observational approaches, for detecting and quantifying the ecological impacts of alien species. These include a four-way experimental plot design for comparing impact studies of different organisms. Furthermore, we identify hypothesis-driven parameters that should be measured at invaded sites to maximize insights into the nature of the impact. We also present strategies for recognizing high-impact species. Our recommendations provide a foundation for developing systematic quantitative measurements to allow comparisons of impacts across alien species, sites, and tim

Ecological impacts of alien species: quantification, scope, caveats, and recommendations

Despite intensive research during the past decade on the effects of alien species, invasion science still lacks the capacity to accurately predict the impacts of those species and, therefore, to provide timely advice to managers on where limited resources should be allocated. This capacity has been limited partly by the context-dependent nature of ecological impacts, research highly skewed toward certain taxa and habitat types, and the lack of standardized methods for detecting and quantifying impacts. We review different strategies, including specific experimental and observational approaches, for detecting and quantifying the ecological impacts of alien species. These include a four-way experimental plot design for comparing impact studies of different organisms. Furthermore, we identify hypothesis-driven parameters that should be measured at invaded sites to maximize insights into the nature of the impact. We also present strategies for recognizing high-impact species. Our recommendations provide a foundation for developing systematic quantitative measurements to allow comparisons of impacts across alien species, sites, and time

Interspecific variation, habitat complexity and ovipositional responses modulate the efficacy of cyclopoid copepods in disease vector control

The use of predatory biological control agents can form an effective component in the management of vectors of parasitic diseases and arboviruses. However, we require predictive methods to assess the efficacies of potential biocontrol agents under relevant environmental contexts. Here, we applied functional responses (FRs) and reproductive effort as a proxy of numerical responses (NRs) to compare the Relative Control Potential (RCP) of three cyclopoid copepods, Macrocyclops albidus, M. fuscus and Megacyclops viridis towards larvae of the mosquito Culex quinquefasciatus. The effects of habitat complexity on such predatory impacts were examined, as well as ovipositional responses of C. quinquefasciatus to copepod cues in pairwise choice tests. All three copepod species demonstrated a population destabilising Type II FR. M. albidus demonstrated the shortest handling time and highest maximum feeding rate, whilst M. fuscus exhibited the highest attack rate. The integration of reproductive effort estimations in the new RCP metric identifies M. albidus as a very promising biocontrol agent. Habitat complexity did not impact the FR form or maximum feeding rate of M. albidus, indicating that potentially population destabilising effects are robust to habitat variations; however, attack rates of M. albidus were reduced in the presence of such complexity. C. quinquefasciatus avoided ovipositing where M. albidus was physically present, however it did not avoid chemical cues alone. C. quinquefasciatus continued to avoid M. albidus during oviposition when both the treatment and control water were dyed; however, when an undyed, predator-free control was paired with dyed, predator-treated water, positive selectivity towards the treatment water was stimulated. We thus demonstrate the marked predatory potential of cyclopoid copepods, utilising our new RCP metric, and advocate their feasibility in biological control programmes targeting container-style habitats. We also show that behavioural responses of target organisms and environmental context should be considered to maximise agent efficacy

INVASIVESNET towards an International Association for Open Knowledge on Invasive Alien Species

In a world where invasive alien species (IAS) are recognised as one of the major threats to biodiversity, leading scientists from five continents have come together to propose the concept of developing an international association for open knowledge and open data on IAS—termed “INVASIVESNET”. This new association will facilitate greater understanding and improved management of invasive alien species (IAS) and biological invasions globally, by developing a sustainable network of networks for effective knowledge exchange. In addition to their inclusion in the CBD Strategic Plan for Biodiversity, the increasing ecological, social, cultural and economic impacts associated with IAS have driven the development of multiple legal instruments and policies. This increases the need for greater co-ordination, co-operation, and information exchange among scientists, management, the community of practice and the public. INVASIVESNET will be formed by linking new and existing networks of interested stakeholders including international and national expert working groups and initiatives, individual scientists, database managers, thematic open access journals, environmental agencies, practitioners, managers, industry, non-government organisations, citizens and educational bodies. The association will develop technical tools and cyberinfrastructure for the collection, management and dissemination of data and information on IAS; create an effective communication platform for global stakeholders; and promote coordination and collaboration through international meetings, workshops, education, training and outreach. To date, the sustainability of many strategic national and international initiatives on IAS have unfortunately been hampered by time-limited grants or funding cycles. Recognising that IAS initiatives need to be globally coordinated and ongoing, we aim to develop a sustainable knowledge sharing association to connect the outputs of IAS research and to inform the consequential management and societal challenges arising from IAS introductions. INVASIVESNET will provide a dynamic and enduring network of networks to ensure the continuity of connections among the IAS community of practice, science and management

Parent–offspring conflict and motivational control of brooding in an amphipod (Crustacea)

Models of parent–offspring conflict concerning levels of caregiving centre on conflict resolution by offspring control, compromise or offspring ‘honest signalling’ that parents use to maximize their own fitness. Recent empirical studies on motivational control of parental feeding of offspring are interpreted as supporting the latter model. Here, we examine parental care in an amphipod, Crangonyx pseudogracilis, which directs care to embryos in a brood pouch. Embryo removal and transplantation elucidated causal factors that determine levels of caregiving. In the short-term, females with all embryos removed reduced care activities, but partial embryo removal did not affect caregiving, evidence of ‘unshared’ parental care. In the long-term, females with all embryos removed ceased care. Thus, females have a maternal state that is maintained by stimuli from offspring. Transplantation of early/late stage embryos among females originally carrying early/late stage embryos revealed that stimuli from embryos indicate their age-dependent needs, but only modify caregiving within the constraints of a changing endogenous maternal state. Thus, we demonstrate that mothers and offspring share motivational control of care. However, we highlight the inappropriate use of motivational data in reaching conclusions about the resolution of parent–offspring conflict