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Much research effort has been invested in understanding ecological impacts of invasive alien species (IAS) across ecosystems and taxonomic groups, but empirical studies about economic effects lack synthesis. Using a comprehensive global database, we determine patterns and trends in economic costs of aquatic IAS by examining: (i) the distribution of these costs across taxa, geographic regions and cost types; (ii) the temporal dynamics of global costs; and (iii) knowledge gaps, especially compared to terrestrial IAS. Based on the costs recorded from the existing literature, the global cost of aquatic IAS conservatively summed to US$345 billion, with the majority attributed to invertebrates (62%), followed by vertebrates (28%), then plants (6%). The largest costs were reported in North America (48%) and Asia (13%), and were principally a result of resource damages (74%); only 6% of recorded costs were from management. The magnitude and number of reported costs were highest in the United States of America and for semi-aquatic taxa. Many countries and known aquatic alien species had no reported costs, especially in Africa and Asia. Accordingly, a network analysis revealed limited connectivity among countries, indicating disparate cost reporting. Aquatic IAS costs have increased in recent decades by several orders of magnitude, reaching at least US$23 billion in 2020. Costs are likely considerably underrepresented compared to terrestrial IAS; only 5% of reported costs were from aquatic species, despite 26% of known invaders being aquatic. Additionally, only 1% of aquatic invasion costs were from marine species. Costs of aquatic IAS are thus substantial, but likely underreported. Costs have increased over time and are expected to continue rising with future invasions. We urge increased and improved cost reporting by managers, practitioners and researchers to reduce knowledge gaps. Few costs are proactive investments; increased management spending is urgently needed to prevent and limit current and future aquatic IAS damages., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

This study assessed numerous histological parameters as markers of health status in mussels (Mytilus spp.) collected from several locations along a contamination gradient on the River Tamar and two coastal sites on the north and south coast of Cornwall, UK. Twenty-seven health parameters were assessed including the presence of pathogens, inflammatory lesions, non-specific pathologies and reproductive condition. Logistic regression showed that reproductive condition and inflammatory lesions showed changes indicative of a contamination gradient response. Mussel populations further upstream within the Tamar were relatively less developed compared to mussels situated downstream in the estuary. Compared to coastal locations, mussels sampled within the Tamar also exhibited a higher prevalence of inflammatory lesions that increased at locations situated furthest upstream. Similarly, levels of lipofuscin within the kidney epithelium were highest in mussels sampled within the estuary and Whitsand Bay compared to Trebarwith Strand. The most prevalent pathogens observed during this survey included Rickettsia/Chlamydia-like organisms (R/CLO), gill ciliates including Ancistrum mytili, the copepod Mytilicola intestinalis, Ciliophora-like organisms and Marteilia sp. Marteilia sp. was observed in 31% of the mussels sampled from the Cremyll Ferry site. Generally, the range and prevalence of pathogens was highest from the two estuarine locations at Cremyll Ferry and Wilcove. No significant differences were observed between estuarine sampling sites and Whitsand Bay with respect to median epithelial cell height of digestive tubules, however mussels from Trebarwith Strand did exhibit a reduced median epithelial cell height compared to mussels sampled from other sampling sites. Species genotyping was also undertaken during this study in order to consider any histological differences in relation to species. Results are discussed in relation to histopathology health parameters and biological effects monitoring., (Crown Copyright © 2011. Published by Elsevier Ltd. All rights reserved.)

Bacteria showing antimicrobial resistance (AMR) pose a significant global healthcare problem. Although many mechanisms conferring AMR are understood, the ecological processes facilitating its persistence and spread are less well characterised. Aquatic systems represent an important milieu for the environmental release, mixing, persistence and spread of AMR bacteria and resistance genes associated with horizontally transferable genetic elements. Additionally, owing to the use and discharge of antimicrobials and biocides, and the accumulation and abundance of other pollutants, mechanisms that confer AMR might evolve in aquatic systems. In this review, we hypothesise that aquatic systems have an important ecological and evolutionary role in driving the persistence, emergence and spread of AMR, which could have consequences when attempting to reduce its occurrence in clinical settings., (Crown Copyright © 2011. Published by Elsevier Ltd. All rights reserved.)

Fishery managers perceive the ectoparasitic crustacean, Argulus foliaceus to be a cause of significant economic loss through reduced fish capture rates. This study investigates the influence of previously identified risk factors on the abundance, egg laying habits and impact of this parasite through a longitudinal study of five trout fisheries of varying management intensity. Low water clarity, slow stock turnover and high temperatures showed a significant association with a high abundance of A. foliaceus. High infection levels, low water clarity and low temperature were also associated with reduced rates of fish capture, suggesting abundance of A. foliaceus alone may not affect the catch rates. Depth of egg laying varied in each site throughout the study, increasing in depth as temperature and water clarity increased. Eggs were found to be most abundant in natural fish holding areas and it is hypothesized that the location of egg laying is determined by the habitat usage of host fish.