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Disseminules have drifted in long distance dispersal from the Americas to the coasts of Europe with records extending to the Arctic Ocean and southwards to the Macaronesian islands. The parent plants originate from tropical wetland forests to boreal conditions. Their disseminules undergo different ocean crossing times according to buoyancy duration. We use plastic-drift as a surrogate for the likely risks that disseminules endure during long-distance oceanic spread relating to their size, behaviour and losses from sinking. While origins of disseminules have a wide latitudinal biogeography we have used the records of the extensive strandings on Floridian, Bermudian and the east coast of North American shores as the region with which to compare the comparatively sparse arrivals in Europe. Studies on plastic drift show that the Atlantic current flow is mainly directed towards the northern coast of Ireland, that also covers the west coast of Scotland and south-west Britain. We have concentrated our records to this region, in particular to the Atlantic coasts of Ireland. Few disseminules arrive on European shores in a viable state, and for those that do, the temperate conditions may not suit germination. Some stranding events are likely to have anthropogenic involvement; but the great majority are most probably naturally distributed. Historically, the ethnographic significance suggests stranding events have taken place over centuries and most probably regularly took place during the Holocene. The increase of records in recent decades is likely to have been due to interested observers with access to taxonomic guides, the popular literature and on-line information.

Nitellopsis obtusa is a large invasive freshwater macroalgae that forms extensive, monotypic beds which have altered habitat and impacted littoral communities in lakes across North America. N. obtusa is native to Eurasia including the UK but is considered to be cryptogenic and likely introduced in Ireland, where it was first recorded in 2016. Recent evidence of its spread prompted this hydroacoustic survey which investigated the distribution and abundance of N. obtusa in two large interconnected lakes, Loughs Ree and Derg, within the Shannon River system. Using a consumer grade depth finder and a simplistic approach, we propose an accessible method of hydroacoustic surveying for macrophytes such as N. obtusa which form dense, often monotypic beds. Nitellopsis obtusa beds quantified within three bays in Lough Ree covered 254.4 hectares with a total biovolume of ~ 2.7 million m3, indicating that it may be one of the most aggressive macrophytes introduced to Ireland. The hydroacoustic survey methodology proved to be cost and time efficient. Measurements of plant height and lake depth gathered from the hydroacoustic survey were comparable to diver gathered measurements which provides confidence in the methodology. The rapid expansion of N. obtusa within Loughs Ree and Derg is a concern for other alkaline waterbodies in Ireland, especially marl lake systems, and warrants monitoring. There is no feasible method to eliminate the extensive populations of N. obtusa in Lough Ree and therefore management interventions should aim to limit the spread of this species to other waterbodies. [ABSTRACT FROM AUTHOR]

The high Arctic is considered a pristine environment compared with many other regions in the northern hemisphere. It is becoming increasingly vulnerable to invasion by invasive alien species (IAS), however, as climate change leads to rapid loss of sea ice, changes in ocean temperature and salinity, and enhanced human activities. These changes are likely to increase the incidence of arrival and the potential for establishment of IAS in the region. To predict the impact of IAS, a group of experts in taxonomy, invasion biology and Arctic ecology carried out a horizon scanning exercise using the Svalbard archipelago as a case study, to identify the species that present the highest risk to biodiversity, human health and the economy within the next 10 years. A total of 114 species, currently absent from Svalbard, recorded once and/or identified only from environmental DNA samples, were initially identified as relevant for review. Seven species were found to present a high invasion risk and to potentially cause a significant negative impact on biodiversity and five species had the potential to have an economic impact on Svalbard. Decapod crabs, ascidians and barnacles dominated the list of highest risk marine IAS. Potential pathways of invasion were also researched, the most common were found associated with vessel traffic. We recommend (i) use of this approach as a key tool within the application of biosecurity measures in the wider high Arctic, (ii) the addition of this tool to early warning systems for strengthening existing surveillance measures; and (iii) that this approach is used to identify high‐risk terrestrial and freshwater IAS to understand the overall threat facing the high Arctic. Without the application of biosecurity measures, including horizon scanning, there is a greater risk that marine IAS invasions will increase, leading to unforeseen changes in the environment and economy of the high Arctic. [ABSTRACT FROM AUTHOR]

Quagga and zebra mussels of the genus Dreissena are two of the most impactful freshwater invasive alien species that have spread widely across the globe. These species attach to natural and artificial substrates, form dense populations and filter large volumes of water causing ecological and economic damage. Following the quagga mussel's discovery in the Shannon River system in Ireland, this study assesses its local distribution, population density, relative abundance, and population structure in the interconnected lakes Lough Ree and Lough Derg in order to determine the likely year and location of its introduction. Polymodal length-frequency analysis was used to distinguish between year cohorts and estimate growth rates. The quagga mussel is established widely across both lakes and is settling on a range of artificial surfaces, natural substrates, dead shells, plant material, and other invasive bivalves. High densities of quagga mussels exceeding 20 000 individuals per m2 were present on artificial surfaces in Lough Ree with total dreissenid densities reaching 26 758 per m2. The relative abundance of quagga mussels to zebra mussels on natural substrates is high in Lough Ree (up to 94.7%) and low in Lough Derg (up to 16.8%). Two to four year cohorts were present at all sites, with quagga mussels attaining large shell sizes over 34 mm in length. Growth varied between sites with a maximum estimated yearly growth rate of 16.8 mm. The time and place of the quagga mussel's initial introduction in Ireland is still uncertain, but its widespread distribution, population structure, and high population density and relative abundance suggest it was first introduced to Lough Ree in 2016 or 2017. [ABSTRACT FROM AUTHOR]

Abstract: The bryozoan Amathia (= Zoobotryori) verticillata was found near the northern entrance to the Port of Kaohsiung in November 2015 and is the first record from Taiwan. This bryozoan [...]