Seafloor macrolitter as a settling platform for non-native species: A case study from UK waters.

Marine litter is increasingly recognised as a vector for the spread of non-native species (NNS). However, our understanding of its role in the propagation of NNS in UK waters remains limited. As part of the Clean Seas Environmental Monitoring Programme, we opportunistically analysed seafloor macrolitter items trawled from various locations around the coast of England and Wales and examined each for the presence of NNS. Of the 41 litter items analysed, we identified a total of 133 taxa, including two non-native and four cryptogenic species. This confirms that NNS are settling on seafloor macrolitter in UK waters and that these can be detected using morphological taxonomic analysis. Furthermore, we propose a methodology to classify litter based on size, rugosity and polymer/material type to explore whether there were detectable patterns governing community composition and litter characteristics. This exploratory investigation provides evidence to inform future risk assessments of NNS vectors and pathways.

Modelling of marine debris pathways into UK waters: Example of non-native crustaceans transported across the Atlantic Ocean on floating marine debris.

The long-distance transfer of non-native, potentially invasive species via floating marine debris is an increasing threat to biodiversity and conservation efforts. To address the lack of understanding around mechanisms and pathways of species transfer via marine debris, a novel modelling approach was applied to recreate the likely trajectory and source of a large piece of debris fouled by non-native species collected from UK marine waters. This approach applied the Oil Spill Contingency and Response (OSCAR) simulation tool, an adapted oil spill modelling programme, which was informed by a combination of biological trait information for the foulant species, marine debris characteristics and hydrodynamic data. The modelling output suggested an origin in the Western Atlantic, a scenario concurrent with the known distribution of the foulant species. This modelling approach represents a valuable tool with which to determine the origin and trajectory of invasive species transferred via marine debris.

Comparative assessment of live cyprinid and salmonid movement networks in England and Wales.

Disease poses a significant threat to aquaculture. While there are a number of factors contributing to pathogen transmission risk, movement of live fish is considered the most important. Understanding live fish movement patterns for different aquaculture sectors is therefore crucial to predicting disease occurrence and necessary for the development of effective, risk-based biosecurity, surveillance and containment policies. However, despite this, our understanding of live movement patterns of key aquaculture species, namely salmonids and cyprinids, within England and Wales remains limited. In this study, networks reflecting live fish movements associated with the cyprinid and salmonid sectors in England and Wales were constructed. The structure, composition and key attributes of each network were examined and compared to provide insight into the nature of trading patterns and connectedness, as well as highlight sites at a high risk of spreading disease. Connectivity at both site and catchment level was considered to facilitate understanding at different resolutions, providing further insight into disease outbreaks, with industry wide implications. The study highlighted that connectivity through live fish movements was extensive for both industries. The salmonid and cyprinid networks comprised 2533 and 3645 nodes, with a network density of 5.81 × 10-4 and 4.2 × 10-4, respectively. The maximum network reach of 2392 in the salmonid network was higher, both in absolute terms and as a proportion of the overall network, compared to maximum network reach of 2085 in the cyprinid network. However, in contrast, the number of sites in the cyprinid network with a network reach greater than one was 513, compared to 171 in the salmonid network. Patterns of connectivity indicated potential for more frequent yet smaller scale disease outbreaks in the cyprinid industry and less frequent but larger scale outbreaks in the salmonid industry. Further, high connectivity between river catchments within both networks was shown, posing challenges for zoning at the catchment level for the purpose of disease management. In addition to providing insight into pathogen transmission and epidemic potential within the salmonid and cyprinid networks, the study highlights the utility of network analysis, and the value of accessible, accurate live fish movement data in this context. The application of outputs from this study, and network analysis methodology, to inform future disease surveillance and control policies, both within England and Wales and more broadly, is discussed.