Updated review of non-native and cryptogenic species from around the Stour and Orwell estuaries

Previous studies have recorded 26 non-native and 14 cryptogenic species from the Stour and Orwell estuaries. Here we present data for an additional 11 non-native and 22 cryptogenic species, to give a total of 73 (37 non-native, 36 cryptogenic) now known from the area. Of these, six are newly reported from the United Kingdom (2 non-native: Eteone lighti, Melita nitida; 4 cryptogenic: Protocirrineris purgamentorum, Tharyx robustus, T. maryae, Tubificoides galiciensis). Eteone lighti is reported outside of its native range for the first time. Nine of the species are rated as High Impact under the Water Framework Directive (WFD) and thirteen are listed in the UK Marine Non-Indigenous Species Priority Species List. The records have been collated from a variety of routine monitoring surveys and environmental impact studies, as well as literature records, and demonstrate that a wide variety of sampling types is required to provide a comprehensive account of non-native species. Most of the non-native species have a native range in the North Pacific (38%) but many (27%) were from the north-west Atlantic; other native ranges were less well represented. Arthropods, particularly crustaceans, were the most represented phylum for non-native species. The number of cryptogenic species, especially amongst the annelids, illustrates knowledge gaps in our native fauna and that further understanding is required to establish how much of the fauna is genuinely native. In comparison with other available synopses of data, the findings presented here would suggest the study area to be one of the most invaded regions in Europe, although comparative studies are sparse. To establish baselines, determine introduction rates and assess the effectiveness of biosecurity measures under the WFD or Marine Strategy Framework Directive (MSFD) will require increased monitoring of key introduction hotspots and more comprehensive local reviews of non-native species.