Investigating the cryptogenic status of the sea squirt Didemnum perlucidum (Tunicata, Ascidiacea) in Australia based on a molecular study of its global distribution

Didemnid species are assessed as species with a high invasive potential for Australia and as such are listed as target species for both state and national monitoring programs. The presence of the sea squirt Didemnum perlucidum (Monniot, 1983) was first documented in Australia in 2010 and has since then been detected extensively throughout the state of Western Australia and in the Northern Territory. These detections have raised important questions as to the origin and potential impact of this species in Australia. The current study was initiated to review the current known global geographic range of D. perlucidum and to obtain specimens that could support molecular studies aimed at evaluating the potential origin of this species in Australia. Characterization of 5’ COI mitochondrial sequences from 286 specimens revealed a remarkably low level of genetic diversity across the current known range of D. perlucidum and the existence of one main widespread genetic haplotype. Such findings suggest that all locations sampled in this study may in fact represent introductions of D. perlucidum and that the natural native range of the species remains unknown. Our demonstration that specimens (n=187) originating from across a broad expanse of the Australian West Coast were comprised of a single haplotype also lends support to the hypothesis that D. perlucidum is a species that has been introduced recently into Australia. This hypothesis is supported by the fact that D. perlucium distribution in Australia is mostly confined to artificial structures, it has displayed invasive characteristics, and its presence is now being detected across an increasingly wide geographical area. Given the demonstrated low level of genetic COI variation across its known global distribution, lack of clarity around its native range, and limited availability of data on this species globally, we recognize the requirement for further work to more fully elucidate the exact origins and patterns of distribution of D. perlucidum in Australia. This study represents the most comprehensive mapping of the current global distribution of D. perlucidum conducted to date and will hopefully motivate further studies aimed at elucidating this species biology, origin, high-risk routes and impacts

Establishment of a taxonomic and molecular reference collection to support the identification of species regulated by the Western Australian Prevention List for Introduced Marine Pests

Introduced Marine Pests (IMP, = non-indigenous marine species) prevention, early detection and risk-based management strategies have become the priority for biosecurity operations worldwide, in recognition of the fact that, once established, the effective management of marine pests can rapidly become cost prohibitive or impractical. In Western Australia (WA), biosecurity management is guided by the “Western Australian Prevention List for Introduced Marine Pests” which is a policy tool that details species or genera as being of high risk to the region. This list forms the basis of management efforts to prevent introduction of these species, monitoring efforts to detect them at an early stage, and rapid response should they be detected. It is therefore essential that the species listed can be rapid and confidently identified and discriminated from native species by a range of government and industry stakeholders. Recognising that identification of these species requires very specialist expertise which may be in short supply and not readily accessible in a regulatory environment, and the fact that much publicly available data is not verifiable or suitable for regulatory enforcement, the WA government commissioned the current project to collate a reference collection of these marine pest specimens. In this work, we thus established collaboration with researchers worldwide in order to source representative specimens of the species listed. Our main objective was to build a reference collection of taxonomically vouchered specimens and subsequently to generate species-specific DNA barcodes suited to supporting their future identification. To date, we were able to obtain specimens of 75 species (representative of all but four of the pests listed) which have been identified by experts and placed with the WA Government Department of Fisheries and, where possible, in accessible museums and institutions in Australasia. The reference collection supports the fast and reliable taxonomic and molecular identification of marine pests in WA and constitutes a valuable resource for training of stakeholders with interest in IMP recognition in Australia. The reference collection is also useful in supporting the development of a variety of DNA-based detection strategies such as real-time PCR and metabarcoding of complex environmental samples (e.g. biofouling communities). ThePrevention List is under regular review to ensure its continued relevance and that it remains evidence and risk-based. Similarly, its associated reference collection also remains to some extent a work in progress. In recognition of this fact, this report seeks to provide details of this continually evolving information repository publicly available to the biosecurity management community worldwid

Short-term movement of barramundi in a seasonally closed freshwater habitat

Despite a broad Indo-Pacific distribution, the movement patterns of barramundi Lates calcarifer have gone largely unstudied, particularly in freshwater systems. This study examined the short-term movement and dispersal patterns of 60 barramundi in a seasonally closed freshwater system in 2 seasons (warm and cool). Data indicated that individuals generally moved small distances during up to 18 d of monitoring and that size was not a factor in movement patterns. Individuals moved farther and had larger activity spaces in the cool season than in the warm season, indicating different behaviour between seasons in this freshwater habitat. However, in both seasons, individuals remained in the permanently flooded sections of the billabong with limited movement into seasonally flooded regions. Further examination of long-term presence and movements of freshwater barramundi populations is required, but these data provide insight into short-term movements in a freshwater system

Genetic diversity of a hitchhiker and prized food source in the Anthropocene: the Asian green mussel Perna viridis (Mollusca, Mytilidae)

Insight into a species’ native and introduced range is essential in understanding the invasion process. Genetic diversity, propagule pressure and environmental conditions all have been recognised as playing a determinant role in invasion success. Here, we aimed to investigate the genetic diversity and population genetic structure (using the COI mtDNA gene region and 22 nDNA microsatellite markers) of the Asian green mussel Perna viridis within its potential native range in Asia and at introduced locations in the USA and the Caribbean. We also analyse genetic data from vessel intercepts and an incursion. By doing so, we aimed to identify genetic signatures that could allow to track vessel samples to their source and provide further insight into potential high-risk invasive populations or areas. Three top hierarchical clusters were identified using the individual-based Bayesian clustering method in STRUCTURE, corresponding to populations in three world regions: (1) USA and Caribbean, (2) India and (3) Southeast Asia. Within Southeast Asia, additional analysis indicate a shallow genetic differentiation of three subgroups consisting of (3a) Thailand, (3b) Taiwan and Hong-Kong, and (3c) a cluster of Singapore–Indonesia samples. Overall, the population structure found in this study suggests that the markers used could be useful in identifying source populations, particularly between the three mains world regions. Most surprisingly however, this study shows that the genetic diversity of samples collected from vessel intercepts and incursions did not differ significantly from established populations in Southeast Asia. In this region, in addition to the high vessel connectivity and number of P. viridis transported, all sampled populations are likely to pose a comparable risk in terms of genetic diversity. The present work represents the most comprehensive population genetic study of P. viridis, and the first to address the potential genetic introduction risk posed by populations of this species. The information and genetic markers in this study constitute a valuable addition to the tools already used to infer on potential high-risk source populations of P. viridis. They should therefore prove useful for biosecurity surveillance and management actions directed at this species