Australian Marine Environment Research Articles

Analyzing and engineering of the biosynthetic pathway of mollemycin A for enhancing its production

Mollemycin A (MOMA) is a unique glyco-hexadepsipeptide-polyketide that was isolated from a Streptomyces sp. derived from the Australian marine environment. MOMA exhibits remarkable inhibitory activity against both drug-sensitive and multidrug-resistant malaria parasites. Optimizing MOMA through structural modifications or product enhancements is necessary for the development of effective analogues. However, modifying MOMA using chemical approaches is challenging, and the production titer of MOMA in the wild-type strain is low. This study identified and characterized the biosynthetic gene cluster of MOMA for the first time, proposed its complex biosynthetic pathway, and achieved an effective two-pronged enhancement of MOMA production. The fermentation medium was optimized to increase the yield of MOMA from 0.9 mg L−1 to 1.3 mg L−1, a 44% boost. Additionally, a synergistic mutant strain was developed by deleting the momB3 gene and overexpressing momB2, resulting in a 2.6-fold increase from 1.3 mg L−1 to 3.4 mg L−1. These findings pave the way for investigating the biosynthetic mechanism of MOMA, creating opportunities to produce a wide range of MOMA analogues, and developing an efficient strain for the sustainable and economical production of MOMA and its analogues.

Sound pressure and particle motion calculations considering pile skin friction

Modelling sound propagation over seabeds where the seabed cannot be approximated as an equivalent fluid due to limestone layers with high shear wave speeds is a common underwater acoustic propagation modelling problem for Australian shallow marine environments. With the increase in prospective areas for offshore windfarm development across Australia, construction operations across large regions of the continental shelf area are set to increase. Windfarm construction will require the installation of a large number of foundation piles near potentially sensitive marine habitat areas. Predicting the underwater noise from these activities requires suitable models. This paper investigates the modelling approaches for including a full elastic parameterisation of the seabed when conducting numerical predictions of pile driving sound emissions. The approach considers buried sources and the excitation of shear waves via a skin friction model for the stress–strain relation at the pile-seabed boundary. Shear waves are considered in the source model and in the propagation model. Sound pressure level metrics and particle motion metrics are considered as part of the numerical predictions.

The Context of the 2018–20 “Protracted” El Niño Episode: Australian Drought and Terrestrial, Marine, and Ecophysiological Impacts

Abstract A “protracted” El Niño episode occurred from March–April 2018 to April–May 2020. It was manifested by the interlinked Indo-Pacific influences of two components of El Niño phases. Positive Indian Ocean dipoles (IODs) in 2018 and 2019 suppressed the formation of northwest cloud bands and southern Australia rainfall, and a persistent teleconnection, with enhanced convection generated by positive Niño-4 region sea surface temperature (SST) anomalies and strong subsidence over eastern Australia, exacerbated this Australian drought. As with “classical” El Niño–Southern Oscillation (ENSO) events, which usually last 12–18 months, protracted ENSO episodes, which last for more than 2 yr, show a similar pattern of impacts on society and the environment across the Indo-Pacific domain, and often extend globally. The second half of this study puts the impact of the 2018–20 protracted El Niño episode on both the Australian terrestrial agricultural and marine ecophysiological environments in a broader context. These impacts are often modulated not only by the direct effects of ENSO events and episodes, but by interrelated local to region ocean–atmosphere interactions and synoptic weather patterns. Even though the indices of protracted ENSO episodes are often weaker in magnitude than those of major classical ENSO events, it is the longer duration of the former that poses its own set of problems. Thus, there is an urgent need to investigate the potential to forecast protracted ENSO episodes, particularly when the mid-2020 to current 2022 period has been experiencing a major protracted La Niña episode with near-global impacts. Significance Statement The major 2018–20 Australian drought and its terrestrial and marine impacts were caused by a “protracted” El Niño episode, exacerbated by global warming. Indo-Pacific ocean–atmosphere interactions resulted in a persistent positive western Pacific Niño-4 sea surface temperature anomaly during the period 2018–20 and positive Indian Ocean dipoles (IODs) in 2018 and 2019. These suppressed rainfall across eastern Australia and limited northwest Australian cloud band rainfall across southern Australia. Australian agricultural and ecophysiological impacts caused by protracted El Niño–Southern Oscillation (ENSO) episodes permeate, overstress, and expose society, infrastructure, and livelihoods to longer temporal-scale pressures than those experienced during shorter “classical” ENSO events. Thus, there is an urgent need to investigate the potential to forecast protracted ENSO episodes.

Marine spatial planning and offshore wind: preliminary principles for Australia

Australia is endowed with some of the richest and most diverse renewable energy resources. Its offshore wind resources alone equate to an estimated 5,000 Gigawatts (GW) of electricity potential. Given these substantial estimates, offshore wind energy will likely represent a key pillar of Australia’s future renewable energy mix. Australia’s palpable offshore energy potential is increasingly understood and acknowledged. Yet, the critical legal and policy question remains of how its new regulatory framework to enable offshore wind development, the Offshore Electricity Infrastructure Act 2021 Act (Cth) (OEI Act), will interact with existing marine sectors and the marine environment. Marine Spatial Planning (MSP) may provide the missing process puzzle piece to enable more strategic coordination of the Australian offshore wind sector within the marine environment. This article adopts a socio-legal approach, examining and drawing upon international experiences to explore the potential adoption of MSP in the Australian offshore wind context. In so doing, the article argues for a coordinated approach to develop a federal MSP process to support and promote strategic offshore wind operations with existing sea users while preserving the Australian marine environment.

Factors affecting the isolation and diversity of marine sponge-associated bacteria

Marine sponges are an ideal source for isolating as yet undiscovered microorganisms with some sponges having about 50% of their biomass composed of microbial symbionts. This study used a variety of approaches to investigate the culturable diversity of the sponge-associated bacterial community from samples collected from the South Australian marine environment. Twelve sponge samples were selected from two sites and their bacterial population cultivated using seven different agar media at two temperatures and three oxygen levels over 3 months. These isolates were identified using microscopic, macroscopic, and 16S rRNA gene analysis. A total of 1234 bacterial colonies were isolated which consisted of four phyla: Actinobacteria, Firmicutes, Proteobacteria, and Bacteroidetes, containing 21 genera. The diversity of the bacterial population was demonstrated to be influenced by the type of isolation medium, length of the incubation period and temperature, sponge type, and oxygen level. The findings of this study showed that marine sponges of South Australia can yield considerable bacterial culturable diversity if a comprehensive isolation strategy is implemented. Two sponges, with the highest and the lowest diversity of culturable isolates, were examined using next-generation sequencing to better profile the bacterial population. A marked difference in terms of phyla and genera was observed using culture-based and culture-independent approaches. This observed variation displays the importance of utilizing both methods to reflect a more complete picture of the microbial population of marine sponges.Key pointsImproved bacterial diversity due to long incubations, 2 temperatures, and 3 oxygen levels.Isolates identified by morphology, restriction digests, and 16S rRNA gene sequencing.At least 70% of culturable genera were not revealed by NGS methods.

Decommissioning Research Needs for Offshore Oil and Gas Infrastructure in Australia

When offshore oil and gas infrastructure is no longer needed, it is either removed, partially removed, left in place, or left in place but repurposed. These processes are collectively referred to as decommissioning. Australian legislation requires oil and gas companies to develop acceptable plans for the safe removal of all offshore infrastructure at the end of a project’s life. Over the next 50 years, the liability for this decommissioning in Australia is expected to exceed US$45 billion. Unlike countries such as Norway, the United Kingdom and the Netherlands, Australian decommissioning activities are in their infancy, with only three cases (to date) in Commonwealth waters where infrastructure has been left in place or partially removed as part of decommissioning. Differences between the Australian marine environment and that of other regions around the world where decommissioning-related research is better progressed include very low sedimentation rates, both tropical and temperate habitats, different species composition, low primary production, and frequent tropical cyclones, as well as unique sociodemographic and cultural characteristics. Accordingly, the outcomes of the decision support tools used in other regions to identify preferred decommissioning options may not be equally applicable in Australia. Here we describe research to support risk and impact assessment for offshore decommissioning in Australia, where full removal of infrastructure is the “base case” regulatory default, but other options including partial removal and/or repurposing might provide similar or better outcomes when environmental, social, economic and seafood safety aspects are considered. Based on our review we propose an integrated framework for research needs to meet legislative requirements for decommissioning and identify research gaps that need to be addressed to inform decision-making for decommissioning in the Australian context.

Exploring the practical implementation of marine biodiversity offsetting in Australia

Biodiversity offsetting with associated aims of no net loss of biodiversity (NNL) is an approach used to align economic development with conservation. Biodiversity offsetting may be more challenging in marine environments, with recent evidence suggesting that the current application of the approach in Australian marine environments rarely follows ‘best practice’ and is unlikely to be meeting stated policy aims. To understand how and why this deviation from best practice is taking place in marine systems, we analysed current practice in Australia through in-depth semi-structured interviews with 31 participants with professional experience in the development and implementation of associated policy. Thematic analysis of results indicated that, despite commitment to best practice in principle, practitioners recognised that operationalisation of marine biodiversity offsetting was inconsistent and unlikely to be meeting stated goals such as NNL. Participants described the central barrier to the adoption of best practice as the technical complexity of assessing and quantifying biodiversity losses and gains, and uncertainty in restoration in marine contexts. With offsetting described as an integral part of development consent for marine economic development, both these barriers and their navigation presents threats to users setting off a chain of accepted activity leading away from best practice. These threats were perceived to arise from low governmental capacity or prioritisation for environmental management, institutional needs for a social licence to operate, and overarching demands for economic growth. We conclude that marine biodiversity offsetting has come to be ambiguous in its practical definition, with a range of conflicting factors influencing its use and preventing the standardisation required to meet rigorous interpretations of best practice necessary to ensure biodiversity protection and NNL.

Antimicrobial Activities of Marine Sponge-Associated Bacteria.

The misuse and overuse of antibiotics have led to the emergence of multidrug-resistant microorganisms, which decreases the chance of treating those infected with existing antibiotics. This resistance calls for the search of new antimicrobials from prolific producers of novel natural products including marine sponges. Many of the novel active compounds reported from sponges have originated from their microbial symbionts. Therefore, this study aims to screen for bioactive metabolites from bacteria isolated from sponges. Twelve sponge samples were collected from South Australian marine environments and grown on seven isolation media under four incubation conditions; a total of 1234 bacterial isolates were obtained. Of these, 169 bacteria were tested in media optimized for production of antimicrobial metabolites and screened against eleven human pathogens. Seventy bacteria were found to be active against at least one test bacterial or fungal pathogen, while 37% of the tested bacteria showed activity against Staphylococcus aureus including methicillin-resistant strains and antifungal activity was produced by 21% the isolates. A potential novel active compound was purified possessing inhibitory activity against S. aureus. Using 16S rRNA, the strain was identified as Streptomyces sp. Our study highlights that the marine sponges of South Australia are a rich source of abundant and diverse bacteria producing metabolites with antimicrobial activities against human pathogenic bacteria and fungi.

Spatial assemblage structure of shallow-water reef fish in Southwest Australia

Bioregional categorisation of the Australian marine environment is essential to conserve and manage entire ecosystems, including the biota and associated habitats. It is important that these regions are optimally positioned to effectively plan for the protection of distinct assemblages. Recent climatic variation and changes to the marine environment in Southwest Australia (SWA) have resulted in shifts in species ranges and changes to the composition of marine assemblages. The goal of this study was to determine if the current bioregionalisation of SWA accurately represents the present distribution of shallow-water reef fishes across 2000 km of its subtropical and temperate coastline. Data was collected in 2015 using diver-operated underwater stereo-video surveys from 7 regions between Port Gregory (north of Geraldton) to the east of Esperance. This study indicated that (1) the shallow-water reef fish of SWA formed 4 distinct assemblages along the coast: one Midwestern, one Central and 2 Southern Assemblages; (2) differences between these fish assemblages were primarily driven by sea surface temperature, Ecklonia radiata cover, non-E. radiata (canopy) cover, understorey algae cover, reef type and reef height; and (3) each of the 4 assemblages were characterised by a high number of short-range Australian and Western Australian endemic species. The findings from this study suggest that 4, rather than the existing 3 bioregions would more effectively capture the shallow-water reef fish assemblage patterns, with boundaries having shifted southwards likely associated with ocean warming.

Assessing the current state of ecological connectivity in a large marine protected area system.

The establishment of marine protected areas (MPAs) is a critical step in ensuring the continued persistence of marine biodiversity. Although the area protected in MPAs is growing, the movement of individuals (or larvae) among MPAs, termed connectivity, has only recently been included as an objective of many MPAs. As such, assessing connectivity is often neglected or oversimplified in the planning process. For promoting population persistence, it is important to ensure that protected areas in a system are functionally connected through dispersal or adult movement. We devised a multi‐species model of larval dispersal for the Australian marine environment to evaluate how much local scale connectivity is protected in MPAs and determine whether the extensive system of MPAs truly functions as a network. We focused on non‐migratory species with simplified larval behaviors (i.e., passive larval dispersal) (e.g., no explicit vertical migration) as an illustration. Of all the MPAs analyzed (approximately 2.7 million km2), outside the Great Barrier Reef and Ningaloo Reef, <50% of MPAs (46‐80% of total MPA area depending on the species considered) were functionally connected. Our results suggest that Australia's MPA system cannot be referred to as a single network, but rather a collection of numerous smaller networks delineated by natural breaks in the connectivity of reef habitat. Depending on the dispersal capacity of the taxa of interest, there may be between 25 and 47 individual ecological networks distributed across the Australian marine environment. The need to first assess the underlying natural connectivity of a study system prior to implementing new MPAs represents a key research priority for strategically enlarging MPA networks. Our findings highlight the benefits of integrating multi‐species connectivity into conservation planning to identify opportunities to better incorporate connectivity into the design of MPA systems and thus to increase their capacity to support long‐term, sustainable biodiversity outcomes.

Spatial and temporal variations of trace metal body burdens of live mussels Mytilus galloprovincialis and field validation of the Artificial Mussels in Australian inshore marine environment

The body burdens of eight trace metals: Cd, Pb, Cu, Zn, Cr, Se, Hg, and As, were measured in live mussels (LMs) Mytilus galloprovincialis at 14 coastal sites in Port Phillip Bay, Victoria, Australia in winter and summer between 2017 and 2018. The spatial and temporal variations of body burdens were evaluated. The results revealed significantly higher body burdens of Cd, Pb, Cu, Zn, Cr, and Hg in summer at the sites where the city centre and industries are located. Elevated levels of most trace metals including 3 toxic, non-essential metals (Cd, Pb, and Hg) were detected in LMs from the site of Geelong. The body burdens of Zn, Cr, Se, and As appeared higher at the sites from the Bellarine Peninsula and the mouth of Port Phillip Bay.Besides, the “Artificial Mussels” (AMs) were deployed at the same sites in summer for 28 d and retrieved when the LMs were collected. The accumulations of the eight metals were compared between AMs and LMs summer results. It indicated significant correlations for Pb, Cu, and Cr, lower correlations in Zn and Hg, and irregular correlations for Se and As. The AM results of Cd were below the detection limit of the analytical method. This study demonstrates that AMs are excellent replacement of LMs for the biomonitoring of multiple kinds of trace metals.

Mercury cycling in Australian estuaries and near shore coastal ecosystems: Triggers for management

Mercury (Hg) sources to estuaries (natural and anthropogenic) as well as Hg concentrations in Australian nearshore marine environment fish are reviewed herein. The question of whether Australian estuaries have a Hg contamination problem is addressed. The Hg concentrations in fish, excluding sharks, tuna, barramundi and some stingrays, in estuaries and near-shore ecosystems with no discernable pollution sources are typically below 0.5 mg/kg wet weight, the level of health concern. There is no relationship of Hg concentration with fish size or age nor any evidence of biomagnification. In locations with historic large discrete Hg input sources (e.g. Derwent Estuary, Tasmania, Princess Royal Harbour WA, Port Phillip Bay Vic, Sydney sewage outfalls NSW), Hg concentrations in some sediment-dwelling fish such as flatheads exceed the health limit of 0.5 mg/kg. In this paper, we also review, within an Australian context, the biogeochemical processes controlling the formation and accumulation of methyl mercury (MeHg). On entering waterways, Hg rapidly partitions to particulate matter and deposits into sediments. The remobilisation of Hg from sediment is dependent on the formation of MeHg by bacteria and ultimately the interplay of S, Fe and Se cycling. Fish species that move and feed in different areas have Hg concentrations that do not reflect the sediment Hg concentrations where they are caught, i.e. there is an uncoupling of diet and potential Hg exposure. Concluding remarks focus on management interventions: source reduction, preventing eutrophication and promoting system biodiversity and biodiverse diets to mediate the accumulation of Hg in marine organisms and limit the intake of Hg by humans when consuming fish.

Characterization of a Halotolerant Fungus from a Marine Sponge.

Introduction Marine sponges have established symbiotic interactions with a large number of microorganisms including fungi. Most of the studies so far have focussed on the characterization of sponge-associated bacteria and archaea with only a few reports on sponge-associated fungi. During the isolation and characterization of bacteria from marine sponges of South Australia, we observed multiple types of fungi. One isolate in particular was selected for further investigation due to its unusually large size and being chromogenic. Here, we report on the investigations on the physical, morphological, chemical, and genotypic properties of this yeast-like fungus. Methods and Materials Sponge samples were collected from South Australian marine environments, and microbes were isolated using different isolation media under various incubation conditions. Microbial isolates were identified on the basis of morphology, staining characteristics, and their 16S rRNA or ITS/28S rRNA gene sequences. Results Twelve types of yeast and fungal isolates were detected together with other bacteria and one of these fungi measured up to 35 μm in diameter with a unique chromogen compared to other fungi. Depending on the medium type, this unique fungal isolate appeared as yeast-like fungi with different morphological forms. The isolate can ferment and assimilate nearly all of the tested carbohydrates. Furthermore, it tolerated a high concentration of salt (up to 25%) and a range of pH and temperature. ITS and 28S rRNA gene sequencing revealed a sequence similarity of 93% and 98%, respectively, with the closest genera of Eupenidiella, Hortaea, and Stenella. Conclusions On the basis of its peculiar morphology, size, and genetic data, this yeast-like fungus possibly constitutes a new genus and the name Magnuscella marinae, gen nov., sp. nov., is proposed. This study is the first of its kind for the complete characterization of a yeast-like fungus from marine sponges. This novel isolate developed a symbiotic interaction with living hosts, which was not observed with other reported closest genera (they exist in a saprophytic relationship). The observed unique size and morphology may favour this new isolate to establish symbiotic interactions with living hosts.

Corrigendum: Protecting Migratory Species in the Australian Marine Environment: A Cross-Jurisdictional Analysis of Policy and Management Plans

Corrigendum: Protecting Migratory Species in the Australian Marine Environment: A Cross-Jurisdictional Analysis of Policy and Management Plans

Enhancing the robustness of a national assessment of the marine environment

The Australian government produces an independent report on the state of the Australian environment every five years. Based on 123 assessments of key pressures, key components of the marine environment, and the effectiveness of management responses to those pressures, the 2016 assessment identified that the overall state of the Australian marine environment can be regarded as good. However, the historical impacts of a number of pressures (e.g. commercial and recreational fishing) and ongoing pressures caused by activities currently inadequately managed (e.g. climate change and marine debris) have, and are continuing to, deteriorate its state. As a result, the outlook for the marine environment can be regarded as mixed. Addressing the challenges facing the marine environment will require a coordinated, collaborative and dedicated effort across jurisdictions and sectors. A number of improvements to the assessment framework were implemented for the 2016 report, the most substantial being the development of clear and repeatable processes for information synthesis and assessment. This improved transparency and supported the robustness of conclusions made. Improved communication of uncertainties associated with assessments, and comparability with assessments in previous reports has furthered the quality of the report and laid the foundation for improvements going forward. Processes that will continue to improve assessments include identifying key indicators that can be reliably and effectively monitored, improving data provision processes, enhancing assessment frameworks and reporting processes to ensure that approaches are integrated and support the delivery of tangible and practical risk mitigation and adaptation pathways.

Protecting Migratory Species in the Australian Marine Environment: A Cross-Jurisdictional Analysis of Policy and Management Plans

Marine migratory species are difficult to manage because animal movements can span large areas and are unconstrained by jurisdictional boundaries. We reviewed policy and management plans associated with four case studies protected under the Australian Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act 1999) in order to identify the coherence of policy and management plans for managing marine migratory species in Australia. Environmental policies (n = 23) and management plans (n = 115) relevant to marine turtles, dugongs, humpback whales, and migratory shorebirds were reviewed. Few of the reviewed policies (n = 7) listed protected species and even fewer (n = 4) listed protected marine migratory species. Marine turtles were most represented in the reviewed policies (n = 7), while migratory shorebirds were most represented in management plans (n = 59). Policies and management plans were much more likely to identify relationships to other policies or plans within the same jurisdiction than to different jurisdictions. The EPBC Act 1999 served as the central link between reviewed policies and plans, but the requirements of that Act were weakly integrated into the other documents. This weak integration and the biases toward specific migratory species in environmental policies and management plans are detrimental to the conservation of these Matters of National Environmental Significance in Australia. Any changes to the EPBC Act 1999 will affect all environmental policy and management plans in Australia and highlights a need for cooperative, multi-level governance of migratory species. Our findings may have relevance to the conservation of marine migratory species in a broader international context.

A summary of oil and gas exploration in the Great Australian Bight with particular reference to southern bluefin tuna

Large numbers of juvenile southern bluefin tuna (SBT; Thunnus maccoyii) migrate into the warm shelf waters of the Great Australian Bight (GAB) each austral summer. Whilst in the GAB, they are the focus of a commercially important Australian fishery. Recent expansion of activities associated with oil and gas exploration in the GAB over the last five years has raised concerns that noise associated with geophysical surveys and exploratory drilling activities may impact on the migration and behaviour of SBT, with potential flow-on effects on the commercial fishery and current monitoring of the population for management purposes.As a first step in identifying the potential impacts of expansion of oil and gas exploration activities in the GAB on SBT, we establish the historical extent of these activities in the GAB with a primary focus on geophysical surveys. Potential overlap with the distribution of juvenile SBT in the GAB determined from an archival tag dataset (1998–2011) was then explored. Geophysical surveys have occurred throughout the vast majority of the region since 1960, with the size of energy sources used in surveys and the extent of areas surveyed increasing through time. The use of more complex, higher density 3D surveys has increased gradually since 2000. The timing and distribution of exploration activity has had varying degrees of overlap with SBT occurrence and distribution as described by tagged fish.Determining robust measures of the responses to surveys however, is difficult due to a paucity of data on the hearing capabilities of SBT, uncertainties in the true extent of spatial overlap of activities and tagged fish resulting from geolocation methods used for position estimation from archival tag data, complexities in the drivers of behaviour in SBT, and limitations with using observational data to determine cause-and-effect relationships. These difficulties are typical not just of SBT and the GAB region, but apply to investigations of the responses of marine animals to geophysical surveys more broadly. The data presented in this study, however, represent a first step towards understanding oil and gas exploration within a defined region of the Australian marine environment, and provide important context for exploring the potential impact of such activities on a commercially important top order predator of the GAB ecosystem.

National research planning accelerates relevance and immediacy of climate-adaptation science

Adapting to climate change is contingent on an ability to adjust before opportunity is lost. Given that research funding to understand adaptation is limited, rapid return on investment is critical. For Australian marine environments, climate-change impacts are well documented and adaptation opportunities have been identified across aquaculture, fisheries, conservation and tourism sectors. Here, we have evaluated the recent Australian scientific literature to determine (1) the degree to which climate-change impacts and adaptation have been addressed across sectors, and, specifically, (2) the role of a major research program instituted in 2009 to address priority climate-change questions for these sectors, namely, Australia’s ‘National Climate Change Adaptation Research Plan for Marine Biodiversity and Resources’ (MNARP). Although the number of priority questions addressed by the general scientific literature increased in the 2009–2015 period, there was a 92% increase in the number of priority questions addressed during the peak of MNARP (2013–2014). MNARP research also addressed a greater range of priority questions than did the general scientific literature, which showed consistency in the questions and study systems examined. Overall, structured research planning focussed attention on key climate-change questions, which is a critical consideration for enacting adaptation in the face of rapid climate change.

Low-Frequency Acoustic Propagation Modelling for Australian Range-Independent Environments

Large portions of the Australian continental shelf have a seabed composed of layered cemented or semi-cemented calcarenite. This work investigates the ability of a wavenumber integration sound propagation model, two normal mode sound propagation models, and a parabolic equation sound propagation model to consistently predict the acoustic field over four types of calcarenite style seabeds. The four geoacoustic models that are presented here represent seabed types that are likely to be found in the Australian marine environment. Transmission loss results for each geoacoustic model are computed using each sound propagation model, which are compared over a broad band of low frequencies in order to assess their relative performance. The performance of the wavenumber integration model, SCOOTER, and the two normal mode models over a broad band of low frequencies was found to be accurate and robust for all the tested scenarios. However, for one of the normal mode models, KRAKENC, long computational runtimes were incurred to produce accurate results. The parabolic equation model RAMSGeo produced accurate transmission loss results at some of the frequencies, but it also produced some unrealistic transmission loss predictions when thin layers were present in the seabed. The normal mode model ORCA was found to have the best balance between accuracy and efficiency because it had the shortest runtimes for most of the calculation frequencies and the shortest overall runtime.

If the Asian green mussel, Perna viridis (Linnaeus, 1758), poses the greatest invasive marine species threat to Australia, why has it not invaded?

ABSTRACTA national approach has been developed to the problem of invasive marine species (IMS) in the Australian marine environment. Fifty-five species were listed as posing significant threats to Australia. A 2005 analysis of the scientific literature concluded that the Asian green mussel Perna viridis (Linnaeus, 1758) poses the greatest threat to Australia. The mussel has in fact successfully invaded many areas of the world’s oceans. Despite the numerous and varied opportunities for P. viridis to be distributed to northern Australia it has not established a known population on the continent, perhaps suggesting there are biological factors inhibiting its establishment. The invasion success of P. viridis in many parts of the world and its failure so far to establish in Australia make the species ideal for testing theories of the factors determining invasion success. Such research will allow a reconsideration of the invasion threat the species poses to the Australian marine environment.