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Pests of bivalve aquaculture are a challenging problem that can reduce productivity, profitability and sustainability. A range of pest management approaches have been developed for bivalve aquaculture, but a general absence of guiding frameworks has limited the scale and permanency of implementation. Applying principles of 'integrated pest management' (IPM) could change this paradigm to improve economic and environmental outcomes. We reviewed existing research and tools for pest management in bivalve aquaculture, with studies grouped under five pillars of IPM: pest ecology (25 studies), bioeconomic cost-benefits (4 studies), continual monitoring (17 studies), proactive prevention (32 studies) and reactive control (65 studies). This body of knowledge, along with insights from terrestrial agriculture, provide a strong foundation for developing and implementing IPM in bivalve aquaculture. For example, IPM principles have been applied by a regional collective of oyster farmers in the US Pacific Northwest to optimize pesticide application and search for other options to control problematic burrowing shrimps. However, IPM has not yet been broadly applied in aquaculture, and data gaps and barriers to implementation need to be addressed. Priorities include establishing meaningful pest-crop bioeconomic relationships for various bivalve farming systems and improving the efficacy and operational scale of treatment approaches. An IPM framework also could guide potential step-change improvements through directing selective breeding for resistance to pests, development of bespoke chemical control agents, applying emerging technologies for remote surveillance and farm management, and regional alignment of management interventions. © 2022 Society of Chemical Industry.

The number, extent, diversity, and global reach of submerged static artificial structures (SSAS) in the marine environment is increasing. These structures are prone to the accumulation of biofouling that can result in unwanted impacts, both immediate and long-term. Therefore, management of biofouling on SSAS has a range of potential benefits that can improve structure functions, cost-efficiency, sustainability, productivity, and biosecurity. This review and synthesis collates the range of methods and tools that exist or are emerging for managing SSAS biofouling for a variety of sectors, highlighting key criteria and knowledge gaps that affect development, and uptake to improve operational and environmental outcomes. The most common methods to manage biofouling on SSAS are mechanical and are applied reactively to manage biofouling assemblages after they have developed to substantial levels. Effective application of reactive methods is logistically challenging, occurs after impacts have accumulated, can pose health and safety risks, and is costly at large scales. Emerging technologies aim to shift this paradigm to a more proactive and preventive management approach, but uncertainty remains regarding their long-term efficacy, feasibility, and environmental effects at operational scales. Key priorities to promote more widespread biofouling management of SSAS include rigorous and transparent independent testing of emerging treatment systems, with more holistic cost-benefit analyses where efficacy is demonstrated.

Disentangling pathways by which nonindigenous species expand and spread regionally remains challenging. Molecular ecology tools are often employed to determine the origins and spread of introduced species, but the complexities of some organisms may be reducing the efficacy of these tools. Some colonial species exhibit complexities by way of chimerism and winter colony regression, which may alter the genetic diversity of populations and mask the connectivity occurring among them. This study uses nuclear microsatellite data and simple GIS‐based modeling to investigate the influence of chimerism and winter regression on the genetic diversity and patterns of genetic population connectivity among colonies of Didemnum vexillum on artificial substrates. Colonies sampled in summer were shown to form a metapopulation, with high levels of admixture, extreme outcrossing, and some substructure. These patterns were consistent within the subsampled winter colonies and with the inclusion of chimeric data. However, allelic richness and diversity were significantly different between winter and summer samples, altering interpretations relating to population connectivity and pelagic larval duration. This study demonstrates the importance of including seasonal sampling and imperative life history traits in genetic studies for clear interpretations and the successful management of introduced species.

Biofouling accumulation is not proactively managed on most marine static artificial structures (SAS) due to the lack of effective options presently available. We describe a series of laboratory and field trials that examine the efficacy of continuous bubble streams in maintaining SAS free of macroscopic biofouling and demonstrate that this treatment approach is effective on surface types commonly used in the marine environment. At least two mechanisms were shown to be at play: the disruption of settlement created by the bubble stream, and the scouring of recently settled larvae through shear stress. Field trials conducted over a one-year period identified fouling on diffusers as a major issue to long-term treatment applications. Field measurements suggest that noise associated with surface mounted air blowers and sub-surface diffusers will be highly localised and of low environmental risk. Future studies should aim to develop and test systems at an operational scale.

Vessel movements are considered the primary anthropogenic pathway for the secondary spread of marine non-indigenous species. In comparison to the well-studied mechanisms of hull fouling and ballast water, the importance of bilge water for domestic and cross-regional spread of non-indigenous species is largely unknown and has the potential to compromise the overall effectiveness of biosecurity management actions. In this study, the diversity and abundance of biological material contained in bilge water from 30 small vessels (

To control the spread of non-indigenous species it is necessary to understand how early stages of the invasion process, such as age of propagule at time of entrainment and transport, influence the quality and quantity of propagules delivered to recipient environments (i.e., the propagule pressure). Using ship biofouling as a model pathway scenario and the bryozoan Bugula neritina, the effect of two early-stage selective filters—the age of recruits and the pattern of the voyage—on reproductive output post-arrival were examined. Voyage scenarios were created by manipulating food levels in a series of field experiments. Recruit Age had three levels (1-day, 1-week and 1-month), and Voyage Pattern (four levels) represented vessels that undertake frequent short voyages or infrequent long voyages, plus control treatments. Spawning success, number of larvae and larval size were measured over multiple spawning events after each scenario. One-day and 1-week old colonies that had been exposed to short-voyage scenarios had higher reproductive output than those that had been exposed to longer and less frequent voyages. In contrast, 1-month old colonies did not release larvae under any voyage scenario. The survivorship of bryozoans in all treatments was relatively high, but reproductive output was influenced by colony age and voyage type. Our results suggest that vessels undergoing frequent, short intra-coastal or domestic voyages are able to deliver viable propagules to subsequent destinations even if they have prior port residencies as short as 1 day. At least for bryozoans, juvenile recruits may even pose a higher risk of spread compared to reproductively mature recruits.

Unwanted biofouling and predatory pests are a universal problem threatening aquaculture productivity and profitability. Various control approaches have been trialled, but industry uptake has been elusive due to the typically fine balance between pest and bivalve physiological tolerances (i.e., ‘therapeutic window’) and operational challenges related to infrastructure, scalability, and quality control. This study aimed to address these factors for acetic acid (AcOH), arguably the best-studied and most broadly applicable reactive treatment for bivalve aquaculture. Using case studies of farmed New Zealand green-lipped mussels (Perna canaliculus Gmelin 1791) and Pacific oysters (Crassostrea gigas Thunberg 1793), AcOH tolerances of various size classes of these bivalves were determined in a series of laboratory experiments, and cross-referenced to corresponding data for biofouling and predatory pests. Resulting ‘therapeutic windows’ formed the basis of provisional treatment parameters, being 2% AcOH for 60 s or 4% AcOH for 30 s for P. canaliculus and C. gigas, respectively. Three independent field experiments on operational P. canaliculus and C. gigas farms subsequently served to refine and validate the treatment parameters and associated operational procedures. For P. canaliculus, AcOH treatment had overall positive impacts on commercially relevant measures of aquaculture production, with the best performing treatment regimens of 1% or 2% AcOH for 60 s resulting in almost three times as many individual P. canaliculus per section of growing rope. Incorporating a subsequent air-drying step was also shown to reduce required AcOH immersion times, providing opportunities to enhance operational efficiencies via more rapid treatments. The provisional treatment parameters for C. gigas of 4% AcOH for 30 s were also highly effective against biofouling pests in the field and resulted in no detectable mortality of the culture species. Overall, this study demonstrates the utility of carefully refined and validated AcOH treatments to control problematic pests in bivalve aquaculture. It is essential to accurately determine ‘therapeutic windows’ for any given bivalve culture species and developing understanding of crop-pest interactions would better inform treatment timing and frequency. Such approaches could feed into wider frameworks to optimally manage pests below economically damaging thresholds, with AcOH ideally being one option in an arsenal of management interventions.

Vessel movements are considered the main anthropogenic pathway for secondary spread of marine non-indigenous species. Recent studies have highlighted the potential for viable organisms to be transported within bilge water of small vessels. In this study, a survey was conducted to (1) describe the bilge water operational profiles of a range of domestic vessels operating in New Zealand and (2) identify factors driving the level of biosecurity risk. The proportion of vessels with pre-discharge treatments was low (13.7%), confirming the potential for organisms to be viable at discharge. Significant differences in risk scores among vessel types were shown; risk scores were highest for yachts, followed by launches, trailer boats and commercial vessels. Yachts were characterised by a high frequency of use, visits to multiple regions and a high likelihood of bilge water on board when leaving port (i.e. high-risk source regions). Almost all yachts operated automatic bilge systems, suggesting that discharge occurs primarily when the volume is sufficient to trigger the pump mechanism and that associated bilge water could be carried significant distances. Validation of vessel risk profiles through targeted sampling is recommended, along with research to identify potential practical and cost-effective mitigation measures such as public awareness campaigns.

The likelihood that viable non-indigenous biofouling species will survive a voyage on a vessel is influenced by a range of factors, including the speed, duration, and route of the voyage and the amount of time the vessel spends in port. In this study, a land-based dynamic flow device was used to test the effect of recruit age, vessel speed and voyage duration on the survivorship and growth of the bryozoan Bugula neritina. In the experiment, one-week-old recruits had a higher likelihood (100%) of surviving voyages than older (one–month-old, 90%) or younger (one-day-old, 79%) recruits, but survival was not influenced by vessel speed (6 and 18 knots) or voyage duration (two and eight days). The results suggest that the non-indigenous species B. neritina can be effectively transferred at a range of ages but one-week-old recruits are more likely to survive the translocation process and survive in the recipient environment.

Tunicates are useful models for exploring microbiomes because they have an innate immune system resembling that of chordates. Automated ribosomal RNA intergenic spacer analysis and High-Throughput Sequencing were used to compare the tunic microbiomes of Ciona robusta (formerly Ciona intestinalis type A), Ciona savignyi, Botrylloides leachi and Botryllus schlosseri sampled from three distinct locations with limited genetic connectivity. Bacterial phylotype profiles were conserved within each species, and there were no detectable differences between tunic and tunic + cuticle subsamples from an individual. Bacterial operational taxonomic unit (OTU) diversity was lowest for C. savignyi (320 ± 190 OTUs) and highest for B. schlosseri (1260 ± 190 OTUs). Each species had a distinct set of bacterial OTUs (pseudo-F = 3.0, p > 0.001), with the exception of B. leachi and B. schlosseri from one sampling location (t = 1.2, p = 0.09). Of note were OTUs assigned to Alphaproteobacteria from C. robusta plus Phyllobacteriaceae and Endozoicomonas from C. savignyi. These OTUs contributed 51, 22 and 10% of sequence reads, respectively, and are related to known bacterial symbionts. The within-species conservation of core OTUs across three distinct and co-occurring populations of tunicates provides compelling evidence that these tunicates foster defined microbiomes.

Biofouling is a significant operational problem for the aquaculture industry globally; however, options for on-farm management are limited. In New Zealand, the green-lipped mussel, Perna canaliculus, has historically been cultivated at inshore locations, but increased competition for space has led the industry to develop offshore farming sites several kilometers from the coast. We hypothesize that the distance to these farm sites from coastal locations, and their placement over extensive soft-sediment habitats, may provide a barrier to colonization by biofouling species with limited natural dispersal abilities. A study of two offshore mussel farms revealed that they supported relatively impoverished biofouling communities by comparison with inshore mussel farms and other artificial structures. Offshore sites had a relatively low number of taxa and a low prevalence of short-dispersing organisms such as ascidians, which are a problematic group of fouling organisms in aquaculture. We suggest that newly established offshore marine farms have the potential to be kept free of a range of problematic fouling organisms, provided the introduction of such species via human transport pathways can be mitigated.

Biofouling pests can have significant economic impacts on aquaculture operations, including increased processing and production costs. An important first step towards improved biofouling management is understanding the density and distribution of the biofouling species within a growing region. In this study, biofouling communities were sampled from 73 commercial mussel farms within New Zealand’s main mussel growing region, Pelorus Sound. At each farm, photoquadrats (0.08 m2, n = 6) of biofouling organisms were obtained at 2 depth ranges (3 per range) from suspended long-line droppers, both at the surface (0 to 3 m of the dropper) and bottom (9 to 24 m, depending on dropper length and water depth). Biomass samples and visual estimates of biofouling biomass were also obtained. Strong spatial variation in the structure of biofouling communities was evident, with increasing dissimilarity between communities along Pelorus Sound. Problematic taxa (e.g. the brown alga Undaria pinnatifida and calcareous tubeworm Pomatoceros sp.) were dominant near the entrance to the Sound, where annual temperature cycles are often reduced and salinity concentrations are higher. Generally, biofouling cover decreased with increasing water depth. A large proportion (48%) of biofouling biomass scores were categorised as high, equating to 121.2 ± 20 g m−2 (or 16%) of long-line for a heavily fouled farm, or 10 t for a typical 3 ha farm. Distributional patterns, such as those identified in this study, could be used by aquaculture industries to better inform the timing and placement of susceptible crop species and production stages (e.g. mussel spat). Refined monitoring methods may also facilitate industry participation in collecting long-term biofouling records.

Marine biofilms are precursors for colonization by larger fouling organisms, including non-indigenous species (NIS). In this study, high-throughput sequencing (HTS) of 18S rRNA metabarcodes was used to investigate four sampling methods (modified syringe, sterilized sponge, underwater tape and sterilized swab) for characterizing eukaryotic communities in marine biofilms. PerspexTM plates were sampled in and out of water. DNA collected with tape did not amplify. Otherwise, there were no statistical differences in communities among the remaining three sampling devices or between the two environments. Sterilized sponges are recommended for ease of use underwater. In-depth HTS analysis identified diverse eukaryotic communities, dominated by Metazoa and Chromoalveolata. Among the latter, diatoms (Bacillariophyceae) were particularly abundant (33% of reads assigned to Chromalveolata). The NIS Ciona savignyi was detected in all samples. The application of HTS in marine biofilm surveillance could facilitate early detection of NIS, improving the probability of successful eradication.

Cladophora is a genus of branched filamentous green algae (Ulvophyceae). It contains many species that are challenging to differentiate based on morphology because of the scarcity of diagnostic characters and extensive phenotypic plasticity. Within the past five years, Cladophora blooms have been observed on the ropes of green-lipped mussel farms in the Marlborough Sounds, New Zealand. When Cladophora reaches high biomass, it can clog mussel-harvesting equipment; thus, it is considered a nuisance organism in the region. This study used morphological and molecular techniques to identify the species responsible for the blooms, and to investigate whether this might be a recent incursion. Cladophora samples (n = 21) were collected from nine mussel farms, one salmon farm, and a marina. Morphological and phylogenetic analyses (partial large subunit and internally transcribed spacer regions 1 and 2 of the nuclear ribosomal cistron), revealed the identity of the bloom forming species as Cladophora ruchingeri (C.Agardh) Kutzing, 1845. This represents the first report of this species in the Southern Hemisphere and Pacific region. Given the distinct morphology of C. ruchingeri (when mature), its absence from previous surveys of macro-algae from this region, and increasing reports of blooms, our findings suggest that this species has only recently been introduced to New Zealand. This study provides a robust taxonomic identification and initial baseline data. Further directed studies on Cladophora are required to advance knowledge on its ecology and distribution in New Zealand, and assist in the development of mitigation strategies.

The occurrence of problematic pest organisms is an increasing global phenomenon, adversely affecting a range of environments and associated values. In marine systems, the efficacy of pest control has to date been constrained by a lack of tools that are not only highly effective, but also applicable across broad spatial scales. Here we consider the extent to which biological control (biocontrol) has the potential to fulfil these needs. We describe different biocontrol approaches and potential ecological mechanisms (e.g. consumption, space competition, habitat modification) through which problematic species could be supressed. We also discuss the ideal traits of marine control agents within the context of the selection criteria commonly applied in terrestrial systems. Classical biocontrol based on the deliberate

The control of marine pest populations in transport hubs has the potential to contain or limit spread by minimizing the infection of vessels and other vectors. We draw on New Zealand experiences with eradication or population control attempts on two marine pests, the Asian kelp Undaria pinnatifida Harvey Suringar and the colonial ascidian Didemnum vexillum Kott, to evaluate the extent to which vector infection was mitigated by management efforts. For both species we compare two levels of effort: sustained control involving intensive regional-scale eradication programs, and shorter-duration less intensive efforts that we refer to as partial control. The mean monthly proportion of vessels infected by Undaria was ~1% in two regions where sustained control reduced densities in marine habitats to 1–5% of the pre-treatment population. By contrast, 39% of vessels were infected during a partial control effort, which was comparable to the proportion of vessels infected in four ports where Undaria populations were not managed. For Didemnum, a reduction of the population to < 0.1% of the pretreatment level almost completely negated vessel infection, to the extent that few vessels were implicated in the further spread of Didemnum while sustained control was in place. By contrast, partial population control led to limited benefit in terms of vector risk reduction. More importantly, a cessation or reduction in population control efforts resulted in relatively rapid vessel re-infection. Both case studies illustrate that intensive control of marine pest populations can greatly reduce the infection of susceptible vectors, but achieving such an outcome requires an indefinite commitment of resources, and may be impractical for multiple pest species or multiple infested locations. Although slowing the spread of marine pests can lead to demonstrable benefits, for population control to have greater practicality and stakeholder support, there is a need for socially acceptable and affordable control tools that are effective across relatively large spatial scales.

Encapsulation of fouled structures is an effective tool for countering incursions by non-indigenous biofoulers. However, guidelines for the implementation of encapsulation treatments are yet to be established. This study evaluated the effects of temperature, biomass, community composition, treatment duration and the biocide acetic acid on biofoulers. In laboratory trials using the model organisms Ciona spp. and Mytilus galloprovincialis, increasing the temperature or biomass speeded up the development of a toxic environment. Total mortality for Ciona spp. occurred within 72 and 24 h at 10 and 19°C, respectively. M. galloprovincialis survived up to 18 days, with high biomass increasing mortality at 10°C only. In a field study, three-month-old and four-year-old communities were encapsulated with and without acetic acid. Mortality took up to 10 days for communities encapsulated without acetic acid, compared to 48 h with acetic acid. The insights gained from this study will be useful in developing standardised encapsulation protocols.

Summary 1. Biofouling, the accumulation of biological growth on submerged surfaces such vessel hulls and artificial structures, is an important transport pathway that can facilitate the establishment of marine non-indigenous species in new locations. Despite efforts to develop effective tools to eradicate newly established populations before they become widespread and beyond control, eradication successes are scarce in the marine environment. This paper describes a dredge-based eradication of the brown mussel Perna perna from a deep (c. 44 m) soft-sediment habitat in central New Zealand, following the discovery of this species amongst biofouling organisms physically removed (i.e. defouled) from a drilling rig. 2. We evaluated the efficacy of dredging in removing P. perna and other target species, and determined whether a density-based eradication success criterion had been achieved. The catchability coefficient (q) of the defouled material was estimated using catch data, and the dredge efficiency (E) was determined. Initial and remaining mussel densities were then calculated using estimates of E. The reliability of these estimates was tested by simulations. 3. A total of 227 dredge tows covering c. 94% of a 12·6 ha target area were undertaken, and an estimated 35 tonnes of material defouled from the rig was dredged from the seabed and disposed of in a landfill. 4. Estimates of q and E were 0·0054 and 0·30 (respectively) and mussel densities at the completion of the eradication programme were estimated to be c. 0·5 m−2, well below the success criterion of 10 m−2. From our simulations, it was estimated that 71 dredge tows would be required to remove 50% of the initial population, whilst 232 dredge tows would be needed to achieve a 90% reduction in population size. 5. Synthesis and applications. The eradication of non-indigenous bivalves from a relatively deep (>40 m) soft-sediment environment is unprecedented and highlights that, with appropriate tools and other resources, eradication is feasible even in challenging circumstances. Where complete elimination of a pest is not feasible, alternative density-based success criteria can be developed that, if achieved, can effectively mitigate risks. This study highlights the need for further development of both vector treatment options and pest eradication tools, and improved policy surrounding in-water defouling in the coastal environment.

The environmental risks associated with the defouling of artificial structures (e.g., vessels, oil rigs, marina pontoons, aquaculture structures) in the marine environment are gaining international attention. This paper presents a series of laboratory- and field-based experiments that collectively aimed to elucidate biotic and abiotic factors that influence re-establishment success of biofouling organisms and fragmented colonial organisms defouled to the seabed. Reattachment success of colonial organisms experimentally fragmented was found to be species specific and dependent on fragment size. In both laboratory and field trials, some colonial ascidians had consistently greater reattachment success for larger size classes of fragments, while other encrusting and erect taxa showed poor reattachment capabilities. This study also revealed that sedimentation and turbidity are likely to have a strong influence on the survivorship of defouled material. Furthermore, for both high and low sedimentary environments, survivorship was found to be greater where predators were excluded. Despite risks posed by non-indigenous species (NIS), it is proposed that in-water defouling may be an appropriate management response in situations where a “do nothing” approach is potentially more detrimental. Moreover, results from this study suggest that environmental risks associated with defouling may be mitigated through appropriate defouling strategies (e.g., defouling location, frequency and method). In order to increase our predictive abilities for NIS establishment success resulting from in-water defouling, future studies should aim to further elucidate the relative importance of factors affecting survivorship of defouled material at locations where defouling is routinely undertaken.

Vessel traffic is the primary pathway for non-indigenous marine species introductions to New Zealand, with hull fouling recognised as being an important mechanism. This article describes hull fouling on seven slow-moving commercial vessels sampled over a 1 year period. Sampling involved the collection of images and fouling specimens from different hull locations using a standardised protocol developed to assess vessel biofouling in New Zealand. A total of 29 taxa was identified by expert taxonomists, of which 24% were indigenous to New Zealand and 17% non-indigenous. No first records to New Zealand were reported, however 59% of species were classified as 'unknown' due to insufficient taxonomic resolution. The extent of fouling was low compared to that described for other slow-movers. Fouling cover, biomass and richness were on average 17.1% (SE = 1.8%), 5.2 g (SE = 1.1 g) and 0.8 (SE = 0.07) per photoquadrat (200 x 200 mm), respectively. The fouling extent was lowest on the main hull areas where the antifouling paint was in good condition. In contrast, highest levels of fouling were associated with dry-docking support strips and other niche areas of the hull where the paint condition was poor. Future studies should target vessels from a broader range of bioregions, including vessels that remain idle for extended periods (ie months) between voyages, to increase understanding of the biosecurity risks posed by international commercial slow-movers.

Oyster farming in estuaries is a globally important industry based primarily around the Pacific oyster Crassostrea gigas , for which a common technique is elevated culture on racks, trestles and other structures. We review literature on cultivation impacts, revealing a research focus and state of knowledge that largely parallels that for other aquaculture species and cultivation methods. Ecological studies of elevated culture effects have focused on changes to the benthos from biodeposition, and largely show that impacts are localized and minor by comparison with many other forms of aquaculture. The broader ecological issues associated with elevated oyster culture include the effects of pests (fouling pests, toxic/noxious microalgae, disease), creation of novel habitat (e.g. by fouling of farm structures and accumulation of shell), alteration to nutrient cycling, depletion of suspended particulate matter by oyster crops, and related effects on higher trophic level animals including fish, seabirds and marine mammals. These issues are less well understood for elevated culture systems, but ecological effects can be inferred from the few studies that have been conducted, from other forms of bivalve aquaculture (e.g. mussels), and to some extent from fundamental knowledge of the role of oysters as ‘ecosystem engineers’. We use a risk ranking method to evaluate ecological risks (and associated uncertainty intervals) for each of the issues associated with estuarine oyster culture, based on subjective assessment of the likelihood and consequences (severity, spatial extent and duration) of adverse effects. Our assessment reveals that the introduction and spread of pest species are potentially important but often overlooked consequences of oyster cultivation. By comparison with most other sources of impact, the spread of pests by aquaculture activities can occur at regional scales, potentially leading to ecologically significant and irreversible changes to coastal ecosystems. We suggest that future studies of cultivation effects redress the balance of effort by focusing more on these significant issues and less on the effects of biodeposition in isolation. Furthermore, the acceptability of aquaculture operations or new developments should recognize the full range of effects, since adverse impacts may be compensated to some extent by the nominally ‘positive’ effects of cultivation (e.g. habitat creation), or may be reduced by appropriate planning and management. Even more broadly, aquaculture developments should be considered in relation to other sources of environmental risk and cumulative impacts to estuarine systems at bay-wide or regional scales, so that the effects of cultivation are placed in context.

Hopkins, G. A., and Forrest, B. M. 2008. Management options for vessel hull fouling: an overview of risks posed by in-water cleaning. – ICES Journal of Marine Science, 65: 811–815. Hull fouling has been identified as an important pathway for the spread of non-indigenous marine species. However, the management of associated biosecurity risks has proven challenging. Left unmanaged, a fouled vessel can pose a biosecurity risk through the detachment and dispersal of viable material, and through spawning by adult taxa upon arrival in a recipient port or region. These risks can be managed effectively through the removal of the vessel to land for defouling (e.g. dry-docking). However, alternative methods are needed for small (e.g. recreational) vessels, as well as for large vessels fouled outside their dry-docking schedule. Among the various treatment options, in-water cleaning is relatively common, although some countries have placed restrictions on this method because of perceived biosecurity risks. Here, we present a conceptual framework that identifies risks posed by in-water cleaning compared with alternatives, including no management. Decisions on the appropriate management option will be influenced by many factors, including the species present, the level of fouling, and the time a vessel spends in a recipient region. It is important that any regulatory changes regarding in-water defouling be supported by relevant research that quantifies the risks associated with the various management options.

The expansion of artificial habitats and aquaculture activities in coastal environments has been accompanied by an increased demand for tools to mitigate the effects of biofouling pests. One approach is to manage anthropogenic pathways to prevent the spread of established pest organisms to uninfected localities that are beyond their natural dispersal capacity. This paper describes the efficacy of acetic acid treatments against a variety of cosmopolitan fouling taxa, and evaluates a potential application in the treatment of foulers transported with movements of shellfish seedstock between mussel farming areas in New Zealand. Laboratory and field experiments demonstrated that immersion in 4% acetic acid (in seawater) for as little as 1 min can eliminate many soft-bodied fouling organisms, with lower concentrations requiring longer immersion times. The effects of immersion treatment were enhanced when combined with a 24-h air exposure phase to simulate the inter-regional transport of mussel seedstock. We demonstrate that it is possible to cost-effectively treat mussels to eliminate the majority of problematical foulers without resulting in significant adverse effects to the stock either by: (i) a 4% treatment followed by a rinse to remove the acetic acid residue before transport, or (ii) application of the 4% treatment at the end of the transport phase. A concentration of 4% is equivalent to the acetic acid content of domestic vinegar, hence does not represent a significant environmental or occupational risk provided appropriate measures are put in place for handling and waste disposal. Acetic acid concentrations remain stable over time in the presence of organic matter, but may change during repeated use of treatment solutions. To ensure treatment criteria are being achieved, field determination of acetic acid levels can be made using simple titration-based approaches. Because of an apparent buffering effect in the case of sequential shellfish seedstock immersion, pH could not be used to estimate acetic acid concentrations in this instance, but may provide a simple and reliable field-based indicator for other fouling treatments. Further work to refine the treatment method should seek to maximise the ‘window’ between pest mortality and mussel survival, to provide assurance that high-risk species can be eliminated with minimal risk of adverse effects on seedstock. Where treatments that are completely effective against all pest organisms result in unavoidable mussel mortality, decisions about whether or not to apply them must balance treatment costs and benefits against the unmanaged risks and consequences of pest incursion.

Tunicates are useful models for exploring microbiomes because they have an innate immune system resembling that of chordates. Automated ribosomal RNA intergenic spacer analysis and High-Throughput Sequencing were used to compare the tunic microbiomes of Ciona robusta (formerly Ciona intestinalis type A), Ciona savignyi, Botrylloides leachi and Botryllus schlosseri sampled from three distinct locations with limited genetic connectivity. Bacterial phylotype profiles were conserved within each species, and there were no detectable differences between tunic and tunic + cuticle subsamples from an individual. Bacterial operational taxonomic unit (OTU) diversity was lowest for C. savignyi (320 ± 190 OTUs) and highest for B. schlosseri (1260 ± 190 OTUs). Each species had a distinct set of bacterial OTUs (pseudo-F = 3.0, p 0.001), with the exception of B. leachi and B. schlosseri from one sampling location (t = 1.2, p = 0.09). Of note were OTUs assigned to Alphaproteobacteria from C. robusta plus Phyllobacteriaceae and Endozoicomonas from C. savignyi. These OTUs contributed 51, 22 and 10% of sequence reads, respectively, and are related to known bacterial symbionts. The within-species conservation of core OTUs across three distinct and co-occurring populations of tunicates provides compelling evidence that these tunicates foster defined microbiomes.

The desiccation tolerance of biofouling taxa (adults and early life-stages) was determined under both controlled and ‘realistic’ field conditions. Adults of the ascidian Ciona spp. died within 24 h. Mortality in the adult blue mussel Mytilus galloprovincialis occurred within 11 d under controlled conditions, compared with 7 d when held outside. The Pacific oyster Crassostrea gigas was the most desiccation-tolerant taxon tested (up to 34 d under controlled conditions). Biofouling orientated to direct sunlight showed faster mortality rates for all the taxa tested. Mortality in Mytilus juveniles took up to 24 h, compared with 8 h for Ciona, with greater survival at the higher temperature (18.5°C) and humidity (~95% RH) treatment combination. This study demonstrated that desiccation can be an effective mitigation method for a broad range of fouling taxa, especially their early life-stages. Further work is necessary to assess risks from other high-risk species such as algae and cyst forming species.

The accumulation of biofouling on coastal structures can lead to operational impacts and may harbour problematic organisms, including non-indigenous species. Benthic predators and grazers that can supress biofouling, and which are able to be artificially enhanced, have potential value as augmentative biocontrol agents. The ability of New Zealand native invertebrates to control biofouling on marina pontoons and wharf piles was tested. Caging experiments evaluated the ability of biocontrol to mitigate established biofouling, and to prevent fouling accumulation on defouled surfaces. On pontoons, the gastropods Haliotis iris and Cookia sulcata reduced established biofouling cover by55% and largely prevented the accumulation of new biofouling over three months. On wharf piles C. sulcata removed 65% of biofouling biomass and reduced its cover by 73%. C. sulcata also had better retention and survival rates than other agents. Augmentative biocontrol has the potential to be an effective method to mitigate biofouling on marine structures.

This study documents eight years of benthic recovery at a highly impacted salmon farm. Substantial recovery occurred in the first 2 years, and was assessed to be complete after ∼5 years. However, minor differences were still evident, along with some on-going benthic instability, attributable to medium-scale spatial movements and successional patterns of macrobenthos. Quantifying the endpoint of ‘recovery’ proved challenging due to: lack of a widely accepted definition, inherent variability in recovering sediments, differing trajectories of impact and reference sites, and statistical challenges. More complex biotic indices and metrics incorporating multiple variables were the most robust indicators. Statistical tests for ‘parallelism’ in the trajectories of Cage and Reference sites proved useful, but results were contingent upon how the method was applied, and should therefore be used in conjunction with data-visualisation methods. The study highlights the importance of a predetermined recovery endpoint, and using multiple indicators and a weight-of-evidence assessment approach.

Augmentative biocontrol aims to control established pest populations through enhancement of their indigenous enemies. To our knowledge, this approach has not been applied at an operational scale in natural marine habitats, in part because of the perceived risk of adverse non-target effects on native ecosystems. In this paper, we focus on the persistence, spread and non-target effects of the sea urchin Evechinus chloroticus when used as biocontrol agent to eradicate an invasive kelp from Fiordland, New Zealand. Rocky reef macrobenthic assemblages were monitored over 17 months in areas where the indigenous algal canopy was either removed or left intact prior to the translocation of a large number of urchins (>50 ind.·m(-2)). Urchin densities in treated areas significantly declined ∼9 months after transplant, and began spreading to adjacent sites. At the end of the 17-month study, densities had declined to ∼5 ind.·m(-2). Compared to controls, treatment sites showed persistent shifts from kelp forest to urchin barrens, which were accompanied by significant reductions in taxa richness. Although these non-target effects were pronounced, they were considered to be localised and reversible, and arguably outweigh the irreversible and more profound ecological impacts associated with the establishment of an invasive species in a region of high conservation value. Augmentative biocontrol, used in conjunction with traditional control methods, represents a promising tool for the integrated management of marine pests.

Augmentative biocontrol, defined as the use of indigenous natural enemies to control pest populations, has not been explored extensively in marine systems. This study tested the potential of the anemone Anthothoe albocincta as a biocontrol agent for biofouling on submerged artificial structures. Biofouling biomass was negatively related to anemone cover. Treatments with high anemone cover (>35%) led to significant changes in biofouling assemblages compared to controls. Taxa that contributed to these changes differed among sites, but included reductions in cover of problematic fouling organisms, such as solitary ascidians and bryozoans. In laboratory trials, A. albocincta substantially prevented the settlement of larvae of the bryozoan Bugula neritina when exposed to three levels of larval dose, suggesting predation as an important biocontrol mechanism, in addition to space pre-emption. This study demonstrated that augmentative biocontrol using anemones has the potential to reduce biofouling on marine artificial structures, although considerable further work is required to refine this tool before its application.

This study examined the efficacy of heated seawater for the treatment and remediation of fouled vessel sea chest habitats. In laboratory trials, three temperature regimes (37.5 °C for 60 min, 40 °C for 30 min and 42.5 °C for 20 min) were tested on a range of temperate taxa commonly found in sea chests. Field validation trials further assessed the efficacy of heat treatment within a replica sea chest environment. During laboratory trials, 100% mortality was achieved across all three treatments for the majority of taxa; the exceptions being the barnacle Elminius modestus and the oyster Crassostrea gigas . Temperature tolerance limits observed in the laboratory were successfully replicated under simulated sea chest conditions; however, a failure to achieve even heat distribution was an obstacle to achieving uniform mortality. This study provides guidance on the temperature/exposure parameters required for vessels plying temperate latitudes, and demonstrates that heated seawater has potential for controlling biofouling in vessel sea chests.

The potential for oil rigs to transport diverse, reef-like communities around the globe makes them high risk vectors for the inadvertent spread of non-indigenous species (NIS). This paper describes two case studies where a suite of pre-border management approaches was applied to semi-submersible drilling rigs. In the first case study, a drilling rig was defouled in-water prior to departure from New Zealand to Australia. Risk mitigation measures were successful in reducing biosecurity risks to the recipient region, but they resulted in the unintentional introduction of the non-indigenous brown mussel (Perna perna) to New Zealand when the rig was defouled in-water by divers. In the second case study, lessons learned from this high-profile incursion resulted in a more structured approach to pre-border management, and this serves as a useful template for future rig transfers.

The present study tested two diver-operated rotating brush systems, coupled with suction and collection capabilities, to determine their efficacy in the management of vessel biofouling. Both rotating brush systems proved effective (80%) in removing low-to-moderate levels of fouling from flat and curved experimental surfaces (Perspex plates). However, performance was generally poorer at removing more advanced levels of fouling. In particular, mature calcareous organisms were relatively resistant to the rotating brushes, with a high proportion (up to 50%) remaining on plates following treatment. On average,95% of defouled material was collected and retained by both systems. The amount of lost material generally increased when treating curved plates with increasing biomass, whereas the material lost from flat plates was typically less and remained relatively constant throughout the trials. The majority (80%) of fouling not captured by the systems was crushed by the brushes (ie non-viable). However, a diverse range of viable organisms (eg barnacles and hydroids) was lost to the environment during the defouling trials. When defouling a vessel, unintentional detachment of fouling organisms is likely to be high through physical disturbance by divers operating the devices and by associated equipment (eg hoses). Furthermore, residual biosecurity risks are also likely to remain due to diver error, persistent fouling remaining on treated surfaces and the inaccessibility of niche areas to the brush systems. To address these limitations, further research into alternative treatment methods is required.