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There is an urgent need for landscape-scale ecological restoration to reverse habitat loss and recover ecosystem functions and services. Given the unique nature of coastal and marine ecosystems a roadmap to overcome current barriers and guide transformative change is needed to achieve large-scale restoration. We conducted a national scale program of engagement with restoration practitioners, decision makers, industry, researchers, community groups, and Indigenous groups in Australia to map out the current state of implementation, barriers encountered and aspirations for the future. In collaboration with a graphic facilitator, we distilled the findings into ten guiding principles which are communicated through an engaging conceptual model. Here we articulate the ten guiding principles for large-scale coastal and marine ecological restoration and include discussion of the rational, the current state in Australia, and ideas for moving forward with respect to each principle. The principles are: 1) Co-design is central; 2) Fit-for-purpose governance; 3) No-gap funding; 4) Access to social, economic and biophysical data; 5) Evidence-based and transparent decision making; 6) Coordinated and at scale; 7) Robust monitoring, evaluation and reporting; 8) Clear strategy to adapt to climate change; 9) Nature-based solutions are implemented; and 10) Knowledge is shared effectively. We then evaluated the principles against three large-scale restoration programs in the UK, USA and Australia and found that their characteristics broadly adhere to each of the principles. Implementation of the roadmap is now necessary and will aid in achieving return of ecological functions in line with international commitments and societal goals. • Scaling up restoration in coastal and marine ecosystems requires a roadmap to overcome key barriers. • We report outcomes from a national program of engagement with the Australian marine restoration community. • Findings are distilled into ten guiding principles for landscape scale coastal and marine ecological restoration. • Assessing the principles against three successful international programs finds that they broadly model these principles. • Following the roadmap will enable development of successful large-scale marine restoration programs. [ABSTRACT FROM AUTHOR]

Ecosystems globally are becoming increasingly degraded necessitating conservation and repair. Alongside restoration of natural habitats, eco-engineering can mitigate the negative impacts of urban seascapes by co-designing marine-built structures for nature as well as humans. The application of eco-engineering to marine built structures is supported by over two decades of research demonstrating the efficacy of this approach in enhancing biodiversity but there remain few examples of interventions moving beyond experimental- to large-scale (10–100 s m) and long-term (decadal) implementation. Using lessons learned from eco-engineering research in Sydney Harbour, Australia, we outline six key steps that facilitate moving from experimental to larger scale retrofitted eco-engineering interventions. These are: (1) identifying the ecological problem and the most tractable solutions; (2) engaging with stakeholders, (3) obtaining approvals, (4) establishing demonstration sites that illustrate to stakeholders the practicality and benefits of the solution, (5) building an evidence base for efficacy of the solution, and (6) scaling up supply. Our framework draws on learnings from the Living Seawalls project, and on the extensive small-scale experimentation that led to it. Living Seawalls is an eco-engineering initiative that grew out of Sydney Harbour and has now been applied to sites across Australia and globally. Our framework also draws on learnings from other existing projects (e.g. Ecostructure, Blue Cube) and frameworks (e.g. Greening the Grey, International Guidelines on Natural and Nature-Based Features for Flood Risk Management) developed elsewhere. This work provides a template by which scientists can work with policy makers, managers, and other stakeholders to effect positive environmental change. • Spatial and temporal scaling of marine eco-engineering can enhance biodiversity. • A six-step framework to scaling up was developed via years of research and practice. • First, identify the ecological problem, engage with stakeholders and obtain permits. • Next, establish sites, build scientific evidence and scale-up commercial supply. • These steps can guide global scaling of eco-engineering for meaningful impact. [ABSTRACT FROM AUTHOR]

Organisms respond to their environment in various ways, including moving, adapting, acclimatising or a combination of responses. Within estuarine habitats, organisms are exposed to naturally variable environmental conditions. In urbanised estuaries, these natural variations can interact with human stressors such as habitat modification and pollution. Here, we investigated trait variation in the golden kelp Ecklonia radiata across an urban estuary - Sydney Harbour, Australia. We found that kelp morphology differed significantly between the more human-modified inner and the less modified outer harbour. Kelp individuals were smaller, had fewer laminae, and lacked spines in the inner harbour where it was warmer, more contaminated and less light was available. Inner harbour populations were characterised by lower tissue nitrogen and higher lead concentrations. These findings provide insights into how environmental variation could affect kelp morphology and physiology, and the high trait variation suggests adaptive capacity in E. radiata. • We assessed spatial variation in Ecklonia radiata traits across an urban estuary. • The inner estuary was warmer, more turbid, and contaminated than the outer estuary. • Outer harbour kelp had thicker stipes, longer and narrower laminae with spines. • Tissue concentrations of lead were higher and nitrogen lower in the inner estuary. • The high trait variation suggests environmental adaptability of E. radiata. [ABSTRACT FROM AUTHOR]

Marine artificial structures provide substrates on which organisms can settle and grow. These structures facilitate establishment and spread of non-indigenous species, in part due to their distinct physical features (substrate material, movement, orientation) compared to natural habitat analogues such as rocky shores, and because following construction, they have abundant resources (space) for species to colonise. Despite the perceived importance of these habitat features, few studies have directly compared distributions of native and non-indigenous species or considered how functional identity and associated environmental preferences drive associations. We undertook a meta-analysis to investigate whether colonisation of native and non-indigenous species varies between artificial structures with features most closely resembling natural habitats (natural substrates, fixed structures, surfaces oriented upwards) and those least resembling natural habitats (artificial materials, floating structures, downfacing or vertical surfaces), or whether functional identity is the primary driver of differences. Analyses were done at global and more local (SE Australia) scales to investigate if patterns held regardless of scale. Our results suggest that functional group (i.e., algae, ascidians. barnacles, bryozoans, polychaetes) rather than species classification (i.e., native or non-indigenous) are the main drivers of differences in communities between different types of artificial structures. Specifically, there were differences in the abundance of ascidians, barnacles, and polychaetes between (1) upfacing and downfacing/vertical surfaces, and (2) floating and fixed substrates. When differences were detected, taxa were most abundant on features least resembling natural habitats. Results varied between global and SE Australian analyses, potentially due to reduced variability across studies in the SE Australian dataset. Thus, the functional group and associated preferences of the highest threat NIS in the area should be considered in design strategies (e.g., ecological engineering) to limit their establishment on newly built infrastructure. [Display omitted] • We assessed effects of habitat features on colonisation by marine biota. • Abundances did not vary between native and non-indigenous species. • Abundance of functional groups varied between features. • Ecologically informed design strategies are important to reduce invasion risk. [ABSTRACT FROM AUTHOR]

Attempts to restore marine ecosystems are increasing, but the success of projects remains variable. For marine invertebrates, the establishment of self‐sustaining populations requires a larval supply as well as conditions that permit recruitment.Abiotic and biotic conditions that determine recruitment can vary across environmental gradients and have opposing or reinforcing effects. We assessed how predation and tidal inundation influence recruitment of the reef‐forming oyster, Saccostrea glomerata, at 15 sites, 5 estuaries and 8 degrees of latitude in eastern Australia.Oysters recruited to all 15 sites, but their density displayed spatially variable effects of tidal inundation and caging. Effects of tidal inundation and caging were weakest at the two lower‐latitude estuaries where recruitment was low overall, average temperature and turbidity were high and dissolved oxygen low.At higher‐latitude estuaries, where abiotic conditions were more favourable for recruitment, recruit density displayed tidal elevation gradients that were dependent on caging and time. Initially, recruit density decreased with tidal inundation (and exposure to finfish predators), in the uncaged but not the caged treatment. However, over time the elevation gradient disappeared, and recruitment and survival of oysters was greater in caged than uncaged treatments irrespective of elevation.Synthesis and applications. Our results suggest that both abiotic (i.e. temperature, turbidity and dissolved oxygen) and biotic (i.e. predation) factors can negatively influence oyster recruitment and, hence, restoration success. Consequently, oyster reef restoration projects should be planned to prioritise sites with low turbidity, high dissolved oxygen and low predation unless these stressors can be mitigated. Restoration projects that are designed with knowledge of local stressors are more likely to be successful. [ABSTRACT FROM AUTHOR]

Ecotones can form hot spots of biodiversity by containing species from multiple ecosystems. Because biodiversity is often linked to ecological function, we posit that rates of key ecological functions are highest at ecotones and decline away from them. Here we test this hypothesis by measuring spatial decays in the function of carrion scavenging on a gradient ranging from ocean beaches upland into abutting coastal dunes. A large field experiment in Eastern Australia, at the ecotone formed by ocean beaches, employed multiple carrion placements and motion-triggered cameras to identify the animals consuming carcasses and the removal rates of necromass. Significantly more carrion was consumed by vertebrate scavengers at the beach interface (50–80% of total necromass removed) and declined significantly with distance (max. 350 m) into the abutting coastal dunes (20–25%). This marked cline was due to the consumption of carrion by both dune-dwelling and beach-dwelling animals at the beach–dune interface and a decline in scavenging activity by both groups farther upland. These spatial effects were consistent between sites, but the lower carrion removal away from the beach became less pronounced as the carcasses putrefied, suggesting that microbial actions can modify carrion suitability for vertebrate scavengers and hence change spatial patterns in ecological function. Our findings provide quantitative support for the widespread notion that ecological transition zones are hot spots of ecological functions and highlight the importance of managing functionally important species at ecotones. [ABSTRACT FROM AUTHOR]

Seawalls are an increasingly conspicuous component of coastlines, which may modify ecological communities through their effects on physical and biological processes. Effects of seawalls on ecological communities may vary spatially according to environmental conditions at the site of seawall placement, the local species pool, and the characteristics of the seawall itself. In the Austral Spring of 2014, we assessed how differences in infaunal communities between paired sedimentary sites with and without seawalls vary with tidal elevation and environmental conditions (i.e. sediment variables, benthic cover), at five locations within Brisbane Waters, New South Wales, Australia. Contrary to the prediction that differences in infaunal communities between sites with and without seawalls would be greatest at high intertidal elevation at which seawalls are built, we found greater differences at mid intertidal elevations. At muddy locations, characterised by high faunal abundance and richness, the abundance of mid intertidal infauna was less at sites with than without seawalls. By contrast, at sandy locations, which were characterised by low infaunal abundance and richness, the reverse pattern was seen. Although the structure of infaunal communities was correlated with sediment characteristics, sites with and without seawalls did not display consistent patterns of difference in sediment grain size or organic carbon content across locations. The greater difference in infaunal communities between sites with and without seawalls at mid than high or low intertidal elevations likely reflects an interaction between the proximity of habitat to seawalls and biological traits of the resident infaunal species that influence their susceptibility to perturbation. [ABSTRACT FROM AUTHOR]

Facilitation cascades are critical to the maintenance of biodiversity in a variety of habitats. Through a series of two experiments, we examined how the morphological traits and density of interacting foundation species influence the establishment and persistence of a facilitation cascade in temperate Australian mangrove forests. In this system, mangrove pneumatophores trap the free-living alga, Hormosira banksii, which, in turn, supports dense and diverse assemblages of epifaunal mollusks. The first experiment, which manipulated pneumatophore height and density, revealed that these two traits each had additive negative effects on the establishment, but additive positive effects on the persistence of the cascade. High densities of tall pneumatophores initially served as a physical barrier to algal colonization of pneumatophore plots, but over the longer term enhanced the retention of algae. The increased algal biomass, in turn, facilitating epifaunal colonization. The second experiment demonstrated that the retention of algae by pneumatophores was influenced more by algal thallus length than vesicle diameter, and this effect occurred independent of pneumatophore height. Our study has extended facilitation theory by showing that the morphological traits and density of basal and intermediary facilitators influence both the establishment and persistence of facilitation cascades. Hence, attempts to use foundation species as a tool for restoration will require an understanding not only of the interactions among these, but also of the key traits that modify interrelationships. [ABSTRACT FROM AUTHOR]

Among the impacts of coastal settlements to estuaries, nutrient pollution is often singled out as a leading cause of modification to the ecological communities of soft sediments. Through sampling of 48 sites, distributed among 16 estuaries of New South Wales, Australia, we tested the hypotheses that (1) anthropogenic nutrient loads would be a better predictor of macrofaunal communities than estuarine geomorphology or local sediment characteristics; and (2) local environmental context, as determined largely by sediment characteristics, would modify the relationship between nutrient loading and community composition. Contrary to the hypothesis, multivariate multiple regression analyses revealed that sediment grain size was the best predictor of macrofaunal assemblage composition. When samples were stratified according to median grain size, relationships between faunal communities and nitrogen loading and latitude emerged, but only among estuaries with sandier sediments. In these estuaries, capitellid and nereid polychaetes and chironomid larvae were the taxa that showed the strongest correlations with nutrient loading. Overall, this study failed to provide evidence of a differential relationship between diffuse nutrient enrichment and benthic macrofauna across a gradient of 7° of latitude and 4°C temperature. Nevertheless, as human population growth continues to place increasing pressure on southeast Australian estuaries, manipulative field studies examining when and where nutrient loading will lead to significant changes in estuarine community structure are needed. [ABSTRACT FROM AUTHOR]

Abstract: Introduced species that alter the physical structure of marine habitats can have large impacts on biodiversity. We assessed whether in south-eastern Australia the invasive Pacific oyster, Crassostrea gigas, differs from the native Sydney rock oyster, Saccostrea glomerata, in the biogenic habitat that it provides to epibiotic communities. We also assessed how within a species (S. glomerata), genotype influences habitat provision. First, we conducted a field experiment in which we compared recruitment of epibiota to concrete plates with either C. gigas, wild-stock S. glomerata, selectively bred S. glomerata or glue (control). Second, we assessed whether within wild S. glomerata populations invaded by C. gigas, communities of epibenthos are correlated to the ratio of non-native to native oysters. On experimental plates C. gigas grew larger, and experienced higher mortality than both selectively-bred and wild-stock S. glomerata at each of two heights on the shore. The two genotypes of S. glomerata, by contrast, displayed similar rates of growth and mortality. The differing growth patterns among oyster types had not, however, translated to consistent differences in the composition of associated benthic communities by 12months following establishment of experimental treatments. Within established wild oyster assemblages, C. gigas were typically much larger than on our experimental plates, and the non-native influenced the abundance of several epibiotic taxa, although not the identity of species present. Where impacts of C. gigas on the abundance of associated benthic species occurred, they were generally negative. Overall, our results indicate that while differences in the population size-structure of C. gigas and S. glomerata may be evident from small-scale experiments, the detection of flow-on effects to associated epibenthic communities may require approaches that incorporate much larger spatio-temporal scales. Nevertheless, the observation that wild C. gigas primarily influenced the abundance rather than the identity of associated epifauna suggests a certain degree of redundancy between the two species in their provision of habitat to epibiota. [Copyright &y& Elsevier]

Co-occurring foundation species can determine biological community structure via facilitation cascades. We examined the density dependencies of facilitation cascades, including how the density of a basal foundation species influences the density of secondary foundation species, and how the density of secondary foundation species influences community structure. The system in which we assessed density dependencies was a temperate mangrove forest in which pneumatophores trap the fucoid alga Hormosira banksii and provide substrate for the oyster, Saccostrea glomerata. The alga and oyster in turn determine benthic community structure. In the field, algal biomass was positively correlated with pneumatophore density. Oysters, by contrast, were highly over-dispersed and correlated with the presence/ absence of pneumatophores. Epifaunal abundance and species richness were positively correlated with algal and oyster abundance, but their effects were independent. The positive effect of pneumatophore density on epifauna was primarily an indirect effect of trapping more algae. Pneumatophores did not directly influence invertebrate communities. Experiments revealed that, at very low pneumatophore densities, algal retention was insufficient to facilitate epifauna above that found on pneumatophores alone. At higher densities, however, increasing the density of pneumatophores increased algal retention, and the density and diversity of associated invertebrates. Shading by the mangrove canopy reduced algal biomass but did not modify the density-dependent nature of the cascade. Our results extend facilitation theory by showing that the density of both basal and secondary foundation species can be critical in triggering facilitation cascades. Our study also reveals that, where foundation species co-occur, multiple, independent cascades may arise from a single basal facilitator. These findings enhance our understanding of the role of density-dependent facilitation cascades in community assembly. [ABSTRACT FROM AUTHOR]

The article discusses a study which assessed contributions of the invasive alga Caulerpa taxifolia to detrital resources of temperate Australian estuaries and the effects of these contributions on sediment-dwelling invertebrates. It was shown that the ratio of organic carbon to nitrogen (C:N) in fresh tissue varied between 7 and 16 based on a sampling of the alga across 6 invaded estuaries. The study also found that experimental enrichment negatively affected the total abundance and species richness of macroinvertebrates relative to controls, and these effects increased with detrital loading.

The article presents a study which investigates the effect of the fucalean macroalga Hormosira banksii on molluscan species abundance in mangroves and the influence of morphology to the outcome of its interspecific interactions. The study conducted a sampling of 3 mangrove sites and 3 rocky shores along the east coast of Australia, which exposes that patches of H. banksii supports a greater species abundance of molluscs than adjacent substratum. Result shows that the transfer of H. banksii from estuarine tidal flats and rocky shores into the mangrove suggests that the source of the algae scalped the magnitude of impact. Conclusion shows that it is important to understand the conditions and mechanics that influence community-level effects of foundation species to conserve biodiversity.

Abstract: Alteration of physical habitat structure is a fundamental mechanism by which invaders produce ecosystem level effects. We assessed whether, along the east coast of Australia, the impacts of the non-native gastropod Maoricolpus roseus on soft-sediment habitats extend beyond the range of live populations as a result of shell export following death of animals. Sampling over an 18 month period revealed that M. roseus shells were temporally persistent in surface sediments of a coastal lagoon devoid of live populations of the gastropod. The well-preserved shells, of which 92% were entire, did not accumulate above a maximal density of 260 m−2 due to periodic burial. Manipulation of M. roseus shell densities indicated that at densities (140 m−2) presently experienced within surface sediments of the lagoon, the structure provided by the shells was weakly facilitative of some invertebrate species. Further increasing shell densities to the possible future scenario of 280 m−2, which may occur under continued expansion of nearby live populations did not, however, strengthen positive effects. To the contrary, plots with higher densities of M. roseus shells contained similar invertebrate assemblages to control plots, without shells. Consistent with the negligible effects of M. roseus shells on infauna, the foraging efficiency of the generalist predator, Carcinus maenas, and the naticid gastropod, Polinices sordidus, were not affected by addition of shells. Surprisingly, even an extreme scenario of 1600 m−2 did not affect their predation. Thus, in this dynamic coastal lagoon, that experiences considerable sediment movement and environmental variability, the structure introduced by import of non-native shells is unimportant in structuring soft-sediment communities. Whether this unrecognised aspect of molluscan invasions impacts the ecology of more stable coastal environments remains unclear and warrants further consideration. [Copyright &y& Elsevier]

The article discusses the restoration of coastal and marine environments in Australia. It outlines the five key elements that need increased attention to increase the scale of marine restoration to levels that are ecologically, socially, and economically meaningful. It suggests to determine the value of marine restoration to job creation, financial return, and social well-being that are favorable for medium-to-long-term investments.

Abstract: Acid sulphate soils (ASS), which occur on floodplains worldwide, pose a significant threat to estuarine ecosystems. In laboratory and field experiments, naïve calcifying organisms that are exposed for even short periods (1–2 mo) to runoff from ASS suffer 80% mortality and slowed growth. Based on these observations we expected that sampling of wild oyster, gastropod and crab populations at sites close to and away from drains discharging ASS runoff would reveal more depauperate populations, of sparser and smaller-sized individuals at the more acidified sites. Sampling within three estuaries of New South Wales, Australia, confirmed that the oyster Saccostrea glomerata and gastropods (primarily Bembicium auratum) were less abundant at ASS-affected than reference sites. Nevertheless, crab abundances did not differ between the acidified and reference sites and impacts to bivalves and gastropods were far smaller than predicted. Although at ASS-affected sites gastropod populations were dominated by smaller individuals than at reference sites, oyster populations were skewed towards larger individuals. Even at ASS-affected sites, oyster and gastropod abundances were within the range encountered in estuaries that are not influenced by ASS runoff. Behaviour, long-term physiological acclimation or genetic selection may be responsible for differences in the responses of wild and naïve macroinvertebrates to acidification. Alternatively, wild populations may exhibit some recovery between the rainfall events that transport ASS runoff into estuaries, despite the persistently lower pH near outflow drains. Irrespective, this study suggests that at the population level, calcifying organisms display a certain degree of natural resistance to recurrent disturbance from ASS runoff. [Copyright &y& Elsevier]

Interest in oyster reef conservation and restoration is growing globally, but particularly in Australia, it is unclear the extent to which oyster reefs complement (versus replicate) habitat provisioning by other structured habitats in the seascape. Remote underwater video surveys of two east Australian estuaries revealed that at high tide, oyster reefs not only supported distinct fish communities to bare sediments but also to adjacent seagrass beds and mangrove forests. Fish observations in oyster reefs were close to double that of mangroves and seagrass, with species richness, abundance, feeding and wandering behaviours similar. Several species of blenny and goby were unique to oyster reefs and oyster-containing mangroves, whilst recreationally fished species such as bream and mullet were more abundant on oyster reefs than in other habitats. Resolving the association between oyster reefs and fish species within the broader seascape will assist in developing restoration and management strategies that maximise fisheries benefit. • The role of intertidal remnant oyster reefs as fish habitat was explored. • Oyster reefs provided habitat to a unique fish community within the seascape. • Fish observations were higher in oyster reefs, than in seagrass, mangroves and bare. • Fish sp. richness was higher in oyster reefs, than in seagrass, mangroves and bare. • Oyster reefs were utilised as refuge and foraging grounds by fish. [ABSTRACT FROM AUTHOR]

It is predicted that the coastal zone will be among the environments worst affected by projected climate change. Projected losses in beach area will negatively impact on coastal infrastructure and continued recreational use of beaches. Beach nourishment practices such as artificial nourishment, replenishment and scraping are increasingly used to combat beach erosion but the extent and scale of projects is poorly documented in large areas of the world. Through a survey of beach managers of Local Government Areas and a comprehensive search of peer reviewed and grey literature, we assessed the extent of nourishment practices in Australia. The study identified 130 beaches in Australia that were subject to nourishment practices between 2001 and 2011. Compared to projects elsewhere, most Australian projects were small in scale but frequent. Exceptions were nine bypass projects which utilised large volumes of sediment. Most artificial nourishment, replenishment and beach scraping occurred in highly urbanised areas and were most frequently initiated in spring during periods favourable to accretion and outside of the summer season of peak beach use. Projects were generally a response to extreme weather events, and utilised sand from the same coastal compartment as the site of erosion. Management was planned on a regional scale by Local Government Authorities, with little monitoring of efficacy or biological impact. As rising sea levels and growing coastal populations continue to put pressure on beaches a more integrated approach to management is required, that documents the extent of projects in a central repository, and mandates physical and biological monitoring to help ensure the engineering is sustainable and effective at meeting goals. [Copyright &y& Elsevier]

Living shorelines aim to enhance the resilience of coastlines to hazards while simultaneously delivering co-benefits such as carbon sequestration. Despite the potential ecological and socio-economic benefits of living shorelines over conventional engineered coastal protection structures, application is limited globally. Australia has a long and diverse coastline that provides prime opportunities for living shorelines using beaches and dunes, vegetation, and biogenic reefs, which may be either natural ('soft' approach) or with an engineered structural component ('hybrid' approach). Published scientific studies, however, have indicated limited use of living shorelines for coastal protection in Australia. In response, we combined a national survey and interviews of coastal practitioners and a grey and peer-reviewed literature search to (1) identify barriers to living shoreline implementation; and (2) create a database of living shoreline projects in Australia based on sources other than scientific literature. Projects included were those that had either a primary or secondary goal of protection of coastal assets from erosion and/or flooding. We identified 138 living shoreline projects in Australia through the means sampled starting in 1970; with the number of projects increasing through time particularly since 2000. Over half of the total projects (59 %) were considered to be successful according to their initial stated objective (i.e., reducing hazard risk) and 18 % of projects could not be assessed for their success based on the information available. Seventy percent of projects received formal or informal monitoring. Even in the absence of peer-reviewed support for living shoreline construction in Australia, we discovered local and regional increases in their use. This suggests that coastal practitioners are learning on-the-ground, however more generally it was stated that few examples of living shorelines are being made available, suggesting a barrier in information sharing among agencies at a broader scale. A database of living shoreline projects can increase knowledge among practitioners globally to develop best practice that informs technical guidelines for different approaches and helps focus attention on areas for further research., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

Concrete infrastructure in coastal waters is increasing. While adding complex habitat and manipulating concrete mixtures to enhance biodiversity have been studied, field investigations of sub-millimetre-scale complexity and substrate colour are lacking. Here, the interacting effects of 'colour' (white, grey, black) and 'microtexture' (smooth, 0.5 mm texture) on colonisation were assessed at three sites in Australia. In Townsville, no effects of colour or microtexture were observed. In Sydney, spirorbid polychaetes occupied more space on smooth than textured tiles, but there was no effect of microtexture on serpulid polychaetes, bryozoans and algae. In Melbourne, barnacles were more abundant on black than white tiles, while serpulid polychaetes showed opposite patterns and ascidians did not vary with treatments. These results suggest that microtexture and colour can facilitate colonisation of some taxa. The context-dependency of the results shows that inclusion of these factors into marine infrastructure designs needs to be carefully considered.

The supply and fate of wrack (dead organic matter) is a critical determinant of the structure and function of shoreline ecosystems, and their role as carbon repositories. The increasingly common practise of armouring urbanised shorelines with seawalls impacts wrack deposits of unvegetated estuarine and coastal shorelines by truncating the intertidal zone and/or by modifying the physical and biological processes that deliver and remove wrack. This study tested whether such effects also extend to mangrove forests. A survey of wrack deposits in mangrove forests with and without seawalls along the Parramatta River, Sydney, Australia, revealed that at sites with seawalls placed at a mid-intertidal elevation wrack deposits were shifted from the high- to mid-intertidal but were otherwise of similar cover and composition. Experiments tracking the fate of wrack determined that, as compared to the mid-intertidal zone of unarmoured shorelines, wrack deposits at sites with seawalls were more readily mobilised. This was in some instances countered by the reduction in Casuarina glauca litter on armoured shorelines, as experiments revealed that Avicennia marina leaf decomposition was slower in the absence than the presence of C. glauca. Overall, the results suggest that effects of armouring on wrack composition and dynamics may be weaker in mangrove forests than on unvegetated shorelines. This could reflect the predominantly autochthonous source of wrack in mangrove forests, the habitat structure of forests minimizing hydrodynamic impacts of seawalls, and/or the differing reasons for which hard structures are constructed in low hydrodynamic energy vegetated as opposed to high hydrodynamic energy unvegetated settings., Competing Interests: Declaration of competing interest The authors of this paper attest there are no financial, personal, or other relationships with other persons or organisations within three years of beginning this submitted work that could inappropriately influence, or be perceived to influence, this work., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The effective use of ecosystem engineers to conserve biodiversity requires an understanding of the types of resources an engineer modifies, and how these modifications vary with biotic and abiotic context. In the intertidal zone, oysters engineer ecological communities by reducing temperature and desiccation stress, enhancing the availability of hard substrate for attachment, and by ameliorating biological interactions such as competition and predation. Using a field experiment manipulating shading, predator access and availability of shell substrate at four sites distributed over 900 km of east Australian coastline, we investigated how the relative importance of these mechanisms of facilitation vary spatially. At all sites, and irrespective of environmental conditions, the provision of hard substrate by oysters enhanced the abundance and richness of invertebrates, in particular epibionts (barnacles and oyster spat) and grazing gastropods. Mobile arthropods utilised the habitat provided by disarticulated dead oysters more than live oyster habitat, whereas the abundance of polychaetes and bivalves were much greater in live oysters, suggesting the oyster filter-feeding activity is important for these groups. In warmer estuaries, shading by oysters had a larger effect on biodiversity, whereas in cooler estuaries, the provision of a predation refuge by oysters played a more important role. Such knowledge of how ecosystem engineering effects vary across environmental gradients can help inform management strategies targeting ecosystem resilience via the amelioration of specific environmental stressors, or conservation of specific community assemblages.

Ecological theory predicts that positive interactions among organisms will increase across gradients of increasing abiotic stress or consumer pressure. This theory has been supported by empirical studies examining the magnitude of ecosystem engineering across environmental gradients and between habitat settings at local scale. Predictions that habitat setting, by modifying both biotic and abiotic factors, will determine large-scale gradients in ecosystem engineering have not been tested, however. A combination of manipulative experiments and field surveys assessed whether along the east Australian coastline: (1) facilitation of invertebrates by the oyster Saccostrea glomerata increased across a latitudinal gradient in temperature; and (2) the magnitude of this effect varied between intertidal rocky shores and mangrove forests. It was expected that on rocky shores, where oysters are the primary ecosystem engineer, they would play a greater role in ameliorating latitudinal gradients in temperature than in mangroves, where they are a secondary ecosystem engineer living under the mangrove canopy. On rocky shores, the enhancement of invertebrate abundance in oysters as compared to bare microhabitat decreased with latitude, as the maximum temperatures experienced by intertidal organisms diminished. By contrast, in mangrove forests, where the mangrove canopy resulted in maximum temperatures that were cooler and of greater humidity than on rocky shores, we found no evidence of latitudinal gradients of oyster effects on invertebrate abundance. Contrary to predictions, the magnitude by which oysters enhanced biodiversity was in many instances similar between mangroves and rocky shores. Whether habitat-context modifies patterns of spatial variation in the effects of ecosystem engineers on community structure will depend, in part, on the extent to which the environmental amelioration provided by an ecosystem engineer replicates that of other co-occurring ecosystem engineers.

Strategies for managing biological invasions are often based on the premise that characteristics of invading species and the invaded environment are key predictors of the invader's distribution. Yet, for either biological traits or environmental characteristics to explain distribution, adequate time must have elapsed for species to spread to all potential habitats. We compiled and analyzed a database of natural history and ecological traits of 138 coastal marine invertebrate species, the environmental conditions at sites to which they have been introduced, and their date of first introduction. We found that time since introduction explained the largest fraction (20%) of the variability in non-native range size, while traits of the species and environmental variables had significant, but minimal, influence on non-native range size. The positive relationship between time since introduction and range size indicates that non-native marine invertebrate species are not at equilibrium and are still spreading, posing a major challenge for management of coastal ecosystems.