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As the world’s population continues to grow, the way in which ocean industries interact with ecosystems will be key to supporting the longevity of food and social securities. Aquaculture is crucial to the future supply of seafood, but challenges associated with negative impacts could impede increased production, especially production that is efficient and safe for the environment. Using the typology established by The Economics of Ecosystems and Biodiversity Initiative, we describe how marine aquaculture could be influential in supporting ecosystem services beyond solely the production of goods, through provisioning services, regulating services, habitat or supporting services, and cultural services. The provision of these services will vary, depending on functional traits of culture species, biotic and abiotic characteristics of the surrounding environment, farm design, and operational standards. Increasing recognition, understanding, and accounting of ecosystem service provision by mariculture through innovative policies, financing, and certification schemes may incentivize active delivery of benefits and may enable effects at a greater scale.

Habitat heterogeneity is considered a primary causal driver underpinning patterns of diversity, yet the universal role of heterogeneity in structuring biodiversity is unclear due to a lack of coordinated experiments testing its effects across geographic scales and habitat types. Furthermore, key species interactions that can enhance heterogeneity, such as facilitation cascades of foundation species, have been largely overlooked in general biodiversity models. Here, we performed 22 geographically distributed experiments in different ecosystems and biogeographical regions to assess the extent to which variation in biodiversity is explained by three axes of habitat heterogeneity: the amount of habitat, its morphological complexity, and capacity to provide ecological resources (e.g. food) within and between co-occurring foundation species. We show that positive and additive effects across the three axes of heterogeneity are common, providing a compelling mechanistic insight into the universal importance of habitat heterogeneity in promoting biodiversity via cascades of facilitative interactions. Because many aspects of habitat heterogeneity can be controlled through restoration and management interventions, our findings are directly relevant to biodiversity conservation. Species interactions that can enhance habitat heterogeneity such as facilitation cascades of foundation species have been overlooked in biodiversity models. This study conducted 22 geographically distributed experiments in different ecosystems and biogeographical regions to assess the extent to which biodiversity is explained by three axes of habitat heterogeneity in facilitation cascades.

Autogenic ecosystem engineers often provide cool microhabitats which are used by associated organisms to reduce thermal extremes. The value of such habitats is, however, dependent on key structural traits of the ecosystem engineer, and the intensity and duration of thermal exposure. Using an experimental mesocosm that mimicked the rocky intertidal environment, we assessed how the spatial configuration of the habitat formed by an autogenic ecosystem engineer, the oyster, influences its capacity to mitigate heat stress experienced by invertebrates during simulated emersion periods on tropical, Hong Kong rocky shores. At the average temperature experienced during summer low tides, oyster habitat ameliorated environmental and organismal temperatures, irrespective of the structural configuration of the oyster bed. As temperatures increased, however, vertically orientated oysters provided microclimates that facilitated cooler invertebrate body temperatures than horizontal beds, which no longer conferred any associational benefit as compared to bare rock surfaces. In the absence of oysters, physiological indicators of stress to associated organisms (i.e., heart rate and osmolality) increased with the intensity and duration of exposure to high temperatures. Such effects were, however, mitigated by association with vertical but not horizontal oyster configurations. In contrast, the osmolality of the oysters was not related to temperature, suggesting they remained in a state of metabolic quiescence throughout emersion. Structural traits such as the spatial configuration of ecosystem engineers are therefore critical to their effectiveness in environmental amelioration. As such, variations in the morphological traits of ecosystem engineers, which have important implications for their ecological role, need to be incorporated into conservation and restoration projects aimed at climate change adaptation. A plain language summary is available for this article. Plain Language Summary

Predator–prey interactions are often highly co-evolved, with selection over time for prey with morphological and behavioral traits that minimize predation risk. Consequently, in many environments prey choose among potential habitats according to their refuge value. It is unclear, however, when presented with new habitats, if prey are able to evaluate the predation risk of these relative to familiar habitats and utilize these in accordance with their value. We tested whether, along the east coast of the USA, native mud crabs Panopeus herbstii utilize the non-native alga Gracilaria vermiculophylla according to its relative refuge value. Experiments examining predation by blue crabs Callinectes sapidus on mud crabs revealed that the non-native alga had an intermediate refuge value relative to native oysters, which were the most protective, and unvegetated sediment, which was the least. In subsequent choice experiments, mud crabs selected oysters over alga over unvegetated sediment, in accordance with habitat refuge values. Further, in field experiments, the use of Gracilaria by mud crabs was inversely related to the proximity of the alga to the preferred habitat type, oysters, and was reduced by the presence of a blue crab predator. Consequently, mud crabs are utilizing the non-native alga Gracilaria in accordance with its intermediate refuge value. The relative refuge value of non-native vs native habitat-forming species may provide a baseline expectation against which to measure the speed of learning and opportunism in the response of native prey to novel protective habitats.

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.

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.

Globally, oyster reef restoration is on the rise. In many instances, restoration is occurring alongside established oyster aquaculture industries that grew to prominence following oyster reef demise. This paper examines the potential positive and negative interactions between the two industries and identifies key factors that may promote positive interactions. Interactions between the two industries result from shared resource requirements (e.g., space, clean water, brood-stock, breeding programs), shared knowledge requirements (e.g. around threats and their mitigation, factors optimizing growth/survival) and biological interactions (e.g. over-catch, disease spill-over, competition for resources). Many of these interactions are reciprocated, and can shift from positive to negative depending on environmental, biological and socio-economic conditions. From our examination, three key factors emerge as shaping the strength and direction (positive or negative) of interactions: (1) whether the focal species is common or different between the two industries; (2) the physicochemical and socio-economic environment in which the two industries are occurring; and (3) whether there is open dialogue and consultation between the two industries and relevant stakeholders. Positive interactions can be maximized where the two industries are able to co-invest in and share infrastructure (e.g. hatcheries, breeding programs), resources (e.g. spat, broodstock, shell) and knowledge (e.g. optimal conditions of growth) – an easier task where the target oyster species is in common. Positive interactions may also be maximized by utilizing marine spatial planning tools, such as suitability modelling, to inform optimal siting of the two industries. As the two industries continue to grow, open and inclusive dialogue between these and key stakeholders will be essential for mitigating risk and maximising positive synergies.

Despite the ecological and socio‐economic benefits of nature‐based solutions (NbS), the application of ecological principles to the design of seawalls (termed ‘seawall eco‐engineering’) to mitigate their impacts remains low. We investigated stakeholder perspectives of, support for and willingness to pay (WTP) for seawall eco‐engineering in one of the most diverse and urbanised harbours in the world, Sydney Harbour, in Australia. Using a series of workshops and surveys targeting the general public, Local Government, built environment and natural environment professionals, we identified and ranked perceived risks and benefits of eco‐engineering seawalls, the most common infrastructure in the Harbour. Additionally, WTP for seawall eco‐engineering was investigated using an existing, large‐scale eco‐engineering project. Overall, workshop participants rated benefits of seawall eco‐engineering to be almost double the risks. The key perceived benefits were increased habitat/biodiversity, improved water quality and enhanced environmental stewardship/awareness. Key perceived risks were potential damage to infrastructure and use of greenwashing to facilitate new development. Across all stakeholder groups, participants were very supportive of statements regarding the benefits of eco‐engineered seawalls and the need for eco‐engineering principles to be included in the design of new seawalls. Despite strong support for seawall eco‐engineering, WTP was estimated at one third of the actual cost and was, in part, attributable to a lack of a shared evidence base from successful projects, and unclear guidance and policy around implementation. Synthesis and applications: Our results showed that establishing rigorous monitoring and evaluation programs that facilitate cost–benefit analyses are critical to enhancing WTP for and uptake of eco‐engineering projects. Furthermore, more cost‐effective technologies and shared funding models may overcome existing financial impediments. We also found integrative legislation may be key to increased implementation of such NbS, given that existing policies were viewed as unsupportive. Read the free Plain Language Summary for this article on the Journal blog. Read the free Plain Language Summary for this article on the Journal blog.

Intraspecific diversity can have as strong an effect on communities and ecosystems as more well‐studied effects of species diversity. Intraspecific variation in prey body size may have particularly strong effects on populations by influencing the outcome of predator–prey interactions, but this has received little attention. We tested the hypotheses that (1) body size of the Sydney Rock Oyster, Sacosstrea glomerata, influences predation risk; (2) increasing intraspecific variation in body size of the oyster will enhance total survivorship; (3) oyster size phenotypes will differ in the magnitude of survivorship benefits they incur from association with other phenotypes; and (4) size‐specific survivorship benefits of associating with other body sizes will vary with predator access. In a fully factorial field experiment, we manipulated the diversity of S. glomerata oyster body sizes (1–3 size classes per treatment) and predator access to prey (small vs. large mesh cages). Oyster total and individual phenotype survivorship was documented over an 8‐week period. Overall, the relationship between diversity in S. glomerata body size and survivorship was positive and was related to changes in density of individual body sizes when grown in mixtures. In fact, no phenotype had lower percent survivorship in mixtures than in monoculture. Nevertheless, individual phenotypes displayed differing responses to predator access treatments and phenotype mixing that reflected differences in the types of predators (e.g., shell drilling or removing) to which they were most susceptible. In general, the greatest survivorship benefits of phenotype mixing were seen in treatments where the most disparate (i.e., small, large) size classes were mixed. Our study adds to growing evidence of the importance of intraspecific diversity in mediating key population processes such as predation. Importantly, different oyster phenotypes benefit from increasing phenotypic diversity depending on the predators that can access the oysters, suggesting that flexible complementarity among oyster phenotypes may be a useful tool for increasing the resistance and resilience of oysters in a range of environments which vary in their predator composition. These results will help to inform strategies for enhancing survivorship of species transplants in restoration projects.