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• Physical complexity increased cryptobenthic fish interaction with the substrate. • Physical complexity hindered foraging activities of pelagic and cryptobenthic fish. • Cryptobenthic fish interacted and fed more from developed fouling assemblages. • Seeding with oysters increased feeding activity of cryptobenthic fish. • We can design better eco-engineering solutions for fish communities with these data. The replacement of natural marine habitats with less structurally complex human infrastructure has been linked to the homogenisation of epibenthic assemblages and associated changes in fish assemblages. To mitigate these impacts, eco-engineering efforts have focussed on increasing the physical and biogenic complexity of artificial structures, in the form of crevices added to seawalls and the seeding of the substrate with habitat-forming organisms such as oysters. While these studies have assessed how these interventions affect epibenthic assemblages, the effect of these strategies on the behaviour, such as feeding and habitat use, of different functional groups of fish (e.g. cryptobenthic and pelagic) remains uncertain. To do this, we manipulated complexity on seawalls by adding concrete tiles with different physical (flat or structured with crevices and ridges) and biogenic (seeding with two common habitat-forming species or naturally recruited fouling) complexities. We assessed pelagic and cryptobenthic fish species composition, abundance, interaction time with the tiles and number of feeding bites on three occasions 8–12 months after deployment. Cryptobenthic fish interacted more with physically complex tiles than flat tiles, regardless of biogenic complexity. In contrast, cryptobenthic fish fed more from flat tiles compared to physically complex tiles, and also appeared to feed more from tiles seeded with oysters. Pelagic fish interacted and fed more from naturally fouled tiles compared to unfouled control tiles, regardless of physical complexity. This study showed that manipulating complexity at the scales used here affects behaviour of fish, but it does not affect fish community. Increasing physical complexity facilitated fish use of seawalls as habitat by providing refuge, while it also hindered fish feeding by providing refuge for their prey. Cryptobenthic fish are important trophic linkages in their ecosystems and we have shown that by changing habitat complexity, we can change the habitat use and feeding activity of these fish, allowing them to fulfil this essential ecosystem role. [ABSTRACT FROM AUTHOR]

Highlights • Water retaining features on built structures can increase diversity and functioning. • Specific designs should always be informed by local ecological knowledge. • To maximise diversity, varying tidal heights, depth and sizes should be incorporated. • Scarce information available on the effects of design metrics on functioning. Abstract The global sprawl of urban centres is replacing complex natural habitats with relatively flat and featureless infrastructure that supports low biodiversity. In a growing countermovement, artificial microhabitats are increasingly incorporated into designs for “Green” and “Blue” infrastructure. In order to maximise the ecological value of such interventions, we need to inform the designs with observations from natural systems and existing Green and Blue infrastructure. Here, we focussed on water retaining features mimicking intertidal rock pools, as this is a widely used intervention in coastal ecosystems. Using a meta-analysis and a qualitative literature review, we compiled information on diversity and function of rock pools on natural rocky shores and built structures to assess the potential ecological benefits of water retaining microhabitats and the design metrics of rock pools that affect diversity and function. Our meta-analysis showed higher species richness in rock pools compared to emergent surfaces on built structures, but this was variable among locations. The qualitative review revealed that rock pools on both natural and artificial shores generally hosted species that were not present on emergent rock and can also host non-indigenous species, suggesting that the addition of these features can sometimes have unwanted consequences and local ecological knowledge is essential to implement successful interventions. Relationships between species richness and design metrics, such as height on shore, volume, surface area and depth of pool were taxa-specific. For example, results from the meta-analysis suggest that building larger, deeper pools could increase diversity of fish, but not benthic organisms. Finally, this study highlights major gaps in our understanding of how the addition of rock pools and design metrics influence diversity and the variables affecting the ecological functioning of rock pools. Based on the knowledge gathered so far, recommendations for managers are made and the need for future studies to add knowledge to expand these recommendations is discussed. [ABSTRACT FROM AUTHOR]

Assessments of human impacts on natural habitats often focus on the abundance of component species, yet physiological and/or sub-lethal effects of stressors on functional attributes may be equally important to consider. Here we evaluated how artificial structures, an integral part of urbanisation in the marine environment, affects key functional properties of the habitat-forming kelp Ecklonia radiata . Given that stressors rarely occur in isolation, we assessed the effects of infrastructure across an urbanised estuary. Estuaries are ideal for studying how multiple anthropogenic and natural stressors influence potential impacts of infrastructure on habitat-forming species because these habitats usually face a wide range and levels of stressors. Here, we compared the abundance of habitat-forming macro-algae as well as the growth, erosion and photosynthetic activity of kelp in artificial and natural habitats across one of the largest urbanised estuaries in the word - Sydney Harbour. We predicted that effects of artificial structures on functional attributes of kelps would be stronger in the inner area of the Harbour, characterised by higher levels of human impacts and low flushing. Contrary to our predictions, we found that effects of infrastructure were consistent across the estuary, regardless of the ecological footprint caused by human activities or natural environmental gradients. When differences were observed between areas of the estuary, they mostly occurred independently of impacts of substrate type. Importantly, we found lower erosion rates of kelp on pilings than on reefs, likely resulting in lower production of detritus in estuaries where natural reefs are degraded or lost and pilings added. Such impacts have important implications for the connectivity among coastal habitats and secondary productivity in adjacent and remote habitats, which are highly dependent on the exportation of kelp detritus. Our study is the first to assess potential functional consequences of urbanisation through physiological and/or biomechanical effects on habitat-formers, an often overlooked mechanism of environmental impact on ecosystem functioning. [ABSTRACT FROM AUTHOR]

Urbanisation in terrestrial systems has driven architects, planners, ecologists and engineers to collaborate on the design and creation of more sustainable structures. Examples include the development of ‘green infrastructure’ and the introduction of wildlife corridors that mitigate urban stressors and provide positive ecological outcomes. In contrast, efforts to minimise the impacts of urban developments in marine environments have been far more restricted in their extent and scope, and have often overlooked the ecological role of the built environment as potential habitat. Urban foreshore developments, i.e. those built on the interface of intertidal and/or subtidal zones, have the potential to incorporate clear multi-functional outcomes, by supporting novel ecosystems. We present a step-by-step eco-engineering framework for ‘building blue’ that will allow coastal managers to facilitate planning and construction of sustainable foreshore developments. Adopting such an approach will incorporate ecological principles, thereby mitigating some of the environmental impacts, creating more resilient urban infrastructure and environments, and maximising benefits to the multiple stakeholders and users of marine urban waterfronts. [ABSTRACT FROM AUTHOR]

Urban land and seascapes are increasingly exposed to artificial lighting at night (ALAN), which is a significant source of light pollution. A broad range of ecological effects are associated with ALAN, but the changes to ecological processes remain largely unstudied. Predation is a key ecological process that structures assemblages and responds to natural cycles of light and dark. We investigated the effect of ALAN on fish predatory behaviour, and sessile invertebrate prey assemblages. Over 21 days fish and sessile assemblages were exposed to 3 light treatments (Day, Night and ALAN). An array of LED spotlights was installed under a wharf to create the ALAN treatments. We used GoPro cameras to film during the day and ALAN treatments, and a Dual frequency IDentification SONar (DIDSON) to film during the night treatments. Fish were most abundant during unlit nights, but were also relatively sedentary. Predatory behaviour was greatest during the day and under ALAN than at night, suggesting that fish are using structures for non-feeding purposes (e.g. shelter) at night, but artificial light dramatically increases their predatory behaviour. Altered predator behaviour corresponded with structural changes to sessile prey assemblages among the experimental lighting treatments. We demonstrate the direct effects of artificial lighting on fish behaviour and the concomitant indirect effects on sessile assemblage structure. Current and future projected use of artificial lights has the potential to significantly affect predator-prey interactions in marine systems by altering habitat use for both predators and prey. However, developments in lighting technology are a promising avenue for mitigation. This is among the first empirical evidence from the marine system on how ALAN can directly alter predation, a fundamental ecosystem process, and have indirect trophic consequences. [ABSTRACT FROM AUTHOR]

Abstract: Most knowledge of the effects of metals on benthic organisms comes from laboratory studies with subsequent extrapolation to field scenarios. Here, we critically reviewed studies on effects of metals on aquatic organisms, with an emphasis on marine systems to determine the “real” state of our current knowledge about effect of metals on assemblages. These studies include experiments in the laboratory and/or micro- and meso-cosms and those done in the field. Laboratory studies have shown lethal and sub-lethal effects of metals on organisms. There is, however, little evidence that these effects occur in natural environments. Conditions in the laboratory are very different from those in natural habitats. It is sensible, then, to assume that organisms may respond differently under field conditions, but how representative laboratory studies are of field conditions is rarely tested. In contrast, many field studies use patterns to infer processes, without any experimental verification. Of the descriptive papers reviewed here, nearly 50% found differences in the assemblages between contaminated and reference areas. Often, however, the differences were definitely not attributable or could not be unambiguously attributed to the presence of metals, because most of the studies lacked proper controls and/or appropriate temporal or spatial replication. Relatively few experimental studies in the field found clear effects. Where they were found experimentally, differences were generally decreased abundances of populations of some species or reduced diversity of species. Indirect ecological interactions can also occur, where abundances of a superior competitor are reduced by metals, leading to increases in abundances of other species. Properly designed experimental field studies are needed to evaluate the effects of metals on organisms and/or assemblages in natural habitats. This is essential for developing realistic environmental guidelines and managerial strategies for protecting aquatic habitats. [Copyright &y& Elsevier]

The marine environment is being increasingly modified by the construction of artificial structures, the impacts of which may be mitigated through eco-engineering. To date, eco-engineering has predominantly aimed to increase biodiversity, but enhancing other ecological functions is arguably of equal importance for artificial structures. Here, we manipulated complexity through habitat structure (flat, and 2.5 cm, 5 cm deep vertical and 5 cm deep horizontal crevices) and seeding with the native oyster (Saccostrea glomerata, unseeded and seeded) on concrete tiles (0.25 m × 0.25 m) affixed to seawalls to investigate whether complexity (both orientation and depth of crevices) influences particle removal rates by suspension feeders and colonisation by different functional groups, and whether there are any ecological trade-offs between these functions. After 12 months, complex seeded tiles generally supported a greater abundance of suspension feeding taxa and had higher particle removal rates than flat tiles or unseeded tiles. The richness and diversity of taxa also increased with complexity. The effect of seeding was, however, generally weaker on tiles with complex habitat structure. However, the orientation of habitat complexity and the depth of the crevices did not influence particle removal rates or colonising taxa. Colonisation by non-native taxa was low compared to total taxa richness. We did not detect negative ecological trade-offs between increased particle removal rates and diversity and abundance of key functional groups. Our results suggest that the addition of complexity to marine artificial structures could potentially be used to enhance both biodiversity and particle removal rates. Consequently, complexity should be incorporated into future eco-engineering projects to provide a range of ecological functions in urbanised estuaries. • Eco-engineering of seawalls often focuses on enhancement of biodiversity. • We manipulated seawall complexity to enhance other ecological functions. • Increased habitat structure and bivalve seeding enhanced particle removal rates. • Habitat structure did not facilitate non-native over native species. • Multifunctional eco-engineering is possible without negative ecological trade-offs. [ABSTRACT FROM AUTHOR]

Natural systems are threatened by a variety of anthropogenic stressors and so understanding the interactive threats posed by multiple stressors is essential. In this study we focused on urban stressors that are ubiquitous to urban estuarine systems worldwide: elevated nutrients, toxic chemical contaminants, built infrastructure and non-indigenous species (NIS). We investigated structural (abundance, diversity and species richness) and functional endpoints (productivity, primary production (chlorophyll-a) and metabolism) commonly used to determine responses to these selected stressors. Through a systematic review of global literature, we found 579 studies of our selected stressors; 93% measured responses to a single stressor, with few assessing the effects of multiple stressors (7%). Structural endpoints were commonly used to measure the effects of stressors (49% of the total 579 studies). Whereas, functional endpoints were rarely assessed alone (10%) but rather in combination with structural endpoints (41%). Elevated nutrients followed by NIS were the most studied single stressors (43% and 16% of the 541 single stressor studies), while elevated nutrients and toxic contaminants were overwhelmingly the most common stressor combination (79% of the 38 multiple stressor studies); with NIS and built infrastructure representing major gaps in multi-stressor research. In the meta-analysis, structural endpoints tended to decrease, while functional endpoints increased and/or decreased in response to different types of organisms or groups. We predicted an antagonistic effect of elevated nutrients and toxic contaminants based on the opposing enriching versus toxic effects of this stressor combination. Of note, biodiversity was the only endpoint that revealed such an antagonistic response. Our results highlight the continuing paucity of multiple stressor studies and provide evidence for opposing patterns in the responses to single and interacting stressors depending on the measured endpoint. The latter is of significant consequence to understanding relevant impacts of stressors in coastal monitoring and management. Unlabelled Image • Multiple stressor interactions remain poorly understood in urban marine systems. • Primary research has focused on nutrients and toxic contaminant interactions. • Interactive effects of nutrients and toxic contaminants were not antagonistic. • Structural endpoints decreased in response to single and multiple stressors. • Functional endpoints responded in different ways to multiple stressors. [ABSTRACT FROM AUTHOR]