Influence of habitat features on the colonisation of native and non-indigenous species

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.

Habitat structure shapes temperate reef assemblages across regional environmental gradients

Intertidal artificial habitats are proliferating, but are generally simpler in structure and host lower biodiversity than natural rocky reefs. Eco-engineering aims to enhance the biodiversity of coastal infrastructure, often through physical structural modifications that mimic topographic properties of natural shores. Relationships between biotic assemblages and structural properties of natural and artificial reefs have been extensively studied at sampling scales of up to 1 m2. But evidence that quantified local structural variation has an appreciable influence on biotic assemblages, at a shore-wide scale across regional environmental gradients, is lacking. Here we addressed this knowledge gap with an observational study at 32 natural and artificial intertidal reef sites in Wales, UK. We used multivariate community analysis and permutation tests to examine associations between local physical structure, regional environmental variables and sessile biotic assemblages. A potential influence of local habitat structure on assemblage composition was evident across regional-scale environmental gradients. Compared to natural sites, artificial reefs had lower taxonomic richness, distinct and more variable assemblage composition, and different physical structure. After removing the effect of habitat (natural or artificial), canonical correspondence analysis showed that environmental variables (wave exposure, sea surface temperature and salinity variation), along with two metrics of physical structure (standard deviation in log-transformed detrended roughness and skewness of surface verticality, both at 0.5 m scale), explained 40 % of the variation in assemblage composition among sites. The two structural metrics independently explained 14.5 % of the variation. Associations identified between individual taxa and environmental variables indicated that sites with a higher proportion of horizontal surfaces hosted more canopy macroalgae, which in turn support other algae and invertebrates. Our findings provide evidence to inform scaling-up of structural eco-engineering interventions from experimental contexts to enhance the biodiversity of coastal infrastructure across regional extents.

Metrics matter: Multiple diversity metrics at different spatial scales are needed to understand species diversity in urban environments

Worldwide, natural habitats are being replaced by artificial structures due to urbanisation. Planning of such modifications should strive for environmental net gain that benefits biodiversity and ecosystems. Alpha (α) and gamma (γ) diversity are often used to assess 'impact' but are insensitive metrics. We test several diversity measures across two spatial scales to compare species diversity in natural and artificial habitats. We show γ-diversity indicates equivalency in biodiversity between natural and artificial habitats, but natural habitats support greater taxon (α) and functional richness. Within-site β-diversity was also greater in natural habitats, but among-site β-diversity was greater in artificial habitats, contradicting the commonly held view that urban ecosystems are more biologically homogenous than natural ecosystems. This study suggests artificial habitats may in fact provide novel habitat for biodiversity, challenges the applicability of the urban homogenisation concept and highlights a significant limitation of using just α-diversity (i.e., multiple metrics are needed and recommended) for assessing environmental net gain and attaining biodiversity conservation goals.

The elephant in the room: Introduced species also profit from refuge creation by artificial fish habitats

Increasingly, ecological rehabilitation is envisioned to mitigate and revert impacts of ocean sprawl on coastal marine biodiversity. While in the past studies have demonstrated the positive effects of artificial fish habitats in port areas on fish abundance and diversity, benthic colonization of these structures has not yet been taken into consideration. This could be problematic as they may provide suitable habitat for Non-Indigenous Species (NIS) and hence facilitate their spreading. The present study aimed to examine communities developing on artificial fish habitats and to observe if the number of NIS was higher than in surrounding equivalent habitats. The structures were colonized by communities that were significantly different compared to those surrounding the control habitat, and they were home to a greater number of NIS. As NIS can cause severe ecological and economical damages, our results imply that in conjunction with the ecosystem services provided by artificial fish habitats, an ecosystem disservice in the form of facilitated NIS colonization may be present. These effects have not been shown before and need to be considered to effectively decide in which situations artificial structures may be used for fish rehabilitation.

Behaviour broadens thermal safety margins on artificial coastal defences in the tropics

Tropical species are predicted to be among the most vulnerable to climate change as they often live close to their upper limits to thermal tolerance and in many cases, behavioural thermoregulation is required to persist in the thermal extremes of tropical latitudes. In concert with warming temperatures, near-shore species are faced with the additional threat of shoreline hardening, leading to a reduction in microhabitats that can provide thermal refuges. This situation is exemplified in Singapore, which lies almost on the equator and so experiences year-round hot temperatures, and much of its coastline is now seawall. To investigate the thermal ecology of a common intertidal gastropod, Nerita undata, on these artificial structures, we measured thermal conditions on two seawalls, the temperatures of habitats occupied by the snail, and compared these with the snail's thermal tolerance by measuring heart rate and behavioural thermoregulation (as preferred temperature, Tpref). At one of the two seawalls (Tanjong Rimau), temperatures experienced by N. undata exceeded all measures of thermal tolerance in the sun, while at the other (Palawan Beach), they did not. Temperatures in habitats occupied by the snails on the seawalls were similar to their measured Tpref in the laboratory and were lower than all measures of thermal tolerance. Behavioural thermoregulation by the snails, therefore, significantly increased the thermal safety margins of N. undata on the relatively homogenous seawalls in Singapore, and at one of the two seawalls were necessary to allow snails to survive. Accordingly, to facilitate motile species to maintain broad thermal safety margins through behavioural regulation, the provision of additional refuges from thermal stress is recommended on artificial coastal defences such as seawalls.

Eco-bioengineering tools in ecohydrological assessment of eutrophic water bodies

Eutrophication of water bodies and deterioration of water quality are emerging environmental crises. The root causes and consequences of eutrophication are multidirectional. Thus, they provide a huge scope of risk-analysis and risk-assessment in the domain of remediation studies. However, recent restoration studies reveal a global trend of utilizing traditional restoration methods combined with advanced pioneer innovative techniques developed in the field of science and technology. This review introduces a novel approach to consider ecohydrological assessment of eutrophication by classical biomanipulation practices emphasising on their evolution into innovative 'eco-bioengineering' methods. The main objective of this study is to critically analyse and recognize the research gaps in classical biomanipulation and appreciate the reproducibility and efficacy of eco-bioengineering methods at micro- and macrolevel aquatic ecosystems. Comprehensive literature review was conducted on offline and online platforms. Our survey revealed (a) continuation of a historical trend in classical biomanipulation practices (61.64%) and (b) an ascending drift in eco-bioengineering research (38.36%) in the last decade (2010-2021). At a global scale, recent biomanipulation research has a skewed distribution in Europe (41.10%), East Asia (32.88%), North America (10.96%), South Africa (4.11%), South America (2.74%), Middle East (1.37%), Oceania (1.37%), and non-specific regions (5.48%). Finally, this review analysis revealed the comprehensiveness of eco-bioengineering methods and their strong ecological resilience to recurrence of eutrophication and fluctuating environmental flows in the future. Therefore, our review reinforces the supremacy of eco-bioengineering methods as cost-effective green technologies providing sustainable solutions to restore the eutrophic waters at a global scale.

Material type influences the abundance but not richness of colonising organisms on marine structures

Urbanisation of coastal areas and growth in the blue economy drive the proliferation of artificial structures in marine environments. These structures support distinct ecological communities compared to natural hard substrates, potentially reflecting differences in the materials from which they are constructed. We undertook a meta-analysis of 46 studies to compare the effects of different material types (natural or eco-friendly vs. artificial) on the colonising biota on built structures. Neither the abundance nor richness of colonists displayed consistent patterns of difference between artificial and natural substrates or between eco-friendly and standard concrete. Instead, there were differences in the abundance of organisms (but not richness) between artificial and natural materials, that varied according to material type and by functional group. When compared to biogenic materials and rock, polymer and metal supported significantly lower abundances of total benthic species (in studies assessing sessile and mobile species together), sessile invertebrates and corals (in studies assessing these groups individually). In contrast, non-indigenous species were significantly more abundant on wood than metal. Concrete supported greater abundances of the general community, including habitat-forming species, compared to wood. Our results suggest that the ecological requirements of the biological community, alongside economic, logistic and engineering factors should be considered in material selection for multifunctional marine structures that deliver both engineering and ecological (enhanced abundance and diversity) benefits.

Initiating pedogenesis of magnetite tailings using Lupinus angustifolius (narrow-leaf lupin) as an ecological engineer to promote native plant establishment

Mine tailings pose physical and chemical challenges for plant establishment. Our aim was to learn from natural processes in long-term soil and ecosystem development to use tailings as novel parent materials and pioneer ecological-engineering plant species to ameliorate extreme conditions of tailings, and facilitate the establishment of subsequent native plants. A glasshouse trial was conducted using magnetite tailings containing various amendments, investigating the potential of the nitrogen (N)-fixing, non-native pioneer species Lupinus angustifolius (Fabaceae), narrow-leaf lupin, as a potential eco-engineer to promote soil formation processes, and whether amendment type or the presence of pioneer vegetation improved the subsequent establishment and growth of 40 species of native plants. We found that L. angustifolius eco-engineered the mine tailings, by enhancing the N status of tailings and mobilising primary mineral P into organic P via a carboxylate-exudation strategy, thereby enabling subsequent growth of native species. The substantial increases of the soil organic P (from ca. 10 to 150 mg kg^-1) pool and organo-bound Al minerals (from 0 to 2 mg kg^-1) were particularly evident, indicating the initiation of pedogenesis in mine tailings. Our findings suggest that the annual legume L. angustifolius has eco-engineering potential on mine tailings through N-fixation and P-mobilisation, promoting the subsequent growth of native plants. We proposed Daviesia (Fabaceae) species as native species alternatives for the non-native L. angustifolius in the Western Australian context. Our findings are important for restoration practitioners tasked with mine site restoration in terms of screening pioneer eco-engineering plant species, where native plants are required to restore after mine operations.

Eco-engineering controls vegetation trends in southwest China karst

The karst area in Yunnan-Guangxi-Guizhou region in southwest China is known for widespread rocky desertification but several studies report a greening trend since the year 2000. While the start of the greening trend seems to match with the implementation of ecological conservation projects, no statistical evidence on a relationship between vegetation greening and eco-engineering exists. Moreover, dominant factors influencing the spatial patterns of vegetation trends have rarely been investigated. Here we use six comprehensive factors representing the natural conditions and human activities of the study area, and several statistical models consistently show that eco-engineering explains large parts of the positive vegetation trends in the karst areas, while negative vegetation trends in non-karst areas of Yunnan were related with a decrease in rainfall. We further show that the interaction of eco-engineering with other factors leads to a heterogeneous pattern of different vegetation trends. Knowing and understanding these patterns is crucial when planning ecological restoration, especially in diverse landscapes like China karst and the methods can be reused in other restoration areas.

Primacy of ecological engineering tools for combating eutrophication: An ecohydrological assessment pathway

Eutrophication of freshwater bodies causes loss of earth's biological resources and aggravates climate change, thus assuming major environmental concern. Both endogenous and exogenous nutrient enrichment are responsible for eutrophication. Numerous monitoring and management studies conducted worldwide have resulted high-level technological innovations. These studies cumulatively uphold the significance of ecohydrological and ecological engineering approaches. However, holistic and insightful reviews with feasible recommendations of such huge academic outputs are rather scanty. Therefore, our main objective was to introduce a new perspective of eutrophication as an ecohydrological component; to discover all possibilities of monitoring and restoration of eutrophic water bodies. Furthermore, the present study critically analyzes various methods of treatment of eutrophication (physical, biological, chemical, and eco-engineering). Comprehensive volume of literature has been surveyed using search engines like Scopus, Google Scholar, PubMed, ScienceDirect etc. Meaningful keywords were used to obtain reliable information on methods of ecohydrological assessment in relation to eutrophication of freshwater bodies. According to our survey, ecohydrological research is diversified into conceptual knowledge (37.2%), assessment (32.6%), climate change (9.3%), algae/cyanotoxins (7%), engineering and restoration (7%), modelling (4.6%) and biodiversity (2.3%), in the instant decade (2010-2020). We have identified a clear trend of transition of restoration methods from traditional towards modern techniques over time. Moreover, this review recognizes a pool of biophysicochemical and ecological engineering techniques, which are very effective in regard to time, cost, and labor and have immense scopes of modification for improved results. This work focuses on the importance of ecohydrology and eco-engineering tools for restoration of eutrophic water bodies for the first time. We have highlighted how these approaches have emerged as one of the best suitable and sustainable water resource conservation routes in the present era.

Provision of refugia and seeding with native bivalves can enhance biodiversity on vertical seawalls

Recent studies have suggested that increasing habitat complexity of artificial seawalls by modifying surface heterogeneity could enhance exploitable habitat and therefore species richness and abundance. We tested the effects of adding complex tiles (with crevices/ledges) of different heterogeneity (i.e., flat tiles resembling the seawall vs. tiles with crevices of 2.5 cm or 5.0 cm depth) and seeding with native rock oysters, Saccostrea cuccullata (unseeded vs. seeded) on species richness and abundances of intertidal marine organisms on two vertical seawalls in Hong Kong. Tiles were affixed to the mid-intertidal zone of the seawalls for 12 months. The results showed that the tiles with crevices had greater species richness and cover of sessile epifauna than flat tiles. Seeding tiles with S. cuccullata also facilitated natural recruitment of the same species. Our results support the hypothesis that using eco-engineering to increase habitat complexity can enhance the biodiversity of intertidal marine organisms on seawalls.

High kelp density attracts fishes except for recruiting cryptobenthic species

As foundation species, kelp support productive and species rich communities; however, the effects of kelp structure on mobile species within these complex natural systems are often difficult to assess. We used artificial reefs with transplanted kelp to quantify the influence of kelp patch size and density on fish assemblages including the arrival of recruiting cryptobenthic species. Large patches with dense kelp supported the highest abundance, species richness, and diversity of fishes, with the addition of dense kelp tripling biomass and doubling richness. The abundance of recruits in artificial collectors declined with patch size and was halved on reefs with sparse kelp compared to reefs with dense kelp or no kelp. These results highlight the importance of dense kelp cover in facilitating biodiversity and indicate that kelp addition could support the recovery of degraded coastal ecosystems. Kelp also apparently drives complex interactions affecting the recruitment/behaviour of some cryptobenthic species.

Geochemical and mineralogical changes in magnetite Fe-ore tailings induced by biomass organic matter amendment

Direct phytostabilization of alkaline and finely textured Fe-ore tailings is a key challenge for sustainable rehabilitation of tailings landscapes, due to limited topsoil resources available for constructing functional root-zones. The eco-engineering of soils (i.e. technosol) from tailings through the deliberate combination of technic materials with ecological inputs (e.g. biomass, water, topsoil and organisms) may provide a cost-effecctive and sustainable alternative to topsoil-based option for tailings rehabilitation. This approach purposefully accelerates in situ mineral weathering and the development of soil-like physicochemical and biological properties and functions in the tailings. The present study aimed to characterize mineralogical and geochemical changes associated with soil formation in Fe-ore tailings, by admixing biomass organic matter (BOM) and soil inoculum under well-watered conditions. Magnetite Fe-ore tailings (pH ~9.5) were amended with 3% (w/w) BOM (Lucerne hay) and natural soil microbial communities and incubated for 68 days in a microcosm study. BOM amendment with soil inoculum resulted in a rapid neutralization of alkaline pH conditions in the tailings. The weathering of magnetite and biotite-like phyllosilicates were accelerated, resulting in increased concentrations of soluble Mg, K, Fe, Ca, and Si in porewater. Evidence of the accelerated weathering was verified by synchrotron-based Fe K-edge X-ray absorption fine structure (XAFS) spectroscopy analysis, showing the presence of possibly Fe (III)-oxalates. The weathering resulted in eroded morphological surfaces of Fe-bearing minerals in the BOM treated tailings. This study confirmed the expected geochemical and mineralogical changes in the magnetite Fe-ore tailings induced by BOM amendment, providing a fundamental basis for eco-engineering tailings into soil-like technosol.

Thermal exposure risks to mobile tropical marine snails: Are eco-engineered rock pools on seawalls scale-specific enough for comprehensive biodiversity outcomes?

To test the model that eco-engineering plant boxes on seawalls sustain water temperatures within thermal tolerance to maximize tropical marine biodiversity, we conducted acute thermal effects (AET) experiments using intertidal gastropods (Nerita albicilla and Littoraria articulata). The AET₅₀ (50th percentile) for N. albicilla (39.6 °C) was higher than L. articulata (32.8 °C). Loggers (Hobo) in boxes on a seawall positioned for full exposure to air temperature at mean sea level (<1.1 m) recorded temperature every 20 min during summer months. Temperature frequency distribution plots were generated for day and night, above and below 1.1 m (which is proximal to mean tide level for the region). Using the AET₅₀, N. albicilla would need to thermoregulate for a lower percentage of time compared to L. articulata regardless of day and night. It is likely that designing eco-engineering improvements to include microclimate refugia are particularly relevant in tropical areas, where extreme environmental conditions mean that scale-specific actions are important components for climate adaptation.

Urban blue: A global analysis of the factors shaping people's perceptions of the marine environment and ecological engineering in harbours

Marine harbours are the focus of a diverse range of activities and subject to multiple anthropogenically induced pressures. Support for environmental management options aimed at improving degraded harbours depends on understanding the factors which influence people's perceptions of harbour environments. We used an online survey, across 12 harbours, to assess sources of variation people's perceptions of harbour health and ecological engineering. We tested the hypotheses: 1) people living near impacted harbours would consider their environment to be more unhealthy and degraded, be more concerned about the environment and supportive of and willing to pay for ecological engineering relative to those living by less impacted harbours, and 2) people with greater connectedness to the harbour would be more concerned about and have greater perceived knowledge of the environment, and be more supportive of, knowledgeable about and willing to pay for ecological engineering, than those with less connectedness. Across twelve locations, the levels of degradation and modification by artificial structures were lower and the concern and knowledge about the environment and ecological engineering were greater in the six Australasian and American than the six European and Asian harbours surveyed. We found that people's perception of harbours as healthy or degraded, but not their concern for the environment, reflected the degree to which harbours were impacted. There was a positive relationship between the percentage of shoreline modified and the extent of support for and people's willingness to pay indirect costs for ecological engineering. At the individual level, measures of connectedness to the harbour environment were good predictors of concern for and perceived knowledge about the environment but not support for and perceived knowledge about ecological engineering. To make informed decisions, it is important that people are empowered with sufficient knowledge of the environmental issues facing their harbour and ecological engineering options.

Building blue infrastructure: Assessing the key environmental issues and priority areas for ecological engineering initiatives in Australia's metropolitan embayments

Ecological engineering principles are increasingly being applied to develop multifunctional artificial structures or rehabilitated habitats in coastal areas. Ecological engineering initiatives are primarily driven by marine scientists and coastal managers, but often the views of key user groups, which can strongly influence the success of projects, are not considered. We used an online survey and participatory mapping exercise to investigate differences in priority goals, sites and attitudes towards ecological engineering between marine scientists and coastal managers as compared to other stakeholders. The surveys were conducted across three Australian cities that varied in their level of urbanisation and environmental pressures. We tested the hypotheses that, relative to other stakeholders, marine scientists and coastal managers will: 1) be more supportive of ecological engineering; 2) be more likely to agree that enhancement of biodiversity and remediation of pollution are key priorities for ecological engineering; and 3) identify different priority areas and infrastructure or degraded habitats for ecological engineering. We also tested the hypothesis that 4) perceptions of ecological engineering would vary among locations, due to environmental and socio-economic differences. In all three harbours, marine scientists and coastal managers were more supportive of ecological engineering than other users. There was also greater support for ecological engineering in Sydney and Melbourne than Hobart. Most people identified transport infrastructure, in busy transport hubs (i.e. Circular Quay in Sydney, the Port in Melbourne and the Waterfront in Hobart) as priorities for ecological engineering, irrespective of their stakeholder group or location. There were, however, significant differences among locations in what people perceive as the key priorities for ecological engineering (i.e. biodiversity in Sydney and Melbourne vs. pollution in Hobart). Greater consideration of these location-specific differences is essential for effective management of artificial structures and rehabilitated habitats in urban embayments.

Application of management tools to integrate ecological principles with the design of marine infrastructure

Globally the coastal zone is suffering the collateral damage from continuing urban development and construction, expanding resource sectors, increasing population, regulation to river flow, and on-going land change and degradation. While protection of natural coastal habitat is recommended, balancing conservation with human services is now the challenge for managers. Marine infrastructure such as seawalls, marinas and offshore platforms is increasingly used to support and provide services, but has primarily been designed for engineering purposes without consideration of the ecological consequences. Increasingly developments are seeking alternatives to hard engineering and a range of ecological solutions has begun to replace or be incorporated into marine and coastal infrastructure. But too often, hard engineering remains the primary strategy because the tools for managers to implement ecological solutions are either lacking or not supported by policy and stakeholders. Here we outline critical research needs for marine urban development and emerging strategies that seek to mitigate the impacts of marine infrastructure. We present case studies to highlight the strategic direction necessary to support management decisions internationally.