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The effects of manipulating microhabitat size and variability on tropical seawall biodiversity: Field and flume experiments
Abstract
Previous studies have shown that concrete tiles on seawalls that incorporate microhabitat size variability (i.e. complexity) can increase species richness compared to unmodified seawalls. In a recent study, we showed that manipulating complexity at the 4-28. mm scale can have an effect on seawall community composition and that the type of structural component (microhabitats such as pits and grooves) can influence assemblage diversity independently of their complexity. It is not known, however, whether these effects will be exhibited at a larger scale; in other words, will the positive relationship be present if the size range of components on concrete tiles is enlarged (8-56. mm). Therefore, in the present study, we examine: (1) the effects of changing the scale of structural manipulation on species richness and, (2) the hydrodynamic properties (i.e. velocity of flow over the whole tile) of different designs. We doubled the size of all x, y and z dimensions to create 400. ×. 400. ×. 64. mm concrete tiles (up from 200. ×. 200. ×. 32 mm in the previous study) with two different basic designs: 'Pits' and 'Grooves'. These were deployed for one year at two island sites off Singapore's mainland along with 'Granite control' tiles so that we could assess what the existing seawall would host within the same timeframe. Results showed that the 'complex' tiles supported greater richness (S) than 'simple' ones, suggesting that the size range tested here (8-56. mm) is relevant to tropical intertidal communities. Flume experiments revealed similar wave amplitude values over the surfaces of all tile types, including the granite controls, suggesting that intertidal organisms are unlikely to colonise the tiles differentially as a result of cm-scale hydrodynamic differences, i.e. the dominant mechanism underlying this 'complexity-diversity' relationship is unlikely to be due to differences in flow velocities over a 400. ×. 400 mm tile surface but, rather, is related to resource (e.g. refuge) availability. These results help identify the "scale of effect" of topographic complexity which can be directly integrated into ecological engineering designs to increase biodiversity on tropical seawalls.
... This human pressure has led to massive shoreline changes, especially near coastal cities [3]. Natural intertidal habitats have been extensively replaced with hard amour such as seawalls to curb land erosion and combat threats arising from climate change (i.e., the impending rise of sea levels and increased frequency of floods and storms [4][5][6][7][8]). These artificial structures often support lower biodiversity and different community assemblages due to novel substrate materials, altered hydrodynamics, and reduced habitat complexity [5,7,9,10]. ...
... Natural intertidal habitats have been extensively replaced with hard amour such as seawalls to curb land erosion and combat threats arising from climate change (i.e., the impending rise of sea levels and increased frequency of floods and storms [4][5][6][7][8]). These artificial structures often support lower biodiversity and different community assemblages due to novel substrate materials, altered hydrodynamics, and reduced habitat complexity [5,7,9,10]. ...
... There is substantial potential to increase the ecological value to seawalls and other marine infrastructure (ocean sprawl) to mitigate the loss of coastal communities [11]. To achieve this, several studies have added enhancements such as crevices and pools to existing seawalls (see review in [5]) to create refuges for organisms and encourage resource partitioning [12,13] with the goal of boosting species richness [7,14]. In the tropics, some researchers have also attempted to increase biodiversity on seawalls by transplanting corals directly onto them [15,16]. ...
There is a growing interest in transplanting corals onto the intertidal section of artificial coastal defences (e.g., seawalls) as an ecological engineering strategy to enhance biodiversity on urban shores. However, this inevitably results in exposure to the harsh environmental conditions associated with emersion (aerial exposure). Although the effects of a multitude of environmental stressors on corals have been examined, their photophysiological and gene expression responses to emersion stress remain understudied, as does the among-genotype variation in these responses. In this study, we conducted an in situ experiment to test the effects of increased daily emersion duration on a locally common intertidal coral, Dipsastraea cf. lizardensis. Coral fragments (n = 3) from five genotypically distinct colonies were subjected to two treatments: (1) increased daily emersion duration (~4.5 h d −1) and, (2) control (~3 h d −1) for three consecutive days during spring low tide. We examined the post-experimental photophysiological responses and expression level of a stress-associated gene, Hsp16. Relative to the controls, coral fragments that were exposed to longer daily emersion duration displayed significantly reduced effective quantum yield, while endosymbiont density varied significantly among genotypes across the experimental conditions. We found no significant differences in chlorophyll a concentration and Hsp16 gene expression level, suggesting that changes in these processes may be gradual and the duration of treatment that the corals were subjected to is likely within their tolerance limits. Taken together, it appears that D. cf. lizardensis displays substantial capacity to cope with sup-optimal conditions associated with emersion which makes it a promising candidate for transplantation onto intertidal seawalls. However, within-species variation in their stress response indicates that not all genotypes respond similarly to emersion, and this should be taken into account when selecting donor colonies for transplantation.
... Alternatively, tridimensional complex habitats always present a concomitant addition of area for recruitment, in a way that the increased diversity could also be a sampling effect. Loke and Todd (2016), Loke et al. (2017) are the only studies that controlled the area available for community development when comparing artificial habitats with distinct complexities. ...
... ,Loke et al. (2017).However, the increased complexity did not affect the species richness as also demonstrated byChee et al. (2021) andO'Shaughnessy et al. (2021), highlighting the risk of extrapolating positive effect of habitat complexity on biodiversity outside the context in which it was tested(O'Shaughnessy et al., 2021). Our results also suggest that the increase in the area associated with more complex habitats can account for part of the species richness changes in other studies rather than habitat complexity. ...
Marine urbanization promotes the addition of hard substrata that barely resembles natural substrate nearby. We manipulated habitat topography in five marinas across one of the most populated regions from the Southwestern Atlantic Ocean to describe the effect of habitat complexity on the diversity of benthic communities across sites with distinct conditions and biotas. The highest biomass was found in the two marinas under high pollution and freshwater disturbances, regardless of habitat complexity. Habitat topography did not affect species richness but determined the structure of sessile communities in all marinas. The structure of mobile communities was affected only in the most diverse site, increasing the abundance of isopods. In general, fragile ascidians, hydrozoans, and non‐calcified polychaetes dominated complex habitats, while structurally defended animals such as barnacles, serpulids, and encrusting bryozoans dominated simple habitats, suggesting that dominant species are selected by habitat complexity based on their morphological traits. However, the final community structure was also determined by differences across marinas, suggesting that the effect of increasing habitat topography is mostly site‐specific. Therefore, strategies to minimize the disparity between natural and artificial habitats must consider historic local community and a multiple stressors scenario.
... However, ecological engineering techniques applied to seawalls have generally targeted the physical (topographical) differences between natural rocky shores and artificial structures. Therefore, hab itat enhancement units tend to focus on manipulating the surface complexity of substrates to incorporate water-retaining features and/or increase structural complexity, via the creation of cavities and the retrofitting of tiles with varying surface topography (Firth et al. 2013, Loke et al. 2017, Strain et al. 2018. Nevertheless, even with ecological engineering ef forts, concrete is often used, as it fulfils industry building and construction safety standards and is easi ly moulded into various shapes and designs (Walt ham & Dafforn 2018). ...
... After algal removal from the smooth surface, the tiles were placed into the freezer (−20°C) for subsequent sorting, counting, and identification using a dissecting microscope. All specimens were identified to species or morphospecies level except for polychaetes, which were identified to family level , Loke et al. 2017, 2019a. ...
Concrete is one of the most commonly used materials in the construction of coastal and marine infrastructure despite the well known environmental impacts which include a high carbon footprint and high alkalinity (~pH 13). There is an ongoing discussion regarding the potential positive effects of lowered concrete pH on benthic biodiversity, but this has not been investigated rigorously. Here, we designed a manipulative field experiment to test whether carbonated (lowered pH) concrete substrates support greater species richness and abundance, and/or alter community composition, in both temperate and tropical intertidal habitats. We constructed 192 experimental concrete tiles, half of which were carbonated to a lower surface pH of 7-8 (vs. control pH of >9), and affixed them to seawalls in the United Kingdom and Singapore. There were 2 sites per country, and 6 replicate tiles of each treatment were collected at 4 time points over a year. Overall, we found no significant effect of lowered pH on the abundance, richness, or community assemblage in both countries. Separate site- and month-specific generalised linear models (GLMs) showed only sporadic effects: i.e. lowered pH tiles had a small positive effect on early benthic colonisation in the tropics but this was later succeeded by similar species assemblages regardless of treatment. Thus, while it is worth considering the modification of concrete from an environmental/emissions standpoint, lowered pH may not be a suitable technique for enhancing biodiversity in the marine built environment.
... A variety of approaches have been applied experimentally and with varying degrees of success (see Table 26.2): for instance, by recreating natural shore elements such as pits and crevices on seawalls (e.g., Borsje et al., 2011;Loke, Liao, Bouma, & Todd, 2016;Loke, Bouma, & Todd, 2017;Martins, Thompson, Neto, Hawkins, & Jenkins, 2010;Moreira et al., 2007); by comparing different materials and textures (e.g., Burt, Bartholomew, Bauman, Saif, & Sale, 2009;Coombes, La Marca, Naylor, & Thompson, 2015;Morris, Golding, Dafforn, & Coleman, 2017;Moschella et al., 2005); and by adding artificial tide pools, for example, attaching flowerpots (Browne & Chapman, 2011) or removing stone blocks to create cavities ). These approaches generally increase small-scale habitat complexity and enhance intertidal biodiversity by facilitating larval settlement or providing organisms refugia from predation and abiotic stressors (Chapman & Underwood, 2011). ...
... At local scales, applied research would benefit from continuing to focus on identifying and enhancing the factors limiting the diversity of life on artificial structures (e.g., moisture retention, thermal stress risk, components of habitat complexity). Low primary productivity and nutrient availability due to lack of water retention and thermal stress, especially on upper shores, are possible explanations for the low trophic complexity and species diversity often observed in these habitats (2016), Loke et al. (2017) Attachment of precast flowerpots to seawalls Chapman (2011, 2014) Drilling pits and deeper rock pools into rock armor Martins et al. (2010), Evans et al. (2016) Deployment of precast concrete units to replace boulder in intertidal rock armor Firth, Thompson, et al. (2014), Sella and Perkol-Finkel (2015) Removing blocks from seawalls to create cavities resembling tidal pools Texturing the surface of concrete Coombes et al. (2015) Altering substrate material Use of "ECOncrete,", that is, a concrete mix with lower pH (~9.0-10.5) Sella and Perkol-Finkel (2015), Perkol-Finkel, Hadary, Rella, Shirazi, and Sella (2017) Use of "Reefcrete,", that is, a concrete mix with the partial replacement of regular Portland cement with recycled ground granulated blast-furnace slag (GGBS) and coarse aggregate with recycled shell material and hemp fibers Dennis, Evans, Banner, and Moore (2017) Addition of artificial turfs (or coir) within flowerpots Morris et al. (2017) Altering the surface chemistry of the substrate Rivera-Ingraham, Espinosa, and García-Gómez (2011) Changing the slope of seawalls Adding blocks of stone to create a stepped wall See Chapman and Underwood (2011) Transplantation Transplanting corals and sponges Ng et al. (2015) Transplanting kelp Marzinelli, Zagal, Chapman, and Underwood (2009) Transplanting other algae Susini, Mangialajo, Thibaut, and Meinesz (2007), Perkol-Finkel, Ferrario, Nicotera, and Airoldi (2012) Adding soft engineering to hard defenses ("hybrid" approach) ...
... Roughness, complexity and heterogeneity of concrete surfaces, through the inclusion of a varied size of crack pits, holes, grooves and crevices (at the mm-cm scale) (Figure 1), are the main factors considered to provide ecological niches close to natural conditions for a variety of marine species (Hall et al., 2018). Examples of such enhancement mechanisms are the creation of holes (10 cm wide, 3 cm deep) and crevices (0.5-1 cm wide) on Antifer armor units (Sella and Perkol-Finkel, 2015), the modification of complexity at the 4-28 mm scale to create microhabitats on tropical seawalls (Loke et al., 2017) or the multiscale design called BioGeo Ecotile (Kosová et al., 2023) that combines all the physical features (pits, holes, grooves and crevices). In the last decade, some studies have shown interest in analyzing the influence of the chemical composition of concrete to enhance colonization. ...
In the last two decades, Eco-engineering has emerged to mitigate and compensate the environmental impacts of man-made structures while integrates benefits to society, being concrete the most widely alternative material used to natural rocks for construction of artificial coastal structures. Over the past three decades, an extensive literature has documented different supplementary cementitious materials (SCMs) to reduce CO2 emissions from Portland cement, with common SCMs used in marine and coastal structures such as fly ashes, ground granulated blast furnace slags, pozzolanas and limestones. However, there is a need to further investigate the suitability of SCMs for the construction of Low-Crested Structures (LCS) to decrease carbon footprint from concrete production and improve the bioreceptivity of concrete armor units during the breakwater lifetime. A literature review conducted in this study shows several advantages of slag cements compared to other SCMs to reduce carbon emissions and enhance biological colonization and durability of concrete submerged in seawater, identifying surface roughness as the most effective factor in design of bioreceptive concrete. This study also highlights the importance of the type and quantity of cement used in concrete mixes to reduce carbon footprint of the manufacture of concrete armor units of LCS and the implementation of long-term monitoring plans to fully understand the functioning of local communities that develop on concrete surfaces of artificial structures, and thus, to improve the integration of environmental parameters in the field of coastal engineering.
... In recent years, diverse casting methods have been applied to create habitat enhancement models for marine ecosystems. These methods encompass a wide array of techniques including the use of steel or iron moulds (Coombes et al., 2015), silicone rubber moulds (Evans et al., 2021;Loke et al., 2017), the innovative practice of moulding concrete between boulders to form habitat-enhancing pools (Firth et al., 2016;Hall et al., 2018), and the application of 3D printed moulds (Vozzo et al., 2021). Molds, crafted from diverse materials, play a pivotal role in retaining freshly poured concrete in its intended form until it achieves the required strength for demoulding (Levitt,1982). ...
Poor quality habitat profiles of artificial coastal structures for biodiversity growth compared to natural shore have led researchers to utilize ecological engineering principles in creating habitat enhancement models mimicking the natural environment to help improve living conditions for marine organisms. Extensive global trials have been conducted with concrete formulations incorporating eco-friendly materials and recycled resources. However, eco-concrete production for marine environment use is still lacking in Malaysia. The technology involved in casting, moulding, and demoulding remains at the experimental stage, with unreported comparisons of different moulding materials used for casting geometrically complex habitat enhancement models. This study evaluated different casting, moulding, and demoulding techniques using locally produced eco-concrete. The main aim of this study is to determine the effect of different materials including plaster of Paris, drilling wood, expanded polystyrene, rubber foam, and vacuum forming on the mould production time, labour requirements and fabrication factors. Vacuum forming mould is highly preferred for its quick production time, less work, design uniformity, and ability to cast larger habitat enhancement models. However, the demoulding methods require improvements and further experimentation to ensure an easier demoulding process and reusability of the mould for long-term production.
... In addition to mitigating environmental fluctuations, rock pools offer microhabitats characterised by variations in light exposure, slope, and sedimentation process (Waltham and Sheaves 2018). These components support diverse communities and enhance species diversity (Aguilera et al. 2014;Loke et al. 2017;Strain et al. 2018) by reducing environmental stress levels, providing distinct resources, reducing competition for space (Seabra et al. 2011;Manna et al. 2017;Schaefer et al. 2023b), and enhancing survival (White and Brown 2015). Furthermore, pools with diverse depths, size, and shoreline heights will add a spectrum of habitats. ...
Context
Driven by growing human populations and climate change-mitigation concerns, artificial coastal structures have become crucial for meeting population needs. However, these structures differ from natural counterparts and can reduce biodiversity and species abundance.
Aims
This study aimed to use rock pools as an eco-engineering approach to mitigate these negative effects and enhance species diversity on coastal infrastructure.
Methods
We incorporated rock pools of two different sizes into three distinct intertidal levels within a concrete-block breakwater at the Strait of Hormuz, Persian Gulf, and conducted an in situ assessment of the biota in rock pools and their adjacent emergent surfaces.
Key results
In total, 17 taxa were identified. The findings showed a five-fold increase in cumulative species number and a 30% rise in abundance owing to the presence of rock pools. PERMANOVA results indicated that rock pool size, intertidal levels, and their interaction, significantly influenced species richness.
Conclusions
Our investigation underscores the effectiveness of integrating rock pools as an ecological engineering approach to enrich species diversity on human-made structures within intertidal zones.
Implications
The selection of rock pool dimensions and tidal positioning should be thoughtfully determined, considering the prevailing environmental conditions and the project’s objectives.
... In recent years, diverse casting methods have been applied to create habitat enhancement models for marine ecosystems. These methods encompass a wide array of techniques including the use of steel or iron moulds (Coombes et al., 2015), silicone rubber moulds (Evans et al., 2021;Loke et al., 2017), the innovative practice of moulding concrete between boulders to form habitat-enhancing pools (Firth et al., 2016;Hall et al., 2018), and the application of 3D printed moulds (Vozzo et al., 2021). Molds, crafted from diverse materials, play a pivotal role in retaining freshly poured concrete in its intended form until it achieves the required strength for demoulding (Levitt,1982). ...
Poor quality habitat profiles of artificial coastal structures for biodiversity growth compared to natural shore have led researchers to utilize ecological engineering principles in creating habitat enhancement models mimicking the natural environment to help improve living conditions for marine organisms. Extensive global trials have been conducted with concrete formulations incorporating eco-friendly materials and recycled resources. However, eco-concrete production for marine environment use is still lacking in Malaysia. The technology involved in casting, moulding, and demoulding remains at the experimental stage, with unreported comparisons of different moulding materials used for casting geometrically complex habitat enhancement models. This study evaluated different casting, moulding, and demoulding techniques using locally produced eco-concrete. The main aim of this study is to determine the effect of different materials including plaster of Paris, drilling wood, expanded polystyrene, rubber foam, and vacuum forming on the mould production time, labour requirements and fabrication factors. Vacuum forming mould is highly preferred for its quick production time, less work, design uniformity, and ability to cast larger habitat enhancement models. However, the demoulding methods require improvements and further experimentation to ensure an easier demoulding process and reusability of the mould for long-term production.
... This approach is advantageous as it allows us to standardize habitat area and niche diversity across all replicates. Only one tile design was used and it comprised two microhabitat component types relevant to intertidal organisms: square pits and grooves 25,26,64 . These structural components varied in their sizes and depths from 0.01 m to 0.04 m; specifically, pits were first positioned randomly on the tile, after which we overlaid the remaining unoccupied space with grooves using a Truchet tiling algorithm. ...
A central goal in ecology is to understand what maintains species diversity in local communities. Classic ecological theory1,2 posits that niches dictate the maximum number of species that can coexist in a community and that the richness of observed species will be below this maximum only where immigration is very low. A new alternative theory3,4 is that niches, instead, dictate the minimum number of coexisting species and that the richness of observed species will usually be well above this because of ongoing immigration. We conducted an experimental test to discriminate between these two unified theories using a manipulative field experiment with tropical intertidal communities. We found, consistent with the new theory, that the relationship of species richness to immigration rate stabilized at a low value at low immigration rates and did not saturate at high immigration rates. Our results suggest that tropical intertidal communities have low niche diversity and are typically in a dispersal-assembled regime where immigration is high enough to overfill the niches. Observational data from other studies3,5 suggest that these conclusions may generalize to other ecological systems. Our new experimental approach can be adapted for other systems and be used as a ‘niche detector’ and a tool for assessing when communities are niche versus dispersal assembled.
... Whereas previous studies, at biodiverse sites, have found strong effects of habitat complexity on the community structure of macrobiota at a mid-intertidal elevation (e.g. Loke et al. 2017, there was no effect in this study of complexity on either the community structure of biofilms or macrobiota, at the mid-intertidal height. This may reflect the relatively contaminated environment in which the tiles were deployed and the small local species pool on which complexity could act. ...
Marine artificial structures often support lower native species diversity and more non-indigenous species (NIS), but adding complex habitat and using bioreceptive materials have the potential to mitigate these impacts. Here, the interacting effects of structural complexity (flat, complex with pits) and concrete mixture (standard, or with oyster shell or vermiculite aggregate) on recruitment were assessed at two intertidal levels at an urban site. Complex tiles had less green algal cover, oyster shell mixtures had less brown (Ralfsia sp.) algal cover. At a low tidal elevation, the non-indigenous ascidian Styela plicata dominated complex tiles. Additionally, mixtures with oyster shell supported higher total cover of sessile species, and a higher cover of S. plicata. There were no effects of complexity or mixture on biofilm communities and native and NIS richness. Overall, these results suggest that habitat complexity and some bioreceptive materials may facilitate colonisation by a dominant invertebrate invader on artificial structures.
... Informational complexity largely overlaps with the concept of 'heterogeneity' in ecology. For example, Loke et al. (2017) manipulated complexity by varying the size range (widths and depths) of different microhabitat elements (pits and grooves) within a given planar surface while standardising for area, and Cardinale et al. (2002) manipulated benthic stream substrate heterogeneity by altering the range of particle sizes while holding the median size constant. ...
Habitat complexity has been considered a key driver of biodiversity and other ecological phenomena for nearly a century. However, there is still no consensus over the definition of complexity or how to measure it. Up‐to‐date and clear guidance on measuring complexity is urgently needed, particularly given the rise of remote sensing and advent of technologies that allow environments to be scanned at unprecedented spatial extents and resolutions. Here we review how complexity is measured in ecology. We provide a framework for metrics of habitat complexity, and for the related concept of spatial heterogeneity. We focus on the two most commonly used complexity metrics in ecology: fractal dimension and rugosity. We discuss the pros and cons of these metrics using practical examples from our own empirical data and from simulations. Fractal dimension is particularly widely used, and we provide a critical examination of it drawing on research from other scientific fields. We also discuss informational metrics of complexity and their potential benefits. We chart a path forward for research on measuring habitat complexity by presenting, as a guide, sets of essential and desirable criteria that a metric of complexity should possess. Lastly, we discuss the applied significance of our review.
... As has been argued elsewhere (e.g. Loke et al., 2017;Loke et al., 2019b), increasing overall habitat complexity by adding a variety of microhabitats, that may include all of the suggestions above, is likely to provide shelter for the greatest range of species and is a potential approach to enabling intertidal ectotherms to persist on tropical, artificially-hardened, intertidal shores. ...
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 refugia. 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 function. Accordingly, to facilitate motile species to maintain broad thermal safety margins through behavioural regulation, the provision of additional refugia from thermal stress is recommended on artificial coastal defences such as seawalls.
... Consequently, there has been significant effort to increase biodiversity and habitat availability via eco-engineering (Firth et al., 2014;Strain et al., 2017;O'Shaughnessy et al., 2019), where habitat is integrated into ACSs (Bergen et al., 2001;Mitsch and Jorgensen, 2003;Odum and Odum, 2003). The predominant aims of eco-engineering on ACSs thus far have been to increase topographical and structural complexity (MacArthur et al., 2019), either via texture (Coombes et al., 2015) or through the creation of microhabitats (Martins et al., 2010(Martins et al., , 2016Loke et al., 2017), and moisture retentive features, such as drill-cored tide pools and retrofitted artificial rockpools (Browne and Chapman, 2014;Hall et al., 2019;Chee et al., 2020). ...
Artificial coastal structures (ACSs) are primarily designed to provide services for human use, such as flood defence or shipping, and are generally poor for marine biodiversity. Consequently, there has been significant research effort to enhance these hard structures to increase biodiversity and habitat availability via eco-engineering. On seawalls and breakwaters, this has included the creation of habitats for benthic species found on natural rocky shores, including the provision of cracks, crevices and water retaining features, such as artificial rockpools. When sediment retention in these features has occurred, it has often been deemed detrimental to the overarching aim of the intervention. Yet, it is soft sediment habitat that is impacted the most through coastal construction. As ecological enhancement of a flood defence scheme, nine concrete retrofit rockpools were installed at three different tidal elevations between mean high water neap tide and mean tide level on steel sheet piling on the Arun Estuary in Littlehampton Harbour, United Kingdom, which naturally filled with mud 1 year after installation. To explore how analogous the faunal assemblages and sediment profile of rockpool mud were to two local mudflats, core samples were taken and analysed for species richness, abundance, biomass, assemblage structure, median grain size, and organic matter content. More benthic species were observed in the artificial rockpool than in the local mudflats. Although the rockpools were placed at higher tidal levels than the lower shore mudflat, their assemblage structure and species richness were more similar to the lower shore mudflat at the base of the sheet piling than the upper shore mudflat. This study demonstrates that retained sediment within eco-engineered features on hard ACSs can create habitat for benthic assemblages. Providing sediment-retentive features on ACSs has the potential to provide a novel eco-engineering option that may be appropriate for some heavily modified waterbodies on sheltered, depositional coasts.
... Seawalls are often more exposed and dissipate wave action less efficiently than boulder habitats, promoting the preferential establishment of certain taxa, such as filter feeding organisms (Sedano et al., 2020a), contributing also to the homogenization of intertidal communities . For these reasons, seawalls are one of the least ecologically valuable artificial structures, which has attracted the attention of researchers who look for mitigation measures in the framework of eco-engineering (Browne and Chapman, 2011;Loke et al., 2017;Moreira et al., 2007). ...
Intertidal ecosystems are key habitats that are being replaced by artificial hard substrates due to the increment of human activities in coastal areas. These new substrates host generally less biodiversity mainly due to differences in complexity and composition. It is a global phenomenon and has led to the development of strategies in the framework of eco-engineering. However, mitigating measures, such as new eco-designs, must cope with the high spatial variability of the region where they are applied. Therefore, in order to assess if differences in biodiversity detected at local scales in previous studies could be scaled up to predict patterns at a wider scale, we studied taxa richness and taxonomic structure of intertidal communities across the Alboran Sea (western Mediterranean Sea). We compared four different types of artificial substrates (cubes, rip-raps, seawalls and tetrapods) to assess which produces less impact. Overall, artificial substrates host low benthic biodiversity, specially on seawalls, whereas boulder-like artificial structures such as rip-raps were more similar to natural ones. Nevertheless, the effect of a particular type of artificial structure at a regional scale seems unpredictable, highlighting the challenge that eco-engineering measures face in order to establish global protocols for biodiversity enhancement and the importance of local scale in management programmes.
... Turbine foundations and SPL could be intentionally designed to be more diverse and complex (i.e., nature-inclusive designs) by providing different spacing, hiding places, feeding places, types of stone, characteristics of concrete, and other characteristics. Topographical habitat complexity drives biodiversity (Liversage et al. 2017, Loke et al. 2017 can be added to surfaces (e.g., addition of large boulders to a regular scour protection layer), which may be desirable as natural hard substrates are often more diverse than artificial ones. ...
This report is one outcome from a broader effort to review the state of knowledge regarding offshore wind energy development's effects on wildlife and identify short-term research priorities to improve our understanding of cumulative biological impacts as the offshore wind industry develops in the eastern United States. This effort, titled State of the Science Workshop on Wildlife and Offshore Wind Energy 2020: Cumulative Impacts, included a week of plenary presentation sessions and contributed talks in November 2020, as well as the formation of six other workgroups similar to the benthos workgroup that met over the winter of 2020-2021. This report, and those from the six other workgroups, are available on the workshop website at http://www.nyetwg.com/2020-workgroups.
... budgets, as the name implies, quantitatively track heat inputs, outputs and stores and when coupled with information on material properties provide estimates of temperature (Porter and Gates, 1969). But, while an increasing number of studies have begun to experimentally explore the role of surface orientation, complexity and construction material on patterns of biodiversity on artificial surfaces (Chapman, 2003;Perkol-Finkel and Sella, 2014;Loke et al., 2015Loke et al., , 2017Lavender et al., 2017;Aguilera et al., 2019), heat budget models have yet to be applied to these questions. This study uses a heat budget modelling approach to estimate the role of surface orientation and material properties as potential drivers of intertidal temperature conditions and their potential relationship to biodiversity patterns on bulkheads in urban intertidal zones. ...
Ecological engineering approaches have been shown to enhance the abundance and species diversity of intertidal organisms living on urban shoreline infrastructure (i.e., bulkheads and seawalls). Ecological studies have long shown the overarching importance of temperature in driving the physiology and survival of these organisms, yet we often do not fully understand what these temperatures are on engineered surfaces, as they can be very different from air or water temperature. The current study used a heat budget model to estimate surface temperature on bulkheads of different construction materials and surface orientations as a potential factor controlling the abundance and distribution of algal and invertebrate species living on armored shorelines. A Land Surface Model previously adapted for mussel beds was modified to incorporate the physical and thermal properties of three construction materials commonly used in shoreline armoring: concrete, granite and steel. Hourly temperature, tide and solar elevation data for Boston, MA, USA were used to simulate temperatures on a total of twelve model surfaces representing each construction material with north, east, south, and west surface orientations, respectively, over a period of 5 years (2014–2018). A rapid species assessment of intertidal epibiota on bulkheads in Boston Harbor provided baseline data about ecological communities that might be targeted in enhancement efforts, and information on physiological sensitivities of key species was determined from published literature. Comparisons between these sensitivities and exposures estimated from the model showed that simulated surface temperatures can exceed the physiological limits of local species but that this depends on surface orientation and material properties of the structure. Results further highlight the influence of material properties (density, specific heat capacity and thermal conductivity) of engineered structures on the incidence and severity of thermal extremes when exposed to direct solar radiation at low tide. Significant differences in the duration and intensity of high temperature values among model surfaces demonstrate that the potential effectiveness of choices in bulkhead construction materials designed to mitigate thermal extremes are likely most effective on south- and west-facing surfaces where incident solar radiation is highest. The ability to predict thermal extremes on existing or planned coastal development projects can improve and further refine ecological enhancement initiatives on shoreline infrastructure. Such collaborations would enable coastal zone managers, shorefront property owners, ecologists, and designers to co-design structures that create physiologically tolerable temperatures as a basis for ecological enhancement.
... However, these artificial structures are poor surrogates of natural ecosystems and are unable to provide suitable habitat for much of the displaced marine biota (Bulleri and Chapman, 2010;Chapman and Underwood, 2011;Lai et al., 2015Lai et al., , 2018. Physical attributes of seawalls, such as their steep slope that compresses the area of the intertidal zone, and lack of complex features that reduces water retention, limit the number of species that can be supported (Chapman, 2003;Loke et al., 2017). As seawalls are proliferating worldwide, there is a growing effort to boost their capacity to host biodiversity via ecological engineering (Chapman and Blockey, 2009;Chapman and Underwood, 2011;Morris et al., 2018;Todd et al., 2019). ...
Stony corals are promising transplant candidates for the ecological engineering of artificial coastal defences such as seawalls as they attract and host numerous other organisms. However, seawalls are exposed to a wide range of environmental stressors associated with periods of emersion during low tide such as desiccation and changes in salinity, temperature, and solar irradiance. All of these variables have known deleterious effects on coral physiology, growth, and fitness. In this study, we performed parallel experiments (in situ and ex situ) to examine among-genotype responses of Pocillopora acuta to emersion by quantifying growth, photophysiological metrics (Fv/Fm, non-photochemical quenching [NPQ], endosymbiont density, and chlorophyll [chl] a concentration) and survival, following different emersion periods. Results showed that coral fragments emersed for longer durations (> 2 h) exhibited reduced growth and survival. Endosymbiont density and NPQ, but not Fv/Fm and chl a concentration, varied significantly among genotypes across different durations of emersion. Overall, the ability of P. acuta to tolerate emersion for up to two hours indicates it has potential to serve as a ‘starter species’ for transplantation efforts on seawalls. Further, careful characterisation and selection of genotypes with a high capacity to withstand emersion can help maximise the efficacy of ecological engineering using coral transplants.
... High within-treatment variability among benthic assemblages on boulders might also be the reason why significant differences in rugosity only explained a small portion of the differences in assemblages. A high degree of habitat complexity, such as the presence of interstices and rough surfaces has been shown to enhance diversity (Loke et al. 2017, Hanlon et al. 2018. Thick layers of small rocky structures, such as in our study, can create shaded interstices, which can support a diverse community by providing favourable environmental conditions and shelter (Choi & Ginsburg 1983, Takada 1999, Liversage et al. 2017). ...
Existing coastal breakwaters are ageing and will need to be upgraded to withstand additional forces associated with rising sea levels and storms. Structural upgrades can affect taxa living on or adjacent to breakwaters. These impacts can be mitigated by ecological engineering of breakwaters, which can enhance habitat quality without losing their primary purpose of protection. A recently upgraded breakwater at Coffs Harbour, NSW, Australia was eco-engineered to use boulder fields to mitigate impacts on a critically endangered alga (Nereia lophocladia) living on and adjacent to the infrastructure. Over a year, we assessed the effect of different rock sizes (small versus large), types (greywacke versus granite) and orientations (top versus bottom) on the composition and diversity of benthic taxa. N. lophocladia has yet to recruit to the eco-engineered habitat; however, we found rock size, type and orientation significantly influenced overall benthic assemblage composition, at least at one of the sites. Furthermore, the bottom of the rocks had a higher taxonomic diversity than the top side, and assemblages on native greywacke rocks were
more diverse than those on granite, but only at one of the two sites. Overall, the magnitude of differences in benthic assemblage structure and diversity showed substantial temporal and spatial variation, with no clear temporal trends or successional patterns. Our results indicate that the ecological outcomes of coastal protection infrastructure upgrades could be improved by including native rocks of a range of different sizes in multiple patches and layers.
... While recent studies have suggested that urbanised sites with artificial surfaces might provide new niches and function as 'marine stepping-stones' that aid in population connectivity [69], such surfaces provide new environments for all species, native species and non-native invasive species alike [109]. Artificial surfaces such as seawalls that are ubiquitous along Singapore's coastline, could aid the colonisation and serve to connect populations for marine organisms like molluscs [110], crustaceans, polychaetes [111] and hard corals [57,112]. Seawalls serving as a 'stepping-stone' remains to be tested for sea anemone species that naturally prefer coral-dominated or sandy substrates, and not hard surfaces like seawalls [79]. ...
Sea anemones are sedentary marine animals that tend to disperse via planktonic larvae and are predicted to have high population connectivity in undisturbed habitats. We test whether two sea anemone species living in two different tidal zones of a highly disturbed marine environment can maintain high genetic connectivity. More than 1000 loci with single-nucleotide polymorphisms (SNPs) were obtained with double-digest RADseq for 81 Stichodactyla haddoni and 99 Entacmaea quadricolor individuals to test for population genetic structure. We find evidence that both species predominantly propagate via sexual reproduction, and asexual reproduction is limited. We observe panmixia that indicates the absence of effective dispersal barriers for these species living in a highly anthropogenically disturbed environment. This is positive news for both species that are also found in the aquarium trade. More fundamentally, our results suggest that inhabiting different parts of a shallow reef may not affect a species' population connectivity nor favour asexual reproduction.
... A common technique is to add physical features that increase habitat structural complexity (e.g. Coombes et al. 2015, Loke et al. 2017, Strain et al. 2018b). Since the functional relationship between organisms and their environment is allometric (contingent on body size) (Hixon & Beets 1993, Ménard et al. 2012, Nash et al. 2013, the effectiveness of these features depends on their size relative to the size of organisms they are intended to accommodate. ...
Retrofitting microhabitat features is a common ecological engineering technique for enhancing biodiversity and abundance of small, epilithic organisms on artificial shorelines by providing refuge spaces and/or ameliorating abiotic conditions. These features are typically too small to be utilised as refugia by larger, highly motile consumers such as fish, but they may affect these organisms through other mechanisms. This study sought to determine whether microhabitat enhancement units alter the fish abundance, richness and assemblage composition on tropical seawalls and explores possible underlying trophic mechanisms. We created 12 experimental plots consisting of 6 enhanced plots, each with 20 microhabitat enhancement tiles, and 6 control plots without tiles on intertidal seawalls at Pulau Hantu, an offshore island south of mainland Singapore. Benthic cover and fish assemblage were surveyed within each plot using photoquadrats and underwater video cameras, respectively, from April 2018 to February 2019. We found greater abundance and species richness and distinct assemblages of fish in the enhanced plots compared to the control plots. These differences were driven largely by an increase in both abundance and richness of fish species with epibenthic-feeding strategies and were significantly associated with higher biotic cover in the enhanced plots, especially epilithic algal matrix (EAM). Our results indicate that, in addition to facilitating epilithic organisms, microhabitat enhancement can provide food resources for epibenthic-feeding fishes, increase fish biodiversity, and alter fish assemblages in tropical urbanised shorelines.
... Ecological engineering was first formally defined as "the design of sustainable ecosystems that integrate human society with its natural environment for the benefit of both" (Mitsch, 2012). Since its inception, ecological engineering has come to encompass approaches such as replacing traditional built infrastructure with newly created or restored coastal ecosystems such as mangroves or salt marshes (Temmerman et al., 2013), or designing new or altering old infrastructure to add structural complexity to promote settlement of marine organisms (Martins et al., 2010;Loke et al., 2017) and reduce settlement of non-indigenous species (e.g., Dafforn, 2017). These same principles could be applied to seagrass restoration, following studies to elucidate conditions where settlement and/or colonization can be promoted. ...
Seagrasses are important marine ecosystems situated throughout the world’s coastlines. They are facing declines around the world due to global and local threats such as rising ocean temperatures, coastal development and pollution from sewage outfalls and agriculture. Efforts have been made to reduce seagrass loss through reducing local and regional stressors, and through active restoration. Seagrass restoration is a rapidly maturing discipline, but improved restoration practices are needed to enhance the success of future programs. Major gaps in knowledge remain, however, prior research efforts have provided valuable insights into factors influencing the outcomes of restoration and there are now several examples of successful large-scale restoration programs. A variety of tools and techniques have recently been developed that will improve the efficiency, cost effectiveness, and scalability of restoration programs. This review describes several restoration successes in Australia and New Zealand, with a focus on emerging techniques for restoration, key considerations for future programs, and highlights the benefits of increased collaboration, Traditional Owner (First Nation) and stakeholder engagement. Combined, these lessons and emerging approaches show that seagrass restoration is possible, and efforts should be directed at upscaling seagrass restoration into the future. This is critical for the future conservation of this important ecosystem and the ecological and coastal communities they support.
... This usually favours natural habitats compared with the featureless surfaces of coastal defence structures. In addition, higher roughness at the scale of centimetres could improve larvae and spore recruitment (Koehl, 2007;Sempere-Valverde et al., 2018) and increase refuge availability against predators (Loke et al., 2017;Strain et al., 2018a). Despite this, it is known that some species (e.g. ...
The increasing deployment of artificial structures into the marine environment is creating new hard substrates that differ from natural ones in physical and biological aspects. However, studies of macrofaunal and meiofau-nal communities associated with artificial structures are very limited. Seawalls, cubes, acropods and rip-raps in Algeciras Bay (southern Spain) were each compared with the nearest natural hard substrate and their community structure was related to substrate roughness, composition, carbonates content, crystallinity and age, using db-RDA. The results showed clear differences between substrates for the three community levels (sessile, macro-and meiofauna). Overall, rip-raps were the most similar to natural substrates. Under similar environmental conditions , substrate roughness, composition (only for sessile) and age of the structures seemed to play important roles in structuring those communities. They especially affected the sessile community, initiating strong cascading effects that were detectable at high taxonomic level in the associated fauna.
... In agreement with our results, a previous experiment focused on ecological engineering revealed the positive response of mobile epibiota (including several families of amphipods) to increasing small-scale complexity of artificial substrates (Lavender et al., 2017). Higher micro-scale roughness can increase refuge availability against stressful environmental conditions and predators (Loke et al., 2017;Strain et al., 2018) giving a competitive advantage to free living or cavity dwelling amphipods. This could be the case of H. stebbingi, a species that normally lives tightly associated with algae (Guerra-García et al., 2011a;Izquierdo and Guerra-García, 2011). ...
... In part, loss of species richness on these infrastructures seems related to their low spatial heterogeneity as compared with natural shores (Aguilera et al., 2014;Coombes, La Marca, Naylor, & Thompson, 2015;Firth et al., 2014Firth et al., , 2013. Specifically, the reduction in frequency of topographic elements related to spatial heterogeneity, like rocks or tide pools, crevices, pits and/or depressions, in artificial infrastructures have been considered one of the main factors related to the reduction in abundance of "rare" and habitat-forming species in these habitats (Coombes et al., 2015;Liversage, Cole, Coleman, & McQuaid, 2017;Loke, Bouma, & Todd, 2017;Loke, Ladle, Bouma, & Todd, 2015;Martins, Jenkins, Neto, Hawkins, & Thompson, 2016). ...
Urbanization is altering community structure and functioning in marine ecosystems, but knowledge about the mechanisms driving loss of species diversity is still limited. Here, we examine rock thermal patterns in artificial breakwaters and test whether they have higher and spatially less variable rock temperature than natural adjacent habitats, which corresponds with lower biodiversity patterns. We estimated rock temperatures at mid‐high intertidal using infrared thermography during mid‐day in summer, in both artificial (Rip‐raps) and natural (boulder fields) habitats. We also conducted diurnal thermal surveys (every 4 hr) in four seasons at one study site. Concurrent sampling of air and seawater temperature, wind velocity, and topographic structure of habitats were considered to explore their influence on rock temperature. Rock temperature was in average 3.7°C higher in the artificial breakwater in two of the three study sites, while air temperature was about 1.5–4°C higher at this habitat at summer. Thermal patterns were more homogeneous across the artificial habitat. Lower species abundance and richness in the artificial breakwaters were associated with higher rock temperature. Mechanism underlying enhanced substrate temperature in the artificial structures seems related to their lower small‐scale spatial heterogeneity. Our study thus highlighted that higher rock temperature in artificial breakwaters can contribute to loss of biodiversity and that integrated artificial structures may alter coastal urban microclimates, a matter that should be considered in the spatial planning of urban coastal ecosystems. We evaluated substrate thermal patterns in artificial breakwaters and natural adjacent boulder fields. We found higher rock and air temperature in the artificial habitat. Species abundance and richness were lower in the artificial habitat and related negatively with rock temperature.
... Wave impact is also more intense on steep shores (Gaylord 1999, Cuomo et al. 2010, potentially dislodging intertidal organisms and/or impeding their settlement Chapman 2008, Iveša et al. 2010). Compared to natural hard-bottom habitats, seawalls are topographically 'simple' (Loke et al. 2014) -having few microhabitats, such as pits, rock-pools, overhangs and crevices (Chapman 2003, Chapman and Bulleri 2003, Moreira et al. 2007, which are important for the persistence of many intertidal and benthic species (Chapman and Underwood 2011, Loke and Todd 2016, Loke et al. 2017. When considering these multiple effects in combination, it is unsurprising that many direct comparisons between rocky shores and seawalls often reveal the latter host lower species richness, reduced functional and genetic diversity, and different community compositions (Chapman 2003, Moschella et al. 2005, Fauvelot et al. 2009, Lai et al. 2018. ...
Human population density within 100 km of the sea is approximately three times higher than the global average. People in this zone are concentrated in coastal cities that are hubs for transport and trade – which transform the marine environment. Here, we review the impacts of three interacting drivers of marine urbanization (resource exploitation, pollution pathways and ocean sprawl) and discuss key characteristics that are symptomatic of urban marine ecosystems. Current evidence suggests these systems comprise spatially heterogeneous mosaics with respect to artificial structures, pollutants and community composition, while also undergoing biotic homogenization over time. Urban marine ecosystem dynamics are often influenced by several commonly observed patterns and processes, including the loss of foundation species, changes in biodiversity and productivity, and the establishment of ruderal species, synanthropes and novel assemblages. We discuss potential urban acclimatization and adaptation among marine taxa, interactive effects of climate change and marine urbanization, and ecological engineering strategies for enhancing urban marine ecosystems. By assimilating research findings across disparate disciplines, we aim to build the groundwork for urban marine ecology – a nascent field; we also discuss research challenges and future directions for this new field as it advances and matures. Ultimately, all sides of coastal city design: architecture, urban planning and civil and municipal engineering, will need to prioritize the marine environment if negative effects of urbanization are to be minimized. In particular, planning strategies that account for the interactive effects of urban drivers and accommodate complex system dynamics could enhance the ecological and human functions of future urban marine ecosystems.
... EH driven by structuring species such as bivalves and macroalgae has been shown to override large-scale geographic trends in environmental conditions (Jurgens and Gaylord, 2017), with implications for predictions of range shifts and resilience to climate change. Increasing surface complexity has also been explored as a mechanism to increase biodiversity on seawalls (Chapman and Bulleri, 2003;Loke et al., 2017). ...
The rocky intertidal zone is a highly dynamic and thermally variable ecosystem, where the combined influences of solar radiation, air temperature and topography can lead to differences greater than 15°C over the scale of centimetres during aerial exposure at low tide. For most intertidal organisms this small-scale heterogeneity in microclimates can have enormous influences on survival and physiological performance. However, the potential ecological importance of environmental heterogeneity in determining ecological responses to climate change remains poorly understood. We present a novel framework for generating spatially explicit models of microclimate heterogeneity and patterns of thermal physiology among interacting organisms. We used drone photogrammetry to create a topographic map (digital elevation model) at a resolution of 2 × 2 cm from an intertidal site in Massachusetts, which was then fed into to a model of incident solar radiation based on sky view factor and solar position. These data were in turn used to drive a heat budget model that estimated hourly surface temperatures over the course of a year (2017). Body temperature layers were then converted to thermal performance layers for organisms, using thermal performance curves, creating 'physiological landscapes' that display spatially and temporally explicit patterns of 'microrefugia'. Our framework shows how non-linear interactions between these layers lead to predictions about organismal performance and survivorship that are distinct from those made using any individual layer (e.g. topography, temperature) alone. We propose a new metric for quantifying the 'thermal roughness' of a site (RqT, the root mean square of spatial deviations in temperature), which can be used to quantify spatial and temporal variability in temperature and performance at the site level. These methods facilitate an exploration of the role of micro-topographic variability in driving organismal vulnerability to environmental change using both spatially explicit and frequency-based approaches.
... New structures should be designed to maximise the intertidal surface area available for colonisation and to include habitat structural complexity (e.g. introducing microhabitats) that increase diversity ( Loke et al. 2014Loke et al. , 2017 and provide refuges for target species (or their prey resources) from predators and environmental stressors ( Moschella et al. 2005, Chapman & Underwood 2011. A greater and more heterogeneous intertidal area may be achieved by stepping structures (e.g. ...
Human population growth and accelerating coastal development have been the drivers for unprecedented construction of artificial structures along shorelines globally. Construction has been recently amplified by societal responses to reduce flood and erosion risks from rising sea levels and more extreme storms resulting from climate change. Such structures, leading to highly modified shorelines, deliver societal benefits, but they also create significant socioeconomic and environmental challenges. The planning, design and deployment of these coastal structures should aim to provide multiple goals through the application of ecoengineering to shoreline development. Such developments should be designed and built with the overarching objective of reducing negative impacts on nature, using hard, soft and hybrid ecological engineering approaches. The design of ecologically sensitive shorelines should be context-dependent and combine engineering, environmental and socioeconomic considerations. The costs and benefits of ecoengineered shoreline design options should be considered across all three of these disciplinary domains when setting objectives, informing plans for their subsequent maintenance and management and ultimately monitoring and evaluating their success. To date, successful ecoengineered shoreline projects have engaged with multiple stakeholders (e.g. architects, engineers, ecologists, coastal/port managers and the general public) during their conception and construction, but few have evaluated engineering, ecological and socioeconomic outcomes in a comprehensive manner. Increasing global awareness of climate change impacts (increased frequency or magnitude of extreme weather events and sea level rise), coupled with future predictions for coastal development (due to population growth leading to urban development and renewal, land reclamation and establishment of renewable energy infrastructure in the sea) will increase the demand for adaptive techniques to protect coastlines. In this review, we present an overview of current ecoengineered shoreline design options, the drivers and constraints that influence implementation and factors to consider when evaluating the success of such ecologically engineered shorelines
... New structures should be designed to maximise the intertidal surface area available for colonisation and to include habitat structural complexity (e.g. introducing microhabitats) that increase diversity ( Loke et al. 2014Loke et al. , 2017 and provide refuges for target species (or their prey resources) from predators and environmental stressors ( Moschella et al. 2005, Chapman & Underwood 2011. A greater and more heterogeneous intertidal area may be achieved by stepping structures (e.g. ...
Human population growth and accelerating coastal development have been the drivers for unprecedented construction of artificial structures along shorelines globally. Construction has been recently amplified by societal responses to reduce flood and erosion risks from rising sea levels and more extreme storms resulting from climate change. Such structures, leading to highly modified shorelines, deliver societal benefits, but they also create significant socioeconomic and environmental challenges. The planning, design and deployment of these coastal structures should aim to provide multiple goals through the application of ecoengineering to shoreline development. Such developments should be designed and built with the overarching objective of reducing negative impacts on nature, using hard, soft and hybrid ecological engineering approaches. The design of ecologically sensitive shorelines should be context-dependent and combine engineering, environmental and socioeconomic considerations. The costs and benefits of ecoengineered shoreline design options should be considered across all three of these disciplinary domains when setting objectives, informing plans for their subsequent maintenance and management and ultimately monitoring and evaluating their success. To date, successful ecoengineered shoreline projects have engaged with multiple stakeholders (e.g. architects, engineers, ecologists, coastal/port managers and the general public) during their conception and construction, but few have evaluated engineering, ecological and socioeconomic outcomes in a comprehensive manner. Increasing global awareness of climate change impacts (increased frequency or magnitude of extreme weather events and sea level rise), coupled with future predictions for coastal development (due to population growth leading to urban development and renewal, land reclamation and establishment of renewable energy infrastructure in the sea) will increase the demand for adaptive techniques to protect coastlines. In this review, we present an overview of current ecoengineered shoreline design options, the drivers and constraints that influence implementation and factors to consider when evaluating the success of such ecologically engineered shorelines.
... This issue has received more attention lately, and mitigatory strategies are being proposed to reduce the impact of flat artificial structures on native diversity. Most of the strategies involve increasing microhabitat complexity of these structures, changing the dynamics of the local community (Firth et al., 2014;Loke et al., 2017). ...
... Wave impact is also more intense on steep shores (Gaylord 1999, Cuomo et al. 2010, potentially dislodging intertidal organisms and/or impeding their settlement Chapman 2008, Iveša et al. 2010). Compared to natural hard-bottom habitats, seawalls are topographically 'simple' (Loke et al. 2014) -having few microhabitats, such as pits, rock-pools, overhangs and crevices (Chapman 2003, Chapman and Bulleri 2003, Moreira et al. 2007, which are important for the persistence of many intertidal and benthic species (Chapman and Underwood 2011, Loke and Todd 2016, Loke et al. 2017. When considering these multiple effects in combination, it is unsurprising that many direct comparisons between rocky shores and seawalls often reveal the latter host lower species richness, reduced functional and genetic diversity, and different community compositions (Chapman 2003, Moschella et al. 2005, Fauvelot et al. 2009, Lai et al. 2018. ...
Human population density within 100 km of the sea is approximately three times higher than the global average. People in this zone are concentrated in coastal cities that are hubs for transport and trade – which transform the marine environment. Here, we review the impacts of three interacting drivers of marine urbanization (resource exploitation, pollution pathways and ocean sprawl) and discuss key characteristics that are symptomatic of urban marine ecosystems. Current evidence suggests these systems comprise spatially heterogeneous mosaics with respect to artificial structures, pollutants and community composition, while also undergoing biotic homogenization over time. Urban marine ecosystem dynamics are often influenced by several commonly observed patterns and processes, including the loss of foundation species, changes in biodiversity and productivity, and the establishment of novel assemblages, ruderal species and synanthropes. Further, we discuss potential urban acclimatization and adaptation among marine taxa, interactive effects of climate change and marine urbanization, and ecological engineering strategies for enhancing urban marine ecosystems. By assimilating research findings across disparate disciplines, we aim to build the groundwork for urban marine ecology – a nascent field; we also discuss research challenges and future directions for this new field as it advances and matures. Ultimately, all sides of coastal city design: architecture, urban planning, and civil and municipal engineering, will need to prioritize the marine environment if negative effects of urbanization are to be minimized. In particular, planning strategies that account for the interactive effects of urban drivers and accommodate complex system dynamics could enhance the ecological and human functions of future urban marine ecosystems.
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... The addition of cm-scale habitat features such as grooves (Hall et al., 2018), pits (Loke et al., 2017) and pools (Firth et al., 2014b) is simple and relatively inexpensive, with several trials showing a sevenfold increase in biodiversity compared to traditional plain-cast, smooth surfaces . However, improving the habitat value of artificial structures using ecologically enhanced designs depends on how successfully the complexity (surface roughness and microhabitats) of natural rocky shores are replicated, including the orientation of features. ...
In order to enhance the ecological value of vertical hard coastal structures, hybrid designs with complex surface textures (such as a combination of grooves and pits) have been recommended. This strategy optimises ecological colonisation at two spatial scales: 1) at the mm-scale for barnacle abundance (shown to have bioprotective capabilities), and 2) at the cm-scale for species richness and abundance through the incorporation/creation of habitat features. To determine the optimal design for improving the intertidal habitat quality of vertical coastal defence structures, we conducted an ecological enhancement trial involving 160 artificial concrete tiles of different designs (and thus topographic complexity) and 24 cleared natural surfaces (150 × 150 mm) at three sites in the UK. Within 18 months, tile designs with intermediate levels of complexity (mm-scale surface roughness) were optimal in increasing barnacle cover compared to plain-cast tiles. Tiles with high complexity (with microhabitat recesses up to 30 mm deep) developed greatest species richness and mobile species abundance and had lowest peak air temperatures and highest humidity. Such textured ecological enhancements can help improve the habitat value of existing and future hard coastal structures by favouring the conservation of intertidal species in urban marine habitats and enhancing otherwise weak or absent ecosystem service provision. Keywords: Coastal engineering, Marine concrete, Intertidal ecology, Ecological engineering, Microclimate
... Though ecological engineering of artificial structures can be used to meet a variety of objectives, its core environmental aims are often to enhance biodiversity and extend the conservation of native marine species to urban habitats that would otherwise be inhospitable ( Loke et al., 2019). One of the most popular techniques for intertidal seawalls is to increase habitat structural complexity ( Loke et al., 2014Loke et al., , 2017, for instance by removing pieces of the seawall to create recesses (Chapman and Blockley, 2009), drilling pits to form rock pools (Martins et al., 2010;Evans et al., 2016;Hall et al., 2018), and attaching "flower pots" and other concave enhancements ( Chapman, 2011, 2014;Firth et al., 2016a;Waltham and Sheaves, 2018). These manipulations have repeatedly been shown to increase the richness and abundance of benthic organisms on intertidal seawalls (reviewed by Loke et al., 2019), and their effectiveness is frequently attributed to increased shade and moisture (i.e., increased niche availability) allotted by structurally complex microhabitat features ( Firth et al., 2014Firth et al., , 2016bPerkol-Finkel et al., 2018;Strain et al., 2018), which can reduce temperature fluctuations, minimize desiccation stress, and facilitate the recruitment of sessile fauna (Metaxas and Scheibling, 1993;Blockley and Chapman, 2006;Seabra et al., 2011;Firth et al., 2013). ...
Over the last decade there has been a global effort to eco-engineer urban artificial shorelines with the aim of increasing their biodiversity and extending their conservation value. One of the most common and viable eco-engineering approaches on seawalls is to use enhancement features that increase habitat structural complexity, including concrete tiles molded with complex designs and precast “flowerpots” that create artificial rock pools. Increases in species diversity in pits and pools due to microhabitat conditions (water retention, shade, protection from waves, and/or biotic refugia) are often reported, but these results can be confounded by differences in the surface area sampled. In this study, we fabricated three tile types (n = 10): covered tile (grooved tile with a cover to retain water), uncovered tile (same grooved tile but without a cover) and granite control. We tested the effects of these tile types on species richness (S), total individual abundance (N), and community composition. All tiles were installed at 0.5 m above chart datum along seawalls surrounding two island sites (Pulau Hantu and Kusu Island) south of Singapore mainland. The colonizing assemblages were sampled after 8 months. Consistent with previous studies, mean S was significantly greater on covered tiles compared to the uncovered and granite tiles. While it is implied in much of the eco-engineering literature that this pattern results from greater niche availability allotted by microhabitat conditions, we further investigated whether there was an underlying species-individual relationship to determine whether increases in S could have simply resulted from covered tiles supporting greater N (i.e., increasing the probability of detecting more species despite a constant area). The species-individual relationship was positive, suggesting that multiple mechanisms are at play, and that biodiversity enhancements may in some instances operate simply by increasing the abundance of individuals, even when microhabitat availability is unchanged. This finding underscores the importance of testing mechanisms in eco-engineering studies and highlights ongoing mechanistic uncertainties that should be addressed to inform the design of more biodiverse seawalls and urban marine environments.
... The present study aimed to document as many non-native species as possible. We focused on molluscs as they are dominant fauna on Singapore's seawalls (Lee et al. 2009a;Loke et al. 2016;Loke and Todd 2016;Loke et al. 2017) and local taxonomic expertise is available. Specific objectives were to add to the number of seawalls surveyed and to produce a comprehensive list of native, non-native, and cryptogenic molluscs on seawalls in Singapore. ...
Marine urbanization and the construction of artificial coastal structures such as seawalls have been implicated in the spread of non-native marine species for a variety of reasons, the most common being that seawalls provide unoccupied niches for alien colonisation. If urbanisation is accompanied by a concomitant increase in shipping then this may also be a factor, i.e. increased propagule pressure of non-native species due to translocation beyond their native range via the hulls of ships and/or in ballast water. Singapore is potentially highly vulnerable to invasion by non-native marine species as its coastline comprises over 60% seawall and it is one of the world’s busiest ports. The aim of this study is to investigate the native, non-native, and cryptogenic molluscs found on Singapore’s seawalls. Seven seawall sites around Singapore were surveyed and all specimens found were either Indo-Pacific species or of unknown origin. To determine whether there were potential non-natives from within the Indo-Pacific, a set of attributes concerning the history, biogeography, detectability, human affinity, invasion pathway, biology, ecology, life-history, pre-history, evolution and genetics of mollusc species was collected from available literature. Only one “possibly introduced” species, Siphonaria guamensis Quoy and Gaimard, 1833 (Gastropoda), was identified. The remaining species consisted of 41 native to Singapore and 23 cryptogenic species. The results from this study add to the increasing pool of literature showing that, contrary to widespread assumption, there is a very low occurrence of non-native marine species in Singapore.
... obs.) indicating alteration of the boundary layer dynamics flowing over the surface of the concrete. Surface roughness has been shown to increase drag, reduce maximum water flow speed and create turbulent eddies over biogenic reefs ( Loke et al., 2017;Whitman and Reidenbach, 2012). These processes can facilitate the retention and aggregation of abiotic propagules (e.g. ...
Worldwide, coastlines are becoming increasingly hardened by infrastructure in response to population growth, need for space, and coastal protection. Coastal and marine infrastructure (CMI) supports fewer species and lower abundance and diversity than analogous natural rocky habitats, which can alter community composition and ecosystem functioning. Efforts to develop ecological engineering solutions that offset these negative consequences on biodiversity while retaining engineering function abound, but to date few studies have investigated the role of multiple factors simultaneously driving patterns of biotic colonisation. Here, the role of surface heterogeneity, chemical composition and surface orientation was evaluated over a 6-month period. An increase in habitat heterogeneity, the replacement of shale for ground oyster shell (cue) and downward orientation was predicted to increase species richness, diversity and abundance. Orientation and heterogeneity greatly affected species richness, abundance, and community composition, and the inclusion of ground oyster shell (cue) increased bivalve recruitment but had only a marginal effect on community structure. Community formation was facilitated by low light but inhibited by sedimentation. On upward-facing surfaces, sediment accumulation on high complexity surfaces expanded niche heterogeneity, and supported communities comprised of burrowing polychaetes and predatory species. Surface orientation and heterogeneity are key factors influencing larval recruitment, and in supporting diverse benthic assemblages on artificial structures. These factors should be considered during the design phase of new engineering projects if the negative consequences of artificial structures are to be minimised while ensuring engineering function is maintained.
Coastal infrastructure has reduced habitat complexity and altered light regimes compared to natural habitats, altering ecological communities and reducing overall biodiversity. Although, many studies have assessed effects of infrastructure on the overall biodiversity, these were often restricted in scope, by assessing only a particular type of infrastructure, such as coastal defence structures, or by focusing solely on diversity metrics. Therefore, we still have little knowledge on the functional impacts of infrastructure, in general, on coastal habitats. To address this knowledge gap, we conducted a systematic review and meta-analysis comparing the functional composition of natural and artificial marine habitats. We analysed a total of 68 publications from 26 countries, with data collected between 1995–2019. We found up to 60% more habitat-forming algae on natural habitats than on infrastructure at most tidal heights, but no differences were found when looking at all species of macro-algal, i.e. including non-habitat-formers. In contrast, we found more habitat-forming filter feeders, such as oysters and mussels, on subtidal vertical and floating structures, such as pylons and pontoons, respectively, than on natural habitats. Differences on the abundance of grazers varied with tidal height and/or the type of infrastructure. For example, in the subtidal, grazers were significantly more abundant on natural boulders than on infrastructure, while at low tidal heights, we found significantly less grazers on artificial floating structures and on vertical structures than on natural habitats. With coastal development on the rise, these differences have significant implications for productivity, energy and nutrient flow in coastal systems. Our findings highlight the importance of adopting a functional approach to have a more holistic understanding on the environmental impacts associated to marine urbanisation and thus better inform management and restoration efforts.
Driven by growing human populations and climate change concerns, artificial coastal structures have become crucial for meeting population needs. However, these structures often differ from natural counterparts and undermine biodiversity. Integrating eco-engineering methods during their construction is, therefore, essential to counteract the negative impact on marine biodiversity. In this study, we incorporated rock pools of two different sizes to three distinct intertidal levels within a concrete block breakwater in Bandar Abbas, Iran, and conducted an in-situ assessment of their biota. A total of 17 taxa were identified, with the barnacle Amphibalanus amphitrite being the most prevalent species. The findings revealed a fivefold increase in cumulative species number and a 30% rise in abundance due to the presence of rock pools. The results of PERMANOVA indicated that both rock pool size and intertidal levels, along with their interaction, significantly influenced species richness. Notably, small rock pools within the low intertidal level exhibited the highest species richness and abundance, whereas larger rock pools situated in high intertidal levels displayed lower richness and abundance. Our investigation underscores the effectiveness of integrating rock pools as an ecological engineering approach to enrich biodiversity on human-made structures within intertidal zones. The selection of rock pool dimensions and tidal positioning should be thoughtfully determined, considering the prevailing environmental conditions and the project's objectives.
High-throughput determination of circadian rhythms in metabolic response and their divergent patterns in various microhabitats are crucial for understanding how organisms respond to environmental stresses. A mid-intertidal limpet Cellana toreuma was collected at various time points across both daytime and nighttime in winter during low tide for investigating the diurnal metabolomic responses to cold stress and elucidating the divergent metabolic responses to temperature variations across microhabitats. Temperatures of emergent rock microhabitats were lower than the tidal pool and even aggravated at night. A series of metabolomic responses exhibited coordinated diurnal changes in winter. Metabolic responses which were associated with cellular stress responses and energy metabolism of emergent rock microhabitat individuals were highly induced compared to the tidal pool ones. This study shed light on the diurnal patterns of metabolomic responses of intertidal molluscs in the field and emphasized the variations in metabolic responses between microhabitats.
This report reviews large protective coastal infrastructure in intertidal and nearshore zones, including trained river entrances, armoured harbours, and groynes. This review finds support for a sustainable, more holistic concept of coastal management, where
interdisciplinary groups (e.g. asset owners, engineers, scientists, stakeholders, and community groups) work together to ensure that coastal areas are safe for communities, without compromising social, cultural and environmental values. Case studies from New South Wales within Australia and around the world give examples of where coastal protection infrastructure has either been modified with ecological engineering techniques or adopted approaches to facilitate multiple uses and add social, cultural and economic value to maximise sustainable outcomes.
Rapid urbanization has resulted in the loss of coastal and marine habitats in cities worldwide. The effective conservation of urban coastal ecosystems requires detailed knowledge of their spatial distribution, necessitating high‐resolution mapping. Our study produces a high‐resolution coastal and marine habitat map and shoreline map for the tropical city‐state of Singapore created through pixel‐based supervised classification of satellite imagery, bathymetry data and expert ground knowledge. These maps can be used as a base reference for multiple applications including ecological research, conservation and urban planning. They also help identifiy trends in the extent of key coastal habitats, providing insight into their differing levels of vulnerability to loss and potential for restoration to ensure long‐term resilience. The method used for mapping shoreline typologies and resulting insights gained, can guide other rapidly urbanizing coastal cities on strategies to assemble useful spatial knowledge for effective conservation of their urban coastal ecosystems.
The proliferation of coastal infrastructure in the context of coastal development, urbanization, and global change is inevitably related to the transformation of coastal community structure. For restoration of biodiversity in these human-disturbed coastal ecosystems, it is vital to untangle the community structure and thermal environments, with the consideration of the microhabitat-scale thermal environment variations. In the present study, we measured the species richness, α-diversity (i.e. the species composition of each surface of breakwaters), and β-diversity (i.e. the dissimilarities among macrobenthic communities of different surfaces of breakwater) of macrobenthos on the breakwaters on a tropical shore for understanding the variation of the community structure of macrobenthos; we also monitored the operative temperatures in different surfaces of the breakwaters during the experimental period for investigating the roles of microhabitat thermal environment on the community structure of macrobenthos on the artificial infrastructure. Our results showed that there were higher species richness and abundance in the thermally benign microhabitats. The variations of β-diversity indicated that the community structure underwent dramatic changes in different microhabitats and seasons. The population dynamics of thermal-sensitive species (e.g. Patelloida pygmaea, Cellana toreuma, and Siphonaria japonica) largely contributed to the changes in community structure. Redundancy analysis (RDA) results showed that maximum temperature, temperature predictability (i.e. the degree to which a temperature data point in a time series is influenced by its historical values), and heating rate were important thermal characteristics driving community structure on the artificial infrastructure. These results indicate the heterogeneity of thermal environments among different microhabitats is crucial for maintaining the community structure of macrobenthos on the artificial infrastructure and suggest that structural complexity should be considered for biodiversity conservation in the design and construction of coastal infrastructure.
Artificial structures such as seawalls increasingly dominate marine urban environments. As compared to natural rocky shore habitats, seawalls are usually flat, featureless, vertical surfaces that support reduced biodiversity. One approach to increase their biodiversity is to add topographic complexity (‘complexity’) that increases microhabitat diversity and surface area. Initial investigations of the effects of complexity on the biodiversity of marine built structures found positive relationships, but more recently spatially variable effects have been found at a biogeographical scale. The present study tested whether at the scale of sites within an estuary (in this case Sydney Harbour), effects of complexity also spatially vary, and whether pollution and estuarine gradients are good predictors of this variation. Comparisons of intertidal communities colonising flat and complex (creviced / ridged) tiles, affixed to seawalls confirmed that effects of complexity were spatially variable at the site-scale, ranging from neutral to highly positive. Proximity to stormdrains, a point source of contaminants including metals, was a poor predictor of complexity effects, but effects were generally greater in the outer harbour, where biodiversity was overall greater, than the inner harbour. These results suggest that eco-engineering interventions based on complexity will not have universally positive effects and instead vary between sites separated by as little as hundreds of meters. Knowledge of spatial variation in physico-chemical conditions and the size and composition of the species pool of available colonists may assist in predicting when and where adding complexity to marine built structures will be of ecological benefit.
Increasing frequency of extreme weather events, driven by climate change, coupled with growing population densities, have contributed to an increasing demand for coastal structures to protect and stabilize shorelines. Concrete seawalls are a common category of coastal protection structures, designed with the primary objectives of absorbing wave action, preventing coastline erosion, and alleviating flooding. Much research has been carried out on improving concrete seawall performance. This work is a review of the current state-of-the-art in concrete seawalls focusing on design aspects including wave loading and innovative seawall designs, ecological considerations, and durability performance. Different conventional seawalls and their advantages and disadvantages are reviewed. Wave loads on seawalls have received significant attention; and multiple approaches for the quantification for the different types of loads are presented. However, wave load quantification remains a challenging task, especially for novel designs, and performance under load for such designs must be quantified through testing in wave tanks. Drawing inspiration from natural shorelines, modification of surface complexity at a multitude of scales can improve the otherwise poor ecological performance of seawalls. Ecological performance can also be improved by the incorporation of natural materials or structures in seawalls although the exact influence of concrete and other material chemistry on benthic diversity is unclear. The corrosion of the steel is a major durability concern, and the use of non-corrosive reinforcement can increase seawall durability toward corrosion. Other durability concerns include alkali silica reaction and sulfate attack, which can be mitigated through proper mixture design, including through the use of supplementary cementitious materials. Examples of innovative seawall designs and systems which have the capability to outperform conventional seawalls are discussed. Advances in structural design, ecological engineering, and infrastructure materials science will drive the development of multi-functional seawalls which are sustainable, durable, and resilient.
Hard coastal protective infrastructure, such as breakwaters, are a common adaptation strategy to protect assets, increase safety and improve navigation by reducing erosion and flood risks along coastlines globally. However, protective structures can have pervasive impacts on use patterns, aesthetics and associated ecosystems, threatening ecosystem goods and services upon which humans depend. Guided by a recent Australian state Government strategy that aims to plan for “a healthy coast and sea managed for the greatest wellbeing of the community, now and into the future”, we present a decision-making support tool for practitioners to help achieve more sustainable solutions to coastal adaptation into the future. Sustainable coastal adaptation needs to consider the environmental and socio-economic consequences of hard protective infrastructure, as well as the increased vulnerability due to rising sea levels. To demonstrate our arguments, we introduce three different coastal scenarios. We also discuss alternatives to coastal protection and make scenario-specific recommendations to enhance environmental and socio-economic outcomes of coastal adaptation. In general, the implementation of hard protective infrastructure should probably be a last resort after retreat and soft approaches have been ruled out as viable options. Where protective infrastructure is the current best option, environmental and socio-economic outcomes can be enhanced using eco-engineering and multi-use features. In the long term, however, retreat from some coastal areas may be necessary and existing infrastructure might be removed or abandoned.
Increasing frequency of extreme weather events, driven by climate change, has resulted in an increasing demand for coastal structures to protect and stabilize shorelines. Concrete seawalls are a common category of coastal protection structures, designed with the primary objectives of absorbing wave action, preventing coastline erosion, and alleviating flooding. Much research has been carried out on improving the seawall performance. This work is a review of the current state-of-the-art in concrete seawalls focusing on design aspects including wave loading and innovative seawall designs, ecological considerations, and durability aspects. Wave loads on seawalls have received significant attention; however, their quantification remains a challenging task especially for novel designs. Drawing inspiration from natural shorelines, modification of surface complexity at a multitude of scales can improve the otherwise poor ecological performance of seawalls. The corrosion of the steel is a major durability concern, and the use of non-corrosive reinforcement can increase seawall durability towards corrosion. Examples of innovative seawall designs and systems which have the capability to outperform conventional seawalls are discussed. Advances in structural design, ecological engineering, and infrastructure materials science will drive the development of multi-functional seawalls which are sustainable, durable, and resilient.
he Singapore Blue Plan 2018 (hereafter ‘The Blue Plan’) is a proposal for the conservation of marine ecosystems, prepared by members of Singapore society, and submitted to the Government for consideration. It was initiated by marine biologists with academics, volunteers, stakeholders, and concerned citizens. The Blue Plan synthesizes the current state of knowledge for marine environments, reviews relevant legislature and advocates comprehensive sustainable methods to manage this important ecosystem
The rock type used in coastal engineering structures impacts biodiversity, but its effect has been understudied to date. We report here on whether different combinations of rock material and rock mass properties can improve habitat suitability and early phase ecological outcomes on coastal engineering structures. We examine two coastal engineering schemes that used different granites during construction. At site one, Shap granite boulders with a high number of cm-dm² surface features (e.g. ledges) were deliberately positioned during construction (called passive enhancement), to a) maximise the provision of cm-dm scale intertidal habitat and b) determine which scale of habitat is best for ecological enhancement. At site two, Norwegian granite boulders were installed without passive enhancement, allowing for a direct comparison. Passive positioning of Shap granite boulders led to an increase in limpet (Patella vulgata, Linnaeus, 1758) abundance within two years but few limpets were recorded on the non-enhanced Norwegian granite. Positioning of boulder thus exerts a strong control on the mm and mm-dm scale geomorphic features present, with clear ecological benefits when suitable features are selected for and optimally positioned (i.e. passive enhancement) to maximise habitat features. An EcoRock scoring matrix was developed to aid in the selection of the most ecologically suitable rock materials for coastal engineering worldwide; this can help improve habitat provision on engineered structures in a rapidly warming world.
HydroLink (IAHR), Number 4, pp 110-113
ISSN 1388-3445
Isolating the effects of fragmentation per se (i.e., spatial configuration of habitat patches) on species richness is an ongoing challenge as habitat configuration often covaries with the amount of habitat. Consequently, there is a lack of experimental evidence for configurational effects on species richness in the whole landscape. Here, we developed a novel experimental system for testing the independent and interactive effects of habitat area and configuration on tropical intertidal species richness. Our results confirmed the expectation that average species richness would increase monotonically with habitat area. More intriguingly, we found mixed evidence for a non‐monotonic relationship between species richness and fragmentation per se, with the highest richness at intermediate fragmentation configuration, that is, when habitat tiles were placed in a “several‐small” configuration. The effect of habitat configuration was not due to passive sampling (since area was controlled for), variation in total individual abundance, or niche specialization of species to different landscape configurations. We postulate that a combination of processes, including local negative density dependence and dispersal limitation, could give rise to the observed pattern. We emphasize the importance of considering configurational effects on biodiversity at broader spatial scales and for more experimental research to delve into the mechanisms driving the patterns seen here.
Species dissimilarity mainly reflects temporal and spatial variation in community composition. Its relationship with random and deterministic factors reveals community assembly, biodiversity formation, and maintenance mechanisms. In this study, we analyzed relationships between species dissimilarity of plant communities and influencing factors in the Dulongjiang River Watershed Area. Jaccard species dissimilarity, geographic distance, difference in climate (Mean Annual Temperature and Mean Annual Precipitation), and altitude between any two communities were calculated. Results showed that the species turnover rate varied from 0.42 to 1. Species turnover significantly linearly increased with Ln-transformed geographic distance and differences in climate and altitude. Results from partial regression analysis showed that these three kinds of factors together can explain nearly 30% of species differences of vascular plant communities in the Dulongjiang River Watershed Area; independent effects of geographical distance, elevation difference, and climatic differences were 18.80%, 3.47%, and 0.10%, respectively. Species dissimilarity in the Dulongjiang Watershed Area results from the combination of environmental and dispersal limitations, which plays an important role in the conservation of plant biodiversity in the Dulongjiang Watershed Area. When biodiversity conservation is undertaken in the area, on the basis of considering the impact of environmental factors, the effects of topographical barriers and dispersal abilities of propagules should be fully considered.
Extensive development and construction in marine and coastal systems is driving a phenomenon known as “ocean sprawl”. Ocean sprawl removes or transforms marine habitats through the addition of artificial structures and some of the most significant impacts are occurring in sedimentary environments. Marine sediments have substantial social, ecological, and economic value, as they are rich in biodiversity, crucial to fisheries productivity, and major sites of nutrient transformation. Yet the impact of ocean sprawl on sedimentary environments has largely been ignored. Here we review current knowledge of the impacts to sedimentary ecosystems arising from artificial structures.
The growing number of artificial structures in estuarine, coastal and marine environments is causing “ocean sprawl”. Artificial structures do not only modify marine and coastal ecosystems at the sites of their placement, but may also produce larger-scale impacts through their alteration of ecological connectivity - the movement of organisms, materials and energy between habitat units within seascapes. Despite the growing awareness of the capacity of ocean sprawl to influence ecological connectivity, we lack a comprehensive understanding of how artificial structures modify ecological connectivity in near- and off-shore environments, and when and where their effects on connectivity are greatest. We review the mechanisms by which ocean sprawl may modify ecological connectivity, including trophic connectivity associated with the flow of nutrients and resources. We also review demonstrated, inferred and likely ecological impacts of such changes to connectivity, at scales from genes to ecosystems, and potential strategies of management for mitigating these effects. Ocean sprawl may alter connectivity by: (1) creating barriers to the movement of some organisms and resources - by adding physical barriers or by modifying and fragmenting habitats; (2) introducing new structural material that acts as a conduit for the movement of other organisms or resources across the landscape; and (3) altering trophic connectivity. Changes to connectivity may, in turn, influence the genetic structure and size of populations, the distribution of species, and community structure and ecological functioning. Two main approaches to the assessment of ecological connectivity have been taken: (1) measurement of structural connectivity - the configuration of the landscape and habitat patches and their dynamics; and (2) measurement of functional connectivity - the response of organisms or particles to the landscape. Our review reveals the paucity of studies directly addressing the effects of artificial structures on ecological connectivity in the marine environment, particularly at large spatial and temporal scales. With the ongoing development of estuarine and marine environments, there is a pressing need for additional studies that quantify the effects of ocean sprawl on ecological connectivity. Understanding the mechanisms by which structures modify connectivity is essential if marine spatial planning and eco-engineering are to be effectively utilised to minimise impacts.
Increasing coastal urbanisation has resulted in the extensive conversion of natural habitats with manmade hard structures, such as seawalls, which tend to support communities with low biodiversity. While seawalls are often colonised by species that can be found on natural rocky shores, some studies have shown that their community structure and dynamics are markedly different. However, relative to rocky shores, ecological research on seawalls is limited, and this is especially so in the tropics. To our knowledge, no research to date has examined, in the context of artificial coastal defences, the ecological succession of communities on substrates of varying complexity near the equator. Hence, the aim of the present study is to quantify the patterns of algal succession on ‘simple’ and ‘complex’ concrete tiles and granite controls mounted onto seawalls at two offshore sites in Singapore (Pulau Hantu and Kusu Island). Our results revealed the development of an algal assemblage that is typical of many tropical rocky shores; i.e., ephemeral green turfs succeeded by high cover of a grazer-resistant mat of erect and encrusting algae with the foliose macroalgal functional group poorly represented. All treatments developed macroalgal cover by the first month. Final mollusc assemblage structure after one year was also quantified, as molluscs are important consumers in structuring algal assemblages. While the succession trajectories were similar at both sites, the rates of succession differed. The transitions from ephemeral green turfs to the mixture of red and brown macroalgal assemblages, as well as the development of encrusting coralline and non-coralline algae, occurred two months later at Pulau Hantu (the more sheltered site). Granite controls did not support foliose or articulated calcareous algal functional groups within the sampling period, probably due to material and structural/ topographical differences. Documenting such small-scale spatial patterns of algal distribution represents the first step towards a better understanding of the processes occurring in artificial habitats—and this should ultimately aid their reconciliation.
Although patellid limpets are influential grazers on many shores, few studies have characterised their diets in detail. These key species can be found as dominant grazers on rocky shores, but this ecosystem is being transformed due to the increase in infrastructures such as jetties, breakwaters or seawalls by commercial, residential and tourist activities. Increasing knowledge about the ecological effects of these artificial substrates on marine environments is available, and many papers have reported that urban infrastructures support different biota and assemblages and do not act as a surrogate for natural rocky shores. However, little is known about the effect of artificial substrata on marine trophic ecology. The aim of the study was to explore the influence of artificial substrata (breakwaters) on the dietary composition of the common grazer Patella caerulea, to provide data about food resource availability, and its influence on the trophic ecology of limpets. A nested design was used to explore potential differences between natural and artificial shores in Algeciras Bay (Strait of Gibraltar). Additionally, the dietary composition of the endangered limpets Cymbula safiana and Patella ferruginea was studied in a single site. Analyses of the chlorophyll a concentration of the substrate did not show differences between substrata. The analysis of the rock surface by SEM indicated a general prevalence of diatoms and cyanoprokaryotes on all of the substrata. P. caerulea specimens collected from artificial substrata showed a lower number of consumed taxa than those collected from natural rocky shores, whereas the assemblages found in the gut contents also differed between artificial and natural substrata. The diet richness of the three species might be due to the differences in the position of the species on the shore. Our results suggest that limpets are a key group in the top-down control of meiofaunal and macrofaunal populations, due to the presence of several animal taxa in their gut contents in this study, despite the fact that they have traditionally been considered herbivorous grazers that regulate only algal populations in the intertidal regions.
Coastal defences are proliferating in response to anticipated climate change and there is increasing need for ecologically sensitive design in their construction. Typically, these structures support lower biodiversity than natural rocky shores. Although several studies have tested habitat enhancement interventions that incorporate novel water-retaining features into coastal defences, there remains a need for additional long-term, fully replicated trials to identify alternative cost-effective designs. We created artificial rock pools of two depths (12 cm, 5 cm) by drill-coring into a shore-parallel intertidal granite breakwater, to investigate their potential as an intervention for delivering ecological enhancement. After 18 months the artificial rock pools supported greater species richness than adjacent granite rock surfaces on the breakwater, and similar species richness to natural rock pools on nearby rocky shores. Community composition was, however, different between artificial and natural pools. The depth of artificial rock pools did not affect richness or community structure. Although the novel habitats did not support the same communities as natural rock pools, they clearly provided important habitat for several species that were otherwise absent at mid-shore height on the breakwater. These findings reveal the potential of drill-cored rock pools as an affordable and easily replicated means of enhancing biodiversity on a variety of coastal defence structures, both at the design stage and retrospectively.
Coastal defences are proliferating in response to climate change, leading to the creation of more vertical substrata. Efforts are being made to mitigate their impacts and create novel habitats to promote biodiversity. Little is known about the effect of aspect (i.e. north–south directionality) and inclination on intertidal biodiversity in artificial habitats. Artificial and natural habitats were compared to assess the role of aspect and substratum inclination in determining patterns of biodiversity at two tidal heights (high and mid). We also compared grazing activity between north- and south-facing surfaces in natural habitats to examine the potential for differential grazing pressure to affect community structure and functioning. Results were variable but some clear patterns emerged. Inclination had no effect on biodiversity or abundance. There was a general trend towards greater taxon richness and abundance on north-facing than south-facing substrata in natural and artificial habitats. On natural shores, the abundance and grazing activity of ‘southern’ limpets (i.e. Patella depressa) was greater on south-facing than north-facing substrata, with possible implications for further range-expansion. These results highlight the importance of incorporating shaded habitats in the construction of artificial habitats. These habitats may represent an important refuge from grazing pressure and thermal and desiccation stress in a warming climate.
Rapid coastal population growth and development are primary drivers of marine habitat degradation. Although shoreline hardening, a byproduct of development, can accelerate erosion and loss of beaches and tidal wetlands, it is a common practice globally. Here, we provided the first estimate of shoreline hardening along United States coasts and predicted where existing or future hardening may result in tidal wetland loss if coastal management changes are not made. Our analysis indicated that 22,842 km of continental U.S. shoreline, 14% of the total, has been hardened. We also considered how socioeconomic and physical factors relate to the pervasiveness of shoreline hardening and found that housing density, GDP, storms, and wave height were positively correlated with hardening. Over 50% of South Atlantic and Gulf Coast shorelines are fringed with tidal wetlands that could be threatened by hardening based on projected population growth, storm frequency, and a lack of shoreline hardening restrictions.
Habitat loss associated with land reclamation and shoreline development is becoming increasingly prevalent as coastal cities expand. The majority of Singapore's mangrove forests, coral reefs and sand/mudflats disappeared between the 1920s and 1990s. Our study quantifies additional coastal transformations during the subsequent two decades, analyses the potential impact of future development plans, and synthesises the mitigation options available. Comparisons of topographical maps between 1993 and 2011 reveals declines in total cover of intertidal coral reef flats (from 17.0 km2 to 9.5 km2) and sand/mudflats has (from 8.0 km2 to 5.0 km2), largely because of extensive land reclamation. Conversely, mangrove forests have increased (from 4.8 km2 to 6.4 km2) due to restoration efforts and greater regulatory protection. However, 15 and 50-year projections based on Singapore's 2008 Master Plan and 2011 Concept Plan show that all habitats are predicted to shrink further as new reclamations are completed. Such decline may be counteracted, at least in part, if ecological engineering is used to help conserve biodiversity. The problems exemplified by Singapore, and the potential future solutions discussed in our paper, provide guidance for urban marine conservation in coastal cities that are experiencing rapid development and land use change.
AimA species–accumulation curve may represent a direct expression of β-diversity, the rate at which diversity increases from local to regional scale. Patterns of variation in β-diversity tend to be consistent when measured across lower levels of the Linnaean taxonomic hierarchy (i.e. using species, genera or families). Our aim was to assess the relationships between species–accumulation curves and β-diversity at different taxonomic levels and to combine the logic of species–accumulation curves with taxonomic surrogacy to provide a new approach for cost-effective and reliable estimates of large-scale species richness (γ-diversity). LocationMediterranean, N Atlantic and SW Pacific. Methods
We provide here a novel framework to extrapolate quantitative measures of species richness in large areas from accumulation curves based on extensive sampling at the family level coupled with estimation of species-to-family ratios from a subset of sampling units where organisms are identified to the species level. We demonstrated the effectiveness of the approach by analysing six datasets of diverse marine molluscan assemblages from different biogeographical regions and habitat types. ResultsThe approach proposed here can be used successfully to gain substantial efficiencies in sampling, potentially reducing the number of sampling units in which organisms have to be identified at species level between 50 and 75%, while still allowing reliable estimates of regional species richness. Main conclusionsOur results highlight the potential of this approach to improve the general exploration of biodiversity, especially for large-scale monitoring programs. The method we propose differs from previously described approaches by taking into account the spatial heterogeneity of species distributions within the sampled area and also by relying on estimates of species-to-family ratios obtained directly from the specific area of interest.
Physical habitat complexity regulates the structure and function of biological communities, although the mechanisms underlying this relationship remain unclear. Urbanisation, pollution, unsustainable resource exploitation and climate change have resulted in the widespread simplification (and loss) of habitats worldwide. One way to restore physical complexity to anthropogenically simplified habitats is through the use of artificial substrates, which also offer excellent opportunities to explore the effects of different components (variables) of complexity on biodiversity and community structure that would be difficult to separate in natural systems. Here, we describe a software program (CASU) that enables users to visualise static, physical complexity. CASU also provides output files that can be used to create artificial substrates for experimental and/or restoration studies. It has two different operational modes: simple and advanced. In simple mode, users can adjust the five main variables of informational complexity (i.e. the number of object types, relative abundance of object types, density of objects, variability and range in the objects' dimensions, and their spatial arrangement) and visualise the changes as they do so. The advanced mode allows users to design artificial substrates by fine-tuning the complexity variables as well as alter object-specific parameters. We illustrate how CASU can be used to create tiles of different designs for application in a marine environment. Such an ability to systematically influence physical complexity could greatly facilitate ecological restoration by allowing conservationists to rebuild complexity in degraded and simplified habitats.
The risk of flood disasters is increasing for many coastal societies owing to global and regional changes in climate conditions, sea-level rise, land subsidence and sediment supply. At the same time, in many locations, conventional coastal engineering solutions such as sea walls are increasingly challenged by these changes and their maintenance may become unsustainable. We argue that flood protection by ecosystem creation and restoration can provide a more sustainable, cost-effective and ecologically sound alternative to conventional coastal engineering and that, in suitable locations, it should be implemented globally and on a large scale.
Nelson W.Y. Lam, Richard Huang, and Benny K.K. Chan (2009) Variations in intertidal assemblages and zonation patterns between vertical artificial seawalls and natural rocky shores: a case study from Victoria Harbour, Hong Kong. Zoological Studies 48(2): 184-195. Development of coastal cities often results in destruction of natural coastlines, which are consequently replaced by artificial coastal urban structures, commonly including smoothly surfaced vertical seawalls. Artificial seawalls can create novel habitats which may affect the diversity, abundances, and distribution patterns of intertidal assemblages. In the present study, the intertidal assemblages on 3 vertical artificial seawalls and 3 natural rocky shores were studied in Victoria Harbour, Hong Kong. Both artificial seawalls and natural rocky shores shared similar assemblages of common species, but the species abundance and percentage cover of certain taxa differed between the 2 habitat types. Artificial seawalls supported a greater abundance of the chiton Acanthopleura japonica and greater percentage coverage of the oyster Saccostrea cucullata and barnacle Amphibalanus (=Balanus) amphitrite. In contrast, a greater abundance of the false limpet Siphonaria laciniosa and a greater percentage cover of the barnacle Tetraclita squamosa occurred on natural rocky shores. Some species were found exclusively on only one of the habitats. The green mussel Perna viridus, tube worms Hydriodes spp., and sea squirt Styela sp. were only found on artificial seawalls, while the black mussel Septifer virgatus was exclusively recorded on natural rocky shores. Artificial seawalls had different zonation patterns compared to natural rocky shores. The barnacle Tetraclita squamosa and chiton Acanthopleura japonica were commonly low on natural rocky shores but they became abundant on the mid-shore of artificial seawalls. Differences in zonation patterns of species could be due to the vertical orientation of artificial seawalls leading to different temperature and humidity profiles compared to natural rocky shores. Spatial variability of the assemblage structure at the scale of tens of meters was greater on natural rocky shores than on artificial seawalls. Greater horizontal spatial variation in species assemblages on natural rocky shores may be associated with greater habitat diversity (e.g., rock pools, crevices, and vertical and horizontal surfaces) on natural shores than on smooth vertical seawalls. http://zoolstud.sinica.edu.tw/Journals/48.2/184.pdf.
The extent to which the 'fragmented' properties of a landscape have actually been caused by anthropogenic fragmentation is often unknown. We can, however, understand links between spatial patterns of habitat in the current landscape and the biota. Built seawalls in Sydney Harbour, Australia, appear to fragment the natural, intertidal habitat. Rocky shores naturally occur, however, in a landscape of 'fragments', i.e. as patches of natural habitat separated by other natural habitats. To examine the extent to which fragmentation, i.e. due to human disturbance, has affected biota, we compared assemblages in these naturally patchy habitats to those in 'fragmented' habitats. Rocky shores were smaller and further apart from one another when surrounded by artificial habitat (called 'complete fragments') than when surrounded by other natural habitats (called 'natural patches'). This pattern matches the physical properties of 'fragmented landscapes'. We therefore tested whether patterns of diversity of biota in complete fragments, in mixed fragments (with one side adjacent to natural habitat and the other to artificial habitat) and in natural patches can be predicted from current models about the effects of the process of fragmentation. The number of taxa, number of unique taxa and variability in the number of taxa were all greater in natural patches than in mixed and complete fragments, although not all analyses were statistically significant. The current study supports notions that the composition and configuration of 'seascapes' is more important to the ecology of many marine organisms than previously thought.
Sub-lethal responses to heat stress were investigated in the limpet Cellana grata. During summer low tides, foot temperatures were hotter than rock temperatures, but positively correlated with, heart rate, air and rock temperatures. Hotter limpets showed mushrooming behaviour, raising their shell from the rock. Over 30 % of monitored limpets were not relocated during the subsequent daytime low tide. Missing animals were mostly situated on horizontal surfaces, were smaller than those recaptured, and had higher body temperatures, mushrooming heights and heart rates. A laboratory protocol was designed to resemble on-shore thermal stress conditions. Firstly, small and large limpets were held on a hot plate for 60 min and either constrained or allowed to mushroom. Secondly, unconstrained, large animals were held on the hot plate for 120 min. Unconstrained limpets were able to mushroom and had lower foot temperatures but higher heart rates than those constrained, suggesting mushrooming is an active response. Small animals had higher heart rates than large individuals. Mantle water could not be collected from most small, mushrooming limpets but was from constrained animals, and was more concentrated in small limpets. Small and constrained limpets had more concentrated haemolymph than large or mushrooming animals. Mantle and haemolymph osmolalities were positively related, except at high mantle water osmolalities. Smaller animals lost relatively more water, and constrained limpets more than those allowed to mushroom. Large limpets on the hot plate for 120 min showed similar mushrooming heights and heart rates but had hotter foot temperatures, higher haemolymph concentrations, lost all their mantle water and nearly twice as much water than those held for 60 min. Mushrooming behaviour appears to be a short-term, high-risk strategy that allows limpets temporary relief from stressful conditions and may increase their chance of survival until the next tidal immersion.
Populations of C. grata were studied on exposed shores around Cape d'Aguilar, Hong Kong. Limpets moved up to 1 m in the vertical plane over a tidal cycle. When not foraging limpets took refuge in habitats that reduced the effects of high temperature and desiccation stress. The quality of these refuges varied both spatially and temporally. Experimental manipulations with specimens restrained 0.5 m above their normal resting height or on horizontal rock surfaces and prevented from returning to refuges caused desiccation, osmotic stress and, in many cases, death as a consequence of prolonged emersion. C. grata exhibits "mushrooming' behaviour, lifting its shell from the rock surface, although the exact benefits of this behaviour are unclear. Summer physical extremes may strongly select for limpet activity rhythms. -from Authors
Recent improvements in mapping of global population distribution makes it possible to estimate the number and distribution of people near coasts with greater accuracy than previously possible, and hence consider the potential exposure of these populations to coastal hazards. In this paper, we combine the updated Gridded Population of the World (GPW2) population distribution estimate for 1990 and lighted settlement imagery with a global digital elevation model (DEM) and a high resolution vector coastline. This produces bivariate distributions of population, lighted settlements and land area as functions of elevation and coastal proximity. The near-coastal population within 100 km of a shoreline and 100 m of sea level was estimated as 1.2 × 109 people with average densities nearly 3 times higher than the global average density. Within the near coastal-zone, the average population density diminishes more rapidly with elevation than with distance, while the opposite is true of lighted settlements. Lighted settlements are concentrated within 5 km of coastlines worldwide, whereas average population densities are higher at elevations below 20 m throughout the 100 km width of the near-coastal zone. Presently most of the near-coastal population live in relatively densely-populated rural areas and small to medium cities, rather than in large cities. A range of improvements are required to define a better baseline and scenarios for policy analysis. Improving the resolution of the underlying population data is a priority.
We measured the variability in hydrodynamic forces among locations separated by only centimeters along three horizontal transects on a steep rocky shore. Our results extend previous work showing that wave forces have the characteristics of 1 /"f"-noise, in which variability in wave forces decreases exponentially with decreasing scales of measurement. Furthermore, our results suggest that protection from hydrodynamic forces is not a certain consequence of a rugose substratum, suggesting that investigators should directly test (rather than assume) small-scale topographic protection from hydrodynamic forces.
The distribution of intertidal organisms can often be determined by processes operating at the time of recruitment. Recruitment has been demonstrated to influence the composition of assemblages of natural habitats, but there is less evidence of its importance in artificial habitats. Coastal areas are becoming increasingly urbanised, with the replacement of many natural habitats by man-made structures. It is, therefore, important to test processes that influence the structure of assemblages in artificial habitats in order to evaluate whether processes act in a way that is predictable from knowledge of natural shores. Much of the foreshore of Sydney Harbour has been replaced by seawalls, many of which are built in association with wharves. It has been shown that features of wharves may cause small-scale differences between assemblages on adjacent sections of seawalls which are under or not under wharves. The present study tested the hypothesis that these patterns are determined by differences in recruitment, by monitoring recruitment to experimental clearings and settlement plates in both habitats. In general, algae and mobile invertebrates had greater cover or abundance on unshaded seawalls, while sessile invertebrates had greater cover on shaded seawalls. Not all taxa in these habitats recruited to experimental clearings or plates, but the abundance or cover of those that did resembled patterns observed in the surrounding established assemblage. This indicates that, at least for some organisms on intertidal seawalls, patterns of distribution are determined at the time of recruitment and are probably influenced by shading. Furthermore, patterns in the present study were similar to what was predicted from work done on natural shores, showing that studies from natural shores can be applied to these artificial habitats.
Intertidal seawalls are increasingly being built in urban estuaries, fragmenting and replacing natural intertidal shores. Many species of animals and plants live on seawalls. Previous work in Sydney Harbour has shown that common species live on seawalls and rocky shores, but vary in their relative abundances according to height on the shore and location. The potential value of seawalls to provide viable intertidal habitat will depend on their ability to support the full diversity of intertidal species, including those that are relatively rare. This study examines the diversity of animals and plants at 2 heights on rocky shore and seawalls, at 4 locations in Sydney Harbour, using presence/absence measures in an intensive sampling schedule in each habitat. The total number and types of taxa found were very variable within and among locations, but clear patterns arose when the data were combined (800 quadrats in each habitat). With few exceptions, algae and sessile animals were similarly distributed across habitats, but approximately 50% of the mobile animals were not found on seawalls. In addition, rocky shores had a greater proportion of rare taxa (only found in 1 or very few quadrats). Of the shared taxa, patterns of occurrence were similar on the 2 structures. Potential reasons for these patterns are discussed and ways to improve seawalls as a habitat for mobile animals are proposed.
Rocky shores occur at the interface of the land and sea. Typically they are open ecosystems, with steep environmental gradients. Their accessibility to man has rendered them susceptible to a variety of impacts since prehistoric times. Access can be regulated, however, and they are more amenable to management than open ocean habitats. This review uses examples from throughout the world to demonstrate the extent to which rocky shores have been, and are currently, affected by pollution (examples used are endocrine disrupters, oil, eutrophication), over-collection of living resources, introduced alien species, modification of coastal processes (coastal defences, siltation) and global change (climate, sea level). These impacts are put into the context of natural fluctuations in time and variability in space of both the environment and the organisms. The relative magnitudes of some anthropogenic disturbances differ between the industrialized, developed world and the developing world. For example, in developed, industrialized countries pollution based impacts should diminish over the next 25 years due to improved regulation and a reduction in older ‘dirtier’ heavy industry. Conversely, in many developing countries pollution will increase as a consequence of growth in the human population and industrialization. Except for large-scale disasters such as oil spills, pollution tends mainly to influence embayed coastlines. Chronic effects such as eutrophication can have broader-scale impacts over whole coastlines and elevated nutrient levels have also been implicated in a trend of increasing frequency of catastrophic kills due to harmful algal. Direct removal of living resources has had major effects on coastlines at both local and regional scales and is likely to increase over the next 25 years, especially in developing countries where rapidly expanding human populations will put further pressure on resources. Impacts from recreational activities are likely to increase with greater leisure time in wealthier regions of the world, and cheaper travel will spread these impacts to poorer regions. Invasions by alien species have increased in frequency during the last 20 years leading to some dramatic effects on native assemblages. Problems associated with alien species, especially pathogens, will continue to increase over the next few decades. The proportion of the coastline modified by artificial structures (breakwaters, seawalls, groynes) will increase because of coastal development and defences against sea-level rise and the greater frequency of storms. This will increase connectivity between areas of rocky habitat. Siltation will continue to increase due to urbanization of catchments and estuaries, and changes in agricultural practice. This may have considerable impacts at local and regional scales, favouring sediment tolerant organisms such as turf algae and anemones. In the future, greater frequency of environmental extremes is likely, including large-scale events such as the El Niño Southern Oscillation (ENSO). Global change in temperature, sea-level rise and increases in the frequency of storms will affect rocky shores throughout the world, but this will occur over long time scales; over the next 25 years most of the responses by rocky shore communities will mostly be quite subtle. Thus rocky shores will be subject to increasing degradation over the next 25 years. They are, however, less vulnerable than many other aquatic habitats due to their hard substratum (rock), their relative lack of large biogenic structures and to their generally open nature. They are also remarkably resilient, and recovery can occur rapidly due to recruitment from unaffected areas. Their susceptibility to both terrestrial and marine disturbances does make them more vulnerable than sublittoral and offshore habitats. There are considerable gaps in knowledge, particularly of certain microhabitats such as crevices, boulders, sand-scoured areas and rock pools. These have been much less studied than more accessible assemblages on open, freely draining rock. More research is needed to establish the effects of increasing sediment loads, ultraviolet radiation and introduced species on rocky shore communities. Strategic and applied research programmes should integrate field experiments and carefully selected monitoring programmes to verify management regimes. Hindcasting from the palaeo-record would be valuable, to compare rates of predicted change with periods when change was rapid in the past. This information could, in principle, be used to help conserve rocky shores through networks of marine protected areas and a general reduction of environmental pollution.
Ecosystem engineers can influence biodiversity by enhancing complexity, and modifying the availability of resources. Understanding the mechanisms by which ecosystem engineers shape biodiversity is central to the concept of ‘ecological engineering’ of anthropogenic structures to enhance biodiversity. Here the presence and complexity of artificial turf was manipulated on an artificial structure to test the hypothesis that the colonisation of sessile invertebrates and mobile epibiota would vary with habitat complexity. Both sessile and mobile assemblage compositions differed according to the presence of artificial turf, and its complexity. Sessile invertebrates occupied greater proportions of available space on topographically simple ‘blank’ surfaces or low complexity artificial turf than those with high complexity turf, whereas mobile taxa were generally more abundant on the turf. However, the mobile assemblage was unrelated to the sessile assemblage when examined within each level of initial substrata complexity. Contrary to the increasing number of studies demonstrating nested hierarchical relationships between co-occurring ecosystem engineers, this study provides an example of an ecosystem engineer mimic (artificial turf) leading to the formation of habitat mosaics at small scales. The introduction of complex substrata to otherwise topographically simple artificial structures is a promising means of actively influencing assemblage composition.
Parasites are ubiquitous throughout nature and can have dramatic effects on their hosts. Although much is known about the pathology of parasites, the environmental factors influencing the distribution and abundance of parasites are poorly understood. Investigations into these factors could help predict the effect of parasites on the functioning of ecosystems. The limpet Patella vulgata is a key grazer on European rocky shores and is the first intermediate host for the trematode parasite, Echinostephilla patellae. This study investigated the spatial distribution of E. patellae in relation to P. vulgata at fourteen rocky shores around Ireland. Despite P. vulgata recruiting into rock pools, adults are more abundant on emergent rock and experience greater mortality in pools compared to emergent rock. It has been suggested that greater parasite prevalence in pools may be a factor driving this disjunct distribution pattern. Prevalence of infection was compared among rock and pool habitats. Size and sex of the host were also investigated in order to determine whether host phenotype influenced levels of infection prevalence. Results varied considerably among study sites, probably due to the heterogeneity of environmental conditions. No clear pattern emerged in relation to infection prevalence between habitats but this may be owing to the low numbers of limpets collected from pools. There was a significant positive relationship between infection prevalence and increasing host size. Individuals for which sex was indeterminate were more likely to be infected than distinct males or females, suggesting that infection may be causing castration and subsequent removal of these individuals from the breeding population. We discuss the importance of considering host-parasite dynamics in a period of rapid environmental change.
Introduction: As discussed by Chapman and Underwood (Chapter 4), urbanisation is expanding rapidly in estuaries and along the coastlines in all continents across the world. This has led to extremely altered coastal environments, with extensive loss, fragmentation and replacement of natural habitats by built structures (e.g. Mann, 1988; Walker, 1988; Glasby and Connell, 1999). Intertidal habitats, which form the interface between the land and the sea, are most strongly affected by urbanisation, because they are frequently disturbed by commercial and recreational activities (e.g. Iannuzzi et al., 1996), or extremely altered by the desire for ‘waterfront’ developments and the need to access the water from the land for transport and travel (e.g. Yapp, 1986). Intertidal mangroves (Young and Harvey, 1996) and saltmarshes (Zedler, 1988) have received most attention with respect to urban development because their loss is immediately obvious and because they can provide habitat for rare or endangered plants or charismatic vertebrates (Zedler, 1993). Intertidal and freshwater wetlands suffered particularly severe loss and fragmentation over many years because they were considered wastelands and, thus, ‘reclaimed’ for urban development. Fortunately, in some parts of the world, this process is being reversed by active programmes of mitigation and restoration (Zedler et al., 1998). Similarly, changes to subtidal seagrass meadows have received attention because of their perceived value as nursery grounds for commercially important fish and crustaceans (Robertson and Duke, 1987; Haywood et al., 1995). In many urbanised estuaries, seagrasses have declined because of overgrowth by algae (Short and Burdick, 1996).
Owing to a combination of increase in coastal population and processes related to global climate change, intense coastal development is inevitable. Shallow-water habitats are prone to be replaced by structures such as seawalls and breakwaters. While adding ample hard substrate to the seascape, these structures are not surrogates to natural habitats, and are often associated with nuisance and invasive species. These differences are attributed to design features including high inclination, low complexity and high homogeneity - all atypical of natural habitats. To date, coastal infrastructure has been designed with limited consideration to marine life developing on it. Consequently, its ability to provide ecosystem services similar to those offered by natural habitats has been severely compromised. This paper presents two case studies implementing ecological enhancement at the Brooklyn Bride Park waterfront. Both strategies are examples for restoring viable ecosystem services while also serving structural and societal goals. The first is an example of structural repairs of aging pier piles, by applying innovative technology of ecological concrete encasement which creates valuable habitat. The second is an example of boosting the ecological performance of a constructed riprap waterfront, by integrating precast tide-pools that add water-retaining habitat features lacking from standard coastal infrastructure.
Complexity is well accepted as one of the primary drivers of biodiversity, however, empirical support for such positive associations is often confounded with surface area and undermined by other potential explanatory factors, especially the type of structural component (e.g., pits, crevices, overhangs, etc.). In the present study, sample units (artificial substrates) of equal surface area (±0.2%) were used to simultaneously examine the independent effects of complexity and different structural component types on species richness (S), abundance (N), and community composition. We created simple and complex concrete substrates of four different geometric designs using novel software. The substrates (n = 8) were mounted onto granite seawalls (at two tidal heights) on two islands south of Singapore Island. After 13 months of colonization, all 384 tiles were collected and their assemblages compared. A total of 53 744 individuals of 70 species/morphospecies were collected and identified. Our results show that greater complexity can support greater species richness and different communities that are independent of surface area. Furthermore, the type of structure (e.g., "pits," "grooves," "towers") can have an effect on richness and community composition that is independent of complexity.
This study examines the importance of thermal refugia along the majority of the geographic range of a key intertidal species (Patella vulgata Linnaeus, 1758) on the Atlantic coast of Europe. We asked whether differences between sun-exposed and shaded microhabitats were responsible for differences in physiological stress and ecological performance, and examined the availability of refugia near equatorial range limits. Thermal differences between sun-exposed and shaded microhabitats are consistently associated with differences in physiological performance, and the frequency of occurrence of high temperatures is most likely limiting the maximum population densities supported at any given place. Topographic complexity provides thermal refugia throughout most of the distribution range, although towards the equatorial edges the magnitude of the amelioration provided by shaded microhabitats is largely reduced. Importantly, the limiting effects of temperature, rather than being related to latitude, seem to be tightly associated with microsite variability, which therefore is likely to have profound effects on the way local populations (and consequently species) respond to climatic changes. This article is protected by copyright. All rights reserved.
Coastal armouring occurs because of the construction of artificial structures along natural shorelines.These include revetments, docks, groynes and seawalls, in addition to numerous minor structures (Table 7.1). This coastal infrastructure not only provides important onshore functions, but also brings shipping onto the shoreline, facilitating loading and unloading. Structures running alongshore, such as revetments and seawalls, are often built to protect shorelines against erosion, or to provide easy access to ships. They are usually steep and constructed of material designed to withstand erosion and wear, and are placed above the high tide level, inter- or subtidally, or offshore. Other structures, built perpendicular to the shore, for example, groynes and jetties, are often built to prevent movement of sand, or to gain access to boats in deeper water. Structures such as drilling platforms and wind turbines have become common features in offshore waters. Dugan et al. (2011)provide a detailed summary of the types and extent of infrastructure common on many shores today.
Rapidly growing populations and expanding development are intensifying pressures on coastal ecosystems. Sea-level rise and other predicted effects of climate change are expected to exert even greater pressures on coastal ecosystems, exacerbating erosion, degrading habitat, and accelerating shoreline retreat. Historically, society’s responses to threats from erosion and shoreline retreat have relied on armoring and other engineered coastal defenses. Despite widespread use on all types of shorelines, information about the ecological impacts of shoreline armoring is quite limited. Here we summarize existing knowledge on the effects of armoring structures on the biodiversity, productivity, structure, and function of coastal ecosystems.
Regional landscape context influences the fate of local populations, yet the spatial extent of this influence (called the "scale of effect") is difficult to predict. Thus, a major problem for conservation management is to understand the factors governing the scale of effect such that landscape structure surrounding a focal area is measured and managed at the biologically relevant spatial scale. One unresolved question is whether and how scale of effect may depend on the population response measured (e.g., abundance vs. presence/absence). If scales of effect differ across population outcomes of a given species, management based on one outcome may compromise another, further complicating conservation decision making. Here we used an individual-based simulation model to investigate how scales of effect of landscapes that vary in the amount and fragmentation of habitat differ among three population responses (local abundance, presence/absence, and genetic diversity). We also explored how the population response measured affects the relative importance of habitat amount and fragmentation in shaping local populations, and how dispersal distance mediates the magnitude and spatial scale of these effects. We found that the spatial scale most strongly influencing local populations depended on the outcome measured and was predicted to be small for abundance, medium-sized for presence/absence, and large for genetic diversity. Increasing spatial scales likely resulted from increasing temporal scales over which outcomes were regulated (with local genetic diversity being regulated over the largest number of generations). Thus, multiple generations of dispersal and gene flow linked local population patterns to regional population size. The effects of habitat amount dominated the effects of fragmentation for all three outcomes. Increased dispersal distance strongly reduced abundance, but not presence/absence or genetic diversity. Our results suggest that managing protected species at spatial scales based on population abundance data may ignore broader landscape effects on population genetic diversity and persistence, lending support to the importance of managing large buffers surrounding areas of conservation concern.
Urbanisation is recognised as a major pressure on coastal biodiversity. Increasing risks of flooding and erosion associated with future climate change indicate that new hard infrastructure will have to continue to be built – and existing structures upgraded – in areas of high social and economic value. Ecological enhancement involves undertaking management interventions at the design stage to improve the ecological potential of these structures, or to improve the ecological value of existing structures. Whilst scientific research into ecological enhancement methods and designs is growing, there has been limited discussion of the non-science drivers and mechanisms by which ecological enhancements can be successfully implemented in coastal infrastructure projects.We explore the science–policy–practice interfaces of the ecological enhancement of hard coastal structures from three perspectives. First, we outline the growing number of European and UK policies and legislative instruments that are increasing the need to consider ecological enhancement in coastal developments. These serve as a facilitative tool for making enhancement projects happen, constituting a significant ‘policy push’ for research and application in this area. Second, we examine the role of people in influencing the uptake of ecological enhancements. The critical role of ‘knowledge brokers’ and the need for effective and sustained collaboration between a range of groups and individuals to get research approved operational trials off the ground is discussed. Third, we examine where in the typical planning, design and build process current enhancement projects have been embedded, serving to illustrate how the science can be used in practice.
In Singapore, breakwaters have replaced natural rocky shores as the predominant hard- substratum intertidal coastal habitat on both the main island as well as the smaller islands to the south. These form isolated and non-contiguous areas of relatively homogenous rock (granite), separated by sandy shore or water. Insular assemblages of species at island locations are expected to be more stochastic in organisation than those on the mainland, due in part to variable patterns of colonisation and extinction. As such, there should be differences between the mainland and islands in terms of assemblage composition, structure and in the variability of abundances of taxa at a range of spatial scales. This study examines the structure of assemblages on seawall habitats located on the Singapore mainland and its southern islands. Analyses revealed differences between island and the mainland in the structure, but not the composition of intertidal assemblages, and also in the magnitude of variation in abundances of individual taxa at the spatial scales examined. Differences were more pronounced in assemblages lower on the shore than in high shore and supralittoral assemblages. In addition, assemblages tended to be more similar within locations, but there was no tendency for variability in the mean abundances of any taxa to be consistently higher at any habitat or spatial scale. On the whole, the results do not support the model of higher stochasticity of assemblages on artificial intertidal rocky habitats on islands. Instead, it revealed that high spatial variability at mainland locations could be linked to highly localised environmental conditions. Community organisation on these seemingly homogenous structures is shown to be complex and idiosyncratic. Factors and mechanisms influencing assemblage structure in natural rocky intertidal habitats are likely to operate differently on these artificial habitats, and should be examined critically prior to management decisions assuming or relying on the surrogacy of these structures as alternative marine habitats.
We briefly review how coastal ecosystems are responding to and being impacted by climate change, one of the greatest challenges facing society today. In adapting to rising and stormier seas associated with climate change, coastal defence structures are proliferating and becoming dominant coastal features, particularly in urbanised areas. Whilst the primary function of these structures is to protect coastal property and infrastructure, they inevitably have a significant secondary impact on the local environment and ecosystems. In this review we outline some of the negative and positive effects of these structures on physical processes, impacts on marine species, and the novel engineering approaches that have been employed to improve the ecological value of these structures in recent years. Finally we outline guidelines for an environmentally sensitive approach to design of such structures in the marine environment.
People have caused major impacts on nearshore and intertidal habitats by building infrastructure associated with shipping, recreation, residential and commercial developments. Together with the desire or need to control erosion, these have led to increased “armouring” of intertidal shorelines, with seawalls, revetments, onshore and offshore groynes and other defence systems, piers and docks replacing natural habitats. Despite the long history of such changes, until relatively recently there had been limited research on the impacts of such alterations to shorelines, especially when compared to research into effects of urbanisation on terrestrial habitats. In addition, most research to date has focussed on the impacts of such changes on the ecological structure of assemblages, i.e. the numbers and types of organisms affected, rather than on ecological processes. With the realisation that most coastal infrastructure cannot be removed, there is now an increasing research effort into ways that infrastructure can be built to meet engineering requirements, but to also increase its value as habitat – ecological engineering. In this review, we discuss the major impacts and the experimental research that has been and is being done to build coastal infrastructure in a more biodiversity-friendly manner. Much of the review has focussed on seawalls, which is where most of the experimental work has been done to date. Finally, we raise some concerns about the types of research effort that are still needed and caution against wholesale implementation of what seem like simple remedies, without evidence that they will have the desired effect in the long term.
Environment-dependent variation in the morphological, physiological, or behavioural expression of a genotype is termed phenotypic plasticity. To test for small-scale morphological plasticity in the Indo-Pacific massive corals Favia speciosa (Dana, 1846) and Diploastrea heliopora (Lamark, 1816), fragments (clone-mates) from 12 colonies of each species were reciprocally transplanted among 6 new habitats located within 2 environmental gradients: a depth cline and a nearshore-to-offshore gradient in sedimentation rates and total suspended solids (TSS). After 7 mo, all fragments were collected, cleared of tissue, and 10 morphometric characters extracted from randomly chosen corallites. Reaction norms, analysis of variance, and canonical discriminant analysis describe environment-induced changes in corallite architecture. These changes are more pronounced in the depth cline than along the sediment gradient. Similarity of response is suggested by exploratory factor analysis where, for both species, size attributes dominate the first factor, antisymmetry the second, and corallite exsertion the third. Highly significant genotype x environment interactions for F speciosa indicate that, for this species, genotypes vary in the level of plasticity expressed. Light and TSS emerge as the primary correlates influencing morphological change, although other parameters might act additively, synergystically or antagonistically with them. In shallow waters, increased corallite exsertion may enhance light capture or, alternatively, protect the central (oral disc) area of each polyp from harmful UV radiation. Morphological variability, combined with environment-induced changes in pigmentation, could impede accurate identification of these taxa.
The range of resources that a species uses (i.e. its niche breadth) might determine the geographical area it can occupy, but consensus on whether a niche breadth-range size relationship generally exists among species has been slow to emerge. The validity of this hypothesis is a key question in ecology in that it proposes a mechanism for commonness and rarity, and if true, may help predict species' vulnerability to extinction. We identified 64 studies that measured niche breadth and range size, and we used a meta-analytic approach to test for the presence of a niche breadth-range size relationship. We found a significant positive relationship between range size and environmental tolerance breadth (z = 0.49), habitat breadth (z = 0.45), and diet breadth (z = 0.28). The overall positive effect persisted even when incorporating sampling effects. Despite significant variability in the strength of the relationship among studies, the general positive relationship suggests that specialist species might be disproportionately vulnerable to habitat loss and climate change due to synergistic effects of a narrow niche and small range size. An understanding of the ecological and evolutionary mechanisms that drive and cause deviations from this niche breadth-range size pattern is an important future research goal.
Selective predation occurs when the relative frequencies of prey types in a predator's diet differ from the relative frequencies in the environment. A measure of preference is proposed which is derived from a simple stochastic model involving probability of encounter and probability of capture upon encounter. The measure is applicable to any number of prey types and methods of estimation are given for both constant and changing prey numbers. Because the measure is based on a biological model, it can be manipulated and interpreted in a meaningful way.
Intertidal seawalls support different assemblages and fewer species than do natural habitats. One explanation for these patterns may be the lack of some microhabitats on seawalls. Preliminary observations suggested that some features of sandstone seawalls, such as the presence of crevices among blocks, may provide chitons with an important habitat. To test the hypothesis that numbers of the chiton, Sypharochiton pelliserpentis, would be greater in crevices than on exposed surfaces of seawalls, sampling was done on sandstone seawalls in Sydney Harbour. S. pelliserpentis were more abundant in crevices among blocks than on exposed surfaces. Experimental manipulations transplanting chitons to exposed surfaces showed that they were found in greater numbers in crevices where those were available than on exposed surfaces. Chitons transplanted to blocks where crevices had been filled tended to move to non-filled crevices on other blocks. The design of seawalls could easily be improved to offer a better habitat for survival and maintenance of species such as chitons by incorporating crevices and similar features. In an increasingly urbanized world, understanding how to improve the value as habitat of man-made structures will be essential for conserving biodiversity.
Range boundaries are a fundamental expression of a species' relationship with other species and with the abiotic environment. In this study, I examined the roles of biotic and abiotic factors in setting the local range limits of Mazzaella parksii (formerly Mazzaella cornucopiae). In Washington State, this turf-forming red alga occurs almost exclusively in a discrete high intertidal band on north-facing, wave-exposed shores. I in-vestigated the mechanisms underlying these distributional patterns via a series of intra-and extra-limital transplant experiments coupled with manipulations of interacting species and abiotic stress. The upper limit of Mazzaella was set by physiological stress; turfs trans-planted above the natural Mazzaella zone bleached and died over the course of a few months. Mazzaella's lower limit was set by herbivory; turfs transplanted below the natural zone were consumed in treatments accessible to grazers but thrived in herbivore-exclusion plots. South-facing transplants at the same intertidal height as the natural north-facing Mazzaella zone declined regardless of interspecific interactions, indicating that Mazzaella's upper limit is lower on south-facing shores. However, the position of the herbivore-deter-mined lower limit was similar between aspects. South-facing transplants could survive below the natural Mazzaella zone if the grazer-determined lower limit was extended down-shore by herbivore exclusions or at Mazzaella's natural intertidal height (i.e., the height at which it persists on north-facing surfaces) if the physiologically determined upper limit was extended upshore by experimental shades. In the absence of such experimental mod-ifications, Mazzaella was effectively excluded from south-facing shores because its upper limit had converged on its lower limit. Thus, abiotic factors and biological factors interact to set the horizontal distributional limits of this alga. This conceptual model is consistent with Mazzaella's distribution at a variety of spatial scales and has broad implications for both spatial patterns and temporal trends in the distribution and abundance of species.