Ecological engineering across organismal scales: trophic-mediated positive effects of microhabitat enhancement on fishes

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

Urban-related distribution patterns of an iconic Salish Sea mesopredator, the giant Pacific octopus (Enteroctopus dofleini)

Like many coastal areas globally, the Salish Sea has undergone rapid urbanization over recent decades. Terrestrial research suggests urbanization facilitates a variety of mesopredators by enhancing food and shelter resources and by limiting apex predation. Yet urbanization’s effect on mesopredators in the marine environment has rarely been examined. The giant Pacific octopus, Enteroctopus dofleini, is an iconic mesopredator of the Pacific Northwest due to its size and cognition, and is thought to reach a particularly large maximum size in inland waters of the Salish Sea. We examined the spatial distribution patterns and habitat use of giant Pacific octopus in Puget Sound using a combination of field surveys and citizen-contributed data from the Reef Environmental Education Foundation (REEF). Specifically, we sought to determine: (1) Whether octopus distribution was related to land-based urbanization indices, (2) Whether octopus abundance correlated with anthropogenic debris, and (3) Whether octopus diets differed relative to urbanization intensity. Our findings suggest that effects from urbanization may depend heavily on the depth of benthic habitats. In deeper subtidal areas (\u3e 24 m), the estimated probability of octopus occurrence increased with adjacent land-based urbanization. Conversely, octopus in shallower subtidal zones (\u3c 18 m) were less likely to occur as urbanization intensity increased. This pattern appears to be unrelated to utilization of prey resources by octopus, as accompanying surveys of octopus middens showed no depth-specific differences in diet relative to urbanization. However, additional video transect surveys at paired sites with high versus low concentrations of anthropogenic debris indicated that artificial structures, which may be extensive in deep-water habitats within heavily urban areas, facilitate higher octopus abundances by serving as den sites. We suggest that den provisioning by urban artificial structures may be a key mechanism driving urban-related distribution patterns of giant Pacific octopus, and should be explored further through future research

Area-Independent Effects of Water-Retaining Features on Intertidal Biodiversity on Eco-Engineered Seawalls in the Tropics

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

Towards an urban marine ecology : characterizing the drivers, patterns and processes of marine ecosystems in coastal cities

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.Peer reviewe

Chapter 4 Design Options, Implementation Issues and Evaluating Success of Ecologically Engineered Shorelines

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

Urban coral reefs: Degradation and resilience of hard coral assemblages in coastal cities of East and Southeast Asia

© 2018 The Author(s) Given predicted increases in urbanization in tropical and subtropical regions, understanding the processes shaping urban coral reefs may be essential for anticipating future conservation challenges. We used a case study approach to identify unifying patterns of urban coral reefs and clarify the effects of urbanization on hard coral assemblages. Data were compiled from 11 cities throughout East and Southeast Asia, with particular focus on Singapore, Jakarta, Hong Kong, and Naha (Okinawa). Our review highlights several key characteristics of urban coral reefs, including “reef compression” (a decline in bathymetric range with increasing turbidity and decreasing water clarity over time and relative to shore), dominance by domed coral growth forms and low reef complexity, variable city-specific inshore-offshore gradients, early declines in coral cover with recent fluctuating periods of acute impacts and rapid recovery, and colonization of urban infrastructure by hard corals. We present hypotheses for urban reef community dynamics and discuss potential of ecological engineering for corals in urban areas

Benthic subtidal assemblages and ecological processes in urbanized seascapes of Puget Sound, Washington, USA

Thesis (Ph.D.)--University of Washington, 2017-08Urbanization is a major process altering nearshore habitats in many parts of the world. One important aspect of urbanization in marine settings is the proliferation of artificial structures, such as seawalls, breakwaters, and jetties. Urban artificial structures can fundamentally shift marine communities and alter ecological processes at multiple spatial scales. Though they are common in both intertidal and subtidal habitats, their effect on subtidal ecosystems is particularly understudied. I examined the communities that form in association with subtidal artificial structures and their effects on surrounding sedimentary habitats in an urbanized estuary. In the first chapter, I evaluated detrital influx from artificial structures to surrounding sediments. Photoquadrat and sediment surveys indicated that red macroalgae and epilithic invertebrates were the major producers of detrital material on artificial structures in the Seattle area and that detritus from artificial structures was moving into adjacent sediments. Through a series of experiments, I then assessed the potential effects of these detrital inputs on macrofaunal assemblages. Sediments receiving one-time additions of red macroalgae and shell material were relatively resilient to detrital influx and exhibited little to no change in macrofaunal composition. However, rapid reductions in sediment chlorophyll and phaeopigment following detrital additions suggested that delivery of red macroalgae into sediments surrounding artificial structures may be frequent. In a follow up experiment, sediments were enriched with red macroalgae on a weekly basis to reflect more frequent delivery rates. Though I hypothesized that red macroalgae would serve as a subsidy for macrofaunal assemblages, I observed no positive opportunistic responses among macrofauna to weekly additions. Rather, frequent inputs of red macroalgal detritus led to decreases in abundance for the majority of macrofaunal taxa. Red macroalgae may therefore have negative impacts on macrofaunal assemblages, though this effect is likely minor compared with hydrodynamic alterations and other changes to sedimentary habitats that are associated with artificial structures. In the second chapter, I examined urban-related spatial distribution patterns and habitat-use the giant Pacific octopus (Enteroctopus dofleini). Urbanization is known to facilitate certain terrestrial mesopredators and I sought to evaluate whether similar patterns relative to urbanization were evident for this marine mesopredator. Modeling of citizen-contributed octopus presence/absence data suggested that urbanization impacts differed with depth. Octopus occurrence probability was positively correlated with urbanization intensity in deeper habitats only (> 24 m). In shallower environments (< 18 m), occurrence probability was higher in rural areas than in urban areas. In separate field surveys, I found that octopus diets were unrelated to urbanization, and that octopus abundance was positively correlated with the number of artificial structures on the seafloor. Though trophic mechanisms for urban-related distribution patterns of giant Pacific octopus are therefore unlikely, provisioning of shelter and denning habitat from artificial structures may be an important factor for octopus populations in urban areas. In the final chapter, I examined benthic composition on rocky artificial structures and natural reefs across an urban gradient. Photoquadrats were collected at 36 sites across Puget Sound. Consistent with studies in other regions, I found that artificial structures supported distinct and more variable benthic assemblages than natural reefs. In addition, rocky subtidal habitats in heavily urban areas had fewer kelps and more filamentous algal turf than those in less urban areas. Importantly, analyses from this study highlighted an important challenge in evaluating benthic composition relative to urbanization. Coastal cities tend to be located in protected bays and at the mouths of rivers, where benthic communities are subject to strong salinity gradients and low water flow. Strong collinearity in these naturally occurring environmental variables and urbanization intensity will be an important consideration for future studies that aim to characterize effects of urbanization on marine ecosystems

Subtidal riprap in Puget Sound: Its ecological structure and function, and its impact on adjacent soft sediment environments

In the past decade, several studies have examined the effects of coastal defense structures, such as riprap, in the intertidal zone in Puget Sound. However, these structures commonly extend well below the intertidal. In subtidal environments, very little is known about the ecological structure, function, and processes on riprap. We conducted photo surveys in the Seattle area to characterize the community composition on subtidal riprap installations. Subtidal riprap was dominated by a wide variety of red algae species and sessile invertebrate fauna. The community on subtidal riprap was not typical of that that observed on natural rocky substrates in the region. We also conducted sediment surveys, which revealed that biogenic materials from subtidal riprap installations were readily incorporated into sediments immediately adjacent to riprap. Two types of biogenic material were particularly common: (1) shell hash from Balanus sp., Pododesmus machrochisma, and other rocky sessile invertebrates, and (2) small pieces of red algae. The density of these materials decreased significantly with increasing distance from subtidal riprap, and may influence the community composition of infauna in surrounding sediments. While previous studies in the intertidal have emphasized the importance of intertidal riprap in altering erosive forces in surrounding habitats, subtidal riprap may serve as growing medium for biogenic materials and resources that subsidize adjacent soft sediment communities

Area-independent effects of water-retaining features on intertidal biodiversity on eco-engineered seawalls in the tropics

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