Shoreline Armoring Research Articles

The Role of Living Shorelines as Estuarine Habitat Conservation Strategies

ABSTRACTGlobally, shoreline protection approaches are evolving towards the incorporation of natural and nature-based features (living shorelines henceforth) as a preferred alternative to shoreline armoring. Emerging research suggests that living shorelines may be a viable approach to conserving coastal habitats (marshes, beaches, shallows, seagrasses) along eroding shorelines. Living shorelines typically involve the use of coastal habitats, such as wetlands, that have a natural capacity to stabilize the shore, restore or conserve habitat, and maintain coastal processes. They provide stability while still being dynamic components of the ecosystem, but due to their dynamic nature, careful designs and some maintenance will be required if habitat conservation is a goal. Living shorelines may represent a singular opportunity for habitat conservation in urban and developing estuaries because of their value to society as a shoreline protection approach and resilience to sea level rise. However, enhanced public acceptance and coordination among regulatory and advisory authorities will be essential to expand their use. To fully understand their significance as habitat conservation strategies, systematic and standardized monitoring at both regional and national scales is vital to evaluate the evolution, persistence, and maximum achievable functionality (e.g., ecosystem service provision) of living shoreline habitats.

Nekton assemblages along riprap-altered shorelines in Delaware Bay, USA: comparisons with adjacent beach

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 548:209-218 (2016) - DOI: https://doi.org/10.3354/meps11685 Nekton assemblages along riprap-altered shorelines in Delaware Bay, USA: comparisons with adjacent beach Michael P. Torre1,2,*, Timothy E. Targett1 1University of Delaware, School of Marine Science and Policy, Lewes, Delaware 19958, USA 2Present address: University of Maine, School of Marine Sciences, Orono, Maine 04469, USA *Corresponding author: torrem27@gmail.com ABSTRACT: Riprap-reinforced shorelines are becoming more prevalent as a result of increasing coastal development and sea level rise. Altered morphology at the land-water interface, associated with riprap shorelines, has the potential to reduce shore-zone habitat quality for associated nekton species. The shore-zone nekton assemblage within a temperate, mid-Atlantic coast, USA, estuary was examined to identify differences in habitat use between sandy beach and riprap shorelines. We found that riprap can have a negative effect on a local scale. Overall nekton density, species richness, and density of dominant species were higher along beach shorelines relative to adjacent riprap, in most instances. Nekton association with shoreline habitat appears to be consistent over the diel cycle. Densities of Atlantic silverside Menidia menidia, striped killifish Fundulus majalis, spot Leiostomus xanthurus, and white perch Morone americana were generally reduced along riprap. In some cases, riprap shorelines also had altered species assemblages. Thus, our findings provide evidence of altered habitat quality for shore-zone nekton associated with shoreline hardening. These impacts were, however, variable spatially and temporally. Further research is needed to identify the biophysical mechanisms associated with riprap shorelines that are most responsible for altered habitat quality. KEY WORDS: Shoreline armoring · Riprap · Beach · Fish assemblage · Nekton density · Estuary · Delaware Bay Full text in pdf format PreviousNextCite this article as: Torre MP, Targett TE (2016) Nekton assemblages along riprap-altered shorelines in Delaware Bay, USA: comparisons with adjacent beach. Mar Ecol Prog Ser 548:209-218. https://doi.org/10.3354/meps11685 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 548. Online publication date: April 21, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Local and regional disturbances associated with the invasion of Chesapeake Bay marshes by the common reed Phragmites australis

The invasion of wetlands by Phragmites australis is a conservation concern across North America. We used the invasion of Chesapeake Bay wetlands by P. australis as a model system to examine the effects of regional and local stressors on plant invasions. We summarized digital maps of the distributions of P. australis and of potential stressors (especially human land use and shoreline armoring) at two spatial scales: for 72 subestuaries of the bay and their local watersheds and for thousands of 500 m shoreline segments. We developed statistical models that use the stressor variables to predict P. australis prevalence (% of shoreline occupied) in subestuaries and its presence or absence in 500 m segments of shoreline. The prevalence of agriculture was the strongest and most consistent predictor of P. australis presence and abundance in Chesapeake Bay, because P. australis can exploit the resulting elevated nutrient levels to enhance its establishment, growth, and seed production. Phragmites australis was also positively associated with riprapped shoreline, probably because it creates disturbances that provide colonization opportunities. The P. australis invasion was less severe in areas with greater forested land cover and natural shorelines. Surprisingly, invasion was low in highly developed watersheds and highest along shorelines with intermediate levels of residential land use, possibly indicating that highly disturbed systems are uninhabitable even to invasive species. Management strategies that reduce nutrient pollution, preserve natural shorelines, and limit nearshore disturbance of soils and vegetation may enhance the resilience of shorelines to invasion.

Multiscale impacts of armoring on Salish Sea shorelines: Evidence for cumulative and threshold effects

Shoreline armoring is widespread in many parts of the protected inland waters of the Pacific Northwest, U.S.A, but impacts on physical and biological features of local nearshore ecosystems have only recently begun to be documented. Armoring marine shorelines can alter natural processes at multiple spatial and temporal scales; some, such as starving the beach of sediments by blocking input from upland bluffs may take decades to become visible, while others such as placement loss of armoring construction are immediate. We quantified a range of geomorphic and biological parameters at paired, nearby armored and unarmored beaches throughout the inland waters of Washington State to test what conditions and parameters are associated with armoring. We gathered identical datasets at a total of 65 pairs of beaches: 6 in South Puget Sound, 23 in Central Puget Sound, and 36 pairs North of Puget Sound proper. At this broad scale, demonstrating differences attributable to armoring is challenging given the high natural variability in measured parameters among beaches and regions. However, we found that armoring was consistently associated with reductions in beach width, riparian vegetation, numbers of accumulated logs, and amounts and types of beach wrack and associated invertebrates. Armoring-related patterns at lower beach elevations (further vertically from armoring) were progressively harder to detect. For some parameters, such as accumulated logs, there was a distinct threshold in armoring elevation that was associated with increased impacts. This large dataset for the first time allowed us to identify cumulative impacts that appear when increasing proportions of shorelines are armored. At large spatial and temporal scales, armoring much of a sediment drift cell may result in reduction of the finer grain-size fractions on beaches, including those used by spawning forage fish. Overall we have shown that local impacts of shoreline armoring can scale-up to have cumulative and threshold effects -- these should be considered when managing impacts to public resources along the coast.

Coastal defences versus coastal ecosystems: A regional appraisal

Societal concern (both real and imagined) over coastal erosion and flooding, often results in construction of sea defences to protect property. Sea defences are, however, damaging to the natural ecosystems that provide quantifiable ecosystem services to the human population. Protection of property is, however, the most common driving force behind construction of sea defences and the basis of any associated economic appraisals. Protection of the coastal ecosystem (sedimentary, biological and chemical) while commonly implied in strategic documents (e.g. Habitats Directive 92/43/EEC, Water Framework Directive 2000/60/EC, OSPAR Convention), remain largely aspirational notions that currently have a much lower priority, or none at all, in sea defence decision-making. Under this anthropic view of coastal protection it is not surprising that defence structures proliferate. In many instances, shoreline armouring is considered on a case by case basis with little regard to the cumulative effects. This is true whether or not there is a strategic approach to coastal protection. In this paper the Northern Ireland coast is used as a case study to document the nature and extent of shoreline protection structures associated with sandy beaches. The nature and extent of sea defence structures were documented from a low-level oblique helicopter-based photographic survey and mapped in a GIS. The implications for the coastal ecosystem are considered. A sustainable approach to shoreline management demands a balance between protection of property and preservation of coastal ecosystem services.

A hybrid shoreline stabilization technique: Impact of modified intertidal reefs on marsh expansion and nekton habitat in the northern Gulf of Mexico

To mitigate shoreline erosion numerous armoring techniques have been employed extensively along the degrading shores of the Gulf of Mexico (GoM). Shoreline armoring strategies incorporating built vertical structures have resulted in numerous undesired ecological consequences. Bioengineering hybrid techniques consisting of “living shorelines” are emerging as an alternative option to mitigating shoreline loss and overcoming ecological shortcomings of hardened structures. Hitherto, only a few studies have assessed efficacy of hybrid techniques on shoreline stabilization and adjacent habitat enhancement. In this study, we integrated permeable intertidal reef-breakwaters (also known as wave attenuation units or WAUs) and predominantly restored native Spartina alterniflora marsh vegetation to mitigate erosion along severely degrading shores of a narrow peninsula in the northern GoM. Particularly, we evaluated impacts of a large-scale WAU reef deployment on a range of physical and biological parameters including erosion mitigation (shoreline stabilization), facilitation of created marsh expansion and habitat provision to marsh-utilizing nekton. We compared WAU reefs to adjacent gap areas without WAUs to evaluate the effects of tidal openings on the metrics measured. Our results of over 3 years suggest that, intertidal WAU reefs facilitate in created marsh expansion and the tidal openings between the reef complexes allow free movement of marsh-utilizing nekton fauna. Based on our results, we conclude that hybrid restoration technique is highly efficacious on erosion mitigation, adjacent marsh expansion and habitat creation. However, more works in other coastal systems are required to confirm the impacts of hybrid techniques on erosion mitigation and consequently on marshes and marsh-utilizing nekton.

Effects of seawall armoring on juvenile Pacific salmon diets in an urban estuarine embayment

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 535:213-229 (2015) - DOI: https://doi.org/10.3354/meps11403 Effects of seawall armoring on juvenile Pacific salmon diets in an urban estuarine embayment Stuart H. Munsch*, Jeffery R. Cordell, Jason D. Toft School of Aquatic and Fishery Sciences, University of Washington, 1122 NE Boat St., Seattle, WA 98105, USA *Corresponding author: smunsch@u.washington.edu ABSTRACT: An important nursery function of estuaries is providing prey resources for juvenile fish. Shoreline armoring compromises epibenthic and terrestrial prey resources, but it is unclear how this affects fish feeding ecology, particularly in urban landscapes where armoring is common. In this study we sampled prey availability and diets from 3 species of juvenile Pacific salmon (Oncorhynchus spp.) in shallow habitats of an extensively armored urban estuary. We compared sites armored by intertidal seawalls with those at small, engineered beaches without armoring. Available prey was different between shoreline types: epibenthic copepods were more abundant and taxonomically diverse at beaches, and barnacles were more abundant at seawall sites. There was no effect of armoring on salmon stomach fullness. Armoring rarely influenced whether salmon selected for or against a prey taxon but did affect diet composition of small (<50 mm) chum salmon (O. keta), which consumed greater abundances of epibenthic copepods at beaches and planktonic copepods at seawall sites. At beaches, these fish selected for epibenthic copepods and against planktonic copepods. At seawall sites, they selected for both epibenthic and planktonic copepods. Armoring did not affect diets of other salmon species or larger chum salmon that had different diets than small chum salmon. Armoring effects on fish diets may depend on differences in prey selection among species and life history stages. Further research is necessary to assess effects of armoring on habitat quality because fish may consume alternative prey when armoring changes the prey field, but it is unclear whether there are energetic costs to the predator. KEY WORDS: Shoreline development · Seawalls · Armoring · Diet composition · Juvenile salmon Full text in pdf format PreviousNextCite this article as: Munsch SH, Cordell JR, Toft JD (2015) Effects of seawall armoring on juvenile Pacific salmon diets in an urban estuarine embayment. Mar Ecol Prog Ser 535:213-229. https://doi.org/10.3354/meps11403 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 535. Online publication date: September 15, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Engineering away our natural defenses: an analysis of shoreline hardening in the US

Rapid population growth and coastal development are primary drivers of marine habitat degradation. Although shoreline hardening or armoring (the addition of concrete structures such as seawalls, jetties, and groins), a byproduct of development, can accelerate erosion and loss of beaches and tidal wetlands, it is a common practice globally. Here, we provide the first estimate of shoreline hardening along US Pacific, Atlantic, and Gulf of Mexico coasts and predict where future armoring may result in tidal wetland loss if coastal management practices remain unchanged. Our analysis indicates that 22 842 km of continental US shoreline – approximately 14% of the total US coastline – has been armored. We also consider how socioeconomic and physical factors relate to the pervasiveness of shoreline armoring and show that housing density, gross domestic product, storms, and wave height are positively correlated with hardening. Over 50% of South Atlantic and Gulf of Mexico coasts are fringed with tidal wetlands that could be threatened by future hardening, based on projected population growth, storm frequency, and an absence of coastal development restrictions.

The Relationship Between Shoreline Armoring and Adjacent Submerged Aquatic Vegetation in Chesapeake Bay and Nearby Atlantic Coastal Bays

Shoreline armoring is an ancient and globally used engineering strategy to prevent shoreline erosion along marine, estuarine, and freshwater coastlines. Armoring alters the land water interface and has the potential to affect nearshore submerged aquatic vegetation (SAV) by changing nearshore hydrology, morphology, water clarity, and sediment composition. We quantified the relationships between the condition (bulkhead, riprap, or natural) of individual shoreline segments and three measures of directly adjacent SAV (the area of potential SAV habitat, the area occupied by SAV, and the proportion of potential habitat area that was occupied) in the Chesapeake Bay and nearby Atlantic coastal bays. Bulkhead had negative relationships with SAV in the polyhaline and mesohaline zones. Salinity and watershed land cover significantly modified the effect of shoreline armoring on nearshore SAV beds, and the effects of armoring were strongest in polyhaline subestuaries with forested watersheds. In high salinity systems, distance from shore modified the relationship between shoreline and SAV. The negative relationship between bulkhead and SAV was greater further off shore. By using individual shoreline segments as the study units, our analysis separated the effects of armoring and land cover, which were confounded in previous analyses that quantified average armoring and SAV abundance for much larger study units (subestuaries). Our findings suggest that redesigning or removing shoreline armoring structures may benefit nearshore SAV in some settings. Because armoring is ubiquitous, such information can inform efforts to reverse the global decline in SAV and the loss of the ecosystem services that SAV provides.

Shoreline Armoring in an Estuary Constrains Wrack-Associated Invertebrate Communities

Beach wrack is an organic subsidy that supports high intertidal and supralittoral invertebrate communities in many coastal systems. Beaches fringed with riparian vegetation accumulate wrack from both terrestrial leaf litter and marine algae/seagrasses, forming a reciprocal connection. Previous research has shown that shoreline armoring disrupts this marine-terrestrial connection and alters the amount and composition of beach wrack. We sampled invertebrates associated with beach wrack at 29 paired armored and unarmored beaches in Puget Sound, WA and conducted wrack decomposition experiments. Armored beaches had significantly fewer invertebrates as well as different assemblages. Unarmored assemblages were characterized by talitrid amphipods and dipteran and coleopteran insects (flies and beetles), and were correlated with the amount of beach wrack and logs, the proportion of terrestrial material in the wrack, and the maximum elevation of the beach. Experiments showed that talitrid amphipods and oligochaete worms were positively correlated with wrack decomposition rates. The substantial reduction in high-shore invertebrates at armored beaches represents a decrease in subsidies to secondary consumers in both adjacent terrestrial and nearshore ecosystems. These armoring effects may thus cascade, via altered food webs, to organisms in other environments. Our sampling of multiple armored-unarmored beach pairs allowed us to control for variability of many environmental parameters, improving our ability to identify armoring-related differences, and greatly expanding the scale of inference of previous studies showing the negative effects of armoring on beach fauna.

Coastal erosion perception and willingness to pay for beach management (Cadiz, Spain)

Coastal zones are complex systems where many different human activities and natural processes converge. One of the most profitable and enjoyable activities is beach tourism and recreation; however, coastal erosion can cause not only loss of land and asset values but also loss of environmental and landscape qualities and therefore their recreational value due to passive erosion from shoreline armouring and coastal development. This paper reports results from economic and demographic factors affecting public coastal erosion awareness and willingness to pay on the urban beaches of Cadiz, SW Spain. Although there is a great public awareness of coastal erosion among the interviewed adults from town, the willingness to pay for beach management improvement is minimal. The fact is possibly explained by the low regional economic status and the large number of local residents among the beachgoers. The majority of the respondents said that there should not be any extra charges because they pay regular local taxes and already pay for using beach services.

Effects of shoreline engineering on shallow subtidal fish and crab communities in an urban estuary: A comparison of armored shorelines and nourished beaches

Shoreline armoring is common worldwide, yet its ecological effects have only recently been investigated. In this study, we surveyed shallow subtidal fish and crab communities at three sites with shorelines modified by seawall and riprap armoring and at three beaches with no armoring, all along the urbanized Elliott Bay shoreline of Seattle, WA (USA). Similar to many urban areas there is little natural shoreline remaining in Elliott Bay and beach sites were nourished with sediment that was similar to the historical structure of ambient nearshore habitats. We visually surveyed fish and crabs along scuba dive transects at these sites for eighteen months to quantify the composition of their communities and the association of fish and crabs with substrate types. The community composition and substrate type associations were similar among seawall sites and distinct from those at nourished beaches. Some species were predominantly associated with one substrate type (e.g., sand, riprap) and their densities at each site corresponded to the availability of this substrate type. Our results suggest that hard structures in engineered subtidal habitats may benefit some species that select for these introduced structures despite these structures not occurring historically. It is also clear that the creation of nourished beaches within armored shorelines can maintain different fish and crab communities than those associated with armoring, even in highly urbanized systems. Our study contributes to a growing literature that suggests that shoreline armoring and other types of habitat modifications affect the ecology of nearshore waters and the composition of nearshore communities.

Movement patterns and feeding behavior of juvenile salmon (Oncorhynchus spp.) along armored and unarmored estuarine shorelines

Estuarine nearshore environments are impor- tant habitats for many organisms, including juveniles of several Pacific salmon species (Oncorhynchus spp.). These habitats provide shallow water and high prey productivity, but are increasingly modified by anthropo- genic activity including shoreline armoring, which dis- rupts connectivitybetween aquatic and terrestrial realms and artificially steepens the shore. Such effects may have adverse consequences for juvenile salmon, partic- ularly Chinook (O. tshawytscha) and chum (O. nerka), which are known to rely on shallow, productive near- shore habitats for foraging and refuge from predators during their outmigration from natal streams to the sea. We developed snorkel methods to quantify feeding rates, movement rates, and path complexity of juvenile salmon along armored and unarmored shorelines in Puget Sound, WA, USA. We found that juvenile salmon had relatively high feeding rates along all shoreline types, but that path straightness and movement rates showed some variation between armored and unar- mored sites. Feeding fish swam in more complex paths and were observed in larger schools than non-feeding fish, and path straightness and movement rate were negatively correlated with proportion of time feeding. Feeding behavior, school size, and movement rates also showed variation byspecies. Shorelinetype(armoredor unarmored)influencedjuvenilesalmondistribution,and unarmored shorelines appear to accommodate a greater diversity ofmovementpatterns thanarmoredshorelines. Our results show that juvenile salmon feed at high rates along armored and unarmored estuarine shorelines, thus decreased prey availability or altered prey resources are likely the most detrimental foraging effects of armoring in estuarine nearshore ecosystems.

Effects of terrestrial–aquatic connectivity on an estuarine turtle

AbstractAimEstuaries world‐wide have been modified or fragmented due to human stressors in their terrestrial and aquatic components. Estuary fragmentation often results in reductions in species richness, diversity and connectivity. Effects of human modification on estuaries have been well studied, but less is known about how land use alters connectivity of the terrestrial–aquatic ecotone. We studied the relationship between terrestrial–aquatic connectivity and the distribution of an estuarine turtle, diamondback terrapin (Malaclemys terrapin).LocationChesapeake Bay, Virginia, USA.MethodsWe conducted diamondback terrapin surveys at 165 sites from late spring to mid‐summer in 2012 and 2013. We evaluated associations between terrapin occurrence, land use, salt marsh, shoreline armouring and crabbing intensity in concentric–circular neighbourhoods ranging from 0.27 to 2 km to cover daily and annual terrapin movements. We used occupancy modelling and model averaging to identify key terrestrial and aquatic variables explaining heterogeneity in terrapin occupancy. We evaluated the final model with an independent data set and identified occurrence thresholds for key variables.ResultsDiamondback terrapin occupy areas with ≥ 10% of marsh within a 750‐m neighbourhood, ≤ 17% armoured shoreline within a 1‐km neighbourhood, ≤ 20% of agriculture within a 500‐m neighbourhood, ≤ 33% low‐density housing within a 270‐m neighbourhood and ≤ 9 active crab pots within a 270‐m neighbourhood. Our model performed well when evaluated with an independent data set.Main conclusionsWe are the first to identify thresholds and quantify negative associations between the distribution of diamondback terrapin and alterations to terrestrial–aquatic connectivity from land development, shoreline armouring, and fishing activity. Because diamondback terrapin responses are reflective of changes in coastal habitats, especially marshes, terrapin occurrence can be used to direct wetlands conservation and restoration efforts.

Shoreline Armoring Impacts and Beach Restoration Effectiveness Vary with Elevation

Abstract Removal of shoreline armoring can potentially restore lost biological functions to intertidal beaches and increase connectivity between aquatic and terrestrial realms. Conceptual models are needed, as ecologists, managers, and engineers are all concerned with finding ways to restore natural aspects to shoreline features that are stable and resilient in the face of global climate change and sea level rise. We identify the main effects of armoring on shoreline biota, examine the ecological response of a restored site where a seawall was removed, and use this to form a conceptual basis for the importance of elevation on armoring effects and restoration potential. Restoration completed in February 2005 at Seahurst Park (Puget Sound, Washington, United States) included seawall removal and creation of a beach. We monitored the site over seven years before and after restoration and compared invertebrate assemblages to a reference beach, spanning four elevations. We present a conceptual model illustratin...

Restoration Considerations of Large Woody Debris in the Elwha River Nearshore, Olympic Peninsula, Washington

Large Woody Debris (LWD) is a critical component of Pacific Northwest marine ecosystems and of growing interest for restoration. This study adds important empirical data to the limited pool of information on the dynamics of LWD at the interface of freshwater, human, and marine ecosystems. In Washington State, the Elwha River nearshore is significantly ecologically altered due to shoreline armoring and upstream dams. The Elwha dam removal project, begun September 2011, is anticipated to change the composition, delivery rate and volume of LWD. We describe baseline characteristics of LWD in the Elwha River’s drift cell relative to unaltered areas with intact hydrodynamic processes by landform type, discuss anticipated changes, and consider the need for future work to understand and promote LWD in this restoration event. Results indicate LWD volumes of the Elwha nearshore were significantly lower than certain comparison areas; average site volume on Elwha’s spit was 0.83 m³ versus 18.6 m³ of the comparison spit. Similarly, the average number of pinned and buried LWD pieces (0.5 vs. 13.7) and count of straight logs (6.5 vs. 36.5) (composition) were significantly lower than those in the comparison spit. Current lower volume and differing structure of LWD likely contributes to impairment of ecological functions in Elwha’s nearshore. While dam removals may result in partial restoration of nearshore processes, ongoing decreased wood recruitment attributable to early logging, harvesting, and shoreline armoring are likely to continue preventing LWD accumulation. Restoration efforts should prioritize actions such as the removal of armoring and reduction of wood harvest.

Impacts of Terrestrial and Shoreline Stressors on Eelgrass in Puget Sound: An Expert Elicitation

We used expert elicitation to examine potential responses of eelgrass to several restoration strategies in Puget Sound. Restoration strategies included shoreline armor removal and modification, removal and modification of overwater structures, and efforts to improve water clarity via reductions in anthropogenic nutrient and sediment loadings. Expert responses indicated a general belief that reducing stressors would increase eelgrass cover; however, responses varied greatly among stressors. Our analyses revealed that removal of overwater structures, nutrient loading and shoreline armoring will have significantly larger effects on eelgrass recovery than would removal of sediment loading, with removal of overwater structures having the largest effect. We then used a probabilistic model to estimate what actions, singularly or in combination, could yield a large increase in eelgrass cover. Reducing single stressors could, in theory, result in recovery of eelgrass in Puget Sound; however, the magnitude of actions required would be so great that it is likely not practical. In contrast, we identified combinations of smaller reductions of stressors that could achieve significant eelgrass recovery. For example, a 40% reduction in overwater structures, combined with 20% reductions in shoreline armor, and nutrient and sediment loadings, was predicted to be one of the more feasible combinations of actions for meeting the target. The importance of eelgrass to Puget requires prompt input of scientific advice, and this work fills an important knowledge gap in the face of rapidly approaching legislative deadlines. While coded expert opinion of the sort we use here is a weak substitute for data, our work clarifies the current extent of scientific uncertainty that can guide management action in the near term and scientific research in the long term.

Effects of Shoreline Armoring on Beach Wrack Subsidies to the Nearshore Ecotone in an Estuarine Fjord

The ecological significance of algal and seagrass wrack subsidies has been well-documented for exposed-coast sandy beaches but is relatively unstudied in lower-energy and mixed-sediment beaches. In marine nearshore environments where beaches are fringed with riparian vegetation, the potential for reciprocal subsidies between marine and terrestrial ecosystems exists. Within the marine-terrestrial ecotone, upper intertidal “wrack zones” accumulate organic debris from algae, seagrass, and terrestrial plant sources and provide food and shelter for many organisms. Human modification also occurs within this ecotone, particularly in the form of armoring structures for bank stabilization that physically disrupt the connectivity between ecosystems. We conducted detailed wrack and log surveys in spring and fall over 3 years at 29 armored–unarmored beach pairs in Puget Sound, WA, USA. Armoring lowered the elevation of the interface between marine and terrestrial ecosystems and narrowed the width of the intertidal transition zone. Armored beaches had substantially less wrack overall and a lower proportion of terrestrial plant material, while marine riparian zones (especially trees overhanging the beach) were an important source of wrack to unarmored beaches. Armored beaches also had far fewer logs in this transition zone. Thus, they lacked biogenic habitat provided by logs and riparian wrack as well as the organic input used by wrack consumers. Results such as these that demonstrate armoring-associated loss of connectivity across the marine-terrestrial ecotone may be useful in informing conservation, restoration, and management actions.

Ecological response and physical stability of habitat enhancements along an urban armored shoreline

Shoreline armoring is prevalent worldwide and has resulted in substantial habitat alteration in heavily urbanized areas. The biological and physical processes associated with these shorelines have in many cases been compromised, which has led to a recent focus on how to design and implement projects to restore some of the lost or impaired functions, termed enhancement. We describe a multi-year effort testing whether an enhanced site has improved conditions in Seattle, WA, USA, along urban marine shorelines of Puget Sound. The Olympic Sculpture Park opened in January 2007 and included construction of two shallow-water features: a low-terrace habitat bench placed in front of an existing seawall, and a constructed pocket beach that replaced existing riprap. Riparian vegetation was also planted in the uplands replacing impervious surfaces and manicured lawn. We measured the functions of these sites by sampling both before and after enhancements (2005, 2007, and 2009), and comparing to adjacent armored shorelines. Although we are limited in our ability to make generalizations beyond this specific site due to only having one replicate of each shoreline type, the unique aspects of this urban enhancement make it useful as a case study that can apply to other urban systems. Fishes that are dependent on shallow water habitat were a main focus of sampling, specifically outmigrating juvenile salmon (Oncorhynchus spp.) and larvae of other species. Terrestrial and aquatic invertebrates were also assessed, both as a metric for habitat quality and as a determinant of available prey resources for juvenile salmon. Physical features of the created habitats were monitored in post-enhancement years to measure their stability. Results showed that shoreline enhancements increased densities of larval fishes and juvenile salmon and measurements of juvenile salmon feeding behavior dependent on the year, and provided habitat for invertebrate assemblages that were different from armored shorelines and had high taxa richness. Physical resilience depended on both natural processes and human activities, demonstrating the need to incorporate anthropogenic use into the management of urban shorelines.

Assessing local and landscape patterns of residential shoreline development in Michigan lakes

We evaluated relationships between residential development intensity and littoral zone habitat and disturbance characteristics in 332 Michigan lakes 4 ha and larger. We also developed a landscape-based model to estimate lakeshore status in more than 6500 unsampled lakes. Residential development had strong negative effects on large woody debris and strong positive effects on shoreline armoring and docks at both local and whole-lake scales. Lakes having greater cumulative residential development showed greater littoral zone impacts at local scales. Littoral habitats were more heavily impacted in larger lakes and in lakes in southern Michigan. Results of our predictive modeling identified the following as important predictors of residential shoreline development: the amount of urban land use, public ownership, and wetlands in a 100 m buffer around a lake as well as distance to major population centers. Statewide estimates of shoreline development showed that in southern Michigan only 8% of lakes were undeveloped and that 23% had low and 69% had high development intensity. In contrast, 30% of northern Michigan lakes were undeveloped and 48% had low and only 22% had high development intensity. Land planning policy and lake management should consider cumulative effects of lakeshore development as well as the effects of region and lake type. Our study provides the basis for developing regional strategies to protect, restore, and manage lake ecosystems.