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Many nearshore ecosystems are modified by aquaculture, including bivalve culture to produce food and restore extirpated populations. Small invertebrates in nearshore ecosystems support fundamental ecological processes, but the effects of bivalve culture on invertebrates are incompletely understood. Here, we compared invertebrate assemblages from multiple studies of bivalve-cultivated and unmodified nearshore habitats along the US west coast. In general, unmodified eelgrass and nearby off-bottom culture habitats with eelgrass present were inhabited by a greater abundance, richness, and diversity of epibenthic invertebrates than bottom culture and bare (mud, sand) habitats that both lacked eelgrass. Findings of individual studies suggested: minor differences in epibenthic invertebrate assemblages associated with various aquaculture practices; restoring native oysters to mudflats did not detectably alter epibenthic invertebrate abundances; epibenthic invertebrates were more abundant on shell hash introduced to mudflats than unmodified mudflats; and benthic invertebrates were less abundant, rich, and diverse in habitats cultured on bottom by Manila clams. Considering the range of these patterns, there appears to be potential for coastal communities to restore extirpated bivalve populations or develop bivalve culture practices that meet objectives to grow food while maintaining nearshore ecosystems’ fundamental processes supported by robust invertebrate assemblages.

Large river estuaries experience multiple anthropogenic stressors. Understanding plankton community dynamics in these estuaries provides insights into the patterns of natural variability and effects of human activity. We undertook a 2-year study in the Columbia River Estuary to assess the potential impacts of abiotic and biotic factors on planktonic community structure over multiple time scales. We measured microplankton and zooplankton abundance, biomass and composition monthly, concurrent with measurements of chlorophyll a, nutrient concentrations, temperature and salinity, from a dock in the lower estuary. We then statistically assessed the associations among the abundances of planktonic groups and environmental and biological factors. During the late spring high flow period of both years, the lower estuary was dominated by freshwater and low salinity-adapted planktonic taxa, and zooplankton grazers were more strongly associated with the autotroph-dominated microplankton assemblage than abiotic factors. During the early winter period of higher salinity and lower flow, nutrient (P) availability exerted a strong influence on microplankton taxa, while only temperature and upwelling strength were associated with the zooplankton assemblage. Our results indicate that the relative influence of biotic (grazers) and abiotic (salinity, flow, nutrients and upwelling) factors varies seasonally and inter-annually, and among different size classes in the estuarine food web.

We present the first comprehensive analysis of the Pacific Northwest estuaries (PNWE) zooplankton time series, which encompasses 38 estuaries distributed across more than 1000 km of the North American Pacific Coast. With observations spanning more than 20 yr, we here examine biogeographic trends among zooplankton communities, patterns of biological invasion across the region, and environmental correlates with dominant native and invasive taxa. Our results show that some estuaries across the region are invaded by multiple zooplankton species and that the geographic extent of invasion is far greater than previously reported for at least five species of copepods: Pseudodiaptomus inopinus, Pseudodiaptomus forbesi, Oithona davisae, Limnoithona sinensis, Sinocalanus doerrii, and the cladoceran Bosmina coregoni. Some of these species appear to be rapidly spreading across the region, while others have occupied a relatively static geographic range for decades. The copepod, P. inopinus, is by far the most abundant and geographically widespread of these invaders, comprising more than 90% of all zooplankton abundance at some sites. We propose that the geographic distribution of these invaders is strongly constrained by geomorphic characteristics that define the salinity and mixing regimes in these estuaries, reflecting the strong role that physical forces play in structuring estuarine zooplankton communities.

In human-impacted coastal ecosystems, living shorelines are becoming a common restoration technique. However, we lack a comprehensive understanding of the ecological and physical benefits, and how they could inform management needs. To address this, we studied effectiveness of living shorelines at a broad spatial scale within the Washington State boundaries of the Salish Sea, USA, with restored site ages spanning 1–11 years. We surveyed 30 beaches at ten locations, each with three strata of: (1) living shoreline beaches with armor removed, (2) armored control beaches altered by seawalls or riprap, and (3) un-armored reference beaches with natural conditions. We sampled eight physical and biological attributes: beach wrack, wrack invertebrates, sediments, terrestrial insects, riparian vegetation, logs, beach profiles, and stable isotope signatures of talitrid amphipods – generating 27 metrics focusing on upper intertidal and supratidal elevations affected by armoring and targeted by living shoreline actions. These metrics spanned the functions of beach stability, ecological diversity, and food web support for juvenile salmon. Statistical tests showed that 19 of the 27 metrics had significant strata differences, indicating that some beach metrics restore quickly (e.g., wrack accumulation), while others take longer (e.g., log accumulation). Terrestrial-associated metrics were higher at reference beaches, but insect taxa richness and logs with plant growth increased at beaches restored for four or more years (the average age of the living shoreline sites). This implies that certain living shoreline functions increase through time, providing improved food web support. Globally, trajectories of restoration have shown a range of functional improvement with time, and will be important to monitor for nature-based solutions to coastal defense given the increasing rate of shoreline stressors from global change and sea level rise.

The rate of aquatic invasions by planktonic organisms has increased considerably in recent decades. In order to effectively direct funding and resources to control the spread of such invasions, a methodological framework for identifying high-risk transport vectors, as well as ruling out vectors of lesser concern will be necessary. A number of estuarine ecosystems on the North American Pacific Northwest coast have experienced a series of high impact planktonic invasions that have slowly unfolded across the region in recent decades, most notably, that of the planktonic copepod crustacean Pseudodiaptomus inopinus. Although introduction of P. inopinus to the United States almost certainly occurred through the discharge of ballast water from commercial vessels originating in Asia (the species’ native range), the mechanisms and patterns of subsequent spread remain unknown. In order to elucidate the migration events shaping this invasion, we sampled the genomes of copepods from seven invasive and two native populations using restriction-site associated DNA sequencing. This genetic data was evaluated against spatially-explicit genetic simulation models to evaluate competing scenarios of invasion spread. Our results indicate that invasive populations of P. inopinus exhibit a geographically unstructured genetic composition, likely arising from infrequent and large migration events. This pattern of genetic patchiness was unexpected given the linear geographic structure of the sampled populations, and strongly contrasts with the clear invasion corridors observed in many aquatic systems.

We examined the effects of two types of piers on composition, abundance, and diversity of small epibenthic invertebrates and on several taxa known to be important prey for juveniles of three species of Pacific salmon. Using an epibenthic pump, invertebrates were sampled under and away from piers. Piers located within a dense urban aggregation of overwater structures and ferry piers occurring singly in less urbanized landscapes negatively impacted small invertebrates. Except for polychaetes at ferry piers and the harpacticoid copepods Tisbe species at urban piers, taxa richness and densities of invertebrate groupings and several juvenile salmon prey taxa were significantly decreased underneath both pier types and also near the edge of ferry piers. Assemblage structure was also greatly influenced by piers, with under-pier assemblages dominated by Tisbe species and several other taxa, and assemblages outside piers characterized by many taxa. Many of the negatively impacted taxa are associates of algae and seagrasses that were reduced under the piers. For juvenile salmon and other fish, reducing shade under piers by adding light to the environment may improve habitat access and quality in areas where piers decrease fish feeding opportunities.

Summary Nearshore ecosystems are increasingly recognized as critical habitats for fish of cultural, ecological and economic significance. These ecosystems are often densely inhabited by juvenile fish, highly productive and refuges from predation, leading ecologists to characterize them as nurseries. However, nearshore ecosystems are being transformed globally to support demands of growing coastal populations. Many shorelines are modified by armouring (e.g. seawalls, riprap) that minimizes erosion, and overwater structures (e.g. piers, docks) that facilitate waterfront use. These modifications affect the ecology of nearshore systems by restructuring, eliminating and shading shallow waters. Here, we review literature examining effects of armouring and overwater structures on coastal and estuarine fishes, and discuss how research and management can coordinate to minimize negative effects. Along armoured shorelines, fish assemblages differed from unarmoured sites, fish consumed less epibenthic and terrestrial prey, beach spawning was less successful and fish were larger. Under large overwater structures, visually oriented fish were less abundant and they fed less. Shade from overwater structures also interrupted localized movements of migratory fish. Thus, shoreline modifications impaired habitats by limiting feeding, reproduction, ontogenetic habitat shifts from shallow to deeper waters and connectivity. Research suggests that restoring shallow waters and substrate complexity, and minimizing shading underneath overwater structures, can rehabilitate habitats compromised by shoreline modifications. Synthesis and applications. Shoreline armouring and overwater structures often compromise fish habitats. These threats to nearshore fish habitats will become more severe as growing coastal populations and rising sea levels increase demands for shoreline infrastructure. Our ability to assess and rehabilitate nearshore fish habitats along modified shorelines will be enhanced by: focusing research attention on metrics that directly indicate fish habitat quality; implementing and evaluating shoreline features that repair compromised habitat functions within human-use constraints; collating natural history knowledge of nearshore ecosystems; and embracing the socio-ecological nature of habitat improvements by educating the public about conservation efforts and fostering appreciation of local nearshore ecosystems. Actions to reduce impacts of shoreline modifications on fish are particularly feasible when they align with societal goals, such as improving flood protection and providing spaces that facilitate recreation, education, and connections between people and nature.

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.

Daily cycles in feeding intensity are common among fish and suggestive of ecological trade-offs and constraints. However, feeding chronologies are typically estimated from diets rather than in situ observations. As a consequence, our understanding of daily feeding patterns is often imprecise, which limits our ability to infer connections between these patterns and their drivers. Here we quantify in unprecedented temporal resolution the real-time diurnal feeding behavior of a fish assemblage. Snorkelers observed juvenile Pacific salmon Oncorhynchus spp. in estuarine waters between dawn and early evening. Fish fed throughout the day, with intake declining after dawn, and individuals allocated about 20% of their time to feeding at sunrise, declining to about 5% in the early evening. Many factors potentially influenced this behavior, including predation avoidance, physiological constraints, prey availability, and mandates for growth and migration. Prey mass in the stomachs of these fish increased shor...

Identifying causes of structural ecosystem shifts often requires understanding trophic structure, an important determinant of energy flow in ecological communities. In coastal pelagic ecosystems worldwide, increasing jellyfish (Cnidaria and Ctenophora) at the expense of small fish has been linked to anthropogenic alteration of basal trophic pathways. However, this hypothesis remains untested in part because baseline description of fish–jellyfish trophic dynamics, and the environmental features that influence them are lacking. Using stable isotopes of carbon (δ13C) and nitrogen (δ15N), we examined spatiotemporal patterns of fish and jellyfish trophic structure in greater Puget Sound, an urbanizing fjord estuary in the NW United States. We quantified niche positions of constituent species, niche widths and trophic overlap between fish and jellyfish assemblages, and several community‐level trophic diversity metrics (resource diversity, trophic length, and niche widths) of fish and jellyfish combined. We then related assemblage‐ and community‐level measures to landscape gradients of terrestrial–marine connectivity and anthropogenic influence in adjacent catchments. Relative niche positions among species varied considerably and displayed no clear pattern except that fish generally had higher δ15N and lower δ13C relative to jellyfish, which resulted in low assemblage‐level trophic overlap. Fish assemblages had larger niche widths than jellyfish in most cases and, along with whole community trophic diversity, exhibited contrasting seasonal patterns across oceanographic basins, which was positively correlated to landscape variation in terrestrial connectivity. In contrast, jellyfish niche widths were unrelated to terrestrial connectivity, but weakly negatively correlated to urban land use in adjacent catchments. Our results indicate that fish–jellyfish trophic structure is highly heterogeneous and that disparate processes may underlie the trophic ecology of these taxa; consequently, they may respond divergently to environmental change. In addition, spatiotemporal variation in ecosystem connectivity, in this case through freshwater influence, may influence trophic structure across heterogeneous landscapes.

We have a limited understanding of habitat use and behavior in nearshore fish communities because they are rarely observed in situ. Consequently, ecologists recommend a process-based conceptualization of nursery habitats, but lack knowledge of nursery processes on fine scales along shore, and studies in controlled settings suggest that context-dependent behaviors allow fish to balance predation avoidance with other objectives, but there is little observational corroboration of these behaviors in situ. We used a long-term dataset of underwater observations to quantify the fine-scale habitat use and behavior of a shallow estuarine fish community. We asked, ‘Within species, how does behavior vary with habitat context and developmental stage?’ and ‘Do species partition habitats in space and time?’ We found that smaller fish occupied shallower depths where predators were less abundant; smaller fish schooled in larger groups; pelagic fish schooled in larger groups in deeper water; demersal fish schooled in larger groups when occupying the water column; and species partitioned habitats by depth and season. Additionally, smaller fish were proportionally less abundant along deep shorelines created by intertidal armoring. Overall, habitat use was suggestive of nursery functions, including ontogenetic habitat shifts, provision of predator refuge, and appropriate food/predation risk tradeoffs. Additionally, fish behaved in a manner consistent with adaptive decisionmaking to avoid predation, and time and space may be important axes on which transient juveniles partition habitats. Some nursery functions appeared to be mediated by a shallow depth gradient, which may be compromised by shoreline infrastructure and rising sea levels along built shorelines.

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.

Compared to benthic and water-column invertebrate assemblages, considerably less is known about terrestrial arthropods inhabiting estuarine wetlands despite their importance to tidal wetland biodiversity and productivity. We also need to know more about how human modification of estuaries, including efforts to restore estuarine wetlands, affects these assemblages. To address this knowledge gap, we assembled data from multiple studies on terrestrial arthropod assemblages from 87 intertidal wetland sites in 13 estuaries along the west coast of North America. Arthropods were sampled between 1998 and 2013 with fallout traps deployed in wetlands for 1 to 3 days at a time. We describe patterns in the abundance and taxonomic composition of terrestrial arthropods and evaluate the relative ability of natural and anthropogenic factors to explain variation in abundance and composition. Arthropod abundance was highly variable. Vegetation assemblage, precipitation, and temperature best explained variation in arthropod abundance, while river discharge, latitude, and developed and agricultural land cover surrounding sampling sites were less important. Arthropod abundance rapidly achieved levels of reference wetlands after the restoration of tidal influence to leveed wetlands, regardless of surrounding land cover. However, arthropod assemblage composition was affected by the amount of developed land cover as well as restoration age. These results suggest that restoration of tidal influence to leveed wetlands can rapidly restore some components of estuarine wetland ecosystems but that recovery of other components will take longer and may depend on the extent of anthropogenic modification in the surrounding landscape.

Urban nearshore ecosystems are built environments that differ structurally and functionally from the natural ecosystems they replace. Eco-engineering offers the ability to enhance these ecosystems by reducing the impacts of shoreline modification. Recent studies have linked shoreline armoring and pier shade—common features of modified shorelines—to lower foraging rates, altered distribution patterns, and increased predation risk for juvenile salmon. The 2017 replacement of the Elliott Bay seawall in Seattle, WA, USA incorporated novel eco-engineering design elements, including glass light penetrating surfaces (LPS) in overwater structures, an elevated seafloor, and textured substrates in the seawall face to enhance nearshore habitat for juvenile Pacific salmon (Oncorhynchus spp.) migrating from natal streams to the ocean. To examine the effectiveness of seawall eco-engineering, we used snorkel surveys to assess changes in juvenile salmon spatial distribution and foraging patterns during peak outmigration (March–August), and measured ambient light penetration before and after seawall replacement. Overall, we found that juvenile salmon were distributed more evenly across a spatial mosaic of habitats following eco-engineering. LPS enhanced ambient light penetration in nearshore under-pier habitats, and juvenile salmon use of these habitats increased concurrently. Salmon densities under piers tended to be greatest at low tides, indicating that light availability may mediate selective habitat use. Feeding rates at sites immediately adjacent to the seawall increased both between and under piers following habitat enhancement. Our findings suggest that the elevated light levels facilitated by LPS, in concert with physical enhancements that provided more complex shallow water habitat, temper the negative effects of pier shade and shoreline armoring on juvenile salmon.

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.

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.

The Asian isopod Ianiropsis serricaudis is now well established in fouling communities, often associated with introduced ascidians, throughout the Northern Hemisphere but has gone largely unnoticed because of its diminutive size (typically less than 3 mm in length) and the difficulties of identifying small peracarid crustaceans. Known locations include the northeastern Pacific (Puget Sound, San Francisco Bay, and Monterey Bay), the northwestern Atlantic (from the Gulf of Maine to Barnegat Bay, NJ), and the northeastern Atlantic (England and the Netherlands). We predict that this species is widespread along North America and European coasts, and may already be introduced to cold temperate waters of the Southern Hemisphere as well.

A key step in identifying global change impacts on species and ecosystems is to quantify effects of multiple stressors. To date, the science of global change has been dominated by regional field studies, experimental manipulation, meta-analyses, conceptual models, reviews, and studies focusing on a single stressor or species over broad spatial and temporal scales. Here, we provide one of the first studies for coastal systems examining multiple stressor effects across broad scales, focused on the nursery function of 20 estuaries spanning 1,600 km of coastline, 25 years of monitoring, and seven fish and invertebrate species along the northeast Pacific coast. We hypothesized those species most estuarine dependent and negatively impacted by human activities would have lower presence and abundances in estuaries with greater anthropogenic land cover, pollution, and water flow stress. We found significant negative relationships between juveniles of two of seven species (Chinook salmon and English sole) and estuarine stressors. Chinook salmon were less likely to occur and were less abundant in estuaries with greater pollution stress. They were also less abundant in estuaries with greater flow stress, although this relationship was marginally insignificant. English sole were less abundant in estuaries with greater land cover stress. Together, we provide new empirical evidence that effects of stressors on two fish species culminate in detectable trends along the northeast Pacific coast, elevating the need for protection from pollution, land cover, and flow stressors to their habitats. Lack of response among the other five species could be related to differing resistance to specific stressors, type and precision of the stressor metrics, and limitations in catch data across estuaries and habitats. Acquiring improved measurements of impacts to species will guide future management actions, and help predict how estuarine nursery functions can be optimized given anthropogenic stressors and climate change scenarios.

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...

Zooplankton are important trophic intermediaries between aquatic primary produc- ers and higher level consumers such as fish, but to date they have been little studied in intertidal marshes. This is particularly true in the San Francisco Estuary (SFE), which is heavily impacted by human activities and is being targeted for restoration of its native wetland communities. As part of a multi-year field study investigating wetland dynamics in the upper SFE, we conducted approximately quarterly sampling of the mesozooplankton (>73 µm) at 3 channels in each of 6 marshes. Here, we describe seasonal and regional variation in the composition and abundance of zooplankton, and relate these to variations in environmental conditions. Cluster analysis identi- fied 6 different marsh zooplankton communities. The 66 taxa identified included both native and non-indigenous species (NIS), with NIS being particularly dominant in the summer and autumn. Ordination analyses indicated that salinity, temperature, and other freshwater-related variables such as freshwater flow and distance to the coastal ocean were the strongest environmental driv- ers of marsh zooplankton community composition and individual abundance. Zooplankton com- munities in intertidal marshes were similar to those of open water habitats of the SFE in many regards, although differences in some taxa were observed, e.g. higher abundances of the copepod Eury temora affinis and lower abundances of tintinnid ciliates in the marshes. Apparent differ- ences in zooplankton between intertidal marsh and open water habitats, and between different regions of the estuary, could have important implications for young fish and other consumers.

Shoreline modifications, such as seawall armoring and piers, are ubiquitous along developed waterfronts worldwide, and recent research suggests that their ecological effects are primarily negative. We utilized snorkel surveys to quantify the effects of seawalls and piers on fish in nearshore habitats of an urbanized estuary in Puget Sound, Washington. We observed 17 species of fish and 4 species of crab during April–August 2012 at sites modified by seawalls and piers and at reference beach sites with minimal anthropogenic structures. Species assemblages at modified sites were significantly different from those at reference beaches. At modified sites, fish distribution and assemblage structure varied with proximity to the shade cast by piers; overall fish abundances were reduced under piers, and the greatest abundances were observed at high tides in areas directly adjacent to piers. Juvenile Pacific salmon Oncorhynchus spp. were the dominant fish species, and piers reduced their presence and feedin...

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.

The freshwater cladoceran Bosmina coregoni (Baird, 1857), native to Eurasia, has established and spread in the Great Lakes region of North America since the 1960s. Here we report the first detection of B. coregoni on the Pacific coast of North America, in three geographically distinct locations: the Lower Columbia River Estuary (LCRE), Lake Washington in western Washington state, and the Columbia River Basin in south eastern Washington state. Bosmina coregoni was detected on multiple sampling dates in Lake Washington and the LCRE between 2008 and 2012.

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.

The non-native tunicates Didemnum vexillum, Ciona savignyi, and Styela clava are of concern to resource managers of Puget Sound, Washington, USA because they have been shown to threaten native species diversity and shellfish aquaculture in other regions. Invasive tunicates in Puget Sound occur mainly on man-made structures such as floating docks and aquaculture facilities. We conducted studies of the three species of concern and a fourth introduced tunicate, Botrylloides violaceus, that occur on these structures to evaluate their effects on mussels and native invertebrate communities. Because most studies of community effects of tunicates have dealt with sessile fouling organisms, we focused instead on epibenthic organisms such as meiofaunal harpacticoid copepods and macrofaunal polychaetes and amphipods that are known to be important prey for juvenile salmon and other small fish. Similar studies have shown mixed results, with negative, positive, or no effects depending on the species. We also found few community-level effects. Abundances of several species were lower when tunicates were present, but only at some of the sites. Several other species, including a non-native isopod, were significantly more abundant in the presence of tunicates. However, in most cases results were not statistically significant and more intensive, controlled sampling or experiments may be needed to demonstrate any consistent tunicate effects. Although invasive tunicates cause problems for mussel growers elsewhere, we did not find negative effects on mussels at four sites in Puget Sound. Given the large impacts known to accompany tunicate invasions elsewhere and their relatively recent invasions into Puget Sound, monitoring of their populations and effects should continue in the region.

As part of a multi-year field study to investigate plankton dynamics in the Lower Columbia River Estuary (LCRE), we conducted monthly sampling of the mesozooplankton (> 73 μm) at a station near Astoria, Oregon. The planktonic copepod community was numerically dominated by three non-indigenous species (NIS), Pseudodiaptomus forbesi, Limnoithona tetraspina, and Sinocalanus doerrii, and two native species, Eurytemora affinis and Diacyclops thomasi. However, seasonal co-occurrence of non-indigenous and native copepods was highly variable between species-pairs. The native E. affinis and the non-indigenous S. doerrii showed the greatest temporal overlap (March-October), but other species-pairs also showed periods of considerable overlap during some seasons (e.g., E. affinis and P. forbesi in June-September). Spatial co-occurrence of native and non-indigenous species was also examined in temperature and salinity “space” (rather than geographic space): all six species-pairs (3 non-indigenous species × 2 native species) showed some degree of overlap, with the greatest (proportional) overlap occurring between the native E. affinis and the two nonindigenous species, S. doerrii and P. forbesi. This suggests the potential for competition to occur between native and non-native copepods in the LCRE, although with variation between seasons and species. Future studies are recommended that explicitly test for and distinguish between the relative importance of biological (e.g., competition and predation) and physico-chemical processes (e.g., freshwater runoff, eutrophication) in regulating the population dynamics of native and invasive copepods in the LCRE.

The Duwamish estuary is an industrialized waterway located in Seattle, WA, USA. Despite a history of habitat loss, naturally produced juvenile Chinook salmon use the estuary. In addition to experiencing degraded habitat in the estuary, wild salmon growth may be affected by competition with more than three million hatchery fish released yearly into the river. Restoring habitat to benefit salmon in the Duwamish River is a priority for trustees of public resources, and a number of wetland restoration sites have been created there. We tested the function of restored sites in the Duwamish estuary for juvenile Chinook salmon by comparing fish densities from enclosure nets or beach seines at three paired restored/un-restored sites and by applying environmental and diet data to a bioenergetics model. We also examined temporal and diet overlap of wild juvenile Chinook salmon with other salmon species and with hatchery-reared Chinook salmon using non-metric multidimensional scaling (NMDS). At a brackish upstream site with a relatively large opening to the river, we found higher densities of juvenile Chinook salmon at the restored site. NMDS results indicated that juvenile Chinook salmon fed on different taxa at the restored sites than at the reference sites. However, modeled growth was similar at restored and reference sites. Co-occurring juvenile chum and Chinook salmon fed differently, with chum eating smaller prey, and Chinook salmon eating larger prey. Co-occurring hatchery and wild juvenile Chinook salmon had similar diets, indicating that they may compete for prey. However, modeled growth was positive and did not differ between hatchery and wild fish, suggesting that food was not limiting. Bioenergetics models indicated that overall juvenile Chinook salmon growth potential at the brackish water site was consistently higher than at more saline sites. Our results suggest that restoration sites in the Duwamish estuary that have larger access openings and are located in brackish water may have increased function over other configurations.

The movement and release of non-indigenous species (NIS) in ship ballast water is a global threat to the conservation of native aquatic species and habitats. One key to successful NIS establishment in coastal waters is propagule pressure – the size and frequency of NIS inoculations. We estimated propagule pressure of high-risk coastal zooplankton delivered in ballast water to Puget Sound, Washington, USA, which receives 7.5 × 10 6 m 3 of ballast water annually. We weighed the relative propagule pressure from domestic and foreign ballast water, in terms of propagule size (number of individuals), frequency of NIS occurrences, and diversity (number of known NIS species). Ship discharge volume was not a good predictor of propagule pressure. Instead route type (domestic or foreign) and ballast water exchange status (exchanged in mid-ocean vs. unexchanged) were much better predictors of propagule supply. Overall, while the diversity of non-indigenous zooplankton was higher in trans-oceanic ballast, the annual discharge of coastal zooplankton propagules to Puget Sound was much greater for ships conducting domestic voyages. These results suggest that intra-coastal ballast water must be further scrutinized as a pathway for NIS introduction, and calls into question regional “common waters” agreements that allow vessels to move ballast without conducting ballast water treatment.

In coastal environments, the supratidal zone bridges marine and terrestrial ecosystems and is important for energy exchange. However, it is also subject to extensive anthropogenic disturbance, such as armoring of shorelines. Shoreline armoring is extensive along many coasts, but the impacts on biota are comparatively unknown. Between 2000 and 2002, paired and synoptic sampling regimes were employed to assess armoring effects on insects and benthic macroinvertebrates in the supratidal zone of Puget Sound beaches. Paired sampling showed natural beach sites had significantly more deposited wrack. Infauna was dominated by oligochaetes and nematodes; talitrid amphipods, insects, and collembolans were significantly more numerous at natural beaches, and crustaceans were more abundant at altered beaches. Insect assemblages were diverse, with taxon richness higher at natural beach sites. In the synoptic sampling, where sites with higher elevation modifications were used, there were fewer differences in invertebrate assemblages between armored and nonarmored sites. The results show that, where shoreline armoring lowers the land–sea interface, benthic infauna and insect assemblages are disrupted. Widespread shoreline modifications may decrease the availability of prey resources for fish and wildlife and decrease the contribution of organic material entering the nearshore ecosystem.

Estuarine ecosystems along the Pacific coast of North America are vulnerable to invasions by non-indigenous planktonic copepods, with documented invasions by at least nine species introduced via ship’s ballast. One of these, the calanoid copepod Pseudodiaptomus inopinus, now occurs in a relatively wide geographical area in coastal estuaries of Washington and Oregon States. Although it appears to be well established in the region, plankton surveys conducted in 1992, 1996, 2000, and 2004 in estuaries from southern Vancouver Island in British Columbia, Canada, to northern California, United States indicate that it has not expanded its range. This static distribution suggests that P. inopinus has reached a distributional limit, and it may thus be a good organism for applying models for predicting planktonic invasions, by characterizing estuaries with and without populations of the copepod. In this study, we applied both parametric, linear (discriminant function analysis, logistic regression) and nonparametric, non-linear (classification trees) techniques to develop models for occurrence of P. inopinus, to identify parameters that may lead to successful invasions and to identify specific estuaries or regions that might be at risk of invasion by this species. Both model types had similar results, identifying relatively simple salinity- and stratification-based models as good predictors of P. inopinus. While different models selected slightly different sets of variables and thresholds, all models identified relatively low salinity and stratification of water column temperature and salinity as important predictors of P. inopinus presence. The models also identified several “false positives” that mainly occurred in more inland waters of Puget Sound—estuaries that did not have P. inopinus, but had the conditions that support it, and which may be at risk for future invasions by this species.

1. Oceanographic characteristics and the presence of international shipping in Puget Sound, Washington, USA contribute to its vulnerability to non-indigenous species (NIS) invasions. To evaluate NIS arriving in ballast water, zooplankton was sampled in 380 ballast tanks of ships after they entered Puget Sound. 2. Taxa were classified into a higher risk group of coastal organisms (including known NIS), and a lower risk group of largely oceanic species. Most ships reported conducting mid-ocean ballast water exchange (BWE). However, despite state regulations requiring BWE, and apparent compliance by ship operators, most sampled tanks from both transpacific and coastal routes had coastal zooplankton densities exceeding internationally proposed discharge standards. 3. BWE efficiency models and controlled before-and-after BWE experiments indicate that BWE consistently removes most coastal zooplankton. However, this study found that although the empty–refill method of BWE significantly reduced coastal plankton compared with un-exchanged tanks, the flow-through method did not, and in either case remaining coastal plankton densities presented appreciable risks of introducing NIS. 4. Densities of high risk taxa were consistently and significantly higher from US domestic trips dominated by tank ships carrying ballast water from California, and lower in samples from trans-Pacific trips dominated by container ships and bulk carriers with ballast from Asia. These findings are probably a result of the dense and diverse NIS assemblages present in California and other US west coast estuaries and the comparatively short transit times between them and Puget Sound. 5. While it appears that BWE can effectively replace NIS with less risky ocean species, new reporting, verification, and operational procedures may be necessary to enhance BWE efficacy. In the long-term, the introduction of ballast water treatment technologies may be required to significantly reduce the discharge of risky organisms from commercial ships if BWE practices do not become more effective. Copyright © 2008 John Wiley & Sons, Ltd.

Open-ocean ballast-water exchange (BWE) is currently the most common treatment used to reduce the ballast transfer of organisms and the subsequent risk of invasions among coastal ecosystems. Freshwater or estuarine organisms remaining after BWE often experience high mortality, due to osmotic shock caused by high-salinity exposure. We conducted 70 salinity tolerance experiments on 54 different taxa to measure mortality rates of freshwater and estuarine organisms after exposure to oceanic seawater (34 psu), simulating both flow-through (F-T) and empty-refill (E-R) BWE methods. We focused especially on larval and adult crustaceans from freshwater and mesohaline habitats adjacent to ports of the Baltic Sea, North Sea, Great Lakes, Chesapeake Bay, and San Francisco Bay. Animals from oligohaline habitats (0-2 psu) experienced the highest mortality: all individuals died in 82% of the F-T treatments and 88% of the E-R treatments. The effectiveness of both treatment types decreased with animals from low-salinity (2-5 psu, 100% mortality in 27% of F-T and 46% of E-R treatments) and mesohaline habitats (5-18 psu, 100% mortality in 40% of F-T and 52% of E-R treatments). In 43% of cases among all salinity categories, empty-refill treatments required less exposure time to cause significant mortality than flow-through treatments. Invertebrates that exhibited significant survivorship were most often peracarid crustaceans including widely introduced species of mysid shrimps and amphipods. Although salinity shock does not completely prevent the transfer of all low-salinity biota, BWE provides a useful management tool to reduce species transfers, especially considering the combined effects of removal and mortality.

Estuaries play an important role as nurseries and migration corridors for Chinook salmon and other fishes. The invasive New Zealand mudsnail, Potamopyrgus antipodarum (Gray, 1843), has been noted in the Columbia River Estuary and other estuaries in the western USA, yet no studies have addressed the estuarine impacts of this invader. Our data show P. antipodarum is currently found in five peripheral bays and many tributaries of the Columbia River Estuary, where it can constitute a major portion of the benthic invertebrate biomass and where it co-occurs with native amphipod species. We review the history of the P. antipodarum invasion in the Columbia River Estuary and discuss potential impacts on estuarine food webs. We also report the first occurrence of P. antipodarum in the diet of juvenile Chinook salmon from the Columbia River Estuary. Although present in Chinook diets at very low frequencies, our observations of P. antipodarum in Chinook gut contents may represent early stages of food web change due to the establishment of dense estuarine snail populations. Additional research is needed to determine the effects of P. antipodarum on benthic resources, native benthic invertebrates, and benthic predators. We encourage biologists working in western USA estuaries to be alert to the possibility of encountering P. antipodarum in benthic habitats and predator diets.

We report the first occurrence in the Pacific Northwest, USA, of the harpacticoid cope- pod genus Harpacticella (Family Harpacticidae), which has previously been recorded only from Asia and from an atoll in the Indian Ocean. Harpacticella paradoxa (Brehm, 1924) is native to streams, lakes and estuaries in Japan and China. H. paradoxa was found in plankton samples taken in 2000 and 2004 from 2 geographically separated estuaries (Samish and Klamath River Estuaries, USA) at salinities ranging from 0 to 15 psu. H. paradoxa was also found associated with plants sampled in 2006 from a freshwater reservoir in the Columbia River, Washington State, USA. Because the genus Harpacticella has previously been found only in Asia and the Indian Ocean; is probably easily trans- ported on ship hulls or in ballast; and appears to have a disjunct regional distribution, we regard it as a probable introduced species to North America.

Compared to other regions, estuaries and coastal bays along the west coast of North America have experienced the largest number of invasions by nonindigenous planktonic copepods. Eight species of copepods from Asia, including 2 species of the genus Pseudodiaptomus, have been reported in coastal bays of northern California, and a third species of Asian Pseudodiaptomus (P. inopinus) has become established in the Columbia River estuary and many smaller estuaries in the northeast Pacific Ocean. It can dominate the plankton in fresh and oligohaline tidal waters of estuar- ies that are utilized as rearing grounds for a variety of larger invertebrates and fishes. In July 1998 we initiated a 16 mo study of P. inopinus in the Chehalis River estuary, Washington State, USA, to docu- ment its biology, ecological relationships with other holoplankton, and importance as prey for fish and invertebrate planktivores. In 1998 P. inopinus reached peak densities in the late summer/early autumn period of low river flow but a similar peak was not seen in the same period in 1999, when densities of the copepod were significantly lower. These interannual density differences did not appear to be caused by between-year differences in predation or river flooding, but could have resulted from cooler temperatures and higher river flows that occurred in the Chehalis River in 1999. Other abundant planktonic copepods were separated from P. inopinus either temporally (Eurytemora affinis) or spatially (Acartia spp., Eurytemora americana) within the estuary, over a relatively short segment of the estuary spanning salinities of 0 to 10 psu. This separation may imply that P. inopinus experienced little competition when it was introduced; alternatively, it may have altered the distrib- ution of other copepods in the estuary. P. inopinus was rare in the diets of estuarine fishes, but com- prised an important and sometimes dominant prey for mysid shrimp Neomysis mercedis and juvenile caridean shrimp Crangon franciscorum. In turn, N. mercedis was an important prey item for estuar- ine fishes, and thus the main impact of P. inopinus on the estuarine food web was via this pathway.

Ballast water is a major pathway for the transfer of non-indigenous species in aquatic environments. The objectives of this study were to determine the ability of ozone to reduce the numbers of a spectrum of marine organisms collected from Puget Sound, Washington in replicated mesocosm (280 l) experiments, and estimate the minimum ozone concentrations as measured by total residual oxidant (TRO) required to reduce organism densities. Ozone treatment was effective in removing bacteria, phytoplankton, and mesozooplankton with initial TRO concentrations of 2–5 mg l −1 as Br 2 . Persistence of TRO resulted in an extended period of toxicity and cumulative mortality. TRO decay allowed bacteria populations to multiply when TRO levels fell below 0.5–1.0 mg l −1 as Br 2 . Phytoplankton chlorophyll a concentrations were rapidly reduced by ozone treatment and did not increase in any treatments or controls because of lack of light. Overall mesozooplankton viability was rapidly reduced by 90–99% in treatment TRO levels above 1.85 mg l −1 as Br 2 . Our study outlines novel protocols that can be used for testing different potential ballast water treatment systems in replicated and controlled mesocosm experiments.

Use of lake habitats by ocean-type Chinook salmon Oncorhynchus tshawytscha is rare under natural conditions. We studied aspects of the trophic ecology of naturally and hatchery-produced juvenile Chinook salmon rearing in the littoral zone of highly urbanized Lake Washington in Washington State. During February through May, naturally produced juvenile Chinook salmon occupied littoral habitats and consumed mostly epibenthic prey, primarily chironomid pupae (Diptera). In June, they switched to a diet dominated by plankton, specifically Daphnia spp. This diet shift from littoral prey to limnetic prey coincided with increasing temperature, a shift by the fish from littoral to limnetic habitats, the spring bloom of Daphnia, and increasing fish size. Bioenergetics modeling for these populations estimated that naturally produced juvenile Chinook salmon had high consumption rates and were generally feeding close to their maximum ration, even after large numbers of hatchery-produced Chinook salmon entered the lake. The feeding rates, growth rates, and proportions of maximum daily ration from the modeling suggested that under current conditions, both naturally produced and hatchery-produced juvenile Chinook salmon were finding ample food in littoral habitats of Lake Washington. These results further reveal that hatchery-produced Chinook salmon did not compete with naturally produced fish and that this was probably a result of hatchery juveniles entering the lake during the spring Daphnia bloom when this prey is abundant. Our results suggest that managers should focus Chinook salmon recovery efforts in the Lake Washington basin on other aspects of the species' lake use, such as predation or disease, or on other life stages (e.g., spawning adults).

Worldwide transfer and introduction of non-indigenous species in ballast water causes significant environmental and economic impact. One way to address this problem is to remove or inactivate organisms that are found in ballast water. In this study, 3 experiments were conducted in Puget Sound, Washington, USA, using a prototype ozone treatment system installed on a commercial oil tanker, the S/T Tonsina. Treatment consisted of ozone gas diffused into a ballast tank for 5 and 10 h. Treatment and control tanks were sampled during the ozonation period for chemistry, cultur- able bacteria, phytoplankton and zooplankton. Selected fish and invertebrates were placed in cages deployed in the treatment and control tanks. Ozone introduced into seawater rapidly converts bro- mide (Br - ) to bromines (HOBr/OBr - ), compounds that are disinfectants. These were measured as total residual oxidant (TRO). Ozone treatment inactivated large portions of culturable bacteria, phyto- plankton and zooplankton. The highest reductions observed were 99.99% for the culturable bacteria, >99% for dinoflagellates and 96% for zooplankton. Caged animal results varied among taxa and locations in the ballast tank. Sheepshead minnows and mysid shrimp were most susceptible, shore crabs and amphipods the least. Distribution of ozone in the treatment tank was not homogenous during experiments, as suggested by the observed TRO concentrations and lower efficacies for inactivating the different taxa in selected ballast tank locations. Low concentrations of bromoform, a disinfection byproduct, were found in treated ballast water.

The potential problems of organisms introduced by ballast water are well documented. In other settings, electrolytic generation of sodium hypochlorite from seawater has proven to be a simple and safe method of handling and injecting a biocide into water. After the hypochlorite oxidizes organisms, it reverts back to the chloride ion. Microcosm-scale testing of this technology combined with filtration, using organisms from Puget Sound, Washington, demonstrated that hypochlorite generation and use may be a viable method to eliminate aquatic nuisance species from ballast water while minimizing disinfection byproducts and residual toxicity. These experiments were conducted at the U.S. Geological Survey Marine Field Station on Marrow stone Island, Washington. Results from the first set of studies of the system showed that hypochlorite levels greater than 3.0 ppm hypochlorite with or without filtration reduced bacteria by more than 99.999%, reduced phytoplankton by more than 99%, and reduced mesozooplankton by more than 99%. Filtration improved efficacy only when hypochlorite concentration was initially less than 1.5 ppm.

The population characteristics, seasonal abundance and tidal flux of Neomysis kadiakensis were studied to determine if tidal marshes serve as sources or sinks for mysids in China Camp, located in the San Francisco estuary. Monthly surveys of the zooplankton community were conducted during spring tide periods between May 2002 and May 2003, using a fyke net (500 mm mesh) fixed at the mouth of a fourth order tidal channel system in a tidal marsh. Mysids were collected and preserved hourly throughout full tidal cycles. Neomysis kadiakensis was the dominant mysid species, comprising 94–100% of mysids throughout the year. Monthly mean abundance of N. kadiakensis ranged from 14 mysids m � 3 in January 2003 to 244 mysids m � 3 in March 2003. Length frequency distributions indicated that reproduction and recruitment were nearly continuous, with abundance peaks occurring throughout the year (e.g., spring, summer and early fall). The resulting flux estimates during this period suggested that China Camp marsh was a sink for N. kadiakensis. The mean daily (ca. 24.8 h) fluxes of N. kadiakensis corresponded to an instantaneous daily population mortality rate within the marsh channel of 0.29 d � 1 . Although all sizes and stages experienced a net import to the marsh, a significant positive relationship was observed between mysid length and mean annual flux, indicating that larger, mature mysids experienced a greater degree of tidal import to the marsh than smaller, juvenile mysids. These analyses suggest that size-specific predation, perhaps from fishes, shrimp, and/or birds may have had a disproportionate impact on large, mature mysids. Mortality rates in the marsh greatly exceeded the overall population growth rates, indicating that predation pressure on mysids was greater in the marsh than in the subtidal estuary. Mysids, therefore, supply a net flux of energy from the subtidal estuary to the marsh during spring tide series; however, the ultimate fate of this energy is unknown (remaining within the marsh system vs. export back to the estuary via trophic relay or other processes). 2005 Elsevier Ltd. All rights reserved.

The South American floating aquatic plant water hyacinth (Eichhornia crassipes) has a history of worldwide invasions, including a 1904 introduction into the Sacramento-San Joaquin Delta, California. The native pennywort (Hydrocotyle umbellata) occupies similar habitats in the Delta and is extensively used by resident invertebrates and fish. We sought to discover if an invader would be functionally equivalent to the native plant, by asking whether the encroadhing hyacinth modified the invertebrate assemblage structure and fish-invertebrate food web relative to pennywort. We sampled epiphytic, epibenthic, and benthic invertebrates, and plant canopy insects in patches of hyacinth and pennywort, and analyzed fish diets at three sites in the Delta during 1998. We also measured habitat structure (leaf density, root biomass, and surface area). In 1999, following control and absence of hyacinth, we again measured epiphytic invertebrates in pennywort. We found differences between hyacinth and pennywort in structure, associated invertebrates, and fish diets. Most measurements inferred functional non-equivalency between hyacinth and pennywort, although some functional equivalency and natural variation existed. Leaf and insect densities were significantly higher in pennywort and there were also significant differences in insect assemblage compositions. Hyacinth roots in the water column had significantly more surface area. Densities of epibenthic and benthic aquatic invertebrates were typically greater in pennywort and taxonomic compositions of aquatic invertebrate assemblages showed significant differences. Amphipods and isopods living epiphytically in the root masses were particularly abundant, including several newly discovered introduced species: the amphipodCrangonyx floridanus and the isopodsCaecidotea racovitai andAsellus hilgendorfii. The native amphipodHyalella azteca was more abundant in pennywort and heavily preyed upon by fish, while the non-indigenousC. floridanus was more abundant in hyacinth and not prevalent in fish diets. The introduction of hyacinth to the Delta has caused significant ecological alterations in the surrounding community, due to hyacinth being functionally different from native patches of pennywort.

In November 1994 dikes were breached around Spencer Island, restoring tidal inundation and connections to the Snohomish River estuary, Washington. Approximately 23.7 ha (58.5 ac) of palustrine wetlands previously dominated by Phalaris arundinacea (reed canarygrass) now experience diurnal tides and are in the process of transition to a freshwater tidal system. It was expected that brackish water would accompany the return of tidal influence to the site, but post-project monitoring has revealed little evidence of salinity. Pre- and post-project monitoring of changes in habitat function included aerial photography, vegetation and fish sampling, and benthic prey studies. To date site changes include (1) die back of pre-project vegetation, development of tidal mudflat, and emergent wetland habitats, with recruitment of vegetation typical of freshwater tidal wetlands; (2) presence of juvenile coho, chum, and chinook salmon that feed on invertebrate prey typical of the site; (3) presence of three distinct benthic invertebrate assemblages in the project area; and (4) some invasion by Lythrum salicaria (purple loosestrife). The unexpected freshwater conditions, the lack of published information about tidal oligohaline marshes in the Pacific Northwest, the use of the site by endangered salmonid species, and the invasion by an undesired plant species underscore the importance of long-term monitoring at the site.

The amphipod Crangonyx floridanus and the isopods Caecidotea racovitzai and Asellus hilgendorfii were discovered in the Sacramento/San Joaquin Delta, California, U.S.A. We applied Chapman and Carlton's (1994) criteria for determining introduced species to test whether these species are non-indigenous to the delta. The majority of the attributes scored positive, indicating that these species are non-indigenous. These populations appear to be firmly established, as they occurred at a variety of freshwater wetland habitats throughout a one-year study. The species are briefly described, and distinguished from similar native and non-indigenous species known to exist in the surrounding area.

Invasions of aquatic habitats by non-indigenous species (NIS), including zooplankton, are occurring at an alarming rate and are causing global concern. Although hundreds of such invasions have now been documented, surprisingly little is known about the basic biology and ecology of these invaders in their new habitats. Here we provide an overview of the published literature on NIS zooplankton, separated by life history (holoplankton vs. meroplankton), habitat (marine, estuarine, freshwater), and biological level of organization or topic (e.g. distribution and range extension, physiology, behavior, feeding, community impacts, ecosystem dynamics, etc). Amongst the many findings generated by our literature search, perhaps the most striking is the paucity of studies on community and ecosystem level impacts of NIS zooplankton, especially in marine and estuarine systems. We also present some results from two ongoing studies of invasive zooplankton in the northeast Pacific Ocean – Pseudodiaptomus inopinus in Washington and Oregon coastal estuaries, and Tortanus dextrilobatus in San Francisco Bay. Both of these Asian copepods have recently expanded their range and can at times be extremely abundant (10 3 m −3 ). We also examine some aspects of the trophic (predator–prey) ecology of these two invasive copepods, and find that they are likely to be important in the flow of material and energy in the systems in which they now pervade, although their impacts at the ecosystem level remain to be quantified. Finally, the findings of both our literature search and our two case studies of invasive zooplankton lead us to make several recommendations for future research.