Scaling Down Habitat Selection by Large River Fishes to Understand Patterns Relevant to Individuals

Modification and homogenization of habitat in large‐river ecosystems have led to the reduction of >50% of native fish species. Rehabilitating these complex ecosystems to recover fish populations requires an understanding of habitat availability and selection at multiple scales. Habitat selection by river fishes is typically assessed at the functional unit scale (100–10 000 m²). For example, in large, sand‐dominated rivers of the Central USA, alluvial islands are critical functional units for endangered sturgeon. Functional units, however, can be subdivided into mesohabitats (<100 m²), but very little is known about mesohabitat selection by large river fishes. We evaluated the mesohabitat selection of the federally endangered pallid sturgeon (Scaphirhynchus albus) and more abundant shovelnose sturgeon (Scaphirhynchus platorynchus) experimentally. We tested for selection among four common mesohabitat types that are nested within alluvial island complexes: (1) sand‐only substratum with no structure; (2) sand substratum with a sand dune structure; (3) sand substratum with simulated vegetation; and (4) a gravel‐only substratum. Sturgeon selected for the sand substratum, structureless mesohabitat, followed by the mesohabitat with a sand dune. Vegetated habitat retained less sturgeon than these two habitats but more than the gravel mesohabitat. Age‐0 pallid sturgeon and shovelnose sturgeon almost completely avoided gravel substrate, perhaps because of increased energetic costs associated with turbulent benthic flow. We posit that age‐0 sturgeon may prefer the sand and sand dune habitats over the vegetation and gravel habitats because flow may be more linear (or unidirectional) and predictable in these habitat types, whereas vegetation and gravel can create substantial benthic turbulence. Lastly, shovelnose sturgeon were on average denser in vegetated habitat than pallid sturgeon. Scaled to the population level, patterns revealed here could have implications for the macro‐distribution of both species. Restoration efforts may want to consider selection differences in the management of these two species and rehabilitation of riverine habitats. Copyright © 2015 John Wiley & Sons, Ltd.     

DYNAMICS OF IN‐STREAM WOOD AND ITS IMPORTANCE AS FISH HABITAT IN A LARGE TROPICAL FLOODPLAIN RIVER

The recruitment of wood from the riparian zone to rivers and streams provides a complex habitat for aquatic organisms and can influence both aquatic biodiversity and ecosystem function. The Daly River in the wet–dry tropics of northern Australia is a highly seasonal, perennially flowing sand‐bed river where surveys of river wood aggregations at the reach scale (~2 km) in 2008 and 2009 recorded densities of 37–78 km^?1 and identified distinct types of river wood aggregations: key pieces, standing trees, fallen trees, wrack and single pieces. After larger than average flows in the 2008/2009 wet season, between 46% and 51% of the surveyed river wood had moved. The distribution of wood age classes indicated continual recruitment and slow turnover of wood within the river. Surveys of fish and habitat characteristics at the mesohabitat scale (~100 m) showed fish species richness; diversity and fish abundance were not correlated to the proportion of wood present. Fish assemblage structure was associated with wood cover as well as other environmental variables such as stream width and depth. The importance of in‐stream wood also varied for different species and age classes of fish. This study documents the dynamic nature of river wood aggregations and their complex and variable distribution and suggests their importance as fish habitat in this tropical river. Copyright © 2012 John Wiley & Sons, Ltd.     

Responses of Chironomid larvae (insecta,Diptera) to ecological quality in Mediterranean river mesohabitats (South Italy)

Chironomid larvae and pupae were studied in selected Mediterranean rivers with the aim of identifying pool and riffle taxa assemblages and of analysing their response to ecological quality gradients. Macroinvertebrate samples were collected in six Italian rivers along a pool‐riffle sequence in three seasons following a multihabitat sampling technique. Chironomids were identified as genus/species, other macroinvertebrates as family/genus. The main physico‐chemical, hydromorphological and geographical data were collected. Samples were ascribed to five quality classes according to the STAR_ICM index. Based on Chironomid taxa, principal component analysis (PCA) axis 1 represented an organic pollution gradient, axis 2 represented seasonality. Pool and riffle samples were significantly different according to taxa assemblages. Similar results were obtained with PCA based on the whole macrobenthic community. Indicator value (IndVal) analysis facilitated the detection of the Chironomid indicators of high/good quality pools (e.g. Conchapelopia pallidula, Rheopelopia ornata, Epoicocladius ephemerae) and riffles (Tvetenia calvescens, Eukiefferiella gracei). The Berger–Parker dominance index based on Chironomid assemblages in pools was correlated to PCA axis 1 and performed well in discriminating between quality classes. In riffles, no correlations to PCA axes were detected and a wide overlap between quality classes was present. Thus, assessment in the analysed river type may focus on pool mesohabitat as this seems to represent best the ecological gradient of sites. Copyright © 2009 John Wiley & Sons, Ltd.     

Variability of mesohabitat characteristics in riffle‐pool reaches: Testing an integrative evaluation concept (FGC) for MEM‐application

This paper investigates the variability of mesohabitat characteristics in various riffle‐pool reaches. The tested river sections (n = 13) feature clear variation in slope (0.0004–0.0132) and low flow discharge (0.05–915 m³s^?1) in different river types (straight to meandering). Mesohabitat characteristics (water depth, flow velocity, bottom shear stress) were calibrated according to the MEM‐concept (MEM—Mesohabitat Evaluation Model). Statistical analysis clearly revealed significant differences (p < 0.001) for the same mesohabitats (e.g. riffles) in different rivers concerning the tested abiotic habitat parameters. A comparative analysis of hydromorphological parameters (width‐depth variance, Froude number) showed no correlation to mesohabitat variability based on 2D/3D numerical modelling related to a range of flows (n = 10) (low flow to annual flood). Only an increasing hydraulic radius (R_hy) was correlated to an increase in fast run and a decrease in run habitats. In a case study, a Fish Guild Concept (FGC) is presented which links mesohabitats to the rheophilic fish guild (12 fish species grouped) at the Sulm River. Mesohabitat suitability (preferred, useable and avoided) for the FGC was determined for spawning, juveniles (0+, 1+), sub‐adult and adult stages based on meso‐unit and point abundance electro‐fishing. Copyright © 2010 John Wiley & Sons, Ltd. This article was published online on March 3, 2010. An error was subsequently identified in Figure 1 . This notice is included in the online and print versions to indicate that both have been corrected [March 10, 2010].     

Partitioning of macroinvertebrate communities in a large New Zealand river highlights the role of multiple shore‐zone habitat types

Bank stabilization is increasing along large rivers as urban areas expand, and the need to protect infrastructure increases in the face of changing climate and flow patterns, but the cumulative effects of different stabilization approaches on reach‐scale biodiversity are not well understood. We investigated physical habitat characteristics and macroinvertebrate community composition and diversity for four shore‐zone habitat types across nested spatial scales over two sampling occasions. Distinct physical conditions were evident for riprap, beach and willow (mixed trees dominated by Salix spp.) habitats, reflecting variations in the combinations of shade, water velocity and substrate size/type, but there was wide variation in habitat conditions for mixed willow‐riprap sites. Additive biodiversity partitioning decomposed reach (γ) diversity into within (α) and among (β₁) sample, among habitat (β₂), and among site (β₃) components, and highlighted significant effects of all spatial scales on macroinvertebrate diversity. Low autumn water levels led to truncated species accumulation curves at beach sites where macrophyte beds that supported macroinvertebrates became stranded, or elevated species accumulation curves for exposed willow‐riprap sites where the river benthos was sampled during hydrological disconnection of bank habitats. Spring and autumn differences in macroinvertebrate community composition were stronger than differences between habitat types. Our findings (a) highlight the interacting effect of river level with shore‐zone habitat function, and (b) underscore the importance of maintaining a diversity of bank habitat types at multiple sites along river shore‐zones to maximize macroinvertebrate diversity.     

Use of mesohabitat‐specific relationships between flow velocity and river discharge to assess invertebrate minimum flow requirements

The benthic macroinvertebrate community in the sixth order lowland River Spree (Germany) was investigated in order to assess ecological effects of a flow reduction. The benthic habitat was composed of visually distinguishable mesohabitats. Eight mesohabitats were delineated, Dreissena‐bank, unionid mussel bed, rip‐rap, coarse woody debris (CWD), alder roots, stable sand, shifting sand and mud. The mesohabitats differed in their physical structure and hydraulic nature. These functional habitats were partly inhabited by distinct invertebrate assemblages. The use of mesohabitat‐specific relationships between flow velocity and discharge seemed the most appropriate approach in order to assess the impact of flow reduction on lotic fauna. In combination with the species‐specific optima and tolerances for flow velocity, this approach can be used to develop a minimum flow level that mitigates the effects of flow reduction and enables the persistence of rheophilic invertebrates in their specific mesohabitat. Copyright © 2001 John Wiley & Sons, Ltd.     

Typology of a Great River Using Fish Assemblages: Implications for the Bioassessment of the Danube River

Matching habitat typology and ecological assemblages can be useful in environmental management. We examined whether a priori defined riverine sections correspond with distinct fish assemblage types along the >2000 km long course of the Danube River, Europe. We also tested whether different sampling methods (i.e. day and night inshore electric fishing and offshore benthic trawling) provide consistent typological results. Analysis of assemblage similarities, indicator species analysis, non‐metric multidimensional scaling (NMDS) and k‐means analyses indicated that fish assemblages of the a priori defined Upper‐, Middle and Lower‐Danubian sections differed slightly, but within class variability was high. Although indicator species analysis showed that the Upper‐Danube belongs to the barbel (Barbus barbus) zone and the Middle‐ and Lower Danube belong to the bream (Abramis spp) zone, indicator values of the character species were generally low. The NMDS analyses suggested a weak gradient in assemblage structure along the course of the river with relatively high variability between neighbouring sites. K‐means analyses revealed that many sampling sites were in a different class than the a priori defined sections, and classifications at other group numbers did not lead to better classification outcome. Overall, the results do not suggest clearly distinguishable assemblage types with distinct boundaries in the potamal section of a great river. Nevertheless, the division of the potamon to smaller sections may explain some variability in fish assemblage structure, and could be used for bioassessment purposes. The study also shows the importance of multihabitat and multigear surveys in the typological assessment of great rivers. Copyright © 2016 John Wiley & Sons, Ltd.     

Recent habitat association and the historical decline of Notropis simus pecosensis

Small‐bodied, riverine minnows that historically characterized fish assemblages of Great Plains rivers in North America have declined because of river fragmentation, dewatering, river channel degradation, river salinization and nonnative species introductions. The Pecos bluntnose shiner Notropis simus pecosensis, a member of this guild, persists in one segment of the Pecos River, New Mexico, USA. We characterized habitat associations for the species at two spatial scales. In general, N. s. pecosensis associated with fluvial habitats, but velocity association depended on body size, with larger individuals using swifter habitats. All N. s. pecosensis associated with relatively low depths (3–51 cm), which were most abundant in sites with relatively wide river channels (>25 m), especially when discharge was between 0.5 and 4.0 m³ s^?1. The Pecos River sub‐segment that is occupied by the core population of N. s. pecosensis (V‐ii) had a unique combination of being buffered from direct dam effects by intervening segments and sub‐segments, high sub‐segment length, substantial sediment inputs from numerous uncontrolled tributaries, substantial base flow provided by irrigation return flows and groundwater inflows, high channel width in relation to discharge and low salinity. Although no unoccupied Pecos River segment appears to be suitable for N. s. pecosensis, habitat restoration opportunities exist within all occupied sub‐segments (V‐i, V‐ii and V‐iii) via base flow enhancement and river channel restoration. Restoration that offsets chronic effects of dams may be necessary to conserve the species. Restoration would also benefit other rare riverine minnows that coexist with N. s. pecosensis. Copyright © 2008 John Wiley & Sons, Ltd.     

The significance of flood regimes for carabid beetle and spider communities in riparian habitats—a comparison of three major rivers in Germany

River regulation and water management practices have led to alteration of the flood regimes of all large rivers in Germany. To investigate its influence on the terrestrial arthropod fauna, a comparative study was carried out on the distribution of ground beetles (Carabidae) and spiders (Araneae) at the potamal sections of three large rivers in northern Germany, the Rivers Weser, Elbe and Oder. The three rivers differ markedly in their flood dynamics, mainly owing to weirs and polder management practices, but also owing to natural conditions in their headwaters. In total, 45 sites were examined with a total capture of 46 727 carabid beetles and 38 066 adult spiders, representing 178 and 209 species, respectively. Using multivariate TWINSPAN analyses we found that the ground beetle species assemblages clearly varied according to the different flood regimes. By contrast, the spiders differentiate well between sites of different habitat structure. In particular, the river margins hosted a specialized carabid fauna, and the alluvial Quercus–Ulmus forests were habitat for some rare and endangered carabid and spider species. Whereas the fauna of the strongly regulated River Weser was impoverished regarding stenotopic hygrophilous species, the fauna of the more natural Rivers Elbe and Oder depended very much on the duration and timing of the flooding, as well as on the local micro‐topographical situation. It is concluded that low lying areas behind dykes of the Elbe, or in polders of the Oder, which become frequently inundated by river or ground water, are extremely valuable for invertebrate conservation. The data suggest that careful polder management may support suitable habitat creation for riparian species, as long as the inundation scheme corresponds to natural flood dynamics conditions. Copyright © 2002 John Wiley & Sons, Ltd.     

EVALUATION OF RIPARIAN HABITAT RESTORATION IN A LOWLAND RIVER

For many years, navigable lowland rivers have been embanked artificially or suffered from substantial shipping wave action, leading to habitat degradation. Recently, riparian habitats were restored by creating foreshores and spawning grounds in the river Yser, a lowland river in Flanders, Belgium. The aim of this paper was to evaluate the role of these restored habitats for spawning and nursery of juvenile fish. To cover a wide range of anthropogenic disruption, four riparian mesohabitat types were selected and compared, ranging from semi‐natural over artificial spawning grounds and foreshores to artificial embankments. Juvenile fish were subjected to sampling by using electrofishing between June and September 2009 at different microhabitats located in five sites of each riparian mesohabitat type. Juvenile fish strongly preferred natural riparian habitats, whereas artificial embankments showed the lowest species richness, abundance and functional organization of juvenile fish species. Restored riparian habitats appeared to be an appropriate alternative for artificial embankments in navigable lowland rivers but still score significantly less than natural habitats. Juvenile fish avoided bare microhabitats but did not prefer any other microhabitat type (reed, woody or grassy vegetation), emphasizing the importance of microhabitat diversity. This paper provides valuable insights into riparian habitat restoration to river managers and stakeholders. Copyright © 2011 John Wiley & Sons, Ltd.     

Using macroinvertebrate biological traits for assessing biotic integrity of neotropical streams

Several recent studies have demonstrated that a functional approach (i.e. analysis of traits indicating species ecological functions) can be successfully used for river biomonitoring. To date this approach has only been applied in temperate rivers, even though it could notably contribute toward the development of an environmental assessment system in developing countries in other climatic zones. Using a multivariate approach (Fuzzy Correspondence Analysis—FCA), we analysed functional invertebrate community characteristics (described by 40 categories of seven biological traits mostly at the family level) at 66 stream sites from neotropical Bolivia with different level of anthropogenic disturbance. We were able to separate the sites on the first FCA axis (F1) (ANOVA test) following the predefined environmental quality classes based on the observed impact. Moreover, the F1 axis scores were significantly related to scores obtained using an independent macroinvertebrate multi‐metric index previously developed to assess streams biotic condition in the same biogeographical region. The F1 axis, which thus represents a gradient of anthropogenic impacts, was significantly correlated to 30 of the 40 studied trait categories. Our results (i) clearly confirm the possible use of functional traits for water quality assessment in neotropical streams, and (ii) provides support to the River Habitat Templet hypothesis since habitat disturbances produced predictable functional changes in macroinvertebrate assemblages. Finally, this study supports the potential worldwide applicability of the species‐trait approach as a biomonitoring tool for stream integrity assessment. Copyright © 2008 John Wiley & Sons, Ltd.     

INTRA‐ANNUAL VARIATION IN RIVER–RESERVOIR INTERFACE FISH ASSEMBLAGES: IMPLICATIONS FOR FISH CONSERVATION AND MANAGEMENT IN REGULATED RIVERS

While much is known about the fish assemblages, habitats, and ecology of rivers and reservoirs, there has been limited study of the fish assemblages in transitional habitats between these lotic and lentic habitats. Data about these river–reservoir interface (RRI) fish assemblages are needed to guide integrated management efforts of river–reservoir ecosystems. The aim of these efforts is to recommend flows for natural river function, conserve native riverine fish assemblages, and maintain reservoir sport fisheries. We used a multigear approach to assess the fish assemblages of four RRIs in the Colorado River Basin, Texas. In addition to characterizing RRI fish assemblages using species richness and evenness metrics, and habitat‐use guilds, we used a multivariate approach to evaluate intra‐annual shifts in species composition and abundance. All RRIs had high species richness and evenness values and included both macrohabitat generalist and fluvial species. RRIs also contained high proportions of the fish species available within each river–reservoir ecosystem, ranging from 55% to 80%. Observed intra‐annual shifts in RRI fish assemblages resulted from changes in abundance of dominant species rather than changes in species composition, with abundance of most species increasing from early spring to summer. Fish species responsible for intra‐annual shifts included mostly floodplain and migratory species, suggesting that species both used littoral habitats within RRIs and migrated through RRIs to river and reservoir habitats. The diversity of fishes found within RRIs highlights the importance of including these areas in future conservation and management efforts of river–reservoir ecosystems. Copyright © 2013 John Wiley & Sons, Ltd.     

ESTIMATION OF JUVENILE SALMON HABITAT IN PACIFIC RIM RIVERS USING MULTISCALAR REMOTE SENSING AND GEOSPATIAL ANALYSIS

We conducted a regional classification and analysis of riverine floodplain physical features that represent key attributes of salmon rearing habitats. Riverine habitat classifications, including floodplain area and river channel complexity, were derived at moderate (30 m) spatial resolution using multispectral Landsat imagery and global terrain data (90 m) encompassing over 3 400 000 km² and most North Pacific Rim (NPR) salmon rivers. Similar classifications were derived using finer scale (i.e. ≤ 2.4‐m resolution) remote sensing data over a smaller set of 31 regionally representative flood plains. A suite of physical habitat metrics (e.g. channel sinuosity, nodes, floodplain width) were derived from each dataset and used to assess the congruence between similar habitat features at the different spatial scales and to evaluate the utility of moderate scale geospatial data for determining abundance of selected juvenile salmon habitats relative to fine scale remote sensing measurements. The resulting habitat metrics corresponded favorably (p < 0.0001) between the moderate scale and the fine scale floodplain classifications; a subset of these metrics (channel nodes and maximum floodplain width) also were strong indicators (R² > 0.5, p < 0.0001) of floodplain habitats defined from the finer scale analysis. These relationships were used to estimate the abundance and distribution of three critical shallow water floodplain habitats for juvenile salmon (parafluvial and orthofluvial springs, and shallow shore) across the entire NPR domain. The resulting database provides a potential tool to evaluate and prioritize salmon conservation efforts both within individual river systems and across major catchments on the basis of physical habitat distribution and abundance. Copyright © 2011 John Wiley & Sons, Ltd.     

An Assessment of Fish Assemblage Structure in a Large River

The Penobscot River drains the largest watershed in Maine and once provided spawning and rearing habitats to 11 species of diadromous fishes. The construction of dams blocked migrations of these fishes and likely changed the structure and function of fish assemblages throughout the river. The proposed removal of two main‐stem dams, improved upstream fish passage at a third dam, and construction of a fish bypass on a dam obstructing a major tributary is anticipated to increase passage of and improve habitat connectivity for both diadromous and resident fishes. We captured 61 837 fish of 35 species in the Penobscot River and major tributaries, through 114 km of boat electrofishing. Patterns of fish assemblage structure did not change considerably during our sampling; relatively few species contributed to seasonal and annual variability within the main‐stem river, including smallmouth bass Micropterus dolomieu, white sucker Catostomus commersonii, pumpkinseed Lepomis gibbosus, and golden shiner Notemigonus crysoleucas. However, distinct fish assemblages were present among river sections bounded by dams. Many diadromous species were restricted to tidal waters downriver of the Veazie Dam; Fundulus species were also abundant within the tidal river section. Smallmouth bass and pumpkinseed were most prevalent within the Veazie Dam impoundment and the free‐flowing river section immediately upriver, suggesting the importance of both types of habitat that supports multiple life stages of these species. Further upriver, brown bullhead Ameiurus nebulosus, yellow perch Perca flavescens, chain pickerel Esox niger, and cyprinid species were more prevalent than within any other river section. Our findings describe baseline spatial patterns of fish assemblages in the Penobscot River in relation to dams with which to compare assessments after dam removal occurs. Copyright © 2014 John Wiley & Sons, Ltd.     

Fish zonation and indicator species for the evaluation of the ecological status of rivers: example of the Loire basin (France)

In the context of river alteration, ecologists are asked to develop tools for the assessment of river integrity. Fish are known to be good bioindicators of the ecological condition of rivers. The Loire basin (France) is often considered as relatively little impacted compared to most other large European systems. But curiously, no study clearly addressed the question of fish assemblages patterns in this system in order to assess this status. Thus, we studied fish assemblages along the river network in the Loire basin using self‐organizing maps (SOMs) and we built a fish typology. Four basic assemblages were described and indicator species were identified. These assemblages varied in terms of individual species patterns as well as in terms of flow preference guilds and species richness. A discriminant analysis carried out on environmental variables revealed that they could be mainly determined by the slope, temperature and depth. Finally, fish assemblages were arrayed along a longitudinal gradient and roughly fitted the theoretical zonation expected in European rivers with the succession of brown trout (Salmo trutta fario), grayling (Thymallus thymallus), barbel (Barbus barbus) and bream (Abramis brama) zones in a downstream direction. Such patterns are still rarely observed in large European systems. However, the fish assemblage characteristic of the bream zone occurred more frequently than predicted on the basis of environmental variables. Such deviations between field data and theory suggest lotic‐to‐lentic shifts probably due to anthropogenic disturbances, especially in the grayling and barbel zones. In these river sectors, eurytopic and limnophilic species tend to replace rheophilic ones. Finally, the method used in this study to investigate fish patterns may be helpful to detect disturbances and may serve as a tool for the establishment of management plans. Copyright © 2007 John Wiley & Sons, Ltd.     

Spatial effects of reservoirs on fish assemblages in Great Plains streams in Kansas,USA

Reservoirs are important components of modern aquatic ecosystems that have negative impacts on native aquatic biota both up‐ and downstream. We used a landscape‐scale geographic information system (GIS) approach to quantify the spatial effects of 19 large reservoirs on upstream prairie fish assemblages at 219 sites in Kansas, USA. We hypothesized that fish assemblage structure would vary with increasing distance from a reservoir and that the abundance of reservoir fishes in upstream reaches would decline with distance from a reservoir. Ordination of sample sites showed variation in fish assemblage structure occurred primarily across river basins and with stream size. Variance partitioning of a canonical ordination revealed that the pure effect of reservoir distance explained a small but significant (6%; F = 4.90, P = 0.002) amount of variability in fish assemblage structure in upstream reaches. Moreover, reservoir species catch per unit of effort (CPUE) significantly declined with distance from a reservoir, but only in fourth‐ and fifth‐ order streams (r² = 0.32, P < 0.001 and r² = 0.49, P < 0.001, respectively). Finally, a multivariate regression model including measures of stream size, catchment area, river basin, and reservoir distance successfully predicted CPUE of reservoir species at sites upstream of Kansas reservoirs (R² = 0.45, P < 0.001). Overall, we found significant upstream effects of reservoirs on Kansas stream fish assemblages, which over time has led to a general homogenization of fish assemblages because of species introductions and extirpations. However, characteristic reservoir species are present throughout these systems and the importance of spatial proximity to reservoirs is probably dependent on the availability of suitable habitat (e.g. deep pools) in these tributary streams. Copyright © 2005 John Wiley & Sons, Ltd.     

Gradients in Catostomid Assemblages along a Reservoir Cascade

Serial impoundment of major rivers leads to alterations of natural flow dynamics and disrupts longitudinal connectivity. Catostomid fishes (suckers, family Catostomidae) are typically found in riverine or backwater habitats yet are able to persist in impounded river systems. To the detriment of conservation, there is limited information about distribution of catostomid fishes in impounded rivers. We examined the longitudinal distribution of catostomid fishes over 23 reservoirs of the Tennessee River reservoir cascade, encompassing approximately 1600 km. Our goal was to develop a basin‐scale perspective to guide conservation efforts. Catostomid species composition and assemblage structure changed longitudinally along the reservoir cascade. Catostomid species biodiversity was greatest in reservoirs lower in the cascade. Assemblage composition shifted from dominance by spotted sucker Minytrema melanops and buffalos Ictiobus spp. in the lower reservoirs to carpsuckers Carpiodes spp. midway through the cascade and redhorses Moxostoma spp. in the upper reservoirs. Most species did not extend the length of the cascade, and some species were rare, found in low numbers and in few reservoirs. The observed gradients in catostomid assemblages suggest the need for basin‐scale conservation measures focusing on three broad areas: (1) conservation and management of the up‐lake riverine reaches of the lower reservoirs, (2) maintenance of the access to quality habitat in tributaries to the upper reservoirs and (3) reintroductions into currently unoccupied habitat within species' historic distributions. Copyright © 2017 John Wiley & Sons, Ltd.     

LONG‐TERM VEGETATION DYNAMICS AFTER HIGH‐DENSITY SEEDLING ESTABLISHMENT: IMPLICATIONS FOR RIPARIAN RESTORATION AND MANAGEMENT

Human disturbances have contributed to the deterioration of many western US rivers in the past century. Cottonwood‐willow communities, present historically along the Colorado River, protect watersheds and provide wildlife habitat, but are now among the most threatened forests. As a result, restoration efforts have increased to re‐establish and maintain cottonwood‐willow stands. While successful establishment has been observed using multiple strategies with varying investments, few projects are evaluated to quantify efficacy and determine long‐term sustainability. We monitored a seeded cottonwood‐willow site over a five‐year period beginning in 2007, with particular interest in how density affected vegetation diversity and stand structure over time. Fremont cottonwood (Populus fremontii) and volunteer tamarisk (Tamarix ramosissma) were the only abundant riparian trees at the site after one year. P. fremontii, compared to T. ramosissma, had higher growth rates, lower mortality, and dominated overstory and total cover each year. Vegetation diversity decreased from 2007–2009, but was similar from 2009–2011 as a result of decreased herbaceous and increased shrub species richness. Diversity was highest in the lowest density class (1‐12 stems/m²), but similar among all other classes (13–24, 25–42, 43+). High initial woody species densities resulted in single‐stemmed trees with depressed terminal and radial growths. Allometry, relating height to DBH at different densities, could prove to be an important tool for long‐term restoration management and studying habitat suitability. Understanding long‐term trends at densely‐planted or seeded sites can benefit restoration managers who aim to establish specific community structure and vegetation diversity for wildlife habitat. Copyright © 2012 John Wiley & Sons, Ltd.     

Influence of Hydrological Connectivity on Plankton Communities in Natural and Reconstructed Side‐Arms of a Large New Zealand River

We sampled natural and reconstructed side‐arms during different stages of hydrological connectivity with a large floodplain river in northern New Zealand, to determine whether re‐establishment of connectivity would be an effective strategy for restoring plankton communities in former side‐arms. Connectivity between side‐arms and the river was moderated by water level and influenced flow rates and closure of inlets and outlets. Physicochemical conditions were more strongly related to the connectivity phase than to habitat type (river, natural or reconstructed side‐arm), except during low connectivity when natural side‐arms in particular were characterised by higher ammonium (NH₄‐N) and total phosphorus (P) concentrations, as well as specific conductivity. Dissolved reactive phosphorus (PO₄‐P), water temperature, conductivity and dissolved oxygen were identified as explanatory variables of phytoplankton and zooplankton community composition, which along with total nitrogen (phytoplankton) or total suspended solids (zooplankton) explained 44–52% of variation. Phytoplankton community composition and the abundance of several dominant or discriminatory taxa were affected by connectivity but not habitat type, whereas habitat and connectivity both had significant effects on zooplankton communities and abundances of the cladoceran Bosmina meridionalis. Significant interactions between connectivity and paired habitat types occurred for abundances of the diatom Asterionella, the cryptophyte Cryptomonas, the rotifer Synchaeta oblonga and cyclopoid copepods, reflecting differential responses to connectivity among habitats by these taxa. Overall, these results underscore the importance of hydrological connectivity between side‐arms and rivers in moderating plankton community composition, and highlight unpredictable trajectories of community development and alternative transient states that can occur soon after side‐arm reconnection. Copyright © 2016 John Wiley & Sons, Ltd.