The effects of stream canopy management on macroinvertebrate communities and juvenile salmonid production in a chalk stream

Abstract  The effects of changes in shading (through riparian canopy removal and re-growth) on juvenile salmon, Salmo salar L., trout, Salmo trutta L., and grayling, Thymallus thymallus (L.) populations, and macroinvertebrate biomass and species composition in a chalk stream in southern England were examined. Low levels of in-stream weed growth, because of shading by closed tree canopy, diminished macroinvertebrate production and diversity. 0+ salmon and trout had lower densities under closed canopy, relative to adjacent open sites with substantial weed cover, where fish were also found to be larger. Canopy removal positively affected the growth of aquatic macrophytes and the availability of potential prey for juvenile salmonids. The findings have implications for the management of chalk streams, in particular, that riparian tree canopy should be managed to prevent complete closure, and excessive cutting of weed should be avoided where salmon production is below sustainable levels.     

Habitat use by Thymallus thymallus in a chalk stream and implications for habitat management

Abstract Results of a number of studies on the interactions between grayling, Thymallus thymallus L., and its habitat in tributaries of the River Itchen, a chalk stream in Hampshire, southern England are reported. These include an investigation into the effect of riparian shading on T. thymallus growth and population density in relation to the development of in‐stream macrophyte cover, and the use of a multi‐point decoder system to record micro‐habitat use and preference of individual T. thymallus. In all stream sections, T. thymallus recruitment fluctuated greatly. Densities were generally low often restricting meaningful comparisons. However, where large differences occurred, wooded sections, with less aquatic macrophyte cover, generally had higher densities of T. thymallus. All age groups of T. thymallus (0+, 1+ and 2+) tended to occupy hard gravel substratum, both by day and by night in the autumn and winter, and used deeper and faster water with increasing age. The 1+ and 2+ groups were generally found in water 40–70‐cm deep with a velocity between 0.3 and 0.5 m s^?1, whilst the 0+ group showed a preference for shallower water with reduced velocity at night, particularly in the winter. The results are discussed in relation to habitat management where T. thymallus occur with other salmonids.     

Experimental provision of large woody debris in streams as a trout management technique

• 1. The natural stock of large woody debris (LWD) in the afforested Douglas River (Fermoy, Co. Cork) is very low relative to old‐growth forests, which seems to arise from deficiency both of supply and retention. Woody debris is important to the ecology and physical structure of forest streams, so its abundance is relevant to aquatic conservation and the maintenance and size of salmonid fish stocks.
• 2. The physical characteristics and fish stocks of 16 contiguous segments of two 200 m stream reaches were surveyed in spring 1998 prior to the installation of 12 partially spanning debris structures on four of the segments. This study investigated the effect of debris structures on the heterogeneity of flow and substratum, and the distribution of brown trout (Salmo trutta), and assessed the potential use of woody debris manipulation as a tool in the management of forest streams.
• 3. Surveys of stream habitat conditions over a 2 year period following the installation of woody debris showed a change in stream architecture. This created more suitable habitat for trout through development of additional pools in which beds of fine sediment developed, and constraining the main current, increasing the amount of eddies and slack water areas.
• 4. There were significant increases in trout density and biomass in the debris segments relative to control segments without debris dams 1 and 2 years after debris addition, although trout condition was not modified by the addition of LWD. These results suggest that the addition of woody debris offers a positive and practical management technique for enhancing fish in plantation forest streams.

Copyright © 2002 John Wiley & Sons, Ltd.     

Comparative assessment of stream acidity using diatoms and macroinvertebrates: implications for river management and conservation

• 1. Macroinvertebrates and phytobenthic organisms (e.g. diatoms) are frequently used as bioindicators of water quality, yet few studies compare their effectiveness despite both being emphasized in the EC Water Framework Directive.
• 2. Here, as a case study, the efficacy of each group in assessing acid–base status in the catchment of the Welsh River Wye was evaluated from surveys in 2 years.
• 3. Ordination showed that both diatom and macroinvertebrate assemblages varied highly significantly with pH, alkalinity and calcium concentrations. Moreover, ordination scores were highly inter‐correlated between these groups in both study years.
• 4. There were also contrasts, with diatoms and macroinvertebrates changing in differing ways with catchment land‐use and channel hydromorphology. These differing responses suggest complementary indicator value, while variation in generation times between diatoms and macroinvertebrates suggests potentially contrasting speeds of response to variations over different timescales.
• 5. These data reveal that significant water quality problems in the River Wye, a proposed Special Area of Conservation, are generated from the continued acidification of low‐order, headwater streams and this has considerable significance for the objectives of the Water Framework Directive, and the EC Habitats Directive.

Copyright © 2006 John Wiley & Sons, Ltd.     

The effects of riparian management and physicochemistry on macroinvertebrate feeding guilds and community structure in upland British streams

1. Patterns in the community structure and feeding guild composition among macroinvertebrates in the margins and riffles of 66 streams in upland Wales and Scotland were appraised and related to site chemistry, physiography and riparian management. We aimed to assess the effectiveness of riparian strips of broadleaves and moorland/grassland in protecting stream communities and their trophic function during commercial forestry. 2. The composition of macroinvertebrate communities in margins and riffles most strongly reflected stream pH and aluminium concentrations; acidic riffles contained fewest species of all major macroinvertebrate groups. However, the character of marginal habitats had some influence on communities in stream margins through the presence of broadleaf trees or moorland/grassland vegetation in the riparian zone. Even at low pH, streams with moorland riparian zones had different macroinvertebrates from those with pure conifer. 3. Stream chemistry was important in explaining patterns among feeding guilds. Species richness and abundances of grazers and filterers were reduced at acidic sites with high aluminium concentrations. The number of shredder species was significantly lower in riffles at low pH than at high pH. 4. In contrast, marginal habitat structure was of overriding importance in explaining patterns among collectors and predators. These functional groups were most abundant at sites with riparian zones of moorland and grassland, but scarce in streams where the bankside vegetation consisted of coniferous or broadleaved trees. Total grazer abundances were lowest at sites with riparian zones of pure conifer. 5. We conclude that riparian management can modify effects of forestry on the trophic dynamics and structure of the macroinvertebrate communities of upland streams, but the effect operates within a strong gradient due to acidity. Thus, the array of macroinvertebrates which may benefit from riparian management in forest streams is liable to be restricted by low pH. 6. We discuss the wider ramifications of riparian management for the conservation of streams during commercial forestry. In particular we assess if management proposals set out by the forestry industry are supported. We also discuss the problem of scale when considering measures implemented for stream conservation, emphasizing that the control of problems such as acidification may only be possible at a regional level.     

杭州湾北部大型无脊椎动物群落结构

为研究杭州湾北部海域大型无脊椎动物群落结构及其变化,根据2016年2月、5月、8月和11月于杭州湾北部进行的桁杆拖网调查数据,利用相对重要性指数、多元统计和ABC曲线等方法对该海域大型无脊椎动物的种类组成、优势种及群落结构特征进行研究。结果显示,杭州湾北部共出现大型无脊椎动物22种,隶属4纲5目15科18属,十足目(Decapoda)所占种类数比例最高,达77.3%,其次为狭舌目(Stenoglossa),占比仅为9.1%。调查海域共出现5种优势种,分别是葛氏长臂虾(Palaemon gravieri)、太平洋长臂虾(Palaemon pacificus)、安氏白虾(Exopalaemon annandalei)、黑龙江河篮蛤(Potamocorbula amurensis)和三疣梭子蟹(Portunus trituberculatus)。其中,安氏白虾为四季优势种,葛氏长臂虾为冬季、春季和秋季优势种。CLUSTER聚类和非度量多维标度显示,杭州湾北部大型无脊椎动物群落在44%相似性水平下可分为2个群组,Ⅰ组为冬春组,Ⅱ组为夏秋组,组间差异系数达到57.76%。ANOSIM显示群组间差异极显著(R=0.4,P0.01)。BIOENV表明,杭州湾北部大型无脊椎动物群落结构与温、盐度组合的相关性最高,相关系数为0.39。研究表明,杭州湾北部大型无脊椎动物群落结构较为简单,优势种以小型虾类为主,群落结构的季节变化显著。群落的演替可能受温度、盐度变化及优势种的洄游习性影响,群落处于严重扰动状态。     

Impact and management of visitor pressure on rocky intertidal algal communities

1. Human trampling was investigated in order to quantify the ‘recreational carrying capacity’ of two rocky intertidal areas in northeast England. 2. Estimation of ‘recreational carrying capacity’ was made by subjecting experimental plots in pristine areas of shore to different intensities of sustained trampling. The algal community was subsequently monitored for 16 months. 3. Changes in algal community composition occurred at both sites at all intensities. Compositional changes were rapid (1–2 months) and timing was dependent on both trampling intensity and site. 4. Trampling resulted in consistently reduced abundances of some species, for example fucoids, Phymatolithon lenormandii and turf species. 5. Open space was present in greater quantities in trampled than untrampled plots. In the summer months, this was subsequently colonized primarily by Enteromorpha spp. 6. ‘Recreational carrying capacity’ is being exceeded in some areas at both sites in the summer months. Possible management strategies are discussed in the light of these experimental results. copy 1996 by John Wiley & Sons, Ltd.     

Complete versus partial macrophyte removal: the impacts of two drain management strategies on freshwater fish in lowland New Zealand streams

Complete macrophyte removal to maintain drainage performance in lowland streams can have a negative effect on resident fish communities, but few studies have quantified this impact. Moreover, limited research has been carried out exploring alternative approaches for macrophyte removal that minimise the impact on the resident fish community. The aims of this study were (i) to determine how the current practice of removing almost 100% of available macrophyte cover affects native fish populations in lowland New Zealand streams and (ii) to see whether this impact can be reduced by limiting macrophyte removal to alternating 50‐m sections of the waterway. Native fish populations were surveyed before and after experimental macrophyte removal for the following three treatments: (i) complete macrophyte removal, (ii) macrophyte removal from alternating 50‐m reaches and (iii) control with no macrophyte removal. Radiotelemetry was used to monitor the behavioural response of individual giant kokopu (Galaxias argenteus) to the different treatments. The results of this study suggest that current drain management practices reduce CPUE of fish by 60%. Although limiting macrophyte removal to alternating 50‐m sections did not minimise the community impacts of drain clearing, large giant kokopu did benefit from this strategy. All tagged giant kokopu remained in stream reaches partially cleared of macrophytes, while in completely cleared reaches all individuals were displaced. These results demonstrate the threat current drain management practices pose to New Zealand native fish and highlight the value of trialling alternative methods of macrophyte removal.     

An assessment of the potential for the application of two simple models to Atlantic salmon, Salmo salar, stock management in chalk rivers

Many salmon populations in the UK are under threat, which is assumed to result from a combination of anthropogenic and natural factors. Positive management is required to bring them back to their former productivity levels. An attempt has been made to use two simple models to assess the suitability of several management approaches for use on chalk rivers. One model is based on the survival rates at each stage of the salmon life cycle and the other estimates the predation of young salmon by other fish. This work highlights the paucity of data available to calibrate even the simplest salmon management models. For those variables where data are available, the variability is very high. Despite the poor quality of input data, the outputs are close to observed numbers in the River Frome, a chalk river in Dorset, UK. The models were used to assess the effect of managing the fishery using reduced rod catches, pike culling, gravel cleaning and trout stocking on adult salmon and smolt numbers.     

Ecology,management, and conservation implications of North American beaver (Castor canadensis) in dryland streams

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Movements of the European eel (Anguilla anguilla) in a chalk stream

Abstract – The movements of wild European eels (Anguilla anguilla L.) were monitored continuously over a 2‐year period in a tributary of the River Itchen, Hampshire, UK, using a passive integrated transponder (PIT) antenna system. The time of these movements was then related to a number of monitored and calculated environmental parameters. No eel movements were recorded in the winter months when mean stream temperature was below 10 °C. The numbers of movements peaked in May, when mean water temperatures and day length were increasing. The movement of eels was significantly (P < 0.001, R² = 0.45, N = 72) correlated with the time of sunset, with the majority (72%) recorded during the hours of darkness. The results of this investigation have implications for the design/timing of surveys of yellow eel populations and their habitat associations and suggest that successfully determining the microhabitat preferences of active resident eels will require remote monitoring throughout the 24‐h period.     

Colonization and use of pine wood versus native wood in New Zealand plantation forest streams: implications for riparian management

• 1. Riparian management is becomingly increasingly recognized as an important tool for reducing harvesting impacts on plantation forest streams. To provide information for a riparian management decision support system, this study investigated effects of riparian tree type (plantation Pinus radiata D. Don versus four native species) on the development of epixylic biofilms, and colonization and feeding by invertebrates on wood at two contrasting stream sites in the central North Island, New Zealand.
• 2. Electron micrographs revealed a diverse microflora colonizing all wood types, which generally had similar ergosterol concentrations, microbial activity and algal biomass after 1–2 years immersion.
• 3. Wood type (pine versus native) did not have a significant effect on densities of total invertebrates or dominant taxa. Percentage abundance of some dominant invertebrate groups differed between wood species, apparently in relation to surface complexity, but overall physical habitat differences appeared to override any effects of wood type on community composition.
• 4. The mass of fine particulate material produced by larvae of the conoesucid caddis fly, Pycnocentria funerea McLachlan, differed significantly among wood species, but this was not related to whether the wood was from native trees or plantation pine.
• 5. Overall, the results indicate that local variations in habitat heterogeneity and differences in wood surface texture were more important than wood type in influencing epixylic biofilm development, and utilization by invertebrates. Alien pine wood generally provided habitat conditions and trophic resources during initial decomposition that were within the range of variation of native wood species expected to colonize riparian planting set‐backs in northern New Zealand pine forests.

Copyright © 2004 John Wiley & Sons, Ltd.     

Aquatic macroinvertebrates and environmental gradients in Phragmites reedswamps: implications for conservation

1. Aquatic macroinvertebrates were sampled from 22 sites in three contrasting reedswamps in the Burry Inlet, south-west Wales, which were respectively estuarine and tidal (Llangennech), coastal and artificial (Ashpits), and inland freshwater (Ffrwd). Species assemblages were ordinated by DECORANA, classified by TWINSPAN and related to physico-chemical factors using correlation, ANOVA and principal components analysis. 2. Reedswamps were not physico-chemically uniform, but varied in dissolved oxygen, nitrogen species, conductivity, water depth and reed character. 3. Among these factors, invertebrate species characteristic of the TWINSPAN groups suggested that conductivity, due to salinity, was an important influence on community composition; different communities were dominated by stenohaline to facultative euryhaline species, or by those characteristic of freshwater. Also, conductivity varied highly significantly across TWINSPAN groups: saline sites supported a higher abundance of fewer taxa, while freshwater sites were characterized by speciose assemblages with more beetles. 4. While major changes due to salinity occurred between and within reedswamps, different reedswamps nevertheless held distinct communities. This suggestion of ‘island’ effects prompts further data on aquatic invertebrates in reedswamps as part of the ‘SLOSS’ debate on their conservation. 5. These data show how salinity in maritime reedswamps provides strong habitat diversity in what appear superficially to be uniform habitats, with importance for example to general site design or managed retreat. The data also reveal that risks to speciose freshwater communities in such sites might arise from tidal inundation or sea level change. © 1997 John Wiley & Sons, Ltd.     

The significance of meandering channel morphology on the diversity and abundance of macroinvertebrates in a lowland river in Japan

• 1. Many rivers and streams across the world have been channelized for various purposes. Channel cross‐sections of meandering rivers are asymmetrical and have cross‐sectional diversity in their physical environment; cross‐sections of a channelized river are typically trapezoidal and have little cross‐sectional diversity, both in physical and ecological conditions. Several programmes to restore stream meanders have been undertaken to improve river ecosystems degraded by channelization. However, the association between diversification in the physical environment due to meander restoration and the macroinvertebrate community structure is poorly known.
• 2. This study of a lowland river in Japan assessed how the cross‐sectional diversity of the physical environment changed with restoration of a meander in a channelized river, and how the macroinvertebrate communities responded to the changes in physical habitat variation. Comparisons were made between the macroinvertebrate communities of a channelized reach, the restored meandering reach, and a natural meandering reach.
• 3. Natural meandering and restored meandering reaches showed higher cross‐sectional diversity in physical variables and total taxon richness across a reach than did the channelized reach. Almost all taxa observed in the natural and restored meandering reaches were concentrated in the shallowest marginal habitats near the banks. Shear velocity increasing with water depth had a negative association with macroinvertebrate density and richness.
• 4. This study demonstrated that the shallow river bed along the inside of bends formed point bars that provided a highly stable substrate, a suitable habitat for macroinvertebrates in a lowland river. It is concluded that meander restoration could be an effective strategy for in‐stream habitat restoration in lowland meandering rivers.

Copyright © 2007 John Wiley & Sons, Ltd.     

The effects of an underwater fish observation technique on stream macroinvertebrates at two spatial scales

Abstract – We examined the effects of snorkeling, a commonly used fish observation technique, on the distribution and abundance of benthic macroinvertebrates at both the reach (i.e., 10 m) and patch scale (i.e.,< 1 m) within a southern Appalachian stream (North Carolina, USA). At the reach scale, we quantified increases in macroinvertebrate drift rates associated with snorkeling and used these values to calculate the percentage of the macrobenthos that drifted out of snorkeled reaches. We also used a simple decay model of macroinvertebrate drift to quantify patch scale effects of snorkeling. The model incorporated size specific macroinvertebrate settling rates to estimate the total number of benthic macroinvertebrates that entered the drift in response to snorkeling disturbance. We found that snorkeling consistently produced significant increases in the number of drifting macroinvertebrates. Nevertheless, these increases comprised a very small percentage (<1%) of the total number of organisms in the benthos, suggesting that snorkeling probably did not strongly affect macroinvertebrate assemblages at either the reach or patch scale. However, our analyses also indicated that snorkeling had a disproportionate effect on the drift of small ephemeropterans (4–5% entered the drift in response to snorkeling) relative to other macroinvertebrate taxa. Consequently, the microdistribution of early instar mayflies may have been altered within snorkeled reaches. We conclude that snorkeling related disturbance to the benthos should have a minimal effect on the behavior and distribution of most stream fishes at either the reach or patch scale. However, because snorkeling had a substantial effect on the drift of small mayflies, snorkeling may influence the behavior of fishes that depend on early instar mayflies as a primary food resource. ^Note     

Riparian coverage affects diets of characids in neotropical streams

Abstract – Aquatic ecosystems are influenced by the surrounding terrestrial environment. This work studied the influence of vegetation of riparian zones on the feeding patterns of two nektonic characids, Astyanax paranae and Bryconamericus iheringii, in a basin surrounded by an agricultural area. Nine streams within the Corumbataí River basin (São Paulo State, Brazil) with varying proportions of adjacent riparian forest (RF) and pastures were set apart in three arbitrary categories: Riparian Forest (>90% RF), Mixed Coverage (banks covered by 30–60% RF; MC) and Pasture (<29% RF, PA); resident characids were sampled in the dry and rainy seasons and evaluated in regard to composition of diets. Astyanax paranae fed on allochthonous food sources in RF and MC, and on autochthonous food sources on PA streams; B. iheringii fed on autochthonous food sources in RF streams and in mixed resources (detritus and sediment) in PA streams. Selection of food source was related to, and altered by, stream channel structure and composition of substratum. Preservation and restoration of native riparian vegetation is key to preservation of resident characids in small streams of this river basin.     

The effect of planting grass filter strips on fishes in agricultural headwater streams

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Riparian vegetation management for water temperature regulation: implications for the production of macroinvertebrate prey of salmonids

The effect of riparian vegetation on the seasonal availability of macroinvertebrate prey for salmonids was examined. Although prey composition changed significantly between sampling seasons, overall prey density remained similar. It is often assumed that there is greater benthic production within streams without riparian vegetation, but this assumption was found to be dependent on stream size. The presence of riparian vegetation increased benthic macroinvertebrate density, but only in larger streams. Greater densities of prey of terrestrial origin were found in the drift of streams with riparian cover but only in spring. An unforeseen contributor to potential prey items for salmonids in streams with riparian vegetation was the increased presence of drifting prey of aquatic origin. The results further support riparian management as a viable tool for regulating instream temperatures without impacting on macroinvertebrate density. The presence of riparian vegetation can even increase salmonid prey availability in some instances.