Macroinvertebrate community dynamics in a temperate European Atlantic river. Do they conform to general ecological theory?

Spatial and temporal dynamics of macroinvertebrate communities have usually been linked to several environmental and anthropic factors. The aim of this study is to elucidate how important are these factors in structuring macroinvertebrate communities from temperate regions. Regarding the macroinvertebrate number of taxa, the Habitat Template Model, the Dynamic Equilibrium Hypothesis and the Intermediate Disturbance Hypothesis will be tested in order to know how important the diversity of instream elements and the hydrological disturbance frequency are in defining the macroinvertebrate taxonomic richness. Thus, the structure and composition of macroinvertebrate communities were analysed in nine sites of the Pas River basin, a temperate Atlantic basin in northern Spain, during winter, spring, summer and autumn 2005, together with water physicochemical and environmental characteristics. Macroinvertebrate abundance increased downstream and during summer, probably favoured by lower hydraulic stress and water organic enrichment. As predicts the Habitat Template Model, the macroinvertebrate number of taxa was related to habitat heterogeneity. However, no clear relationship amongst macroinvertebrate richness and water quality was found. The macroinvertebrate taxonomic richness did not correspond exactly with the Dynamic Equilibrium Hypothesis and the Intermediate Disturbance Hypothesis because it was relatively high in the absence of hydrological disturbances (summer). Thus, disturbance events may play a secondary role in determining the seasonal dynamic of the number of taxa. However, hydrological disturbances can be considered the most important factors explaining the seasonal pattern of macroinvertebrate abundance. On the other hand, spatial patterns of macroinvertebrate community structure and composition were mainly determined by resource availability, hydraulic conditions, habitat heterogeneity and human alterations, whilst hydrological predictability and resource availability might play a major role in determining seasonal dynamics.     

The influence of substrate type on macroinvertebrate assemblages within agricultural drainage ditches

Artificial drainage ditches are common features in lowland agricultural catchments that support a wide range of ecosystem services at the landscape scale. Current paradigms in river management suggest activities that increase habitat heterogeneity and complexity resulting in more diverse floral and faunal assemblages; however, it is not known if the same principles apply to artificial drainage ditch systems. We examined the effects of four artificial substrates, representing increasing habitat complexity and heterogeneity (bricks, gravel, netting and vegetation), on macroinvertebrate community structure within artificial drainage ditches. Each substrate type supported a distinct macroinvertebrate community highlighting the importance of habitat heterogeneity in maintaining macroinvertebrate assemblages. Each substrate type also displayed differing degrees of community heterogeneity, with gravel communities being most variable and artificial vegetation being the least. In addition, several macroinvertebrate diversity metrics increased along the gradient of artificial substrate complexity, although these differences were not statistically significant. We conclude that habitat management practices that increase habitat complexity are likely to enhance macroinvertebrate community heterogeneity within artificial drainage channels regardless of previous management activities.

     

Re-Meandering of Lowland Streams: Will Disobeying the Laws of Geomorphology Have Ecological Consequences?

We evaluated the restoration of physical habitats and its influence on macroinvertebrate community structure in 18 Danish lowland streams comprising six restored streams, six streams with little physical alteration and six channelized streams. We hypothesized that physical habitats and macroinvertebrate communities of restored streams would resemble those of natural streams, while those of the channelized streams would differ from both restored and near-natural streams. Physical habitats were surveyed for substrate composition, depth, width and current velocity. Macroinvertebrates were sampled along 100 m reaches in each stream, in edge habitats and in riffle/run habitats located in the center of the stream. Restoration significantly altered the physical conditions and affected the interactions between stream habitat heterogeneity and macroinvertebrate diversity. The substrate in the restored streams was dominated by pebble, whereas the substrate in the channelized and natural streams was dominated by sand. In the natural streams a relationship was identified between slope and pebble/gravel coverage, indicating a coupling of energy and substrate characteristics. Such a relationship did not occur in the channelized or in the restored streams where placement of large amounts of pebble/gravel distorted the natural relationship. The analyses revealed, a direct link between substrate heterogeneity and macroinvertebrate diversity in the natural streams. A similar relationship was not found in either the channelized or the restored streams, which we attribute to a de-coupling of the natural relationship between benthic community diversity and physical habitat diversity. Our study results suggest that restoration schemes should aim at restoring the natural physical structural complexity in the streams and at the same time enhance the possibility of re-generating the natural geomorphological processes sustaining the habitats in streams and rivers. Documentation of restoration efforts should be intensified with continuous monitoring of geomorphological and ecological changes including surveys of reference river systems.     

河流岸带湿地沉积物重金属分布对植被物种多样性和底栖动物群落特征的影响

河流岸带湿地栖息地完整性对河流水环境、水生态和水文的安全与健康具有重要意义,为探究河流岸带湿地表层沉积物重金属分布特征及其对植被和底栖动物的影响,对滦河干流上中下游河段表层沉积物、植物群落和底栖动物调查分析,采用生物毒性效应系数法和综合潜在生态风险指数法评价沉积物重金属污染特征,采用植被物种多样性指数和底栖动物完整性指数评价滦河植物和底栖动物群落特征,探究岸带湿地沉积物重金属空间分布与植被及底栖动物群落特征之间关系。结果表明,滦河表层沉积物总体呈清洁水平,但不同河段重金属空间分布差异较大,下游重金属生态危害系数和潜在生态风险指数高于上中游。湿地物种调查共识别维管束植物219种,大型无脊椎底栖动物105种,综合评价结果表明下游植物群落物种多样性和底栖动物群落完整性低于上中游。滦河下游岸带湿地沉积物重金属对生物群落具有生物毒性和潜在的生态风险,降低了植被物种多样性和底栖动物群落完整性。大型底栖动物完整性指数能够综合反映底栖动物群落结构特征变化,对河岸带湿地生态健康评价和监测具有重要意义。     

Spatio-temporal patterns of eukaryotic biodiversity in shallow hard-bottom communities from the West Antarctic Peninsula revealed by DNA metabarcoding

Aim

We studied molecular eukaryotic biodiversity patterns in shallow hard-bottom Antarctic benthic communities using community DNA metabarcoding. Polar ecosystems are extremely exposed to climate change, and benthic macroinvertebrate communities have demonstrated rapid response to a range of natural and anthropogenic pressures. However, these rich and diverse ecosystems are poorly studied, revealing how little is known about the biodiversity of the Antarctic benthos associated with hard-bottom habitats.

Location

West Antarctic Peninsula and South Shetland Islands.

Methods

Using data collected in seven localities along the western Antarctic Peninsula, we calculated spatial patterns of alpha and beta diversities. Furthermore, we analysed temporal changes in benthic composition in one location (Deception Island) over 3 years. We calculated the temporal alpha and beta diversities to reveal changes in this community over time.

Results

We obtained a final list of 2057 molecular operational taxonomic units. We found significant differences in benthic community composition between localities and among years. Our dataset revealed a total of 10 different kingdom-level lineages and 34 different phyla in the samples. The most diverse phylum was Arthropoda, followed by Bacillariophyta, and Annelida, while the highest relative read abundances belonged to Annelida, Porifera and Echinodermata. Benthic community compositions changed between 2016 and 2018 in Deception Island, and decreasing species richness was the main component of temporal beta diversity.

Main Conclusions

Direct sampling methods are required for monitoring these complex communities. Informative biodiversity patterns can be retrieved even though most of the benthic biodiversity found in Antarctic habitats is yet to be taxonomically described and barcoded. Hard-bottom assemblages exhibit high spatial variability and heterogeneity, not related to depth, which represent a huge challenge for large-scale studies in the Southern Ocean. Local patchiness and structure within these communities are probably a consequence of a combination of several biotic and abiotic factors (i.e. ice disturbance, food supply and competition).     

Stream community structure in relation to spatial variation: the influence of mesohabitat characteristics

Community structure of benthic macroinvertebrates was studied in six first- through fourth-order streams in northeast France, to elucidate changes in richness, abundance, diversity and evenness of mesohabitat assemblages as a function of environmental conditions. Patch samples were subjected to multivariate analyses to determine: (i) relationships among seven indices describing community structure (structure parameters); (ii) relationships among seven environmental variables; (iii) the relationship between community structure and environmental characteristics of patches. Faunal data showed that indices measuring the distribution of individuals among taxa (evenness, dominance) and richness are prominent in describing the structure of macroinvertebrate communities of mesohabitats. The analysis of environmental data demonstrated a major differentiating ability of current velocity and strong inter-relations among in-stream hydraulic-dependent parameters in structuring the mesohabitat environment. The co-structure (= relationship) between community organization and environmental variables indicated that substrate may be a primary determinant of community structure. Current velocity and water depth emerged as secondary factors. Trends in community structure were closely related to the spatial variability of mesohabitats. Species richness increased with habitat heterogeneity. Total abundance increased with trophic potentialities of patches. Equitability and diversity seemed to increase with patch stability. This revised version was published online in July 2006 with corrections to the Cover Date.     

Relationship between Riparian Vegetation and Stream Benthic Communities at Three Spatial Scales

We examined the influence of riparian vegetation on macroinvertebrate community structure in streams of the Upper Thames River watershed in southwestern Ontario. Thirty-three μ-basins (129–1458 ha) were used to identify land cover variables that influenced stream macroinvertebrates. Micro-basins represented the entire drainage area of study streams and were similar in stream order (first, second) and land cover (agricultural or forest; no urban). We described the structure and composition of riparian vegetation and benthic macroinvertebrate communities at the outflow reach. The nature of the land cover was quantified for the stream network buffer (30 m) and the whole μ-basin. The objective of this study was to measure the magnitude and nature of the relationship between the riparian vegetation and benthic macroinvertebrate community at the outflow reach, stream network buffer, and whole μ-basin scales. Taxon richness (including total number of Ephemeroptera, Plecoptera, and Trichoptera taxa) and Simpson’s diversity of the macroinvertebrate community all increased with increased tree cover in the riparian zone at the outflow reach scale. Simpson’s equitability was lower with greater agricultural land cover in the stream network buffer. No relationship between the macroinvertebrate community and land cover was found at the whole μ-basin scale. Analysis of the influence of land cover on stream communities within a spatial hierarchy is important for understanding the interactions of stream ecosystems with their adjacent landscapes.     

Relationship of Farm Level Pesticide Use and Physical Habitat on Benthic Community Status in a California Agricultural Stream

The objectives of this study were to: (1) evaluate temporal and spatial trends in water quality parameters, physical habitat metrics, and benthic community metrics in the Orestimba Creek from years 2000 to 2005, and (2) assess the relationship of benthic community condition from ten Orestimba Creek stations and both pesticide use at the farm level and physical habitat conditions. Significant year effects were reported for temperature, pH, dissolved oxygen, and turbidity. In general, most of the 17 physical habitat metrics did not show statistical variability over the 6-year period. Most of the benthic metrics were variable over the 6-year period. A total of 41 herbicides, 14 organophosphorus (OP) insecticides, and 5 pyrethroids were applied to 23 sections of land bordering the Orestimba Creek from 2000 to 2004. The OP insecticides showed the strongest relationship to benthic metrics using univariate regression models when all three classes of pesticides were compared; however, these statistical relationships had low R² values. Stepwise regression analysis showed statistically significant relationships between most benthic metrics and habitat metrics. In general, both pesticide applications and physical habitat have a similar but modest statistical association with benthic communities. However, the relationship of both pesticide applications and physical habitat on benthic communities in the Orestimba Creek appear to be insignificant compared to the magnitude of spatiotemporal patterns reported.     

Stability and Persistence of Alpine Stream Macroinvertebrate Communities and the Role of Physicochemical Habitat Variables

Macroinvertebrate communities in alpine streams have rarely been examined over more than two consecutive years or at sub-monthly temporal resolution during the summer melt season, in relation to a range of stream physicochemical habitat measurements. This paper addresses these research gaps by investigating the inter- (late melt season, 1996–2003) and intra-annual (bi-weekly; June–September, 2002–2003) community compositional stability and persistence of three alpine streams fed from different water sources (snow, glaciers and groundwater) in the Taillon–Gabiétous catchment, French Pyrénées. Inter-annual community stability and persistence decreased from 1996 to 2003; however, groundwater stream communities changed less than those in the main glacial stream. Intra-annual community stability varied spatially and temporally, particularly in relation to water quality variables (water temperature and suspended sediment concentration); water quantity (stream discharge) was less important perhaps due to taxa possessing adaptations to flow variability. The 15 most abundant taxa were consistently more stable and persistent than the entire stream community suggesting a common pool of taxa in these streams. Overall, the results support the view that streams originating from different alpine water sources are characterised by distinct benthic macroinvertebrate assemblages, and demonstrate the value of sampling at nested temporal scales (inter-annual to bi-weekly) for understanding how these stream ecosystems function.     

Structure of Macroinvertebrate Communities in Relation to Environmental Variables in a Subtropical Asian River System

Subtropical Asian rivers support a highly diverse array of benthic macroinvertebrates. Yet, their biodiversity and functionality has been poorly investigated. We choose the Chishui River system, one of the largest un‐dammed, first level branches upstream of the Yangtze River, China, to: 1) determine the spatial pattern of macroinvertebrate diversity and community structure, and 2) examine the influence of variables at local habitat and basin scales on the distribution of macroinvertebrate communities. Samples were collected from 43 sites in spring of 2007. After Canonical Correspondence Analysis, two basin and five habitat variables were found to be significant predictors of the macroinvertebrate community structure. Variance partitioning analysis showed that habitat physical variables had a greater influence than other environmental variables in macroinvertebrate community, which suggested that preserving habitat, especially upstream, should be strongly considered in biological conservation. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of siltation on stream fish communities

Synopsis The effect of siltation on stream fish in northeast Missouri was evaluated using community structural measurements and a functional approach that emphasized feeding and reproductive guilds. As the percentage of fine substrate increased, the distinction among riffle, run, and pool communities decreased, primarily because the number of individuals of typical riffle species decreased. Within the riffle communities the abundance of fish of two feeding guilds — benthic insectivores and herbivores — was reduced as the percent of fine substrate increased. The abundance of fish in other feeding guilds was not affected. The only reproductive guild to be similarly affected was the simple and lithophilous, whose members require a clean gravel substrate for spawning. Species within each guild affected by siltation had significantly similar trends in abundance. The guild analysis indicated that species with similar ecological requirements had a common response to habitat degradation by siltation.     

Response of freshwater macroinvertebrates to rainfall-induced high flows: A hydroecological approach

Hydraulic-habitat and biological data were integrated within a twofold-purpose study: (i) to investigate the response of freshwater macroinvertebrates to a rainfall-induced high flow event of moderate magnitude and (ii) to derive hydroecological relationships between habitat variability and macroinvertebrate microdistribution. 142 microhabitats (unique combinations of flow velocity, water depth and substrate type) allocated in four sites of no or very minor anthropogenic influence were sampled and analyzed, before and after the event. Freshwater macroinvertebrates were additionally collected and specific community metrics were derived. To identify possible pre- and post- impact benthic community differences, independent sample t-tests were applied, while Boosted Regression Tree models were developed to quantify the response of macroinvertebrates to flow alteration. Macroinvertebrate abundance, taxonomic richness, EPT richness and diversity decreased significantly by 90%, 60%, 50% and 25% respectively between the pre- and post- impact microhabitats. The relative abundance of macroinvertebrate predators and passive filter feeders increased after the event, mainly in specific substrate types (boulders and large stones), which served as flow refugia, maintaining less degraded (compared to finer substrates), still heavily impacted, benthic communities. According to the hydroecological analysis, the high flow event exerted the strongest impact on all macroinvertebrate metrics. Optimal (suitable) ranges of the hydraulic-habitat variables for benthic macroinvertebrates were identified (optimal flow velocity from 0.3 m/s to 0.7 m/s, optimal water depth at 0.2 m), while boulders and large stones were the most suitable substrate types. The aforementioned data provide valuable information for the provisioning of biologically-derived environmental flows and an essential input of hydrodynamic habitat models to facilitate the selection of the optimal environmental flow scenario towards ensuring the integrity of aquatic ecosystems downstream of anthropogenic activities provoking hydrological alteration.     

Macroinvertebrate community in the lower Ebro river (NE Spain)

We examine the macroinvertebrate community composition and dynamics in the last 60 km of the Ebro river (NE Spain). Different sampling methods (individual stones, Surber, kick samplers and artificial substrate) were used depending on the characteristics of the sites chosen (substrate, current velocity, saline influence).The high nutrient content and the abundance of UFPOM is the origin of a high density in stones although no clear pattern exists between stone surface area and density or species richness. The high spatial heterogeneity and moderate disturbance intensity and frequency because of river regulation explains the relatively rich macroinvertebrate community and the low temporal changes in the community.     

山地河流浅滩深潭生境大型底栖动物群落比较研究——以重庆开县东河为例

浅滩和深潭是山地河流中常见的河流生境结构。2011年7月,在重庆开县东河上游双河口-杉木桥河段,选择21个浅滩和深潭,调查大型底栖动物,研究影响不同生境中底栖动物组成、分布和多样性的生态机理。结果表明:调查河段浅滩和深潭中大型底栖动物分别为31种和24种,密度分别为450.62 个/m²和86.24 个/m²,生物量分别为2.88 g/m²和0.55 g/m²。浅滩有指示种11种,即纹石蛾(Hydropsyche sp.)、假蜉(Iron sp.)、假二翅蜉(Pseudocloeon sp.)、舌石蛾(Glossosoma sp.)、高翔蜉(Epeorus sp.1)、背刺蜉(Notacanthurus sp.)、Heterocloeon sp、锯形蜉(Serratella sp.)、朝大蚊(Antocha sp.)、等蜉(Isonychia sp.)、溪颏蜉(Rhithrogena sp.)。深潭指示种仅蜉蝣(Ephemera sp.)和黑大蚊(Hexatoma sp.)两种。刮食者为两类生境的优势功能摄食类群。浅滩中滤食者和刮食者比例显著高于深潭,而收集者和捕食者显著低于深潭。两类生境中大型底栖动物群落结构差异显著。浅滩中大型底栖动物的密度、生物量、丰富度指数、Shannon-Wiener 指数、改进的Shannon-Wiener指数均明显高于深潭。受地貌形态、水力特征和冲淤变化规律影响的生境稳定性和异质性差异是导致大型底栖动物群落差异的主要原因。     

Effects of chronic bottom trawling disturbance on benthic biomass, production and size spectra in different habitats

Bottom trawling has widespread impacts on benthic communities and habitats. It is argued that the impact of chronic bottom trawling on benthic infauna depends on the natural disturbance levels to which benthic communities are adapted. We analysed biomass, production and size structure of two communities from a muddy and a sandy habitat, in relation to quantified gradients of trawling disturbance on real fishing grounds. We used an allometric relationship between body mass and individual production to biomass ratio to estimate community production. Chronic trawling had a negative impact on the biomass and production of benthic communities in the muddy habitat, while no impact was identified on benthic communities from the sandy habitat. These differences are the result of differences in size structure within the two communities that occur in response to increasing trawling disturbance.     

Temporal dynamics of benthic macroinvertebrate communities and their response to elevated specific conductance in Appalachian coalfield headwater streams

Coal mining in central Appalachia USA causes increased specific conductance in receiving streams. Researchers have examined benthic macroinvertebrate community structure in such streams using temporally discrete measurements of SC and benthic macroinvertebrates; however, both SC and benthic macroinvertebrate communities exhibit intra-annual variation. Twelve central Appalachian headwater streams with reference quality physical habitat and physicochemical conditions (except for elevated SC in eight streams) were sampled ≤fourteen times each between June 2011 and November 2012 to evaluate benthic macroinvertebrate community structure. Specific conductance was recorded at each sampling event and by in situ data loggers. Streams were classified by mean SC Level (Reference, 17–142 μS/cm; Medium, 262–648 μS/cm; and High, 756–1535 μS/cm). Benthic macroinvertebrate community structure was quantified using fifteen metrics selected to characterize community composition and presence of taxa from orders Ephemeroptera, Plecoptera, and Trichoptera. Metrics were analyzed for differences among SC Levels and months of sampling. Reference streams differed significantly from Medium-SC and High-SC streams for 11 metrics. Medium-SC streams had the most metrics exhibiting significant differences among months. Relative abundances of Plecoptera and Trichoptera were not sensitive to SC, as the families Leuctridae and Hydropsychidae exhibited increased relative abundance (vs. reference) in streams with elevated SC. In contrast, Ephemeroptera richness and relative abundance were lower, relative to reference, in elevated-SC streams despite increased relative abundance of Baetidae. Temporal variability was evident in several metrics due to influence by taxa with seasonal life cycles. These results demonstrate that benthic macroinvertebrate communities in elevated-SC streams are altered from reference condition, and that metrics differ in SC sensitivity. The time of year when samples are taken influenced measured levels and differences from reference condition for most metrics.     

Among-habitat and Temporal Variability of Selected Macroinvertebrate Based Metrics in a Mediterranean Shallow Lake (NW Spain)

According to the European Water Framework Directive, waterbodies have to be classified on the basis of their ecological status using biological quality elements, such as macroinvertebrates. This needs to take into consideration the influence of natural variation (both spatial and temporal) of reference biological communities as this may obscure the effects caused by anthropogenic disturbance. We studied the influence of among-habitat and temporal (seasonal and interannual) changes on the macroinvertebrate communities of an Iberian shallow lake and the variability of 21 measures potentially useful for bioindication purposes. Two series of data were examined: (a) macroinvertebrate samples taken on four occasions over an annual cycle were used to assess the effects of seasonality and among-habitat variability; (b) macroinvertebrate samples collected in three consecutive summers were used to assess interannual variability. Coefficients of variation, expressed as percentage, were used to quantify the effect of among-habitat and temporal variability on the selected metrics. According to our results, % Insecta, Shannon–Wiener diversity index and the qualitative taxonomic metrics (measures based on number of taxa) were robust in terms of temporal (seasonal and interannual) and among-habitat variability. Abundance ratio and some metrics based on functional feeding groups were highly variable. Therefore, qualitative taxonomic metrics may be promising tools in biomonitoring programs of Mediterranean shallow lakes due to their comparatively low variability.     

Long-term population and community patterns of benthic macroinvertebrates and fishes in Northern California Mediterranean-climate streams

Long-term studies can document temporal patterns in freshwater ecosystems, and this is particularly important in mediterranean-climate (med-climate) regions because of strong interannual variation in precipitation amounts and consequently stream flow. We review long-term studies of populations and communities of benthic macroinvertebrate and fishes from sites throughout the med-climate region of California and develop generalities that may apply broadly to med-climate streams worldwide. Severe drought may result in community shifts, and alter age-structure in both macroinvertebrates and fishes. Within-year seasonal patterns in macroinvertebrate communities can be influenced by annual variability in flow regimes. Macroinvertebrate biological-monitoring metrics with consistently low intra-annual variability may be especially applicable in med-climate streams, as is the use of different temporal windows to describe reference periods to reduce influence of interannual variability on impact detection. Long-term data can be used to develop macroinvertebrate-based metrics that can either show or be independent of climate-change effects. Most macroinvertebrate species are temporally rare in their annual occurrence. Multiple components of natural flow regimes can favor native over invasive fishes. Long-term, quantitative information from med-climate streams is generally lacking, which is a hindrance to both management practices and development of appropriate ecological constructs.     

Differential influence of a monotypic and diverse native aquatic plant bed on a macroinvertebrate assemblage; an experimental implication of exotic plant induced habitat

Aquatic plants mediate ecological processes in aquatic habitats, specifically predator–prey (bluegill sunfish (Lepomis macrochirus Rafinesque)-macroinvertebrate) interactions. Macroinvertebrate colonization is directly and indirectly influenced by substrate heterogeneity, interstitial space, and surface complexity. Exotic invasive plant species, such as Hydrilla verticillata L.F. Royle, may alter the available structure in aquatic habitat by creating a shift to a homogeneous habitat, thus affecting the macroinvertebrate community. Since macroinvertebrates provide a food base for young phytophilic fishes, changes in their density and abundance may alter food webs. We investigated the hypothesis that macroinvertebrate community structure is influenced by differences in habitat heterogeneity by measuring difference between a heterogeneous native aquatic plant bed, homogenous hydrilla plant bed, and habitat with no plants. Studies were conducted in the field (pond) and the experimental treatments were: (1) no plants, (2) monotypic bed of hydrilla, and (3) diverse native plants. Aquatic plants, regardless of species, supported greater macroinvertebrate abundance, richness, and biomass. Macroinvertebrate abundance, richness, and biomass in a hydrilla-dominated habitat did not differ significantly from a diverse plant habitat, except for richness in October. Indicator taxa did differ significantly between respective treatments, suggesting a change in species composition. However, no significant effect of fish predation on macroinvertebrate populations and/or community structure was documented. The data suggest that a shift from a natural mosaic of vegetated habitat to a highly complex monotypic habitat (e.g., exotic hydrilla) may reduce spatial heterogeneity important to structuring a macroinvertebrate assemblage. Handling editor: S. M. Thomaz     

Short-term recovery of benthos following disturbance from stream habitat rehabilitation

The recovery of benthic macroinvertebrates after disturbance from stream rehabilitation was studied in the River Livojoki, northern Finland. The stream that had been channelized for log transport was rehabilitated on 1 July 1992 by digging holes and inserting boulders. We measured habitat characteristics and sampled benthic animals before and after rehabilitation, including an unrehabilitated control site. The immediate effect of rehabilitation was a slight decrease in the abundances of benthic insects. Recolonization occurred rapidly, within 10 days. Disturbance of the rehabilitation did not have a detectable effect on the macroinvertebrate community. Most species-level changes and community patterns reflected seasonal life history events. Timing of such rehabilitation work can be critical for the recovery rate, which depends on the colonization abilities of the species present after disturbance. We suggest that many disturbances (including minor floods and moderate rehabilitation procedures) may have only small, short-term effects on benthic communities. We emphasize the importance of considering seasonality in studies of disturbance in streams.