Modification of an index of biotic integrity based on fish assemblages to characterize rivers of the Seine Basin,France

The Index of Biotic Integrity (IBI) is a measure of fish assemblage health that has been used to assess catchment and stream quality throughout North America. It reflects human perturbations on natural environmental structures and processes. While preserving the ecological foundation of the original North American metrics, we have modified and adapted the IBI to the mainstem Seine River and its major tributaries in France. This successful modification of the IBI to a considerably different fish fauna on a different continent further supports its wider use outside the midwestern United States. Using data collected in 1967, 1981, and 1988–1989 from a total of 46 sites, we show spatial and temporal variation in the Seine as indicated by IBI scores. Statistically significant relationships were found between IBI and catchment area but insignificant relationships existed between IBI and an independent Water Quality Index (WQI) based on water chemistry. Comparisons between the IBI and the WQI indicate that the former is a more sensitive and robust measure of water body quality. Our results demonstrate that the IBI, combined with a statistically designed national monitoring program, would offer a reliable means of assessing spatial patterns and temporal trends in water body improvement or degradation in France. The more primitive fish families in the Basin were affected first by perturbations. These families include all the diadromous species found in the Seine and suggest serious disruption of their life histories.     

Assessment of an index of biological integrity (IBI) to quantify the quality of two tributaries of river Chenab,Sialkot, Pakistan

Nullah Aik and Nullah Palkhu, two tributaries of river Chenab, were investigated for the assessment of fish habitat degradation as indicator of stream health. Fish abundance data were collected from 18 sites from September 2004 to April 2006 to develop multimetric indices for fish assemblage integrity and to detect the intensity of habitat degradation. A total of 12 metrics were calculated on the basis of taxonomic richness, habitat preference, trophic guild, stress tolerance and origin of species to develop stepped and continuous index of biological integrity (IBI) criteria. Cluster analysis (CA) classified sites based on species composition into three groups, viz., reference, moderately impaired and impaired groups. Non-metric multidimensional scaling (NMDS) was applied to identify underlying ecological gradient to highlight the habitat degradation. NMDS segregated two sites as less impaired, five sites as moderately impaired and eleven sites as impaired groups. Axes 1 and 2 explained a total variation of 53.3%. First axis explained the level of habitat impairment, whereas axis 2 indicated species richness along longitudinal gradient of streams. Sites located upstream of Nullah Aik showed higher IBI scores which dropped to its lowest in downstream sites near Sialkot city. Lowest values of IBI of sites in close proximity of city indicated the role of anthropogenic activities in catchment areas. The results indicated that variability in water chemistry can be related as a function of stream sites impairments (i.e., unimpaired, moderately impaired, and severely impaired). Water quality parameters showed strong correlation with IBI scores. Significantly negative correlation of IBI scores with COD, TDS, turbidity, Fe, Cr, Zn and positive correlation with DO and pH was found. The results can be used for restoration and future management of small streams passing through urban areas of Pakistan. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: J. A. Cambray     

The Index of Biological Integrity and the bootstrap: Can random sampling error affect stream impairment decisions?

Multimetric indices, such as the Index of Biological Integrity (IBI), are increasingly used by management agencies to determine whether surface water quality is impaired. However, important questions about the variability of these indices have not been thoroughly addressed in the scientific literature. In this study, we used a bootstrap approach to quantify variability associated with fish IBIs developed for streams in two Minnesota river basins. We further placed this variability into a management context by comparing it to impairment thresholds currently used in water quality determinations for Minnesota streams. We found that 95% confidence intervals ranged as high as 40 points for IBIs scored on a 0–100 point scale. However, on average, 90% of IBI scores calculated from bootstrap replicate samples for a given stream site yielded the same impairment status as the original IBI score. We suggest that sampling variability in IBI scores is related to both the number of fish and the number of rare taxa in a field collection. A comparison of the effects of different scoring methods on IBI variability indicates that a continuous scoring method may reduce the amount of bias in IBI scores.     

A fish index of biotic integrity for South Dakota's Northern Glaciated Plains Ecoregion

Ecosystem goods and services in streams are impaired when their biotic communities are degraded by anthropogenic stressors. An index of biotic integrity (IBI) translates community structure into a standardized ecoregion-specific stream health score. Documenting stream health is especially important in the Northern Glaciated Plains (NGP) Ecoregion, which is undergoing rapid landscape alterations through increased agriculture production. Our objectives were to develop a fish IBI and validate candidate reference sites for NGP wadeable perennial streams. Fish were sampled from 54 sites (consisting of reference sites, known-condition least and most disturbed sites, and random sites) during summers 2006–2011. Candidate metrics were sorted into nine metric classes based on attributes of fish assemblage form and function. Metric values were screened using metric range, signal-to-noise ratios, responsiveness to disturbance, and redundancy tests until each metric class contained only those metrics most responsive to anthropogenic stressors. The final IBI consisted of six metrics that were reflective of prairie stream fish assemblages, and differentiated between known-condition least and most disturbed sites. The mean reference sampling site IBI scores were found to be similar to both least and most disturbed sites (Mann–Whitney U-test; P < 0.05). Twelve reference site scores were below the NGP's median (69), whereas the other 11 sites were above the median and were representative of least disturbed conditions. We now have developed a standardized bioassessment tool for evaluating stream health, as well as a baseline for long-term monitoring in a dynamic ecoregion.     

Small scale application and assessment of a Index of Biotic Integrity for a large boreal river

Modifications and use of Karr’s Index of Biotic Integrity (IBI) for assessing the effects of anthropogenic impacts to aquatic ecosystems have typically occurred using data collected at the macro scale. However, some non-point sources of habitat degradation occur at small scales. One possible source of perturbation to fish habitat in boreal rivers is the application of rip rap shoreline armouring in human use areas. In this study we assess the use of IBI in a small scale setting and discuss the potential impact of rip rap shoreline armouring. We captured small and juvenile fishes weekly during 2002–2003 from 12 sample sites within the littoral zone of a human use area using a modified beach seine. Principal component analysis (PCA) was performed on the data to examine the relationship between species composition and IBI scores. We also performed PCA on the IBI metrics to assess our modifications. The IBI method produced higher scores for armoured sites than for unarmoured sites. We found a strong rank order correlation (Spearman’s ρ > 0.93; p < 0.001) between the modified IBI scores and the first principal component, suggesting that Karr’s original empirically-based IBI is strongly linked to species composition. We found a high degree of redundancy between the metrics of the IBI that validate our modifications. These results suggest that IBI can be a suitable method for assessing non-point impacts from within a small study area. Our results also indicate that fish habitat from rip rap armoured sites within the test area had consistently higher IBI scores that unarmoured sites.     

Effects of coalbed natural gas development on fish assemblages in tributary streams of the Powder and Tongue rivers

1. Extraction of coalbed natural gas (CBNG) often results in disposal of large quantities of CBNG product water, which may affect aquatic ecosystems. We evaluated the effects of CBNG development on fish assemblages in tributary streams of the Powder and Tongue rivers. We used treatment and control, impact versus reference sites comparisons, surveys of CBNG product‐water streams and in situ fish survival approaches to determine if CBNG development affected fish assemblages. 2. Several of our results suggested that CBNG development did not affect fish assemblages. Species richness and index of biotic integrity (IBI) scores were similar in streams with and streams without CBNG development, and overall biotic integrity was not related to the number or density of CBNG wells. Fish occurred in one stream that was composed largely or entirely of CBNG product water. Sentinel fish survived in cages at treatment sites where no or few fish were captured, suggesting that factors such as lack of stream connectivity rather than water quality limited fish abundance at these sites. Fish species richness did not differ significantly from 1994 to 2006 in comparisons of CBNG‐developed and undeveloped streams. Biotic integrity declined from 1994 to 2006; however, declines occurred at both impact and reference sites, possibly because of long‐term drought. 3. Some evidence suggested that CBNG development negatively affected fish assemblages, or may do so over time. Specific conductivity was on average higher in treatment streams and was negatively related to biotic integrity. Four IBI species richness metrics were negatively correlated with the number or density of CBNG wells in the catchment above sampling sites. Bicarbonate, one of the primary ions in product water, was significantly higher in developed streams and may have limited abundance of longnose dace (Rhinichthys cataractae). Total dissolved solids, alkalinity, magnesium and sulphate were significantly higher in developed streams. 4. Biological monitoring conducted before the development of CBNG, and continuing through the life of development and reclamation, together with data on the quantity, quality and fate of CBNG product water will allow robust assessment of potential effects of future CBNG development worldwide.     

Fish assemblage structure in an estuary of the Atlantic Forest biodiversity hotspot (southern Brazil)

We described the fish assemblage in the estuary of the Guaraguaçu River (one of the largest tributaries of the Paranaguá Bay Estuary, located within Brazil’s Atlantic Forest Biosphere Reserve) from June 2005 to May 2006, and assessed the seasonal and spatial effects of abiotic environmental attributes on the fish assemblage structure. Despite some oscillations in salinity, the upper and lower estuaries had year-round persistent oligohaline and polyhaline conditions, respectively. Despite high species richness (55 species), the Guaraguaçu River Estuary fish community contains a few dominant taxa; 11% of the richness accounts for >60% of its density and biomass. The most abundant species (in terms of both biomass and density) was Atherinella brasiliensis. Species whose densities were most strongly associated with the upper estuary were Centropomus parallelus, Ctenogobius schufeldti, Eucinostomus melanopterus, Platanichthys platana, Trinectes paulistanus, and Eugerres brasilianus. Those whose densities were most strongly associated with the lower estuary were A. brasiliensis, Sphoeroides greeleyi, Eucinostomus argenteus, Sphoeroides testudineus, Diapterus rhombeus, and Harengula clupeola. Throughout the year, canonical correspondence analysis identified: (1) the pattern of horizontal stratification of salinity along the river as being the most important variable for explaining most of the fish fauna structure; and (2) a strong relationship between the fish fauna and the salinity gradient along the estuary. Analysis of similarity further confirmed that each estuarine zone supports a year-round persistent and relatively homogeneous fish species assemblage. Total mean density and biomass remained constant over time in each estuarine habitat, but density shifted in the most abundant species, which appears related to recruitment patterns. Such species and abundance persistence likely occurs because seasonal rainfall-induced changes in river discharge are not sufficient to significantly shift runoff and salinity and thus fish assemblage structure (species composition, density and biomass) along the estuary. Such a lack of seasonal fish fauna movement as a response to changes in river flow contrasts with other estuarine systems around the world.     

Temporal and spatial variation in an index of biological integrity for the middle Wabash River, Indiana

Few studies have addressed within-year temporal variation of IBI scores. We compared index of biotic integrity (IBI) scores for two summer sampling events from a large river during 25 annual periods. The results indicated that IBI scores calculated from June samples were not significantly different from July samples. Spatial autocorrelation was present, such that sites that were closer together produced similar IBI scores and could not be considered independent. Temporal autocorrelation was present, but was not strong. Lower quality sites (low IBI score) did not have higher variation than higher quality sites. Our results show that a single sample of fishes by boat electrofisher during the summer in a large river such as the Wabash River can produce a repeatable estimate of IBI score. Thus, repeated or additional sampling within the summer season to improve the quality of the evaluation is not warranted. Handling editor: J. Trexler     

Beetle assemblages in ponds: effects of habitat and site age

• 1 Water beetle assemblages were sampled in each of 18 freshwater ponds, including 11 recently constructed sites designed to provide mitigation for wetlands destruction elsewhere, and seven older reference sites. There were three objectives: (a) to relate taxon richness and biomass of the beetles to the same properties of the wider aquatic invertebrate community, (b) to evaluate changes in beetle assemblage structure over time, and (c) to determine habitat effects on taxonomic composition, mean body size and trophic guild structure of the beetle assemblage.
• 2 Forty‐seven beetle genera were identified, representing 77 species. The beetles represented an average of 21.5% of total generic richness, but only 3.7% of total wet biomass of the wider invertebrate community.
• 3 Of all variables evaluated using canonical correspondence analysis (CCA), site age had the greatest influence on the beetle assemblage. Predatory dytiscids were early colonists at younger sites, while herbivorous curculionids and chrysomelids associated with particular types of vegetation typically occurred in older ponds. Mitigation ponds and reference ponds supported similar numbers of species. Reference sites, however, harboured substantially more unique species found at only a single site within the study area.
• 4 The presence of fish was also strongly related to beetle assemblage structure. Ponds with few or no fish contained about 3‐fold higher biomass and 3‐fold greater mean wet weight per individual compared to ponds with substantial fish assemblages.
• 5 Beetle assemblage composition varied among sites and sampling years, but beetle biomass, richness and species composition may be useful tools in evaluating the success of wetland mitigation efforts.

     

Persistence of community structure: what happens when you change taxonomic scale?

It is common in community ecology to use the species as the taxonomic category of interest, yet in rich tropical assemblages containing guilds of very similar species this may not be appropriate. Such assemblages may be organized at the level of guilds rather than at the finer species level. In a ten-year study of assemblages of fish at One Tree Reef, Great Barrier Reef, we found species composition and the number of fish on a given lagoonal patch reef vary greatly across time (Sale and Douglas 1984; Sale et al. in preparation). The mean average proportional similarity of a reef's assemblage to itself at different times (censuses) is usually low at a value of around 0.5. This apparent variability may be ecologically irrelevant noise if organization is at the higher guild level. We have recast our database at the guild level to test this possibility. Thirteen guilds were defined by the diets, foraging habitats and times of the individual species comprising them. Similarity of an assemblage to itself at successive censuses was re-calculated using the number of individuals in each guild instead of the numbers in each species. This analysis yielded significantly higher levels of similarity (P<0.01) among censuses. To test whether this increase in similarity was due solely to the smaller number of categories used to calculate the similarity indices, 5 sets of randomly generated guilds were constructed using a Monte Carlo approach. No significant difference (P>0.05) was found between the average similarity among censuses when assemblages were classified into these null guilds and when they were classified according to the real guilds. These results indicate that shifting to the larger taxonomic scale of guilds does not reveal a significantly more persistent assemblage structure than that revealed when analysis is at the smaller scale of species. There is no evidence of an underlying organization of these assemblages at the guild level.     

Macroinvertebrate community response to natural and forest harvest gradients in western Oregon headwater streams

1. To examine the effects of forest harvest practices on headwater stream macroinvertebrates, we compiled a 167 site database with macroinvertebrate, fish, physical habitat and catchment land cover data from the three forested ecoregions in western Oregon. For our analysis, headwater streams were defined by catchment areas <10 km² and perennial water during summer low flows. Almost all sites in the database were selected using a randomised survey design, constituting a representative sample of headwater streams in these ecoregions. 2. Macroinvertebrate taxonomic and functional feeding group composition were very similar among the three ecoregions in the study area (Coast Range, Cascades and Klamath Mountains). On average, 55% of the individuals at each site were in the orders Ephemeroptera, Plecoptera or Trichoptera. Dipteran taxa (mostly chironomids) accounted for another 34%. At almost all sites, non‐insects made up <10% of the macroinvertebrate assemblage. Almost half (49%) of the assemblages were collectors; remaining individuals were about evenly divided among scrapers, shredders and predators. 3. There were 189 different macroinvertebrate taxa at the 167 sites with richness at individual sites ranging from 7 to 71 taxa. Ordination by non‐metric multidimensional scaling revealed a strong association between % Ephemeroptera, especially Baetis, and site scores along the first axis. This axis was also strongly related to % coarse substratum and fast water habitat. The second axis was strongly related to % intolerant individuals, site slope and altitude. No strong relationships were evident between any ordination axis and either logging activity, presence/absence of fish, catchment size or ecoregion. 4. Based on macroinvertebrate index of biotic integrity (IBI) scores, 62% of the sites had no impairment, 31% of the sites had slight impairment and only 6% of the sites had moderate or severe impairment. IBI scores were not strongly related to forest harvest history. All four severely impaired sites and five of the seven sites with moderate impairment were lower altitude, shallower slope stream reaches located in the Coast Range with evidence of agricultural activity in their catchment or riparian zone. % sand + fine substratum was the environmental variable most strongly related to macroinvertebrate IBI.     

丹江口水库鱼类群落特征及其历史变化

为了解丹江口水库鱼类群落现状及历史变化, 作者于2018-2019年采用多网目复合刺网采样和渔民渔获物调查的方式对丹江口水库进行了鱼类群落调查。本次调查共采集鱼类33种, 隶属5目11科29属, 以鲤科鱼类为主, 占总数的63.6%。基于多网目复合刺网采样的鱼类群落多样性指数和单位努力捕捞量(catch per unit effort, CPUE, g·day ^-1·m ^-2)在各采样点间具有一定的差异。目前丹江口水库以定居性、喜静缓流、杂食性和肉食性鱼类为主。与20世纪50年代和80年代的历史资料相比, 丹江口水库鱼类物种丰富度先升高后下降; 而生态类型则呈现杂食性鱼类、喜流水性鱼类和洄游性鱼类比例持续下降的趋势。2018-2019年丹江口水库鱼类组成与20世纪80年代的相似性指数为0.35 (中等不相似), 与20世纪50年代的相似性指数为0.29 (中等不相似)。调查结果表明半个世纪以来丹江口水库鱼类群落结构发生了较大变化, 目前趋于小型化和简单化。这些变化可能是由大坝建设、渔业放养、不合理捕捞、外来鱼类引入等人类活动所致。     

Proposed methods and endpoints for defining and assessing adverse environmental impact (AEI) on fish communities/populations in Tennessee River reservoirs

Two multimetric indices have been developed to help address fish community (reservoir fish assemblage index [RFAI]) and individual population quality (sport fishing index [SFI]) in Tennessee River reservoirs. The RFAI, with characteristics similar to the index of biotic integrity (IBI) used in stream fish community determinations, was developed to monitor the existing condition of resident fish communities. The index, which incorporates standardized electrofishing of littoral areas and experimental gill netting for limnetic bottom-dwelling species, has been used to determine residential fish community response to various anthropogenic impacts in southeastern reservoirs. The SFI is a multimetric index designed to address the quality of the fishery for individual resident sport fish species in a particular lake or reservoir[4]. The SFI incorporates measures of fish population aspects and angler catch and pressure estimates. This paper proposes 70% of the maximum RFAI score and 10% above the average SFI score for individual species as "screening" endpoints for balanced indigenous populations (BIP) or adverse environmental impact (AEI). Endpoints for these indices indicate: (1) communities/populations are obviously balanced indigenous populations (BIP) indicating no adverse environmental impact (AEI), or are "screened out"; (2) communities/populations are considered to be potentially impacted; and (3) where the resident fish community/population should be considered adversely impacted. Suggestions are also made concerning how examination of individual metric scores can help determine the source or cause of the impact.     

Modeling wetland plant metrics to improve the performance of vegetation-based indices of biological integrity

The objective of this study was to determine if the accuracy and precision of wetland plant indices of biological integrity (IBIs) could be improved through the use of modeling techniques. To do this, we developed a modeled vegetation IBI (MVIBI) based on metrics previously used to develop vegetation indices of biological integrity (VIBIs) for Ohio wetlands (e.g. % invasive grass, % sensitive species, shrub richness). We selected 82 emergent, forested, and shrub-dominated reference sites distributed across the State of Ohio and built Random Forest models to predict plant metric scores at reference wetlands from naturally occurring environmental features related to climate, hydrology, geology, soils, and landscape position. The models explained between 14 and 52% of the variance in the scores of 21 metrics indicating that variation in wetland plant assemblages was significantly associated with naturally occurring environmental gradients. We used principal component analysis to identify ten groups of statistically independent metrics and selected one metric from each group that discriminated most strongly between reference and most degraded sites based on t-scores. Two axes did not contain discriminating metrics so we used eight metrics in the MVIBI. Analysis of variance of reference site MVIBI scores indicated that we could use one distribution of reference site scores to assess multiple wetland types, thus eliminating the need to separately designate wetland types. We used the MVIBI to assess 170 test sites and compared the accuracy, precision, responsiveness, and sensitivity of the MVIBI to those of the original VIBIs. The MVIBI was up to twice as accurate and precise as the original VIBIs, indicating that modeling can be used to improve the performance of vegetation-based IBIs. The use of model-based IBIs for wetland plants should reduce assessment errors associated with natural variation in plant metrics and should increase confidence in wetland assessments.     

Seasonal variation in the composition of fish assemblages in small Amazonian forest streams: evidence for predictable changes

1. The effects of seasonal inundation on the biology of fishes on floodplains of large Amazonian rivers are well studied. However, the small seasonal changes in headwater streams are generally considered to have little effect on fish assemblages. 2. In this study, we analysed seasonal changes in the species composition and abundance of fish in small Amazonian forest streams. We sampled fish with hand and seine nets in headwater streams in a 10 000 ha terra‐firme forest reserve near Manaus, Brazil. Each stream was surveyed at the end of the 2005 dry season, at the beginning of the 2006 rainy season and at the beginning of the 2006 dry season, by means of a standardized sampling effort. 3. The numbers of individuals and species caught were higher in the dry season, but rarefaction analyses indicated that greater species numbers could have been due simply to the larger number of individuals caught. 4. Between the dry and rainy season, the direction of changes in species composition in multivariate space varied among sites, especially for quantitative (abundance) data. However, the observed variation among sites was the less than expected if the directions of change were random. 5. Fish assemblages in the second dry season were more similar to those in the previous dry season than expected if changes in species composition among seasons were random. This indicates that a general seasonal pattern in fish assemblages can be detected, despite the existence of some erratic site‐specific changes. 6. Most of the species that showed large seasonal variations in density occupy temporary ponds during the rainy season, when much of the valley is inundated and pond networks form adjacent to streams. Short‐duration lateral migrations to these ponds may play an important role in the seasonal fish‐assemblage dynamics in Amazonian headwater streams. 7. Our results contrast with previous studies on small Amazonian streams, which have found little seasonal change in fish assemblages, and highlight the importance of the abundance of common species as an indicator of general fish assemblage structure in biological monitoring programmes.     

Composition of Endemic Fish Assemblages in Relation to Exotic Species and River Regulation in a Temperate Stream

Spatial variation in the fish community of the regulated Raia stream (Portugal) was examined during the summer of 1995. Variation in the native fish community (abundance of species-size combinations) was explicitly related to both the abundance of exotic species and habitat variables. The fish community changed in space from assemblages characterised by the high relative abundance of Leuciscus pyrenaicus, Leuciscus alburnoides and the smaller size classes of Barbus bocagei (all Iberian endemics with total length, TL, < 100mm to assemblages characterised by the high relative abundance of Chondrostoma polylepis (Iberian endemic) and B. bocagei with TL > 200mm and of exotics Micropterus salmoides and Lepomis gibbosus (> 100mm TL). The former assemblages used shallow sites far from downstream dams with some current whereas the latter assemblages used deeper sites closer to downstream dams without current velocity and with abundant floating macrophytes. Both exotic species and habitat variables were significant correlates of endemic assemblage composition in the Raia stream and the abundance of M. salmoides > 150mm in TL was the best biotic predictor of endemic assemblage composition. The total variation in the community of endemic fish was partitioned into four components: (i) associated uniquely with exotic species - 12.6%, (ii) associated uniquely with habitat variables - 27.6%, (iii) associated both with exotic species and habitat variables - 14.5%, and (iv) that unexplained - 45.3%. A significant association of exotic species with the endemic fish community remained after accounting for the selected environmental variables and a strong (habitat) x (exotic species) interaction was indicated.     

A healthy Fraser River? How will we know when we achieve this state?

Assessing the condition of an ecosystem to ascertain its health presupposes that we can diagnose pathological states in system measures. Frequently this means comparing current conditions to reference states, either historical or other sites, which also exhibit some natural range of variation. In the Fraser River, a 9th order river on the west coast of Canada, and one of the most productive salmon rivers in the world. we have studied assemblages of fish and benthos to assess ecosystem health. The biggest challenge to using species composition and abundance measures as indicators of system condition is the absence of appropriate reference conditions in many instances. There are few unperturbed rivers of large size in western North America, and indeed in much of the world, with which to compare the Fraser River or any other large river ecosystem. Multiple insults from point and non-point sources make it difficult to isolate factors from natural longitudinal changes in terms of their effects on river biota. Potential solutions include analysis of fragmentary historical data, making comparisons with other large rivers, and conducting extensive surveys within the basin to account for spatial gradients. An absolute diagnosis of ecosystem health of large rivers in natural science terms is unlikely, and otherwise will depend on relative changes through time assuming these can be isolated from natural variation and local effects. Definition of health for large, riverine ecosystems remains largely a case of expert opinion and weight of evidence rather than a testable hypothesis.     

Pattern of invasion by Weed Shiner (<Emphasis Type="Italic">Notropis texanus</Emphasis>), a nonindigenous cyprinid in the Bear Creek system (Tennessee River drainage), USA

Invasive species increasingly threaten global biodiversity with faunal homogenization, and are of specific concern in the highly diverse aquatic systems of the Southeast United States. However, patterns of invasion and variables influencing invasion success remain poorly understood. This study followed the introduction, establishment, and invasion processes of nonindigenous Weed Shiner (Notropis texanus, Family: Cyprinidae), and examined environmental correlates of their persistence. Potential shifts in the native fish assemblage in Bear Creek, Alabama and Mississippi, USA, due to Weed Shiner presence were also investigated. Assemblage shifts were evaluated using Jaccard and Morisita similarity indices and nonmetric multidimensional scaling (NMDS) ordination. Weed Shiner exhibited an initial rapid expansion in range and abundance, followed by a range contraction in 2012, and range and abundance decline in 2013 and 2014. Weed Shiner persists at the most human-impacted, downstream sites in Bear Creek. Similarity indices and NMDS indicated that despite rapid initial proliferation of Weed Shiner, native fish assemblage did not significantly change. Rather, the native fish assemblage structure in Bear Creek is temporally variable and influenced by watershed area, land-use, high intensity development, mixed-hardwood forest and evergreen forest (pine monoculture). Limiting future Weed Shiner impacts in the system and successful conservation of the Bear Creek fish assemblage will rely on managing land use changes and mitigating development effects in the watershed.     

Fish assemblage in the Pearl River Estuary: Spatial‐seasonal variation,environmental influence and trends over the past three decades

The Pearl River Estuary is the largest estuary in South China and plays a considerable role in the local fisheries economy, yet little is known about the current state of fish assemblage in this ecosystem. To quantify spatial‐seasonal variations, environmental influences, and trends over the past three decades of the fish assemblage in the Pearl River Estuary, we sampled 11 sites seasonally from December 2013 to September 2016. Throughout the study, 285 species from 88 families and 195 genera were collected. There were obvious spatial and seasonal variations of the fish assemblage in terms of the dominant species, species richness, and composition of ecological types. Mouth distance, NH₄⁺ N, chlorophyll‐a, flow, DO, salinity and water transparency were the main variables influencing the spatial‐temporal dynamic of fishes within the estuarine systems. Compared with the record of 330 species in the 1980s, the number of fish species in the Pearl River Estuary has declined by 45 fish species. The Jaccard's similarity of fish composition between the historical investigation (the 1980's) and the present investigation (2013–2016) was 0.62, with 95 species undiscovered and 50 species increased in the present study compared to the 1980s, indicating the assemblage structure has obviously changed. However, in term of ecological guilds, there was no significant difference in the composition of all the selected ecological traits between these two periods. Anthropogenic activities including overfishing, introducing alien fish, dam construction and pollution were considered the main disturbance on fish composition over the past three decades. We conclude that there existed pronounced spatiotemporal changes of fish assemblages, which arises from the compounding effects of environmental factors and anthropogenic activities. These findings are beneficial to understanding and developing suitable conservation strategies for the management and protection of fish resources in the Pearl River Estuary.