Stream Assemblages Research Articles

Stochastic species loss and dispersal limitation drive patterns of spatial and temporal beta diversity of fish assemblages in tropical agroecosystem streams

Beta diversity quantifies changes in assemblages among sites and can identify how anthropogenic changes affect species distributions patterns. We investigated how spatial and temporal beta diversity of fish assemblages responded to recent environmental changes within an established agroecosystem and investigated whether the observed pattern of spatial and temporal beta diversity was different from null expectations. Fish assemblages in 38 streams were sampled in 2003 and 2013, and local and regional variables were quantified in both periods. Species were classified into functional groups based on 15 ecomorphological traits. We tested for relationships between spatial and temporal patterns of beta diversity and its components (turnover and nestedness) and environmental distances and degree of changes over time, and for differences with null expectations. Spatial beta diversity was mostly due to turnover and remained relatively unchanged between periods. Spatial beta diversity was not different from randomness. Temporal beta diversity was lower than expected by null models and not correlated with environmental changes. Past environmental filters related to a long history of agricultural development homogenized habitats and fish assemblages by selecting for habitat-generalist species. In this context, contemporary fish assemblage dynamics in these streams are driven primarily by stochastic processes, likely stochastic local species loss.

Landscape factors modulating patterns of salmonid distribution during summer in north Patagonian rivers.

Understanding how ecosystem processes influencing fish distribution operate across spatial scales is important to understand biological invasions. Salmonids, originally from the Northern Hemisphere, have been repeatedly introduced throughout the world, making them an ideal group to test hypotheses about factors driving invasions. We assessed the influence of environmental variables at the watershed scale on the abundance and structure of salmonid assemblages in the breeding streams of the Upper Limay river basin, Rio Negro, Argentina. We combined field captures with digital map data and geographic information systems to examine landscape-level patterns of salmonid abundance in 35 representative sub-basins of the environmental gradient. We employed a hierarchical cluster analysis and classification and regression tree models to relate the abundance of salmonids and types of species assemblages with environmental characteristics at watershed level. We found stream localization, precipitation regime, altitude and air temperature to be important predictors of the abundance and assemblage structure of salmonids. Total catches showed an increasing gradient of catch-per-unit-effort from west to east and from north to south, with Oncorhynchus mykiss being the most abundant species. O. mykiss relative abundance was westward skewed, where smaller catchments with steeper and shaded valleys are drained by less productive streams with more irregular hydrological regimes, like those found in this species' North American native range. In contrast, the abundance of Salmo trutta abundance was eastward skewed, where larger, sunnier and more gently sloped catchments result in more productive streams with stable hydrological regimes, like those found in that species' European native range. Thus, differential salmonid abundance could result from the interplay between the evolutionary fingerprint left by each species' native environment (especially flow and temperature regimes) and the availability of those conditions in new environments to which they have been translocated. By furthering our understanding of how landscape conditioned invasion success, these findings can help guide the management of economically important introduced fish.

Catchment-scale urbanization diminishes effects of habitat complexity on instream macroinvertebrate assemblages.

While provision of in-stream habitat complexity remains common practice in efforts to restore streams, the evidence of positive effects on in-stream communities is inconsistent. In streams of urban catchments, where both reach-scale habitat manipulation and catchment-scale actions to ameliorate the disturbance regime of urban stormwater runoff are common management responses, clearer understanding of the effects of habitat complexity under different degrees of urban impact are needed. We experimentally assessed the effect of increased surface complexity in wood, the dominant hard substrate in our 18 study reaches on 14 small streams, on in-stream macroinvertebrate assemblages across a range of urban impact. Increased surface complexity increased abundance of most taxa, but this effect was less pronounced in urban streams, partly because of the reduced species pool tolerant of urban stormwater impacts, and partly because of a lesser response of some species to increased complexity in more urban streams. Collectively these taxon-specific effects resulted in small, uncertain increases in taxon richness with increased complexity in rural streams, and no change in richness of the less diverse assemblages of urban streams. Increased abundances suggest increased availability of refugia or resources with increased surface complexity, while the reduced effect of complexity in urban streams suggests that any refuge or resource provided by greater surface complexity is less effective in more disturbed environments receiving urban stormwater runoff. The reduced abundance of sensitive taxa in more urban streams, and the resultant reduced richness, confirms that urban stormwater runoff acts as a strong environmental filter, limiting the species pool available for community assembly. Restoration of habitat complexity in streams without catchment-scale drivers of degradation is likely to have positive benefits to in-stream biotic assemblages, but the efficacy of such approaches in catchments subject to urban stormwater runoff will be greatly diminished. In such cases, restoration activities should first be aimed at controlling the larger-scale problem.

Agriculture impairs stream ecosystem functioning in a tropical catchment

The expansion of agriculture is particularly worrying in tropical regions of the world, where native forests are being replaced by crops at alarming rates, with severe consequences for biodiversity and ecosystems. However, there is little information about the potential effects of agriculture on the functioning of tropical streams, which is essential if we are to assess the condition and ecological integrity of these ecosystems. We conducted a litter decomposition experiment in streams within a tropical catchment, which were subjected to different degrees of agricultural influence: low (protected area, PA), medium (buffer area, BA) and high (agricultural area, AA). We quantified decomposition rates of litter enclosed within coarse-mesh and fine-mesh bags, which allowed the distinction of microbial and detritivore-mediated decomposition pathways. We used litter of three riparian species representing a gradient in litter quality (Alnus acuminata > Ficus insipida > Quercus bumelioides), and examined detritivore assemblages through the contents of litterbags and benthic samples. We found that the increasing agricultural influence promoted microbial decomposition, probably due to nutrient-mediated stimulation; and inhibited detritivore-mediated and total decomposition because of reduced detritivore numbers, most likely caused by pesticides and sedimentation. Effects were evident for Alnus and Ficus, but not for Quercus, which was barely decomposed across the gradient. Our study provides key evidence about the impact of agriculture on tropical stream ecosystem functioning, which is associated to changes in stream assemblages and may have far-reaching repercussions for global biochemical cycles.

Key environmental drivers structuring stonefly assemblages in the mid-sized streams on the southern slope of the Western Carpathians

Rivers and streams possess many characteristics that result from features of their surrounding landscape, e.g. from climate conditions, superficial lithology, soil profile, topography, vegetation cover, and human activities as well. In this study, we determined the impact of superficial geology and catchment land use, as the key landscape drivers affecting the physico-chemical and biological conditions in stream ecosystems, on the structure and values of selected ecological metrics relating to stonefly assemblages. In order to achieve this goal, we sampled 10 mid-sized submountain Carpathian streams flowing through two different geological bedrocks and draining the catchment areas with different dominant land use. As a consequence, these differences, we analyzed together 16 physico-chemical and biological parameters of stream environment. Our results demonstrate that 4 environmental parameter (particulate organic matter, transported inorganic matter, phosphorus and silicon ions), reflecting difference in superficial geology and landuse of the catchment area, played a significant role in the structuring of stonefly assemblages. We also found that catchment land use had an impact on values of the SAS and Saprobic indices as well as on the proportion of Leuctridae/Nemouridae and Brachyptera species in stonefly assemblages. The difference in catchment geology were reflected in values of total species richness and in the proportion of Leuctridae/Nemouridae and Brachyptera species as well.

Effect of substrate type on diatom-based water quality assessments in the Mount Lofty Ranges, South Australia

Diatoms have been widely used in stream health assessments as they are highly sensitive to water quality. There is no standardised method for diatom-based stream health assessments causing many substrates, both natural and artificial, to be used. Few studies have investigated the impact of substrate type on diatom assemblages in streams with highly variable water levels. To determine if the substrate type affects these assessments, diatoms were analysed from an artificial substrate (rope), rock and mud, from 17 sites in the Mount Lofty Ranges, South Australia. Rope has been advocated as a substrate as it mimics aquatic plants, while having advantages of artificial substrates (e.g. standardised habitat). We found that substrate type did not affect the stream health assessment based on the Diatom Species Index for Australian Rivers and hence the additional cost of deploying ropes in such studies is unlikely to be warranted. However, substrate type influenced diatom–nutrient relationships, with no relationship between nutrients in the stream water and diatoms in the mud substrate—possibly due to the nutrient subsidy provided by mud. Therefore, by contrast, the absence of nutrients provided by the rope substrate indicates it is suited to studies of nutrient status and sensitivity in streams.

Environmental concentrations of pharmaceuticals alter metabolism, denitrification, and diatom assemblages in artificial streams

AbstractOur understanding of the effects of pharmaceuticals on key biogeochemical processes and biofilm assemblage composition in surface waters is limited despite the prevalence of ng/L to µg/L co...

Environmental and Fish Assemblage Contrasts in Blackwater and Clearwater Streams

AbstractWe compared 15 blackwater and clearwater streams in coastal drainages of Alabama by quantifying fish assemblages and associated environmental conditions across multiple seasons and characterizing potential relationships using multivariate statistical approaches. Clearwater stream channels tended to be deeper, to have sandier substrates, and to have higher dissolved oxygen concentrations than blackwater streams. In contrast, blackwater streams showed higher dissolved organic carbon levels and higher benthic macroinvertebrate densities. Discriminant function analysis based on environmental and invertebrate data resulted in 90% discrimination between the two stream types. Nonmetric multidimensional scaling (NMDS) of seasonal fish assemblages indicated separation by stream type, with no overlap in fish assemblages of blackwater and clearwater streams in any season, and 12 (39%) of the 31 species captured were indicative of stream type. A suite of environmental and biological variables representing invertebrate density, discharge, stream size, water chemistry, and land use was correlated with NMDS axes separating fish assemblages by stream type. Fish traits were somewhat distinctive between stream types, as there were unique lie‐in‐wait predators and short‐lived species in each stream type. A fourth‐corner analysis indicated potential linkages between fishes preferring woody substrate and stream type, further suggesting that stream type may explain fish functional structure. These results emphasize the need to consider these coastal systems as biotically unique ecosystem types in conservation plans as well as to focus more attention on better understanding the diversity patterns in headwater streams within the Coastal Plains region.

Local and regional environmental factors drive the spatial distribution of phototrophic biofilm assemblages in Mediterranean streams

Temporary streams are submitted to high seasonal hydrological variations which induce habitat fragmentation. Global change promotes longer non-flow periods, affecting hydrological continuity and the distribution of biological assemblages in river networks. We aimed to investigate the effects of hydrological discontinuity on phototrophic biofilm assemblages in a Mediterranean stream, at both network and habitat scales. At the network scale during basal flow conditions, mostly nitrate and DOC concentrations were associated to the taxonomical and trait distribution of algae and cyanobacterial assemblages. Cyanobacteria dominated at the upstream and downstream sites of the network, while green algae and diatoms were abundant in its middle part. At the habitat scale, hydrological discontinuity promoted large changes in biofilm composition between riffles and pools, where pools were inhabited preferentially by green algae and riffle habitats by cyanobacteria. Our findings emphasize the myriad of factors affecting the spatial distribution of phototrophic biofilms, which become more heterogeneous according to water flow interruption. Under the predicted climate change scenarios, spatial heterogeneity in temporary streams may increase, which will lead to change phototrophic biofilm assemblages.

Temporal and environmental drivers of fish-community structure in tropical streams from two contrasting regions in India

Environmental and anthropogenic factors are known to drive fish community structure in aquatic systems across the world. This study investigates fish assemblages in lower order streams across contrasting landscapes in central and eastern India. We documented the species diversity of these monsoon driven lower order streams in the two regions. We also investigated the potential common environmental drivers of richness and diversity and effect of season in these tropical streams. The study was based on seasonal data on abundance of fishes and environmental parameters collected between 2015–2017 from streams in states of Madhya Pradesh and West Bengal. Species diversity were compared across regions and seasons, based on their richness (SR) as well as diversity (Shannon index H'). Drivers of overall richness and diversity were analyzed using multiple linear regression methods, based on best subset selection. Analysis of data revealed high diversity in these streams in both regions. Cyprinidae, Bagridae and Channidae were the most dominant families in both regions. Despite the geographical and local ecological differences across the regions, common environmental parameters were found to influence richness and diversity across the two regions, indicating these as being key drivers of fish community structure. Water flow was a common factor driving both richness and diversity across both regions. Our study revealed a lack of seasonal effect in structuring fish communities in tropical streams. With stream and river ecosystems facing increasing threats due to habitat alterations and water quality degradation in countries such as India, a clear understanding of regional and local drivers of community structure of aquatic fauna is crucial. These results on the role of common environmental factors across ecoregions provides baseline information for understanding their ecological roles and developing management plans for important river basins and fish conservation in future.

Biodiversity patterns of Arctic diatom assemblages in lakes and streams: Current reference conditions and historical context for biomonitoring

Abstract Comprehensive assessments of contemporary diatom distributions across the Arctic remain scarce. Furthermore, studies tracking species compositional differences across space and time, as well as diatom responses to climate warming, are mainly limited to paleolimnological studies due to a lack of routine monitoring in lakes and streams across vast areas of the Arctic. The study aims to provide a spatial assessment of contemporary species distributions across the circum‐Arctic, establish contemporary biodiversity patterns of diatom assemblages to use as reference conditions for future biomonitoring assessments, and determine pre‐industrial baseline conditions to provide historical context for modern diatom distributions. Diatom assemblages were assessed using information from ongoing regulatory monitoring programmes, individual research projects, and from surface sediment layers obtained from lake cores. Pre‐industrial baseline conditions as well as the nature, direction and magnitude of changes in diatom assemblages over the past c.200 years were determined by comparing surface sediment samples (i.e. containing modern assemblages) with a sediment interval deposited prior to the onset of significant anthropogenic activities (i.e. containing pre‐1850 assemblages), together with an examination of diatoms preserved in contiguous samples from dated sediment cores. We identified several biotypes with distinct diatom assemblages using contemporary diatom data from both lakes and streams, including a biotype typical for High Arctic regions. Differences in diatom assemblage composition across circum‐Arctic regions were gradual rather than abrupt. Species richness was lowest in High Arctic regions compared to Low Arctic and sub‐Arctic regions, and higher in lakes than in streams. Dominant diatom taxa were not endemic to the Arctic. Species richness in both lakes and streams reached maximum values between 60°N and 75°N but was highly variable, probably reflecting differences in local and regional environmental factors and possibly sampling effort. We found clear taxon‐specific differences between contemporary and pre‐industrial samples that were often specific to both ecozone and lake depth. Regional patterns of species turnover (β‐diversity) in the past c.200 years revealed that regions of the Canadian High Arctic and the Hudson Bay Lowlands to the south showed most compositional change, whereas the easternmost regions of the Canadian Arctic changed least. As shown in previous Arctic diatom studies, global warming has already affected these remote high latitude ecosystems. Our results provide reference conditions for future environmental monitoring programmes in the Arctic. Furthermore, diatom taxa identification and harmonisation require improvement, starting with circum‐Arctic intercalibrations. Despite the challenges posed by the remoteness of the Arctic, our study shows the need for routine monitoring programmes that have a wide geographical coverage for both streams and lakes.

Pre-imaginal black fly assemblages in streams of Eastern Spain: environmental and substrate requirements

A growing interest in the importance of simuliids in health and animal welfare in certain areas in Europe, such as around the Mediterranean basin, together with the fact that there is fragmentary ecological information on the pre-imaginal stages of these dipterans has led to the need to carry out further research. We studied the abundance and distribution of pre-imaginal stages—mainly the pupae—of simuliid species, and examined their assemblages in relation to environmental gradients identified in Mediterranean basins of eastern Spain. We report a total of 21 black fly species from the set of studied streams, where largely the most common species were Simulium (Simulium) intermedium and Simulium (Simulium) ornatum, two species of medical and veterinary concern. We found that pre-imaginal simuliid assemblages were strongly related to elevation, water temperature and turbidity, dissolved oxygen concentration and water velocity. The analysis of the optima and tolerances for these environmental factors suggests differences in ecological requirements of the pre-imaginal stages of the reported simuliid species. Likewise, it was found that the pupae of some species were strongly associated with specific substrates. We hope that our research results on autoecology of black fly species will contribute to the improvement of pest management programs.

Relationships Between Environmental Conditions And Fish Assemblages In Tropical Savanna Headwater Streams

Riparian vegetation plays an important role in providing energy to small watercourses and maintaining ecological processes through organic matter input and together with hydrological and geomorphological watercourse characteristics influence on fish assemblages. The goal of this paper was partitioning and quantifying the influence of riparian zone (type of riverbank substrate, bank slope, type of riparian vegetation cover and percentage of riparian vegetation cover on the main channel), physical habitat (stream channel width and depth, type of substrate and aquatic habitat in channel, water velocity and organic matter), water quality (turbidity, temperature, conductivity, pH, dissolved oxygen and chlorophyll concentration) and spatial variables (linear distances between sampled points) on fish assemblages (richness and abundance per species) in headwater streams of the Upper Paraná River basin, Central Brazil. For this purpose, it was performed a variation partitioning analysis between riparian, physical habitat, water and spatial variables sets and a Redundancy Analysis to quantify the influence of variables on the fish assemblages. Only the physical habitat and water quality variables influenced the fish assemblages (richness and abundance per species).

Nestedness of insect assemblages in agriculture-impacted Atlantic forest streams

Agricultural land use causes habitats fragmentation and riparian vegetation removal, driving variability in the composition of aquatic insect assemblage in streams. We explored the effect of agriculture on the beta diversity of insect assemblages of Ephemeroptera, Plecoptera and Trichoptera (EPT) in Atlantic forest streams. We measured water physical and chemical variables and quantified the land cover of 10 stream catchments to determine the environmental integrity of the streams. The percentage of vegetation range was ∼6% to ∼47%, and agricultural land use range was ∼24% to ∼88%. We collected a total of 2632 individuals distributed in 30 genera. Trichoptera was the most abundant order (57%), followed by Ephemeroptera (41%) and Plecoptera (2%). The abundance was influenced by the higher agriculture practices in the streams adjacent areas. On the other hand, the oxygenated waters and higher percentages of riparian vegetation influenced the EPT rarefied richness. The beta diversity of EPT assemblages was structured by nestedness due to the influence agricultural activities. The variation in the agricultural intensity that occurs in the streams generated more intense limnological variability, which caused the nestedness of EPT insects as well as the reduction of taxonomic richness. Thus, the streams with low environmental integrity had EPT assemblages nested in streams of high environmental integrity.

Horticulture affects macroinvertebrate assemblages in adjacent streams (Buenos Aires, Argentina)

The agrochemicals used on crops can reach watercourses, affecting water quality and biologic communities. The aim of this research was to study the effects of horticulture on the water quality and invertebrate assemblages of adjacent streams in Buenos Aires province, Argentina. Four streams draining horticultural basins were compared with another four considered less disturbed: two of the latter located in a Biosphere Reserve and the other two in extensive livestock-raising basins. Pesticides were detected in the horticulture-related streams, while nutrient concentrations were significantly higher than in the less-disturbed streams. The macroinvertebrate assemblages differed: the less-disturbed streams exhibited a significantly higher taxa richness and density. Hyalella sp. and Simocephalus vetulus were dominant, whereas Entomobryoidea, Dugessidae, and Glossiphoniidae were dominant in the horticulture-associated streams. Ephemeroptera (Caenis and Baetidae) were well represented in the less-disturbed streams and rare or absent in the horticulture-adjacent streams. Multivariate analysis indicated that the horticulture-impacted sites contained high nutrient concentrations and tolerant taxa, while the less-disturbed sites corresponded to lower nutrient concentrations and sensitive taxa. We propose Hyalella sp. and S. vetulus as water-quality indicators in pampean streams and conclude that intensive agrochemical applications in horticulture increase nutrient and pesticide loads affecting the macroinvertebrate assemblages of adjacent streams.

Alpha and beta diversities of Trichoptera (Insecta) assemblages in natural and rural subtropical streams

Abstract: Aim The aim of this study was to determine the diversity of Trichoptera in subtropical streams and the effects of environmental variables and geographical position on alpha and beta diversity in natural and rural streams. Methods We collected Trichoptera with a Surber sampler in 12 small order subtropical streams (six streams with apparent absence of anthropic disturbance and six streams with rural activity in their drainage areas) and measured limnological variables. We evaluated the effects of environmental variability and geographical distance on the dissimilarity of the assemblage and calculated the contribution of alpha and beta diversity for each stream. Results We collected a total of 1,264 Trichoptera larvae distributed in 17 genera and 11 families. The genera Phylloicus and Smicridea were found in almost all streams. We observed a positive effect of environmental variability on biological variability but not of geographical distance. The environmental variability was basically generated by the influence of higher concentrations of dissolved organic carbon and nutrients. We observed the greatest contribution of the alpha diversity of the Trichoptera assemblages in natural streams and of beta diversity in the rural streams. Conclusions Our results demonstrate that the variability of Trichoptera is affected by environmental characteristics, but not by geographical position.

The role of spatial and environmental variables in shaping aquatic insect assemblages in two protected areas in the transition area between Cerrado and Amazônia

Abstract: The distribution of aquatic insects of the orders Ephemeroptera, Plecoptera, and Trichoptera (EPT) can be influenced by factors such as water quality, habitat integrity and biogeography. The present study evaluated the structure of EPT assemblages in streams in the Cerrado, a global biodiversity hotspot. Samples were collected from 20 streams in two protected areas: Parque Estadual do Mirador (10 streams) and Parque Nacional da Chapada das Mesas (10 streams). A total of 1987 specimens were collected, representing 46 taxa of EPT. The two study areas did not differ significantly in taxonomic richness of EPT genera (t = -1.119, p = 0.279) and abundance of individuals (t = 0.268, p = 0.791) but did differ in genus composition (Pseudo-F = 2.088, R2 = 0.103, p = 0.015) and environmental variables (Pseudo-F = 2,282, R2 = 0.112, p = 0.014). None of the tested environmental variables were correlated with the community but a spatial filter captured an effect of the spatial distribution of streams. The region of the study is located in MATOPIBA, which is the last agricultural frontier of the Cerrado. Therefore, it is important that there is police and monitoring so that the “Parque Estadual do Mirador” and the “Parque Nacional da Chapada das Mesas” continue to play their role in conserving biodiversity in the future.

Fish Assemblages in Pampean Streams (Buenos Aires, Argentina): Relationship to Abiotic and Anthropic Variables.

The present study reported the effect of natural and anthropic environmental variables on the fish assemblages in the pampean streams, in the coastal strip along the Río de la Plata, Buenos Aires province, Argentina. Five streams were sampled at 12 sites surrounded by land devoted to different uses. A correspondence analysis sorted the streams into two groups: a less impacted group formed by sites surrounded by livestock- raising pastures and a more impacted one passing through urban sites and including a stream adjacent to a modest rural urbanization with a dairy in the stream's basin. The nutrient concentrations were significantly higher in the more impacted group; with species richness, diversity, abundance, and biomass being significantly lower. A canonical-correspondence analysis linked the more impacted sites to high concentrations of soluble reactive phosphorus and impoverished fish assemblages, composed of species tolerant to environmental pollution. On the other hand, sites with higher oxygen concentrations and pH were related to richer assemblages pointing to good environmental conditions at the sites surrounded by livestock-raising pastures. The downstream sites on the less impacted streams contained fish assemblages in which the juvenile stages of species corresponding to the Río de la Plata were dominant.

When roads cross streams: fish assemblage responses to fluvial fragmentation in lowland Amazonian streams

ABSTRACT Roads affect biodiversity by increasing mortality rates, habitat loss, and natural landscape fragmentation. Poorly installed culverts can impound streams, changing the environmental conditions, and affecting aquatic communities. We evaluated the effects of road crossings on the taxonomic composition and functional structure of fish assemblages in lowland eastern Amazonian streams, Brazil. We tested the hypothesis that the presence of road-derived impoundments affects assemblage taxonomic and functional composition and structure. Two predictions were addressed: (1) Species and functional group composition will differ in impounded reaches in relation to lotic reaches; (2) Assemblages in downstream lotic reaches will be richer in species and functional groups in relation to upstream lotic and impoundment reaches. We sampled five streams crossed by roads presenting impoundment formation, conducted by visual census (day, dusk, and night) in 200 m line transects. Assemblage composition from lentic reaches was different from lotic reaches, and Shannon diversity from downstream reaches was different from upstream and impoundment, however, beta diversity partitioning between lotic reaches showed higher nestedness contribution, reinforcing the role of impoundment in limiting fish dispersal between lotic reaches. These results suggest that impoundments impose environmental and dispersal constraints to fish, affecting their longitudinal distribution in streams fragmented by roads.

Simulation of over‐exploitation of ornamental fish and its consequences for the functional structure of assemblages of Amazonian streams

AbstractThe consequences of over‐exploitation may seriously impair the integrity and functioning of ecosystems. When loss of species is accompanied by the loss of ecological processes, the effects are no longer just taxonomic and may affect the stability of the environments. Ornamental fishing is one of the main economic activities of the middle Negro River. Such activity is directed to a small number of species and has the Cardinal Tetra (Paracheirodon axelrodi) as the main target species. Given the potential effects this pressure and the lack of information on its consequences, the present study analysed, through simulations, the possible effects of depletion of ornamental fish populations on the functional structure of fish assemblages, represented by functional diversity (FD) and functional redundancy (FR) indexes. We sampled 13 streams exploited by the ornamental fishery, where we collected 4,286 specimens of 110 species, of which 22 were targeted as ornamental fishing. We found that the ornamental species corresponded, on average, to 27.8% of the species and 33.3% of the FD of the assemblages. In a scenario of complete exclusion of ornamental species, local communities would lose 24.6% of the FD and reduce up to 12% of the FR. With these results, it is possible to infer that the local extinction of exploited species would cause negative impacts on the multifunctionality and the resilience of the streams ecosystems. In this way, we emphasise the need for proper management of the ornamental fisheries aiming to the sustainability of the activity and to the conservation of ecosystem functionality.