Variation in fish assemblages across dry-season pools in a Mediterranean stream: effects of pool morphology, physicochemical factors and spatial context

Pires DF, Pires AM, Collares-Pereira MJ, Magalhães MF. Variation in fish assemblages across dry-season pools in a Mediterranean stream: effects of pool morphology, physicochemical factors and spatial context. Ecology of Freshwater Fish 2010: 19: 74–86. © 2009 John Wiley & Sons A/S
Abstract –  Knowledge of patterns of refuge use by fish is critical for maintaining biodiversity in drought-prone streams. In this study, the fish assemblages of 21 dry-season pools in a Mediterranean stream were characterised and related to three sets of factors reflecting pool morphology, physicochemistry and spatial context. Fish were associated with the three sets of variables, with variation partitioning indicating that overall species richness and abundance were primarily related to pool morphology but relative species abundances were mainly associated with physicochemical contexts. In general, species richness was the highest but overall fish abundance was the lowest in large pools. Pools well shaded by riparian canopy held the highest richness and abundance of native fish, but relative species abundances and assembly structure varied among pools contingent on canopy cover, substrate composition and spatial location. These results suggested that conservation of fish diversity in Mediterranean streams requires networks of pools with diverse sizes and physicochemical contexts.     

Big impacts from small abstractions: The effects of surface water abstraction on freshwater fish assemblages

1. Abstractions and diversions are prevalent in river networks worldwide; however, specific mechanisms and measures reflecting changes in functional characteristics of aquatic assemblages in response to flow abstraction have not been well established. In particular, the influence of small takes on fish assemblages is poorly understood.
2. Field surveys and stable‐isotope analyses were used to evaluate the impact of differing levels of flow abstraction on fish assemblage structure, and native–non‐native patterns of coexistence, associated with small surface water abstractions in four streams in New Zealand. Study design accounted for longitudinal processes (spatial autocorrelation) to isolate the effects of abstractions on fish assemblages.
3. Reaches with reduced flows downstream of abstraction points had significantly lower fish abundances per metre of stream length, probably because of decreased habitat size, altered interspecific interactions and barriers to movement. The loss of larger fish in reaches with high abstraction resulted in shallower mass–abundance slopes and shorter stable isotope‐derived food‐chain lengths, likely to have been caused by fewer trophic links in the food web. The large fish absent from these reaches were flow‐sensitive introduced salmonids, resulting in higher relative abundances of small‐bodied native fish, probably as a result of predatory and competitive release.
4. Quantification of metrics designed to characterize ecosystem functioning as well as abundance and species composition indicated that small water abstractions can alter both the structure and composition of stream fish assemblages and modify the outcomes of native–non‐native species interactions. Thus, a better understanding of the effects of small abstractions could be used to improve the strategic management of fish in invaded riverscapes.

     

Beaver dams shift desert fish assemblages toward dominance by non‐native species (Verde River,Arizona, USA)

The reintroduction of beaver (Castor canadensis) into arid and semi‐arid rivers is receiving increasing management and conservation attention in recent years, yet very little is known about native versus non‐native fish occupancy in beaver pond habitats. Streams of the American Southwest support a highly endemic, highly endangered native fish fauna and abundant non‐native fishes, and here we investigated the hypothesis that beaver ponds in this region may lead to fish assemblages dominated by non‐native species that favour slower‐water habitat. We sampled fish assemblages within beaver ponds and within unimpounded lotic stream reaches in the mainstem and in tributaries of the free‐flowing upper Verde River, Arizona, USA. Non‐native fishes consistently outnumbered native species, and this dominance was greater in pond than in lotic assemblages. Few native species were recorded within ponds. Multivariate analysis indicated that fish assemblages in beaver ponds were distinct from those in lotic reaches, in both mainstem and tributary locations. Individual species driving this distinction included abundant non‐native green sunfish (Lepomis cyanellus) and western mosquitofish (Gambusia affinis) in pond sites, and native desert sucker (Catostomus clarkii) in lotic sites. Overall, this study provides the first evidence that, relative to unimpounded lotic habitat, beaver ponds in arid and semi‐arid rivers support abundant non‐native fishes; these ponds could thus serve as important non‐native source areas and negatively impact co‐occurring native fish populations.     

Spatial and temporal variation in fish community structure and diversity in the largest tropical flood‐pulse system of South‐East Asia

The Tonle Sap River and Lake (TSRL) is South‐East Asia's largest tropical flood pulse with a flow‐reversal system that supports one of the world's largest freshwater fisheries. However, among the world's tropical floodplains, the resources of the TSRL have received little ecological research. Here, we described the spatiotemporal TSRL fish diversity and community variation using daily records from 2012 to 2015 on fish abundance from six sites covering the TSRL system. We found that high fish diversity occurred in sites located in the middle of Tonle Sap Lake, and the lowest diversity was observed in the southern section. The spatial abundance distribution patterns displayed a river–lake gradient, with three fish assemblages that were clustered based on their composition similarities and were characterised by 96 indicator species. In the southern section, fish assemblages were characterised by longitudinal migratory fishes; in contrast, in the middle system, fish assemblages were represented by species with combined ecological attributes (i.e. longitudinal and lateral migratory species and floodplain residents). Towards the northern section, fish assemblages were composed of lateral migratory and floodplain resident species. Species richness and abundance peaked at approximately 2–2.5 and 4 months, respectively, after the peak flow in early October, during which Tonle Sap River resumes its normal flow direction (outflow). This suggests that seasonal flood pulses (i.e. rising and falling water levels) play a pivotal role in structuring spatiotemporal variation in the TSRL fish assemblages. Our study has implications for fisheries monitoring and conservation initiatives.     

Effects of within-patch habitat structure and variation on fish assemblage characteristics in the Bernecei stream, Hungary

Abstract –  Over a 3-year period we examined variability in physical habitat structure and species richness, abundance and assemblage composition of fishes in 13 habitat patches in the Bernecei stream, Hungary. Principal component analysis of habitat structure data from patches elucidated a riffle-run-pool habitat gradient across patches. Temporal habitat variability increased significantly from riffle to pool patches. Fish assemblage characteristics displayed relatively continuous change over the habitat gradient and were relatively stable within patches. Assemblage structure properties (e.g., species richness) displayed different responses to the habitat gradient and to within-patch habitat variability. In general, pool patches had more diverse assemblages and greater within-patch assemblage variability than riffle patches. However, within-patch dynamics were largely determined by the population dynamics of a habitat generalist (i.e., minnow). Broad scale environmental variability (i.e., a catastrophic 100-year flood) also appeared to affect within-patch fish assemblage characteristics. Our results demonstrate that fish assemblage structure is influenced by physical variability (i.e., both floods and spatio-temporal habitat variability) within the Bernecei stream.     

Responsiveness of fish mass–abundance relationships and trophic metrics to flood disturbance,stream size,land cover and predator taxa presence in headwater streams

Characterisation of food webs, by summarising energy transfer and trophic relationships, allows more functional measurement of ecosystems and may reveal threats (e.g., land‐cover change) in sensitive environments that are not obvious from conventional biomonitoring. However, typical methods used to achieve this are time‐consuming and expensive. Therefore, we tested the usefulness of fish‐focused food‐web proxies as functional measures, specifically mass–abundance relationships of fish assemblages and stable isotope (SI)‐derived metrics in headwater stream reaches. These metrics have been trialled before for similar use in other settings, but have yielded varying results, and have not been employed in tandem in temperate freshwaters. Sampling reaches (N = 46) were spread across a variety of streams, and the effects of habitat predictors at multiple scales on metrics were assessed using model selection. We found that habitat size positively correlated with food‐chain lengths in streams, possibly because of increased abundance of fish at multiple trophic levels in habitats with more space. Additionally, flood disturbance was negatively associated with fish mass–abundance and carbon range, likely due to the harshness of flood‐prone streams. Riparian land‐cover variables were correlated with multiple metrics, indicating the importance of terrestrial–aquatic linkages. Additionally, variations in all metrics were influenced by the presence of native, predatory longfin eels. Overall, we conclude that mass–abundance relationships and SI‐derived metrics are sensitive to drivers of trophic organisation and likely reflect processes occurring at multiple spatial scales in freshwaters. Thus, these metrics could be an insightful monitoring tool for managers because they reflect functional measures of aquatic ecosystems.     

Development and evaluation of a fish‐based index to assess biological integrity of Mediterranean streams

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Complex influences of low-head dams and artificial wetlands on fishes in a Colorado River tributary system

Abstract  Low-head dams in arid regions restrict fish movement and create novel habitats that have complex effects on fish assemblages. The influence of low-head dams and artificial wetlands on fishes in Muddy Creek, a tributary of the Colorado River system in the USA was examined. Upstream, fish assemblages were dominated by native species including two species of conservation concern, bluehead sucker, Catostomus discobolus Cope, and roundtail chub, Gila robusta Baird and Girard. The artificial wetlands contained almost exclusively non-native fathead minnow, Pimephales promelas Rafinesque, and white sucker, Catostomus commersonii (Lacepède). Downstream, fish assemblages were dominated by non-native species. Upstream spawning migrations by non-native white suckers were blocked by dams associated with the wetlands. However, the wetlands do not provide habitat for native fishes and likely inhibit fish movement. The wetlands appear to be a source habitat for non-native fishes and a sink habitat for native fishes. Two non-native species, sand shiner, Notropis stramineus (Cope), and redside shiner, Richardsonius balteatus (Richardson), were present only downstream of the wetlands, suggesting a beneficial role of the wetlands in preventing upstream colonisation by non-native fishes.     

Macroalgal meadow habitats support fish and fisheries in diverse tropical seascapes

Canopy‐forming macroalgae can construct extensive meadow habitats in tropical seascapes occupied by fishes that span a diversity of taxa, life‐history stages and ecological roles. Our synthesis assessed whether these tropical macroalgal habitats have unique fish assemblages, provide fish nurseries and support local fisheries. We also applied a meta‐analysis of independent surveys across 23 tropical reef locations in 11 countries to examine how macroalgal canopy condition is related to the abundance of macroalgal‐associated fishes. Over 627 fish species were documented in tropical macroalgal meadows, with 218 of these taxa exhibiting higher local abundance within this habitat (cf. nearby coral reef) during at least one life‐history stage. Major overlap (40%–43%) in local fish species richness among macroalgal and seagrass or coral reef habitats suggest macroalgal meadows may provide an important habitat refuge. Moreover, the prominence of juvenile fishes suggests macroalgal meadows facilitate the triphasic life cycle of many fishes occupying diverse tropical seascapes. Correlations between macroalgal canopy structure and juvenile abundance suggests macroalgal habitat condition can influence levels of replenishment in tropical fish populations, including the majority of macroalgal‐associated fishes that are targeted by commercial, subsistence or recreational fisheries. While many macroalgal‐associated fishery species are of minor commercial value, their local importance for food and livelihood security can be substantial (e.g. up to 60% of landings in Kenyan reef fisheries). Given that macroalgal canopy condition can vary substantially with sea temperature, there is a high likelihood that climate change will impact macroalgal‐associated fish and fisheries.     

Assessing biotic integrity in a Mediterranean watershed: development and evaluation of a fish-based index

Abstract  Biological indicators for Mediterranean rivers are poorly developed. This study evaluates the effectiveness of the Index of Biotic Integrity approach (IBI) with fish assemblages in the Guadiana catchment, a typical Mediterranean watershed in Southern Portugal. Reference sites were selected from a set of 95 sites, using a multivariate approach. Fifty-five candidate metrics were screened for range, responsiveness, precision and redundancy. Final metrics included: proportion of native fish, number of intolerant and intermediate species, number of invertivore native fish, number of phyto-lithophilic and polyphilic species, and catches of exotics. The IBI scores correlated with composite gradients of human impact and differed significantly between reference and non-reference sites. Application of the IBI to an independent validation set with 123 sites produced results congruent with the development set and repeatable assessments at 22 sites showed concordance in IBI scoring. This application highlights the effectiveness of the IBI approach even with fish assemblages of limited diversity and ecological specialisation as in Mediterranean streams.     

Putting marine sanctuaries into context: a comparison of estuary fish assemblages over multiple levels of protection and modification

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The role of oceanographic conditions and plankton availability in larval fish assemblages off the Catalan coast (NW Mediterranean)

In the northwestern Mediterranean, most fish species reproduce in early summer and fewer in the autumn mixing period. This study analyses and compares larval fish assemblages (LFA) in both seasons, and is the first attempt to characterize LFA structure for the autumn period. We analyze horizontal and vertical distribution of fish larvae and the micro- and mesozooplankton biomass and abundance of the main zooplankton groups. The oceanographic situation was analyzed through the study of data from CTD, Nν-Shuttle and ADCP surveys. LFA were determined by ordination analyses based on larval abundance, and the relationships between larval assemblages and environmental variables were investigated through canonical correspondence analysis. The importance of some hydrographic variables (temperature, salinity and stability of the water column), current fields (along-shelf and across-shelf transport) and the abundance of zooplankton are discussed as important factors shaping the structure of larval assemblages. In early summer, LFA were mainly structured by a combination of bathymetry and trophic components, although sea surface temperature also played a role in shaping the horizontal larval distributions. In autumn, trophic variables were the main factors influencing the shelf-dwelling species assemblage. Larvae of oceanic species, on the other hand, were not related to trophic variables but were more affected by current fields.     

基于河流网络体尺度的皖河河源溪流鱼类群落的空间格局

2013年7-8月对大别山皖河河源1～3级溪流的鱼类进行了调查,着重从河流网络体空间尺度研究了鱼类多样性及群落结构的空间格局,探讨了局域栖息地条件和支流空间位置对鱼类群落的影响.1～3级溪流间,鱼类物种数随溪流级别增大显著增多,但个体数无显著变化(P＞0.05);长河、潜水和皖水3条支流间鱼类物种数和个体数均无显著差异(P＞0.05).鱼类物种数受局域栖息地条件(海拔)和支流空间位置(河流级别和下游量级)的联合影响,但鱼类个体数仅受局域栖息地条件(海拔)的影响.不同溪流级别和不同支流间的群落结构均无显著差异(P＞0.05).同物种数类似,鱼类群落结构也受局域过程(海拔)和空间过程(汇合量级和下游量级)的联合影响.本研究表明,总体上皖河河源溪流网络体中的鱼类群落是局域过程和空间过程联合作用的产物.因此,为合理保护和管理皖河河源的溪流鱼类物种,有必要兼顾局域栖息地条件与河流网络连通性的保护和恢复.     

Introduction of exotic fish species and decline of native species in the lower Po basin,north‐eastern Italy

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Fish assemblages in Atlantic Forest streams: the relative influence of local and catchment environments on taxonomic and functional species

Streams are under environmental pressures acting at different scales that influence the ecological organisation of their fish assemblages. However, the relative influence of the different scale‐related variables on assemblage composition and function is poorly understood. We evaluated the importance of local‐ and catchment‐scale environmental variables, as well as the spatial structure of the sampling sites, in shaping fish assemblages in Atlantic Forest streams. Local‐scale variables were those measured at the sampling sites, describing the local habitat conditions (e.g. depth, substrate type, altitude). Catchment‐scale variables were those integrating the upstream landscape of the sampling sites (e.g. catchment land use). Spatial distances were calculated from watercourse distance using principal coordinates of neighbour matrices. Altogether, 28 local and seven catchment variables were initially subjected to two processes of eliminating co‐linearity. Redundancy analysis was applied to the three matrices (spatial, local and catchment) to quantify the variance in the structure of the fish assemblages explained by each matrix. Local variables explained more variability in both taxonomic and functional assemblage structure, than catchment and spatial variables. Local variables also changed along the longitudinal gradient, which consequently influenced fish assemblage structure. This pattern was also influenced by anthropogenic alteration and non‐native species, which were more abundant in downstream sites. These results highlight the need to assess Atlantic Forest streams under different environmental scales, especially through the use of quantitative local‐scale metrics, and to consider the effects of longitudinal patterns in structuring fish assemblages when developing and implementing monitoring programmes, impact studies and conservation plans.     

Large‐bodied fish migration and residency in a flood basin of the Sacramento River,California, USA

River–floodplain complexes represent some of the most variable and diverse habitats on earth, yet they are among our planet's most threatened ecosystems. Use of these habitats by large‐bodied fishes is especially poorly understood, particularly in temperate regions. To provide insight into the factors that affect floodplain assemblages and migration, we sampled large‐bodied fishes with a fyke trap for 7 years in the Yolo Bypass, the primary flood basin of the Sacramento River, California. We collected a total of 18,336 individual fish comprised of 27 species, only 41% of which were native. Year‐round resident species white catfish Ameiurus catus, channel catfish Ictalurus punctatus and common carp Cyprinus carpio (all alien species) were the most abundant and comprised 74% of the total catch. Splittail Pogonichthys macrolepidotus (3.8%), white sturgeon Acipenser transmontanus (2.3%) and Sacramento sucker Catostomus occidentalis (1.1%) were the primary native species. We found that seasonal variation in water temperature and flood stage were important factors affecting the fish assemblage structure and the presence of migratory species. American shad Alosa sapidissima, an alien species, showed highest abundance during the early summer upstream migration, when temperatures were warmer. For native species, the abundances of white sturgeon, splittail, Sacramento pikeminnow Ptychocheilus grandis and Sacramento sucker were all highest during flood pulses. While our results suggest that flow alone is not sufficient to control alien species, the strong linkage between native fish migration and flow pulses highlights the importance of river–floodplain connectivity for the conservation of native fishes.     

Assessing long‐term fish responses and short‐term solutions to flow regulation in a dryland river basin

Water resource development and non‐native species have been cited as primary drivers associated with the decline of native fishes in dryland rivers. To explore this topic, long‐term trends in the fish community composition of the Bill Williams River basin were studied over a 30‐year period (Arizona, USA). We sampled 31 sites throughout the basin that were included in fish surveys by Arizona Game and Fish in 1994–97 and the Bureau of Land Management in 1979–80. We found that non‐native species have proliferated throughout the entire basin, with greater densities in the lower elevations. Native species have persisted throughout most of the major river segments, but have experienced significant declines in frequency of occurrence and abundance in areas also containing high abundances of non‐native species. Next, we assessed the short‐term response of the fish assemblage to an experimental flood event from the system's only dam (i.e. Alamo Dam). In response to the flood, we observed a short‐term reduction in the abundance of non‐native species in sites close to the dam, but the fish assemblage returned to its preflood composition within 8 days of the event, with the exception of small‐bodied fish, which sustained lower postflood densities. Our findings demonstrate the importance of natural flow regime on the balance of native and non‐native species at the basin scale within dryland rivers and highlight minimal effects on non‐native fishes in response to short duration flood releases below dams.     

Fish nursery habitat function of the main channel,floodplain tributaries and oxbow lakes of a medium‐sized river

Small, adventitious tributaries (<3 orders of magnitude smaller than the stream it flows into) are a conspicuous feature of many river–floodplain systems, but their value as fish reproduction and nursery habitat is not well understood compared to oxbow lakes and the main river channel (MRC). Moreover, connectivity of tributaries to the MRC is often less impacted by anthropogenic modifications (e.g., dams and levees) compared to oxbow lakes. From April to July 2012, larval and juvenile fish were collected in the Fourche LaFave River (Arkansas, USA) system to better understand fish nursery habitat function of tributaries relative to oxbow lakes and the MRC. Nonmetric multidimensional scaling ordination of juvenile and larval fish genera revealed distinct fish assemblages in MRC and floodplain habitats. Ordination of juvenile fish at the species level resulted in distinct fish assemblages in tributary versus oxbow lake habitats. Tributaries had more unique species and higher abundance of shared species than oxbow lakes and MRC. Additionally, of the 46 species identified, all but six were collected in lower tributary reaches. Connectivity was strongly associated with both ordinations and was important in describing patterns of fish variation among habitats and between tributaries. Of the tributaries sampled, the least fragmented stream had the most similar fish assemblages between upper and lower sections. Findings of this study revealed tributaries are an important, yet overlooked, feature in the river–floodplain model. Especially in years of drought, channel–floodplain connectivity can be limited, but tributaries can be used by fishes for reproduction and nursery habitat.     

Pushed to the edge: Environmental factors drive ecological responses of Aphanius fasciatus when in sympatry with invasive Gambusia holbrooki

1. Interspecific competition may be particularly exacerbated when occurring between native and invasive alien species, with environmental conditions affecting drivers of natural selection and shaping spatio-temporal dynamics of animal communities. The effects of invaders are particularly evident in aquatic ecosystems with delicate and complex balances, such as Mediterranean coastal wetlands, characterized by unpredictable water flows and variable reserves. Understanding how native species respond to human-induced biological invasions is of paramount importance for planning management measures aiming at conservation purposes.
2. This study investigated whether the occurrence of a competing invader species resulted in changes in the ecological adaptations of a native species by comparing two coastal wetland fish species: the invasive eastern mosquitofish Gambusia holbrooki and the native Mediterranean killifish Aphanius fasciatus of conservation concern. The hypothesis was tested by sampling fishes at a coastal Ramsar site in central Italy, over 2 years.
3. Generalized linear mixed models were used to examine the occurrence of killifish in relation to water parameters and the presence of its putative competitor. The aim was to determine whether salinity, temperature, and water depth influenced the presence and abundance of killifish when in sympatry with mosquitofish.
4. Both the probability of presence and abundance of killifish increased with water salinity, but this increase was stronger when mosquitofish was present. Increasing water temperature and water depth were associated with a higher probability of presence and abundance of killifish respectively, although the effect of water depth was small. Both salinity and the presence of the invader acted synergistically in characterizing and shaping the population structure of the native species.
5. Living in the most extreme and stressed environments, the killifish is potentially at higher risk of extinction. These results highlight the importance of considering the interplay between multiple abiotic stressors combined with comparative data between invasive and native species as increasingly critical to aid in conservation efforts.