Can a highly invasive species re-invade its native community? The paradox of the red shiner

Red shiners (Cyprinella lutrensis) are among the most widespread, ecologically general, and environmentally tolerant fish species in North America, and are highly invasive where they have been introduced outside their native range. However, long-term data on fish assemblages showed that red shiners gradually (1980s to 2006) disappeared from creeks that are direct tributaries of Lake Texoma (Oklahoma, USA) where they are native and historically had been numerically dominant. Following a major flood in 2007, red shiners were detected anew in some of these creeks, but repeatedly disappeared and re-appeared through November 2009. Given their invasive abilities where they are not native, their failure to become re-established prompted us to examine factors that affect their apparent inability to re-invade their native habitat. We established assemblages of five common fish taxa native to Brier Creek in 12 large, outdoor mesocosm stream units. Subsequently, we introduced red shiners at two densities of 10 or 30 per unit, six replicates each, to examine potential effects of propagule pressure on establishment success. Approximately six months later, we ended the experiment and recovered all fish. Red shiners failed to become established in the experimental units, regardless of initial stocking density. They also exhibited much lower survival than other species in the native community, which not only survived well but exhibited some recruitment. Red shiner survival was significantly negatively related to the number of sunfish (Lepomis spp.) that grew to adult size in experimental units, suggesting that predation can inhibit early stages of invasion by red shiners.     

Red shiner invasion and hybridization with blacktail shiner in the upper Coosa River,USA

Human disturbance increases the invasibility of lotic ecosystems and the likelihood of hybridization between invasive and native species. We investigated whether disturbance contributed to the invasion of red shiner (Cyprinella lutrensis) and their hybridization with native blacktail shiner (C. venusta stigmatura) in the Upper Coosa River System (UCRS). Historical records indicated that red shiners and hybrids rapidly dispersed in the UCRS via large, mainstem rivers since the mid to late 1990s. We measured the occurrence and abundance of parental species and hybrids near tributary-mainstem confluences and characterized populations at these incipient contact zones by examining variation across morphological traits and molecular markers. Red shiners represented only 1.2% of total catch in tributaries yet introgression was widespread with hybrids accounting for 34% of total catch. Occurrence of red shiners and hybrids was highly correlated with occurrence of blacktail shiners, indicating that streams with native populations are preferentially colonized early in the invasion and that hybridization is a key process in the establishment of red shiners and their genome in new habitats. Tributary invasion was driven by post-F1 hybrids with proportionately greater genomic contributions from blacktail shiner. Occurrence of red shiners and hybrids and the relative abundance of hybrids significantly increased with measures of human disturbance including turbidity, catchment agricultural land use, and low dissolved oxygen concentration. Red shiners are a significant threat to Southeast Cyprinella diversity, given that 41% of these species hybridize with red shiner, that five southeastern drainages are invaded, and that these drainages are increasingly disturbed by urbanization.     

Nonhost species reduce parasite infection in a focal host species within experimental fish communities

The dilution effect describes the negative association between host biodiversity and the risk of infectious disease. Tests designed to understand the relative roles of host species richness, host species identity, and rates of exposure within experimental host communities would help resolve ongoing contention regarding the importance and generality of dilution effects. We exposed fathead minnows to infective larvae of the trematode, Ornithodiplostomum ptychocheilus in minnow‐only containers and in mixed containers that held 1–3 other species of fish. Parasite infection was estimated as the number of encysted worms (i.e., brainworms) present in minnows following exposure. The results of exposure trials showed that nonminnow fish species were incompatible with O. ptychocheilus larvae. There was no reduction in mean brainworm counts in minnows in mixed containers with brook sticklebacks or longnose dace. In contrast, brainworm counts in minnows declined by 51% and 27% in mesocosms and aquaria, respectively, when they co‐occurred with emerald shiners. Dilution within minnow + shiner containers may arise from shiner‐induced alterations in minnow or parasite behaviors that reduced encounter rates between minnows and parasite larvae. Alternatively, shiners may act as parasite sinks for parasite larvae. These results highlight the role of host species identity in the dilution effect. Our results also emphasize the complex and idiosyncratic effects of host community composition on rates of parasite infection within contemporary host communities that contain combinations of introduced and native species.     

Ecosystem effects of water column minnows in experimental streams

We used red shiner (Cyprinella lutrensis) as a model to examine ecosystem effects of water column stream minnows (Cyprinidae) in experimental streams. Benthic primary productivity, benthic invertebrate abundance, water column nutrient concentrations, size distribution of benthic particulate organic matter (BPOM), and sedimentation rates were measured across a range of fish densities (0–26.6 fish m^–2) over a 35-day period. In addition, effects of fish density on algal standing crop and benthic invertebrates in experimental streams were examined over a longer time span (156 and 203 days). After 35 days, benthic primary productivity was positively associated with fish density, with an approximate three-fold increase in productivity between experimental streams stocked with no fish and those with 26.6 fish m^–2. No effects on other ecosystem properties were detected after 35 days. Additionally, there was no effect on algal standing crop after 156 or 203 days and no effect on benthic invertebrates after 203 days. Because red shiners fed primarily on terrestrial insects, this experiment suggests that water column minnows can affect primary productivity in streams by transporting nutrients from terrestrial sources to the benthic compartment of the ecosystem. However, this effect may only be important in streams or during periods when nutrients are limiting.     

Herbivorous fish assemblages and herbivory pressure on Laamu Atoll, Republic of Maldives

While herbivory is recognized as a fundamental process structuring coral reef communities, herbivore assemblages and processes are poorly described for reefs in the Indian Ocean region. We quantified herbivorous fish assemblage structure (abundance and diversity) in Laamu Atoll, Republic of Maldives, in four reef habitat types: faro reef flats, faro reef slopes, inner and outer atoll reef slopes (20 sites in total). Herbivorous fish assemblages, representing a total of 30 species, grouped strongly by habitat type, with the highest absolute abundance observed on faro reef flats and lowest abundance on inside atoll rim reef slopes. Removal of Thalassia seagrass blades by ambient herbivore assemblages was used in a bioassay to assess relative herbivory pressure among four habitat types (eight sites). Also, at one site a choice herbivory assay was performed to assess herbivore preference among four benthic plants across three depth zones. Relative herbivory, as indicated by Thalassia assays, was highest on inside atoll rim reef slopes and lowest on outside atoll rim reef slopes. Thalassia consumption did not correspond to overall herbivorous fish abundance, but corresponded more closely with parrotfish abundance. In the choice assays, herbivores showed strong preferences among plant types and consumption of most plant types was higher at mid-depth than in the shallow reef flat or deep reef knoll zones.     

Upstream effects of a reservoir on fish assemblages 45 years following impoundment

Fish assemblage structure, rarefied species richness, species diversity and evenness of assemblages upstream of a reservoir in Oklahoma, U.S.A., were compared pre and post‐impoundment as well as in contemporary collections from streams above and below the reservoir. There were significant shifts in assemblage structure between historical and contemporary collections above the reservoir but not between contemporary assemblages above and below the impoundment. Indicator species analysis revealed that the sand shiner Notropis stramineus and fathead minnow Pimephales promelas have declined, whereas largemouth bass Micropterus salmoides and western mosquitofish Gambusia affinis have increased in relative abundance in assemblages upstream of the impoundment. Species richness was lower in contemporary assemblages compared with historical assemblages. Furthermore, contemporary assemblages below the dam had lower species richness, diversity and evenness compared with contemporary collections above the dam. These results highlight the spatial and temporal extent of reservoirs altering fish assemblages upstream of impoundments.     

Differential survival of two minnow species under experimental sunfish predation: implications for re‐invasion of a species into its native range

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Geographic independence and phylogenetic diversity of red shiner introductions

Identifying areas at risk of invasion can be difficult when the distribution of a non-native species encompasses geographically disjunct regions. Understanding genealogical relationships among native and non-native populations can clarify the origins of fragmented distributions, which in turn can clarify how fast and far a non-native species may spread. We evaluated genetic variation across the native and invasive ranges of red shiner (Cyprinella lutrensis), a minnow known to displace and hybridize with native species, to reconstruct invasion pathways across the United States (USA). Examination of mitochondrial cytochrome-b variation found that native range populations of red shiner fall into four highly divergent lineages that likely warrant species recognition. Introduced red shiner populations in the eastern and western USA are derived from only two of these lineages. Western USA populations originate from the mid-western and western genetic lineages, whereas eastern introductions derive only from the mid-western lineage. Western USA invasive populations exhibit fewer, but more diverse haplotypes compared to eastern USA invasive populations. We also recovered an undescribed, divergent lineage of Cyprinella that has been cryptically introduced into the western USA, which raises the possibility that hybridization has proceeded following secondary contact between previously allopatric lineages. Approximate Bayesian Computation modeling suggests that the disjunct distribution of red shiner across North America is an agglomeration of independent regional invasions with distinct origins, rather than stepwise advance of an invasion front or secondary introductions across regions. Thus localized control may be effective in managing non-native red shiner, including further spread to areas of conservation concern.     

Spatio-temporal distribution patterns and conservation of fish assemblages in a Chilean coastal river

River environments are characterized by extreme spatial and temporal variation in the physical environment. The relationship of fish assemblages to environmental variation is poorly understood in many systems. In Chile zonation patterns of fish assemblages have been documented in several Andean river drainages. Coastal river drainages are comparatively small, but inordinately important because of their highly endemic flora and fauna and their proximity to major human populations. For conservation purposes it is important to understand what environmental factors affect assemblage structure of fishes especially in the comparatively high diversity coastal drainages. We studied patterns of fish distribution and abundance in three rivers of the coastal, Andalien drainage near Concepción, Chile. We used multi-dimensional scaling analyses to compare patterns among zones (rithron, transition and potamon) and high and low flow seasons. Species assemblages differed by zone, but not with season. Assemblages consisted of nested subsets of species characterized by their range of distribution among zones. One species group was composed of widespread species that occurred in all three zones, another species group consisted of species found only in transitional and potamal zones, and a final group was comprised of species found only in the potamal zone. The potamal zone contained the most diverse and abundant fish assemblage. Fish assemblages were related to both water quality and habitat structure variables. This study suggests that the key to conserving the diversity of native fish communities in coastal Chilean rivers is in the conservation of potamal regions. Unfortunately, most protected areas in Chile are in the depauperate headwaters of drainages. Protection of only headwaters is clearly inadequate and will not contribute to the conservation of this unique freshwater fish fauna.     

Effects of natural hydrological variability on fish assemblages in small Mediterranean streams: Implications for ecological assessment

Small Mediterranean streams are shaped by predictable seasonal events of flooding and drying over an annual cycle, and present a strong inter and intra-annual variation in flow regime. Native fish assemblages in these streams are adapted to this natural environmental variability. The distinction of human-induced disturbances from the natural ones is thus a crucial step before assessing the ecological status of these streams. In this aim, the present study evaluates the effects of natural hydrological variability on fish assemblages from disturbed and least disturbed sites in small intermittent streams of south Portugal. Data were collected over the last two decades (1996–2011) in 14 sites located in the Guadiana and Sado river basins. High variability of fish assemblages was strongly dependent on human-induced disturbances, particularly nutrient/organic load and sediment load, and on natural hydrological variability. Natural hydrological variability can act jointly with anthropogenic disturbances, producing changes on fish assemblages structure of small intermittent streams. In least disturbed sites, despite the natural disturbances caused by inter-annual rainfall variations (including drought and flood events), fish assemblages maintained a long-term stability and revealed a high resilience. On the contrary, disturbed sites presented significantly higher variability on fish assemblages and a short and long-term instability, reflecting a decrease on the resistance and resilience of fish assemblages. Under these conditions, fish fauna integrity is particularly vulnerable and the ecological assessment may be influenced by natural hydrological variations. High hydrological variability (especially if it entails high frequency of dryer years and meaningful cumulative water deficit) may affect the impact of the human pressures with significant and consistent consequences on fish assemblage composition and integrity. In this study, fish metrics that maximize the detection of human degradation and minimize the response to natural variability were based on the relative abundance of native species (insectivorous species, eurytopic species, water column species, native lithophilic species), relative abundance of species with intermediate tolerance and relative number of exotic species. Results highlight the importance of assessing temporal variability on stream biomonitoring programs and emphasize the need to improve the assessment tools, accounting for long-term changes in fish assemblages, namely by selecting the most appropriate fish metrics that respond to anthropogenic disturbances but exhibit low natural temporal variability, essential both in the characterization of the biological reference conditions and in the development of fish indexes in intermittent streams.     

Differences in Swimming Ability and Behavior in Response to High Water Velocities among Native and Nonnative Fishes

We conducted swimming performance tests on native and nonnative fishes commonly found in Arizona streams to evaluate the extent of differences in swimming ability among species. Fishes with similar mean lengths were subjected to stepwise increases in water velocity in a laboratory swim tunnel until fish could no longer maintain position. Nonnative fathead minnows Pimephales promelas and red shiners Cyprinella lutrensis exhibited swimming abilities similar to native longfin dace Agosia chrysogaster, speckled dace Rhinichthys osculus and spikedace Meda fulgida. Nonnative mosquitofish Gambusia affinis exhibited swimming ability similar to native Gila topminnows Poeciliopsis occidentalis. Desert suckers Catostomus clarki, bluehead suckers Catostomus discobolus and speckled dace exhibited behavioral responses to high water velocities that may confer energetic advantages in swift water. Differences in swimming ability do not appear to adequately explain the disproportionate removal of nonnative fishes via flooding. Behavioral responses to high flows are more likely the mechanism that allows native fish to persist in streams during flood events.     

Altitudinal gradients in stream fish diversity and the prevalence of diadromy in the Sixaola River basin,Costa Rica

Landscape-scale patterns of freshwater fish diversity and assemblage structure remain poorly documented in many areas of Central America, while aquatic ecosystems throughout the region have been impacted by habitat degradation and hydrologic alterations. Diadromous fishes may be especially vulnerable to these changes, but there is currently very little information available regarding their distribution and abundance in Central American river systems. We sampled small streams at 20 sites in the Sixaola River basin in southeastern Costa Rica to examine altitudinal variation in the diversity and species composition of stream fish assemblages, with a particular focus on diadromous species. A set of environmental variables was also measured in the study sites to evaluate how changes in fish assemblage structure were related to gradients in stream habitat. Overall, fish diversity and abundance declined steeply with increasing elevation, with very limited species turnover. The contribution of diadromous fishes to local species richness and abundance increased significantly with elevation, and diadromous species dominated assemblages at the highest elevation sites. Ordination of the sampling sites based on fish species composition generally arranged sites by elevation, but also showed some clustering based on geographic proximity. The dominant gradient in fish community structure was strongly correlated with an altitudinal habitat gradient identified through ordination of the environmental variables. The variation we observed in stream fish assemblages over relatively small spatial scales has significant conservation implications and highlights the ecological importance of longitudinal connectivity in Central American river systems.     

Concordant variation in thermal tolerance and allozymes of the red shiner,Notropis lutrensis,inhabiting tailwater sections of the Brazos River,Texas

Synopsis Critical thermal maxima (CTM) and genetic variation were compared for red shiners, Notropis lutrensis, from regulated and unregulated sites on the Brazos River in northcentral Texas. Tailwater fish acclimated to 25°C had significantly lower CTM's than those from a site upstream from the dam and unregulated downstream sites. Significantly different intrasite variances were observed, with two- and four-fold larger CTM variances in fish from within 1 km and 30 km of the dam. Genetic variation was determined from electrophoretic comparisons at 21 structural gene loci. Mean heterozygosity was greatest at regulated sites. Tests for locus heterogeneity at five variable loci indicated that regulated and unregulated populations are not homogeneous. Fish under regulation were genetically more similar to each other than they were to those not affected by regulation. The proportions of the gene variance attributable to habitat alteration were partitioned, and fully one-third of the gene variation was attributed to stream regulation. Patterns of variation in thermal tolerance and metabolic enzymes in the red shiner correlated closely with temperature regimes associated with hypolimnion release from the dam. These adaptive responses have occurred in less than 40 years.     

Influences of low-head dams on the fish assemblages in the headwater streams of the Qingyi watershed, China

The influences of low-head dams on the fish assemblages were examined in this study, using fish data collected in six treatment and five reference sites at three low-head dams in the headwater streams of the Qingyi watershed, China. Comparing with those in the reference sites, local habitat variables were significantly altered by low-head dams in the treatment sites, involving wider channel (only in the impoundment area), deeper water and slower flow. Fish species richness varied significantly across seasons, not across site categories, suggesting that these low-head dams did not alter species richness. However, significant decreases in fish abundance and density were observed in the impoundment areas immediately upstream of dams, but not in the plunge areas downstream. Fish assemblage structures kept relative stability across seasons, and their significant difference between-site was only observed between the impoundment areas and the sites far from dams upstream. This variation in assemblage structures was due to the differing relative abundance of some co-occurring species; more lentic but less lotic fish was observed in the impoundment areas. The spatial and temporal patterns of fish assemblages were correlated with local habitat in this study area. Wetted width had negative correlation with fish species richness, abundance and density, respectively. Water temperature also positively affected species richness. In addition, wetted width, water depth, current velocity and substrate were the important habitat variables influencing assemblage structures. Our results suggested that, by modifying local habitat characteristics, low-head dams altered fish abundance and density in the impoundment areas immediately upstream of dam, not in the plunge areas immediately downstream, and thereby influenced fish assemblage structures in these stream segments.     

Associations between fish assemblages and environmental factors for Mediterranean-type rivers during summer

The structure of summer fish assemblages was examined along longitudinal gradients in 31 Mediterranean-type rivers of the middle Guadiana basin (south-west Iberian Peninsula), using data from 157 sites including small streams to deep rivers. An ordination analysis, based on 16 variables, was applied to species presence, using principal component and canonical correspondence analysis. The results for the habitat data were compared with those for the biological data using a Mantel analysis, and the agreement was highly significant. Spatial structure was considered by partitioning the total variability among the environmental and geographical variables. The fish assemblages showed longitudinal zoning during the summer, with species distributed over gradients of habitat size (depth), water quality (current and physico-chemical variables), and cover (substratum and vegetation), according to their adult size and life history. The size of the habitat that remained available in summer had the greatest biological effect, being the most important factor explaining fish species distribution and assemblage structure during this stressing season. Strictly spatial variation was low, but there was still a high residual variation. Habitat associations and life-history strategies are discussed for native and exotic species.     

The spatial scale of homogenisation and differentiation in Chihuahuan Desert fish assemblages

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Diel variation in diet composition of a riverine fish community

Although diel food habit studies have been undertaken on a number of individual species, few studies have examined diel variation in the diets of fish communities. We examined the diel diet variation and feeding periodicity of a fish community in the Juniata River, Pennsylvania. Nine species, totalling 1,098 fish, were collected at 4-h intervals over a 24-h period in October 1989, in numbers sufficient to describe their diel variation in diet composition. Diel variation in diet composition was evident in all species, as no single prey taxon was dominant in the diet of any species during any 4-h interval. Ephemeropterans were the most important prey taxa for four species of centrarchids, whereas chironomids were the main prey of banded killifish, mimic shiners, and spotfin shiners. Algae was the major component in the diet of spottail shiners, whereas bluntnose minnows contained mostly detritus. Feeding activities of rock bass, redbreast sunfish, and pumpkinseed occurred at low levels throughout the day; peak feeding occurred from 2000 to 0400 hours. Food consumption of smallmouth bass increased throughout the day with peak consumption occurring at 2000 hours. Non-centrarchids fed little during daylight hours and showed peak activity at 2000–2400 h. Construction of a 24-hour diet from six 4-h interval estimates and feeding periodicity data provided a comprehensive representation of the diel feeding ecology of all species collected.     

Space use and feeding patterns of an offshore fish assemblage in a shallow mesotrophic lake

Synopsis Diel and spring/summer space-use and feeding patterns were investigated in an assemblage dominated by five fish species occupying the offshore waters of Lake Opinicon, a shallow mesotrophic lake in southeastern Ontario. We assessed fish distribution and diel movement in May and July through the use of gill nets set at various depths in 1.5–7.0 m depth contour zones, supplemented by observations of fish reaction to the nets. Golden shiners and alewives occupied the upper part of the water column, with the former concentrated at the littoral zone-open water interface, and the latter in the open water. Yellow perch occupied the lower part of the water column in all depth contours. Bluegills were abundant in the upper to midwater depths in all contour zones; black crappies were concentrated in the 2.5–3.5 m zones. All of these species showed either a diel or a spring-summer change in distribution pattern. Bluegills were more abundant in offshore locations in July, whereas golden shiners and yellow perch were more abundant onshore in May. Alewives and black crappies showed distinct diel movements in July, as they were largely absent from the study area during the day, but returned at night to feed. In general, there was more spatial separation among the five species in July than in May.Patterns of spatial distribution among the species generally corresponded with the type and variety of prey consumed, and with diel movement of prey in the case of water column feeders. Other factors that apparently affected spatial distribution and seasonal shifts in this assemblage were risk of predation (golden shiner), spawning activity (alewife), and a decline in prey abundance from spring to summer (bluegill and yellow perch).     

Shoaling species drive fish assemblage response to sequential large floods in a small midwestern U.S.A. stream

I assessed the short-term impact of two sequential scouring floods on the fish assemblage of a small prairie stream. I tested for changes in fish abundance, fish assemblage composition, and fish-habitat associations within individual pools and across a suite of pools following each flood. Before the second flood, 30–90% of fish were removed by seining in five of eight pools. Overall fish abundance was reduced by approximately 50% following the first flood, but effects varied widely among individual pools. Fish abundance was unaffected by the second flood, despite prior removal of a known proportion of fish, suggesting recolonization of defaunated pools during the flood. Fish assemblage similarity across the entire suite of pools was low following each flood, but varied considerably within individual pools. Defaunated pools were more similar to pre-flood assemblages than control pools, though the mechanism behind this pattern was unclear. Changes in abundance and assemblage composition were driven by interpool movement of two minnow species with the shared behavioral trait of shoaling: bigeye shiner Notropis boops and central stoneroller Campostoma anomalum. Shifts in abundance showed no upstream or downstream pattern, suggesting that flooding allowed fish to move actively among pools that are typically isolated by partial barriers (riffles). This study highlights the importance of considering species’ behavioral traits when assessing the impacts of flooding, and suggests that shoaling behavior may be useful trait for predicting fish assemblage change following flooding.