Patterns of fish communities and limnological conditions relative to floodplain landscapes

The Yazoo River Basin of Mississippi includes several rivers and hundreds of floodplain lakes within an area greatly impacted by agriculture. I studied 17 of these lakes distributed over the lower half of the Yazoo River Basin to document fish assemblages and limnological patterns and to identify environmental variables that might influence these assemblages. Potential connectivity of the lake to parent river and wetland-lake area ratio in the watershed were related to the limnological conditions and fish communities. Lakes with greater potential connectivity tended to be deeper and had greater specific conductance and greater fish species richness including more riverine species. Conversely, as the potential connectivity decreased, lakes were shallower, had greater chlorophyll-a fluorescence, wetland-lake area ratio, and a less speciose lacustrine fish community. Species richness and assemblage composition of riverine species were related directly to potential connectivity. Lacustrine species assemblages were linked to wetland-lake area ratio and turbidity

Patterns of fish communities and limnological conditions relative to floodplain landscapes

The Yazoo River Basin of Mississippi includes several rivers and hundreds of floodplain lakes within an area greatly impacted by agriculture. I studied 17 of these lakes distributed over the lower half of the Yazoo River Basin to document fish assemblages and limnological patterns and to identify environmental variables that might influence these assemblages. Potential connectivity of the lake to parent river and wetland-lake area ratio in the watershed were related to the limnological conditions and fish communities. Lakes with greater potential connectivity tended to be deeper and had greater specific conductance and greater fish species richness including more riverine species. Conversely, as the potential connectivity decreased, lakes were shallower, had greater chlorophyll-a fluorescence, wetland-lake area ratio, and a less speciose lacustrine fish community. Species richness and assemblage composition of riverine species were related directly to potential connectivity. Lacustrine species assemblages were linked to wetland-lake area ratio and turbidity

Long-term changes in seasonal fish assemblage dynamics in an adventitious desert stream

Tornillo Creek, a tributary of the Rio Grande in Texas, United States, has historically been an important nursery and spawning habitat for several native fish species. We examined variation in the seasonal fish assemblages in Tornillo Creek within and between two time periods (1967–1970 vs. 2009–2011), and contemporary fish assemblage–environment associations, in order to understand what environmental factors were associated with seasonal fish abundance and occupancy patterns. Our results indicated that fish assemblages were very different between the two time periods. Contemporary seasonal fish assemblage patterns in Tornillo Creek were less variable than historical assemblages and were linked to several environmental factors including water temperature, stream depth, and current velocity. We suggest that the maintenance of stream flow and connectivity are important for the immigration and emigration of certain riverine fishes in Tornillo Creek and that decreases in stream flow could accelerate the domination of the tolerant species in the creek. - Tornillo Creek, un afluente del rıo Grande en Texas, Estados Unidos, ha sido historicamente un importante criadero y habitat de desove para varias especies de peces nativas. Examinamos la variación en los ensamblajes de peces estacionales en Tornillo Creek dentro y entre dos periodos de tiempo (1967–1970 vs. 2009–2011), y las asociaciones del ensamblaje de peces y el ambiente contemporáneo para entender qué factores ambientales se asociaron con los patrones estacionales de presencia y abundancia de peces. Nuestros resultados indican que los ensamblajes de peces fueron muy diferentes entre los dos periodos de tiempo. Patrones de ensamblaje de peces estacionales contemporáneos en Tornillo Creek fueron menos variables que los ensamblajes hist ´oricos y estuvieron vinculados a varios factores ambientales como la temperatura del agua, profundidad del arroyo y velocidad de la corriente. Sugerimos que el mantenimiento del flujo y la conectividad son importantes para la inmigración y la emigración de ciertos peces fluviales en Tornillo Creek y que las disminuciones en el flujo de corriente podr´ıan acelerar la dominancia de las especies tolerantes en el arroyo

Long-term changes in seasonal fish assemblage dynamics in an adventitious desert stream

Tornillo Creek, a tributary of the Rio Grande in Texas, United States, has historically been an important nursery and spawning habitat for several native fish species. We examined variation in the seasonal fish assemblages in Tornillo Creek within and between two time periods (1967–1970 vs. 2009–2011), and contemporary fish assemblage–environment associations, in order to understand what environmental factors were associated with seasonal fish abundance and occupancy patterns. Our results indicated that fish assemblages were very different between the two time periods. Contemporary seasonal fish assemblage patterns in Tornillo Creek were less variable than historical assemblages and were linked to several environmental factors including water temperature, stream depth, and current velocity. We suggest that the maintenance of stream flow and connectivity are important for the immigration and emigration of certain riverine fishes in Tornillo Creek and that decreases in stream flow could accelerate the domination of the tolerant species in the creek

Quantitative environmental DNA metabarcoding shows high potential as a novel approach to quantitatively assess fish community

水に含まれる環境DNAから「どんな魚」が「どれだけいるか」を同時に推定 --定量的な魚類群集モニタリングを容易に実現--. 京都大学プレスリリース. 2023-01-20.The simultaneous conservation of species richness and evenness is important to effectively reduce biodiversity loss and keep ecosystem health. Environmental DNA (eDNA) metabarcoding has been used as a powerful tool for identifying community composition, but it does not necessarily provide quantitative information due to several methodological limitations. Thus, the quantification of eDNA through metabarcoding is an important frontier of eDNA-based biomonitoring. Particularly, the qMiSeq approach has recently been developed as a quantitative metabarcoding method and has attracted much attention due to its usefulness. The aim here was to evaluate the performance of the qMiSeq approach as a quantitative monitoring tool for fish communities by comparing the quantified eDNA concentrations with the results of fish capture surveys. The eDNA water sampling and the capture surveys using the electrical shocker were conducted at a total of 21 sites in four rivers in Japan. As a result, we found significant positive relationships between the eDNA concentrations of each species quantified by qMiSeq and both the abundance and biomass of each captured taxon at each site. Furthermore, for seven out of eleven taxa, a significant positive relationship was observed between quantified DNA concentrations by sample and the abundance and/or biomass. In total, our results demonstrated that eDNA metabarcoding with the qMiSeq approach is a suitable and useful tool for quantitative monitoring of fish communities. Due to the simplicity of the eDNA analysis, the eDNA metabarcoding with qMiSeq approach would promote further growth of quantitative monitoring of biodiversity

Effects of habitat size and isolation on species immigration–extinction dynamics and community nestedness in a desert river system

Habitat fragmentation is one of the major causes of local and regional species extinctions in freshwater ecosystems. To predict future trends in community composition, and the potential sequence of extinctions due to fragmentation of the river continuum, it is important to understand how habitat size and isolation affect the dynamics of species immigrations and extinctions and patterns of abundance and occupancy. We examined fish immigration and extinction rates, and abundance and occupancy patterns, in relation to habitat isolation, size and variability in the Rio Grande and its tributaries in the Trans-Pecos region of Texas, U.S.A. Our results indicated that as habitat isolation increased in tributaries, fish immigration and extinction rates and riverine species abundances decreased. Fish assemblages showed significant nested subset patterns across the study sites, and the influence of habitat size and isolation on the nested subset patterns varied with spatial scale. Certain non-native fish taxa were idiosyncratic, reducing the strength of the nested subset pattern. The high temporal species turnover in connected habitats was related to the movement of riverine fish species between the mainstem and mouths of tributaries. High persistence of spring-adapted species decreased extinction rate in isolated habitats. Increasing the spatial scale of the study system probably resulted in an increased ability to detect dispersal limitation between the mainstem and its tributaries. Large, deep pools decreased local extinction of certain native fish taxa in upstream tributaries. The deviation from the nested subset pattern was attributed to the unique regional occupancy of non-native fish taxa that could be associated with their artificial introduction into this system. Our results suggest that increased habitat fragmentation by human activities can accelerate the regional extinction of certain native fish taxa and the dominance of ecologically tolerant, possibly non-native fish, leading to a decline in regional diversity

Fish species incidence patterns in naturally fragmented Chihuahuan Desert streams

We investigated how stream fragmentation affects local fish species persistence and extinction from three Rio Grande systems (Texas, USA) stream reaches with different levels of natural fragmentation. We examined species–volume (SV) relationships of fish assemblages in 42 pools across the watersheds and predicted greater fragmentation would correspond to an increase in the slope of the SV relationship due to decreased within-reach rescue effects. In addition, we examined relationships among tributary-specific nested subset patterns, local habitat features and spatial position of the reaches relative to the Rio Grande mainstem to better understand the importance of local and regional processes on fish species richness patterns in the stream reaches. Slopes of the SV curves did not differ among the stream reaches, but the intercepts of the SV curves were significantly different. These results indicated rescue effects among habitats within a stream reach were not apparent; however, rescue effects from the mainstem largely determined the species richness of a given stream reach. The nested subset patterns in all stream reaches were related to several local environmental factors, and large, deep pools provided important aquatic refugia in all three systems. We suggest declines in mainstem and tributary flows will likely continue to impact local and regional fish assemblage attributes. High flow events are important for dispersal and can reset tributary fish communities for the next extinction-driven, successional cycle

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

We examined riverine desert fish assemblages in the Chihuahuan Desert, U.S.A. at multiple spatial scales of similarity to assess long-term changes to assemblage distinctiveness, identify individual species responsible for changes, and determine the importance of geographic context and species resolution in interpreting patterns of change. We used a well-documented historical data set on fish distribution and abundance, and recent collections of fishes that provided a paired analytical design across 36 localities spanning nearly 3 decades. Patterns of faunal homogenisation and differentiation were assessed at basin-wide, sub-basin and river-reach scales with species occurrence and relative abundance data. Individual species responses were examined to identify the drivers of assemblage change across time. Patterns of assemblage similarity varied across spatial scales and produced seemingly incongruous trends across time. Assemblage distinctiveness depended on the spatial extent of the analyses, the geographical structuring of the fish assemblages, and whether occurrence or relative abundance data were used. These dependencies led to interesting and conflicting patterns of homogenisation and differentiation. The Rio Grande sub-basin showed strong homogenisation with convergence between upstream and downstream reaches that corresponded to declining water quality and quantity from the Rio Conchos in Mexico. In contrast, the Pecos River sub-basin showed strong differentiation between upstream and downstream reaches that corresponded to the successful colonisation and spread of the non-native gulf killifish (Fundulus grandis) in the upper reach, where water quantity and quality have declined. Spatial variability in fish assemblages and their degree of change from historical conditions were largely congruent with anthropogenic modifications to the flow regime and variability in the success of invasive gulf killifish in the basin. The use of species occurrence as opposed to relative abundance data, and the spatial scale of analysis are crucial choices in studies of faunal homogenisation and differentiation, and we have demonstrated how these choices lead to variable results for our study system. Our multi-scale approach and examination of individual species responses identified the ultimate drivers of these differences and illustrated the importance of scale-dependent effects and geographical context on patterns of assemblage distinctiveness, especially with regard to species invasion, species loss and relative abundance shifts