Multifaceted fish diversities respond differently to impounding age and longitudinal location along a reservoir cascade

Damming usually modifies riverine habitats, which affects various aspects of fish diversity, especially in a reservoir cascade. Their influence on fish assemblage has been studied widely, but a lack of data from the diversity perspective remains. The Gezhouba Reservoir and Three Gorges Reservoir are two of the largest cascaded reservoirs located on the upper Yangtze River. In this study, we investigated the current fish assemblages in 2020∼2021 and retrieved 22 previous investigations in different sections of this cascade system to analyze how fish taxonomic, functional, and phylogenetic alpha- and beta-diversity change with the distance from the dams and the impounding age during 1998∼2021, and all sampling sites are located in the upper section of the dams. The total species richness and phylogenetic diversity increased significantly with the distance from the dams, but the functional diversity did not change substantially. No significant difference was found in the influence of impounding age on the three aspects of fish diversity. We observed a noticeable increase in non-indigenous fish species richness, functional diversity, and phylogenetic diversity over time, these effects were similar in areas at different distances from the dams. The species richness and phylogenetic diversity of lotic fish decreased from the lotic to lentic zones, whereas the functional and phylogenetic diversities decreased significantly with impounding age. The taxonomic beta-diversity was remarkably higher than the functional and phylogenetic beta-diversities. The differences among the three facets of beta-diversity were driven by a lower functional turnover than the taxonomic and phylogenetic turnovers, and their nestedness components were low without exception. The present study suggests that trade-offs should be considered when designing policies to protect fish diversity based on different objectives

Advances in Ecology Research on Integrated Rice Field Aquaculture in China

Integrated rice field aquaculture, a practice normally used by rural small-scale farmers, is not only supporting farms and livelihoods but is also reducing poverty and is playing a more and more important role in China. It is also becoming one of the main freshwater aquaculture systems, in addition to ponds, lakes, reservoirs, streams, and other aquaculture systems. During the past 40 years, both the production and areas of integrated rice field aquaculture in China have significantly increased from 0.13 million t and 0.74 million ha in 1990 to 3.25 million t and 2.56 million ha in 2020, respectively. Advances in ecology research on integrated rice–fish aquaculture were one of the main contributors to this achievement. In this paper, we systematically reviewed the advances in ecology research on three major integrated rice field aquaculture systems in China, namely rice–fish, rice–crab, and rice–crayfish coculture systems, the contribution of the research, and future prospects. We found that progress in ecology research on theories, biological studies, models, and eco-engineering techniques, coupled with policy support promoted the development of the rice field aquaculture industries. This review could assist individual small-scale farmers to make better use of rice field space to produce safer aquatic and rice products at a lower cost and help aquaculture scientists to further study the ecology of integrated rice field aquaculture systems

Impoundment led to spatial trophic segregation of three closely related catfish species in the Three Gorges Reservoir, China

The construction of the Three Gorges Reservoir (TGR), the largest dam in the world, created novel spatial and seasonal fluctuations in food availability along the Yangtze River. We studied changes in diet and niche overlap of three co-occurring catfish species between the upper and lower sections of the TGR and across four hydrological seasons to investigate whether the diets of native catfish species reflect the fluctuations in food availability. Zoobenthos dominated the diets of the three species in the upper section, but shrimp made the bulk of the diet in the lower section. This was the case in every season except during the rising-water season when all three species increased the consumption of allochthonous foods. Diet breadth was significantly broader in the upper section relative to the lower section, and expanded during the rising-water season in the lower section. Niche overlap was significantly lower in the upper section than in the lower section. A non-significant trend of reduced niche overlap during the rising-water season was observed in both sections. Our results suggest that, in less than a decade, dietary plasticity facilitated the adaptation of these species to novel habitats and a shifted food-resource base formed by the impoundment

Spatial and interspecific comparisons of the reproductive biology of two species of co-occurring freshwater shrimps (Decapoda: Caridea: Palaemonidae) in the Three Gorges Reservoir, China

Exopalaemon modestus (Heller, 1862) and Macrobrachium nipponensis (De Haan, 1840) (Palaemonidae) are ecologically and commercially important fishery resources in the Three Gorges Reservoir (TGR), China, and co-occur in demersal habitats. Little information is available on their biology. We compared the reproductive traits of both species on the upper, middle, and lower sections of the TGR. Both species differed in mean size at maturity, which increased from upper to middle and lower sections. Sex ratios were significantly biased toward females, but no significant differences were observed among the three sites for either species. Both species displayed an obvious trade-off between embryo size and fecundity, with the size of embryos being the smallest but with the highest fecundity at the upper section, followed by the middle and lower sections. Exopalaemon modestus spawned from early April to late September, with a peak in May and June, whereas M. nipponensis spawned from late April to early October with a peak in June and July. The spatially distinct reproductive traits, which were concordant across species, are likely related to differences in habitat characteristics such as water flow. We suggest that management strategies should account for the reproductive biology of the two species in order to maintain a sustainable fishery in the reservoir

Zooplankton Compositions in the Danjiangkou Reservoir, a Water Source for the South-to-North Water Diversion Project of China

The Danjiangkou Reservoir (DJKR) serves as the water source for the world’s biggest water diversion project, the Middle Route of the South-to-North Water Diversion Project (MR-SNWDP) in China, and this project concerns the water security of tens of millions of people in northern China. Hence, the maintenance of ecosystem health and optimization of management necessitate studies to assess the composition and dynamics of key aquatic living resources. Zooplankton represent a critical component of the reservoir ecosystem and are sensitive to environmental changes and anthropogenic disturbances. In this study, the zooplankton compositions in DJKR were quantified and compared in May, August, and November 2017. Simultaneously, the effects of water trophic states on the zooplankton community structure were analyzed at three levels (overall, taxonomic, and functional groups). A total of 65 zooplankton taxa were recorded, with the taxonomic richness of Rotifera (28 taxa) being the highest among taxonomic groups, which were further classified into 10 functional groups. The community was characterized by low diversity and high evenness. Compared with historical studies, the biomass had increased remarkably, while the abundance showed a decreasing trend in DJKR, and there were more large-bodied zooplankton in this study. The multivariate analysis revealed that zooplankton compositions changed significantly among the three sampling months without distinguishable spatial variations. Moreover, the zooplankton compositions at all three levels correlated significantly with total nitrogen, water transparency, and permanganate index in most situations, as verified by db-RDA and Mantel’s test. However, the contributions of chlorophyll a and total phosphorus were only significant for the LCF group, implying that the bottom-up effects of phytoplankton on zooplankton were weak in DJKR. Therefore, analysis based on functional groups may reflect a more accurate snapshot of the relationships. Our findings will contribute to enriching the long-term fundamental ecological knowledge of the DJKR and the MR-SNWDP, as well as provide key taxonomic information for ecosystem assessment and management

Zooplankton Compositions in the Danjiangkou Reservoir, a Water Source for the South-to-North Water Diversion Project of China

The Danjiangkou Reservoir (DJKR) serves as the water source for the world’s biggest water diversion project, the Middle Route of the South-to-North Water Diversion Project (MR-SNWDP) in China, and this project concerns the water security of tens of millions of people in northern China. Hence, the maintenance of ecosystem health and optimization of management necessitate studies to assess the composition and dynamics of key aquatic living resources. Zooplankton represent a critical component of the reservoir ecosystem and are sensitive to environmental changes and anthropogenic disturbances. In this study, the zooplankton compositions in DJKR were quantified and compared in May, August, and November 2017. Simultaneously, the effects of water trophic states on the zooplankton community structure were analyzed at three levels (overall, taxonomic, and functional groups). A total of 65 zooplankton taxa were recorded, with the taxonomic richness of Rotifera (28 taxa) being the highest among taxonomic groups, which were further classified into 10 functional groups. The community was characterized by low diversity and high evenness. Compared with historical studies, the biomass had increased remarkably, while the abundance showed a decreasing trend in DJKR, and there were more large-bodied zooplankton in this study. The multivariate analysis revealed that zooplankton compositions changed significantly among the three sampling months without distinguishable spatial variations. Moreover, the zooplankton compositions at all three levels correlated significantly with total nitrogen, water transparency, and permanganate index in most situations, as verified by db-RDA and Mantel’s test. However, the contributions of chlorophyll a and total phosphorus were only significant for the LCF group, implying that the bottom-up effects of phytoplankton on zooplankton were weak in DJKR. Therefore, analysis based on functional groups may reflect a more accurate snapshot of the relationships. Our findings will contribute to enriching the long-term fundamental ecological knowledge of the DJKR and the MR-SNWDP, as well as provide key taxonomic information for ecosystem assessment and management

Spatial changes of fish assemblages in relation to filling stages of the Three Gorges Reservoir, China

To study how fish assemblages changed at different fillings stages, we compared the present fish assemblages (2015-2017; after the third filling in 2009) with those from periods prior to impoundment (1975), after the first closure (1997-2000), after the first filling (2005-2006), and after the second filling (2006-2009) in the upper, middle and lower sections of the Three Gorges Reservoir, the largest in the world. Our results demonstrated that species richness was higher in the upper section than in the lower and middle sections, whereas the overall richness was lower than that prior to damming. The present assemblages were different among sections associated with their specific habitats; i.e., the proportion of rheophilic fishes decreased, whereas those of limnophilic and eurytopic fishes increased from the upper to the lower sections. Temporal comparisons suggested significant declines in proportions of rheophilic and migratory fishes, whereas small-bodied and eurytopic fishes increased after the impoundment. Fish biomass (CPUE) was greater in the upper section than in the lower and middle sections, and significantly increased after the third filling in the upper section. Overall, our results indicated that the Three Gorges Dam significantly impacted fish assemblages, and the effects of impoundment were magnified by the increased filling scales. The fish assemblages in the upper section were less impacted, demonstrating the high conservation value offered by the upper section to the fish species inhabiting the upper reaches of the Yangtze River

Thermal Preference May Facilitate Spatial Coexistence of Two Invasive Fish Species in Lake Bosten, China

As aquaculture food production is expected to increase, introduced aquaculture species play an important role in meeting the rising demand for aquatic food products and contributing to great societal benefits. Species introduction forces sympatric species to coexist within the same ecosystem by niche segregation. Japanese smelt Hypomesus nipponensis and sharpbelly Hemiculter leucisculus are ecologically similar species and were introduced to Lake Bosten, the largest inland lake in Northwest China, accounting for more than 60% of the total production. We predicted that the coexistence of the two invasive species is mediated by habitat segregation. We analyzed spatiotemporal patterns of Japanese smelt and sharpbelly abundance in Lake Bosten to determine the patterns of spatial segregation between the two dominant fish species. Our results showed that, in Lake Bosten, sharpbelly are typically littoral dwellers when the surface temperature increases in spring and summer, while Japanese smelt often prefer pelagic waters, especially during summer and autumn when the surface temperature rises. Japanese smelt showed an affinity for deeper waters, using median depths 1.7 m deeper than those of sharpbelly, irrespective of the sampling season. Water temperature was the main underlying driver of such spatial segregation and coexistence of these two closely related species in Lake Bosten. Spawning, food resources, and fishing were also important possible factors affecting spatial segregation between the two species. Our results provide new information on niche partitioning patterns as strategies for the coexistence of the two dominant non-native fish in Lake Bosten, supporting the idea that ecologically similar species can avoid resource competition through spatial habitat segregation

Species-specific variations in reproductive traits of three yellow catfish species (<i>Pelteobagrus</i> spp.) in relation to habitats in the Three Gorges Reservoir, China

<div><p>The reproductive biology of three yellow catfish congeners was studied in the Three Gorges Reservoir of the Yangtze River, China. We compared reproductive traits among the lentic, transitional, and lotic zones. A total of 4502 individuals of the three species was collected, and the sex ratio, size at 50% maturity, spawning season, fecundity, and egg size were determined. Results showed that populations inhabiting the lotic zone spawned earlier than those inhabiting the lentic zone. For the three species, fecundities were significantly higher for populations in the lotic zone than for those in the lentic and transitional zones (<i>P</i> < 0.05). <i>Pelteobagrus vachelli</i> (Richardson) and <i>P</i>. <i>fulvidraco</i> (Richardson) displayed an obvious trade-off between egg size and fecundity, whereas <i>P</i>. <i>nitidus</i> (Sauvage <i>et</i> Dabry) produced the largest eggs in the lotic zone. Sex ratios were significantly different among zones (<i>P</i> < 0.05, for each species), but the bias patterns were different. Sizes at 50% maturity of female <i>P</i>. <i>nitidus</i> and <i>P</i>. <i>vachelli</i> were the largest in the lotic zone and the smallest in the transitional zone, but was similar among zones for <i>P</i>. <i>fulvidraco</i>. Overall results suggest that the three yellow catfish species developed different reproductive traits among the three habitats in the TGR, whereas the variations reflected further interspecific differences. Our study indicates the importance of riverine habitats for the conservation of species of fish, even for species such as these eurytopic catfish inhabiting the upper reach of the Yangtze River. This study further suggests that species-specific responses should be considered when evaluating the influences of new hydropower projects, even for such closely related species of fish.</p></div

Monthly changes in water temperatures (°C) (mean ± S.E.) and water levels (m) in the Three Gorges Reservoir.

<p>Data were collected from August 2014 to July 2015.</p