Aquatic Ecology最新文献

There is still a fundamental gap in our knowledge regarding the dormant egg bank in the littoral zone, as much of the existing information stems from studies conducted in the pelagic zone. We investigated cladoceran egg banks attached to macrophyte roots (Eichhornia azurea) and the soil surface collected from the littoral site of four Brazilian lakes. We test the hypothesis that sediment supports egg bank communities that are taxonomically distinct from those in macrophyte roots. We took replicate samples from paired examples of each egg bank and later incubated the diapausing eggs in a hatching experiment. Another aspect of our study involved classifying the egg bank community based on the traditional separation of cladocerans according to their microhabitat (pelagic vs. phytophilous). Results from the study indicated that the number of individuals and taxon richness was higher in the sediment egg banks than in those from the macrophyte roots in two of the lakes studied. The proportions of pelagic and phytophilous hatched varied between sediment and macrophyte roots egg banks within each lake studied. These findings partially supported our hypothesis that sediment contains taxonomically distinct egg bank communities compared to those in macrophyte roots. Our results suggest that the littoral zone, particularly the sediment habitat, may serve as a substrate for a persistent dormant egg bank of some pelagic cladocerans. Further comparative research among different macrophyte species and littoral sediments can help to gain more insights into cladoceran ecology and restoration programs for lakes experiencing environmental impacts.

Small hydroelectric power plants (SHPPs) are often promoted as clean and renewable energy sources. However, SHPPs are often characterized by hydropeaking, which is a practice involving the sudden release of water from turbines. Hydropeaking may have multiple detrimental effects on downstream ecosystems, among which is fish stranding. This phenomenon involves trapping fish in isolated pools or dry riverbeds, which detrimental effects on fish populations and assemblages are often poorly quantified. Here, we investigated the implications that hydropeaking may have on fish populations in small Brazilian rivers. Specifically, we recorded fish stranding events (including the number of individual fish stranded) while monitoring the practice of hydropeaking by SHPPs in two watersheds. By combining observational and modeling approaches, we examined the relationships between fish stranding events and the operation of six SHPPs along a 5 km downstream stretch. For this analysis, we focused primarily on fish families which were dominant in the rivers. Our results indicate an exponential increase in fish stranding due to hydropeaking, which significantly affects fish populations as we move away from the SHPPs axes and towards downstream sections. The principal affected fish families were Characidae (23.7% of stranding), Heptaperidae (23.2%), Loricariidae (19.8%), and Pimelodidae (11.1%). In the monitored watersheds, our models predicts that if even one fish stranding event occurs annually, it could results in the stranding of nearly 500,000 individuals. This, in turn, could have severe adverse effects on the ability of these fish families to replenish themselves. We thereby emphasize the importance of adaptive management for flow regulation and incorporating lateral fish passage structures into the riverbed. This approach is essential for achieving sustainable hydroelectric power generation in Brazil while safeguarding the ecological integrity of small rivers and their fish populations.

Bacterial communities play key roles in freshwater reservoirs, affecting their functioning and services. Understanding their occurrence in the reservoirs will help to predict how these ecosystems change in response to human activities and climate change. In this study, 16S rRNA gene sequencing was used to investigate the composition and structure of bacterioplankton in two drinking water tropical reservoirs with different trophic state in Puerto Rico: Cerrillos (mesotrophic) and Lucchetti (eutrophic). The dominant lineages were typical of freshwaters such as Actinobacteria (26.7%), Gammaproteobacteria (23.3%), Alphaproteobacteria (17.7%), Firmicutes (8.2%) and Cyanobacteria (5.9%). However, the bacterioplankton composition and diversity were variable throughout the water column in both reservoirs, indicating that environmental gradients such as temperature, dissolved oxygen, and nutrient create a variety of habitats that support different bacterial assemblages in these reservoirs. Frankiales and Micrococcales were dominant in the metalimnion, whereas Bacillales were common in the deep layers, mainly in the anoxic zone of Lucchetti. The trophic state of these reservoirs also affects the bacterioplankton structure. Picocyanobacteria were represented mainly by Cyanobium PCC-6307, with higher abundance in Cerrillos compared to Lucchetti, indicating its preference for less eutrophic reservoirs. The detection of potentially pathogenic species such as Acinetobacter lwoffii and A. Schindleri, and cyanobacteria ecotypes as possible indicators of eutrophication, indicate the importance of monitoring these aquatic ecosystems, to implement mitigation programs and conservation strategies in tropical reservoirs used as drinking water sources.

Invasive plants have been shown to alter ecosystem functions. However, there is limited information available on the effect of the invasive species litter input on native litter decomposition and home-field advantage (HFA, increased decomposition at a home environment compared to a guest environment). To investigate this, we conducted a field experiment using leaves of native Trapa natans and Typha orientalis with and without invasive species Alternanthera philoxeroides and then incubated them at T. natans and T. orientalis habitats in a eutrophic lake for 50 days. In control and treatment, the decomposition and N release rate of T. natans were significantly higher than that in T. orientalis species litter at two habitats, indicating no HFA occurrence. A. philoxeroides litter input promoted the decomposition and N decay rate of T. orientalis, not T. natans. The mean decomposition rate of T. orientalis in control and treatment were 0.0138 and 0.0342 day⁻¹; for T. natans, it was 0.0703 and 0.0754 day⁻¹, respectively. The mean N decay rate of T. orientalis in control and treatment were 0.0235 and 0.0468 day⁻¹; for T. natans, it was 0.0511 and 0.0544 day⁻¹, respectively. Invasive species presence increased microbial respiration rate of T. orientalis, but not for T. natans species litter in two habitats. These results suggested that A. philoxeroides litter input accelerated low quality litter decomposition though increased microbial activity. However, it did not influence the HFA performance, which may be closely related to the lake eutrophication.

Aquatic invasive species decrease biodiversity and disrupt economic systems worldwide. Apple snails (Ampullaridae) from the genus Pomacea are globally invasive species that are highly damaging to aquaculture and aquatic ecosystems. Pomacea maculata was introduced to Louisiana in the early 2000s and rapidly spread throughout the southern half of the state, where invasive populations now threaten valuable aquaculture economies and a large area of aquatic ecosystems that sustain biodiversity important to commercial and recreational fisheries. Despite these risks, little work has been dedicated to understanding how apple snails disperse through invaded areas in Louisiana. To shed light on potential dispersal dynamics, we assessed population genetic structure of P. maculata in Louisiana at multiple spatial scales using microsatellites of snails collected from seven sampling locations. Overall, genetic diversity was relatively high across all sampling locations. Significant genetic structure was observed among sampling sites, indicating Barataria Preserve and the four sampling locations within Terrebonne Basin as distinct populations. Genetic distances were smallest among the four sampling locations within Terrebonne Basin. These findings suggest that dispersal within hydrologic units is higher than between units, meaning that apple snails may primarily move through systems through passive downstream dispersal. However, geographically distant populations also showed evidence of genetic mixing, pointing toward human-aided long-distance dispersal events. Regular dispersal of apple snails within and among hydrologic units highlights the risk of invasions in highly interconnected aquatic systems where dispersal rates may be especially high due to human modifications.

Watercress (Nasturtium officinale) has spread widely from Europe and commonly occurs in Oklahoma (USA) springs. Watercress is usually an emergent plant and affects water flow patterns and may provide habitat for biota. Although watercress is not considered an invasive species, its impacts in springs have not been reported. With a goal to describe possible impacts of watercress in springs, 14 karst-associated springs (12 with watercress) were surveyed for sediment characteristics, macroinvertebrates, and diatoms in July 2021. The effects of watercress were evident. Sediment particle size was unaffected by the presence of watercress but sediment organic matter was higher under watercress beds than outside of beds. Although there was no difference in total benthic macroinvertebrate density or richness, higher organic matter was associated with slightly higher abundances of detritivorous and predatory macroinvertebrates (SIMPER). Submerged portions of watercress had significantly much lower diatom density than other spring substrates, with diatom composition similar to other plants but different from that of rocks. Self-shading or possible allelopathy may cause the low diatom density. The significantly lower macroinvertebrate density within watercress mats relative to that of other plants may result from a reduced food source because the plant’s low diatom density. Only predatory damselflies were more common in watercress than in other plants, which had more abundant grazers. Although watercress can increase heterogeneity in sediments and is sometimes valued as an edible plant, watercress supports low algal and macroinvertebrate densities, such that extensive growth of watercress can have an overall negative impact on spring ecosystems.

Temporal variation in the taxonomic structure of microphytobenthos (MPB) in a riverine mangrove ecosystem was studied along the southwest coast of India. About 122 species of microphytobenthos comprising diatoms (113 species), cyanobacteria (seven species), dinoflagellate (one species), and euglenophyte (one species) were observed, in which pennate diatoms dominated by 92%. Major subclasses of diatoms identified were Bacillariophycidae, Fragilariophycidae, Thalassiosirophycidae, Melosirophycidae, and Coscinodiscophycidae. Average levels of fluvial nutrients estimated in the porewater were NO₃–N (28 ± 19.7 µmol L⁻¹), PO₄–P (3.77 ± 4.6 µmol L⁻¹), and SiO₄–Si (33.12 ± 27.2 µmol L⁻¹). The colonization and persistence of dense cyanobacterial mats during monsoon resulted in less abundance and diversity of diatoms than in other seasons. The numerical abundance of MPB was at its maximum during July (monsoon season) due to the dense cyanobacterial mat formed by Oscillatoria princeps. MPB diversity was at its maximum during MON (H´- 3.2), followed by POM (H´- 3.08) and lowest during PRM (H´- 2.23). The statistically significant seasonal variations in the diversity of MPB were noticed during the study period (ANOVA F value 8.120; df 2; p value < 0.05). The present study identifies sediment temperature and porewater salinity (freshwater preference) along with rainfall, sediment pH and C:N ratio as the major governing factors in the benthic microalgal mat formation of the study area.

Lakes are among the main sources of protein and livelihood to huge communities of rural people, and some of them house endemic fish species. The livelihood of about 200,000 rural people depends on Lake Manyara resources which also houses a population of the endemic and endangered fish, the Manyara Tilapia (Oreochromis amphimelas). Despite this importance, fishery in the lake is nearly under open access and it is not known how this has affected fish stocks. The lake is also under strong influence from overgrazing and poor farming practices in the highlands and adjacent areas which are polluting the lake. However, it is also not known how this has affected the growth and survival of fish in the lake. We assessed the impact of artisanal fishing and anthropogenic pollution on the stock of Manyara Tilapia and Nile Tilapia in Lake Manyara. We found that fish stocks in the lake are under heavy fishing pressure. Nearly all harvested Nile Tilapia were immature, and the majority of Manyara Tilapia were first time spawners caught at the length of their first maturity. This prevented the fishes from spawning at least once in their lifetime. Anthropogenic pollution has also hypereutrophied the lake and degraded the ecological quality for growth of Tilapia fish. Therefore, urgent site-specific mitigation measures and conservation actions are required to safeguard community livelihood and continued existence of the endangered Manyara Tilapia.

Dunaliella salina (microalgae), Fabrea salina (ciliate) and Artemia salina (crustacean) are the most abundant halophile Eukaryote organisms present in solar salterns at Sfax (Tunisia) when salinity is up to 150 PSU. We analysed the predator/prey relationship between the three organisms in laboratory conditions. In this study, aquatic food web relations were analysed by studying the grazing and energy transfer rates. In solar saltern, the dynamic population of Dunaliella displays a negative relationship with that of Fabrea and Artemia. Grazing experiments confirm that Fabrea and Artemia exercise a top-down control on Dunaliella populations. While Artemia and Fabrea occupy the same trophic level in food chain, the grazing rate of Fabrea on Dunaliella is strongly high reaching 0.85 × 10⁶ ± 0.05 cells mL⁻¹ day⁻¹. The fatty acids (FAs) appeared as good tracers to define the energy transfer along the food chain studied. Effectively, the FA composition of consumers appeared correlated to the FA of their prey. In parallel, the saturated fatty acids (SFAs) content decreased according to the trophic levels, and the opposite was observed for monounsaturated fatty acids (MUFAs). Therefore, palmitic acid (C16:0) showed trends that rendered it useful for tracing trophic transfer to consumers (Artemia). The polyunsaturated fatty acid (PUFA) and especially linoleic acid (C18:2) and linolenic acid (C18:3) were able to be traced across the transfer to Fabrea. This study increased our knowledge of the energy transfer between the major halophile organisms living in the solar salterns at Sfax (Tunisia). We proposed also that the fatty acids are used in future investigations to understand the predator/prey ecological relationship in marine eukaryote organisms.