International Review of Hydrobiology最新文献

Hydrodynamic processes can lead to the accumulation and/or dispersal of water column constituents, including sediment, phytoplankton, and particulate detritus. Using a combination of field observations and stable isotope tracing tools, we identified how hydrodynamic processes influenced physical habitat, pelagic communities, and food web structure in a freshwater tidal system. The pelagic habitat of a terminal channel differed spatially, likely aligning with differences in hydrodynamics. Three zones that we classified by exchange with downstream habitat had distinct water quality characteristics, supported different densities of zooplankton and nekton, and exhibited disparate support from benthic and pelagic trophic pathways to pelagic consumers. Hydrodynamically driven zones and their emergent characteristics appeared sensitive to hydrology, as elevated runoff was correlated with a shift in hydrodynamic habitat and organismal distributions. The results of our study highlight the relationship between hydrodynamic processes, biological responses, and climate, and suggest that understanding the physical process can improve understanding of pelagic habitats and communities.

In theory, the phytoplankton community of freshwater ecosystems with low concentrations of dissolved inorganic nitrogen (DIN) can obtain this element by atmospheric nitrogen (N₂) fixation. This process could explain the dominance of cyanobacteria in tropical reservoirs, yet is rarely quantified in these systems. Assessing the factors related to N₂ fixation can assist in the management of cyanobacterial blooms. Our study characterized environmental factors related to N₂ fixation in Brazilian tropical reservoirs with contrasting trophic states, and defined quantitative thresholds for water chemistry and physical characteristics that stimulated N₂ fixation. We used field assays with ¹⁵N for estimating N₂ fixation rates by phytoplankton. The highest rates normalized by chlorophyll-a (maximum of 143 × 10⁻⁴ μg-N μg-Chl-a⁻¹ h⁻¹) coincided with eutrophic conditions and presence of diazotrophs. Receiver operating characteristic (ROC) analysis provided significant thresholds for water temperature (≥22°C), soluble reactive phosphorus (SRP) (≥3.0 μg-P L⁻¹), total phosphorus (TP) (≥20.5 μg-P L⁻¹), DIN:SRP (≤487) and DIN:TP (≤82) molar ratios, chlorophyll-a (≥12 μg L⁻¹), and total suspended solids (≥4 mg L⁻¹). Censored regressions confirmed that temperature, chlorophyll-a, and phosphorus were important predictors of N₂ fixation rates. In general, the N₂ fixation rates determined in this study were lower than those found for temperate reservoirs. However, the temperature threshold of 22°C or above, identified in our analysis, suggests that phytoplankton have the potential to fix N₂ throughout the year in tropical reservoirs. Our results suggested that phosphorus is the main nutrient controlling the rates of N₂ fixation when N₂-fixing cyanobacteria were present. Phosphorus abatement is, thus, crucial for managing the trophic state and controlling N₂-fixing cyanobacteria in these ecosystems.

Rock pool metacommunities are shaped by the dispersal ability of organisms, which together with environmental heterogeneity, determine whether the metacommunity is structured more by environmental or spatial factors. To understand the effect of interspecific differences in dispersal capacity on beta diversity patterns and metacommunity structure, we studied aquatic Heteroptera (an actively dispersing insect group with species exhibiting flight polymorphism) in the rock pools on three outcrops in the Western Ghats, India. We used an abundance-based gamma diversity partitioning framework to assess the percent contributions of similarity (S) and the decompositions of beta diversity-abundance difference (D) and abundance replacement (R) to community structure for two mobility groups, that is, flying and flightless species. We compared the variation in beta diversity components “D” and “R” within and between outcrops for both mobility groups. We also studied the effects of the local environment on both mobility groups using redundancy analysis. Percent contributions of “S”, “D” and “R” changed according to the mobility group, with higher nestedness (S+D) in flying species (74.2%) and higher beta diversity (R+D) in flightless species (76.3%). There was a significant variation in overall beta diversity between outcrops for the respective mobility groups, caused by abundance difference for flying species (p = .003) and by abundance replacement for flightless species (p = .003). Flying and flightless species were not associated with different environmental variables. Our study demonstrates that dispersal capacity is responsible for structuring regional diversity, with distinct sources of dissimilarity being associated with each mobility group: Abundance replacements between assemblages imposed by dispersal limitation for flightless species and abundance differences in assemblages of flying species, which might reflect the carrying capacity of the habitats.

Beavers are an exception among animals in terms of the scale of environmental transformations they achieve. This study investigated primary environmental factors influencing the occurrence of aquatic invertebrates in lowland streams inhabited by the Eurasian beaver. The study was conducted in two forest streams inhabited by beavers, and in an uninhabited stream. In streams inhabited by beavers, the study covered seven ponds. Sections with flowing water were also analysed downstream and upstream of the ponds. Benthos and water samples were collected at each site. Dissolved oxygen (DO) concentration and saturation were the only physicochemical parameters that indicated decreases in water quality in beaver ponds. The benthic communities of different beaver ponds were similar. The taxa that exerted the greatest influence on the similarity of the invertebrate fauna in the ponds were Oligochaeta and Chironomidae. Ostracods were also abundant in the ponds, whereas they were few in the flowing sections. Mayflies (Cloeon) and caddisflies belonging to the family Phryganeidae were also closely associated with the ponds. Caddisflies (Plectrocnemia and Sericostoma), mayflies (Baetis) and stoneflies (Nemourella and Leuctra) exhibited the highest correlation with DO concentrations, which is typical of flowing sections, and avoided stream fragments dammed by beavers. Bivalvia (Pisidium) were also abundant in each of the streams along the flowing sections. The highest number of taxa and greatest taxonomic diversity was observed in sections flowing below the beaver ponds. The engineering activity of beavers transformed the studied lowland streams, resulting in the development of rheophilic and stagnophilic communities of aquatic invertebrates, in free-flowing and dammed sections, respectively.

In floodplains, rotifers are among the most abundant zooplankton organisms and play an important role in ecosystem functioning. Here, we evaluated the distribution of six feeding guilds of rotifers including filter C1 (body size: <200 µm), filter C2 (body size: >200 to <600 µm), filter C3 (body size: >600 to <1000 µm), filter C4 (body size: >1000 µm), suctor, and predator for 11 years. We also analyzed the relationship between guild distribution and environmental parameters (i.e., chlorophyll-a, phosphate, nitrate, ammonia, and inorganic suspended matter). Finally, we investigated the relationship between feeding guilds heterogeneity (abundance inconsistency) and environmental heterogeneity. Sampling occurred every 3 months from 2000 to 2010 in six shallow lakes of the Upper Paraná River floodplains. Filters C1, Filter C2, and suctors were the dominant feeding guilds. Nitrate and chlorophyll-a shaped the temporal distribution of the guilds. An intermediate value of environmental heterogeneity was correlated with greater feeding guilds heterogeneity, potentially indicating that intermediate disturbance in the environmental variables may allow for greater differences in abundance distribution between rotifer guilds in shallow floodplain lakes. Our study elucidated the role of rotifers in food resource consumption, energy transfer, and competitive relationships in response to temporal environmental heterogeneity in subtropical floodplains.

Larvae of the sessile rotifer Cupelopagis vorax swim using their ciliated corona, but do not feed. Once they attach to a substratum and metamorphose into adults, they are predatory on protozoans and micrometazoans. Here we present information on ingestion time, feeding behaviour and food preference of C. vorax using protozoans and non-sessile rotifers as prey. We also tested effects of physical, chemical and biological stimuli on settlement of C. vorax larvae and, using life table experiments, determined their survivorship and fecundity on three, free-floating macrophytes. Ingestion time was shortest on prey species smaller than 100 µm. Capture/attack ratio was low for Brachionus calyciflorus, but high for Lecane inermis and Peranema sp. The ingestion/capture ratio was lowest for Oxytricha sp. and highest for Euchlanis lyra and Squatinella lamellaris. Species that swim slowly and close to the surface of hydrophytes (E. lyra, Lepadella patella, L. inermis, Peranema sp., Philodina sp. and S. lamellaris) had lower ingestion time, higher encounter/attack ratio, and were the preferred prey in selectivity experiments. Larval settlement was higher on macrophyte leaves of Ceratophyllum demersum, Lemna valdiviana and Wolffiella sp., but lower on Azolla filiculoides and Wolffia columbiana. Coverslips coated with dried extracts of macrophytes showed lower rates of larval settlement compared to live macrophytes, as well as coverslips that had been allowed to develop natural biofilms or were physically roughened. Contrary to what might be expected from the settling tests, life-table experiments showed that W. columbiana enhanced survivorship (mean lifespan and life expectancy) and rate of population increase, while animals attached to Wolffiella sp. had lower values for life history characteristics. This study adds to our understanding of the impact of Cupelopagis predation on protozoans and rotifers and the importance of substratum selection on larval settlement, adult survival, and reproductive potential after larval settlement.

The study of beta diversity patterns, as well as their underlying mechanisms, is fundamental for the understanding of community structure in aquatic ecosystems. Here, we aimed to investigate patterns of beta diversity in cladoceran, copepod, and rotifer assemblages in the Parnaíba and Poti rivers, along the urban perimeter of the city of Teresina (Piaui, Brazil) and to evaluate the effect of environmental, spatial, and temporal factors on beta diversity in the zooplankton assemblages. We used the Simplex analysis to represent the relative importance of replacement and abundance difference to beta diversity. The decomposition of beta diversity into its components was performed using the Ruzicka dissimilarity index, for abundance data. Distance-based Redundancy Analyses and variation partitioning were used to explore the relations between explanatory variables and beta diversity and its components. We found that beta diversity was high both spatially and temporally, and the abundance difference component showed greater relative importance than the replacement component. Environmental factors showed a greater contribution to the total explained variability in beta diversity and abundance difference, while replacement received most importance of temporal and spatial variables. Our study provides new insights on how environmental, spatial, and temporal factors shape beta diversity patterns in zooplankton assemblages in impacted aquatic ecosystems.

Climate change models predict a possible increase in air temperature of 2–8°C. This means that global warming will significantly affect the functioning of various types of hydrogenic ecosystems. However, the effect of the temperature increase on microbial loop function in small water bodies associated with peat ecosystems (peat pools and Sphagnum hollows) is still unknown. We used mesocosm experiments (control and treatments with a 2°C, 4°C and 8°C temperature increase) to determine the response of bacterioplankton, flagellates, testate amoebae and ciliates to simulated temperature changes, taking into account seasonal variation in the temperate climate zone. The simulated increase in climate warming increased the species richness of ciliates and the abundance of bacteria, flagellates and ciliates. In contrast, there was a decrease in the species number and abundance of testate amoebae, the top predators in peat ecosystems. The sensitivity of the various microbial groups to temperature was size-dependent; large-sized testate amoebae declined under warming. These shifts caused a decrease in the predator–prey mass ratio. An increase in the abundance of top predators promotes increased abundance of ciliates, and thus changes the architecture of the food web. At the same time, we observed the increase in phycoflora biomass thus can cancel the potential negative effects of warming on heterotrophic microbial activity. So, the potential effect of warming on the C budgets of peat pools and hollows is evident. A better understanding of what regulates microbial populations and activity in small reservoirs in peat bogs and unravelling of these fundamental mechanisms are particularly critical to more accurately predict how peat bogs will respond to climate disturbances.

Hybridization seems frequent among Cichla species (peacock bass), as studies have reported hybrids in populations within and outside their natural range (the Amazon and Orinoco river basins). Cichla kelberi and C. monoculus were introduced to the São João river (Southeast Brazil) more than 20 years ago, where they successfully colonized different environments. In this system, specimens have coloration and morphology that differ from patterns observed in their native range, indicating that the contact between C. monoculus and C. kelberi eliminated reproductive isolation, leading to introgressive hybridization. In this context, we used the LWS and dlx2 genes and the random amplified polymorphic DNA technique to characterize Cichla species in the São João river and to detect possible hybridization processes. The genetic markers identified here showed mismatches between mitochondrial and nuclear DNA in C. monoculus and C. kelberi, sampled both in the reservoir and in the estuarine stretch. Fragments of nuclear DNA from both species, as well as the presence of mitochondrial DNA from one species associated with the nuclear genome of the other, provide strong evidence of hybridization associated with bidirectional genetic introgression. Because hybrids may be more resistant, competitive, and aggressive than their parental species, these invaders may pose a significant threat to native biodiversity in this and other coastal rivers of the region.