Hydrobiologia最新文献

Leaf litter breakdown is a critical process in streams, as it plays a significant role in influencing food webs and biogeochemical cycles. Highland grasslands are often understudied landscapes, yet they are an excellent model system for evaluating how natural differences in riparian forest cover can influence litter breakdown in streams. We experimentally examined the effects of the presence and absence of riparian forest on temporal leaf litter breakdown and the associated biota in highland grassland streams. The 3-year experiment examined leaf litter breakdown in three stream reaches with riparian forest and three without. The results indicate that temperature could potentially mediate the temporal dynamics of leaf litter breakdown (mainly fine mesh) and the associated biota in highland grassland streams. No differences were found in leaf breakdown between stream reach types, but there was evidence of an increase in invertebrate density. Finally, leaf litter breakdown in the highland grasslands was more affected by annual variation than riparian forest presence, suggesting a context-dependent relationship.

Ecological speciation, driven by divergent selection across varying environments, is crucial for the evolution of biodiversity. To comprehend this phenomenon fully, investigating ongoing speciation events is imperative. Telmatochromis temporalis, a herbivorous cichlid endemic to Lake Tanganyika, recently revealed the existence of a slender morph inhabiting deep waters. Despite genetic similarity, it is reproductively isolated from the parapatric population of the normal morph inhabiting shallow waters. This study examined substrate features and life history traits to propose a mechanism that maintains the parapatric distribution, which likely contributes to reproductive isolation. The normal morph displayed a preference for natural shelters between rocks and invested significant energy on reproduction, likely well-adapted to shallow waters abundant in natural shelters and food resources. In contrast, the slender morph seemed to construct nests beneath rocks tailored to its body size and exhibited energy-saving reproduction, likely suited to deep waters with scarce natural shelters and food resources. These adaptive differences are likely responsible for parapatric distribution. Additionally, I discussed the potential for the slender morph and another morph, the dwarf morph, to have evolved in parallel from the normal morph through divergent natural selection, depending on the environmental challenges faced by the normal morph.

Understanding environmental features that impact population structure in marine systems is fundamental for sustainable fisheries management. In sardines and herrings, temperature is usually indicated as an important attribute in recruitment. Here, we investigate the hypothesis of additional structuring along the Brazilian coast in the scaled sardine Harengula sp. and possibility of using the highly variable mitochondrial control region as a molecular marker along continuous studies. We sequenced the mitochondrial control region of 152 individuals of Harengula sp. from 10 locations along the Brazilian coast and the archipelagoes of Fernando de Noronha (FNO, oceanic) and Abrolhos (ABR, continental) in the western South Atlantic. Analyses of molecular variance and haplotype network indicate that Harengula sp. is structured in three populations: one in FNO, isolated from the mainland by depth; and two in the Brazilian coast, mainly separated by temperature. Considering that FNO is a marine protected area and that sardines from this archipelago form a stock separated from the coast, their fisheries should be managed separately by participative cooperation among environmental agencies and local community. Additionally, it indicates that the mtDNA control region can be used in a long-term phylogeographic study of Harengula sp. as samples from other localities are obtained.

Sustainable development assessments in hydrographic sub-basins are powerful tools used to guide stakeholders. However, there remains a gap in incorporating new indicators (e.g., biodiversity indicators) into sustainability indexes, which have generally underestimated the environmental dimension. We propose an update to these indexes by incorporating biodiversity data on hydrographic sub-basins. Our goal was to introduce a new ecological sustainability index for hydrographic sub-basins (ESI-sb) that utilizes aquatic ecological indicators. We selected 16 indicators and aggregated them into four sustainability dimensions: economic, social, eco-environmental and negative environmental. We used a multi-criteria analysis based on the analysis hierarchy process (AHP) method to catch stakeholders' importance level of each indicator. The ESI-sb was calculated using the weighted average between the sub-indexes that represent the dimensions. Finally, we applied Gi* statistics to identify the ecological sustainability hotspots and coldspots regions, and the results showed in the Serra do Mar region, the southern region, and the Federal District had high ecological sustainability values; meanwhile, the hydrographic sub-basins that formed the coldspot clusters were located in the western region of the Upper Paraná River basin. The incorporation of aquatic biodiversity data into the index represents an innovation in sustainability indexes recently proposed to hydrographic sub-basins.

Graphical abstract

The pumpkinseed Lepomis gibbosus (Linnaeus, 1758) is a small centrarchid fish species from North America that has invaded most European basins, with pronounced expected impacts. Analyses of pumpkinseed diet in its invasive range using gut content analysis (GCA) show macrozoobenthos as the most common dietary item, suggesting a competitive effect on native fish communities. Our study uses a combination of GCA and stable isotope analysis (SIA) to document pumpkinseed diet at two sites in its invaded range and relates pumpkinseed diet preferences with parasitic load. SIA revealed juvenile fish as a major prey item at one of the sites (63 and 50% of the diet of small and the large fish), while GCA showed pumpkinseed preying mostly on macroinvertebrates (chironomids, gastropods, Ephemeroptera, and Zygoptera larvae) at both sites. While infrequent infection by trophically transmitted parasitic nematodes could be related to low consumption of zooplankton, substantial infection by metacercariae of Posthodiplostomum centrarchi Hoffman1958 appears to reflect relatively high consumption rates of its intermediate host, physid snails. Using SIA allowed to demonstrate that pumpkinseed feeding in its non-native range can be based on piscivory, emphasising the need for combining multiple methods when studying the impact of non-native species on food webs.

To date, seasonal dynamics of the denitrifying bacterial community in floodplain lakes is unknown. Here, we investigated the alpha diversity, abundance and composition of the sediment nirS-type denitrifying bacteria in Poyang Lake during the wet, mid-dry and dry seasons using Illumina MiSeq sequencing and quantitative polymerase chain reaction assay. The results showed that only a small part of the total operational taxonomic units (OTUs) were shared by the three seasons. OTU richness, Chao richness estimator and Shannon index exhibited higher values in the wet season than in the dry season. Some regular patterns of variation in the composition of the nirS-type denitrifying community at three classification levels (phylum, class and genus) were found among seasons. Community structures of nirS-type denitrifying bacteria were significantly different across seasons. In addition, the abundance of nirS gene showed no seasonal pattern. Total nitrogen, total phosphorous and pH were the most significant factors elucidating the compositional variation of the nirS-type denitrifying community. This study provided a new evidence for the ecological effects of seasonal water level fluctuations and improved our understanding of the nitrogen removal processes in floodplain lakes.

Groundwater-fed helocrene springs constitute hydrologically heterogeneous environment, vulnerable to human and climate-induced changes. Using quantitative samples of clitellate assemblages, we investigated whether hydrologically stable nearby streams can serve as refugia for species inhabiting helocrenes, prone to seasonal desiccation. As water conductivity constitutes the main environmental gradient of helocrene springs, we categorized them as low or high-conductivity sites and compared their assemblage diversity. We hypothesized that the spring–stream association can change along this gradient, expecting assemblage homogenization is promoted by high tufa precipitation, creating differences with tufa-free nearby streams. Contrary to this prediction, the assemblages of low-conductivity helocrenes were more homogeneous, being also significantly different from those in the streams. This result is related to the apparently more favorable tufa-free substrate at low-conductivity fens, as shown by the high taxa richness and the number of indicator species. Contrary to the other invertebrates, the clitellates differed between spring fens and streams only under acidic conditions. It seems that small adjacent streams can only serve as potential refugia for spring fen biota at sites with high conductivity, while at sites with low conductivity, clitellate assemblages differ more from those in adjacent streams and thus are more susceptible to disturbance.

The wide-ranging photic conditions found across aquatic habitats may act as selective pressures that potentially drive the rapid evolution and diversity of the visual system in teleost fish. Teleost fish fine-tune their visual sensitivities by regulating the two components of visual pigments, the opsin protein and the chromophore. Compared with opsin protein variation, chromophore usage across photic habitats has received little attention. The Nicaraguan Midas cichlid species complex, Amphilophus cf citrinellus [Günther 1864], has independently colonized seven isolated crater lakes with different photic conditions, resulting in several recent adaptive radiations. Here, we investigate variation in cyp27c1, the main enzyme modulating chromophore exchange. We measured cyp27c1 expression in photic environments in the wild, its genetic component in laboratory-reared fish, and its response to different light conditions during development. We found that photic environments significantly predict variation in cyp27c1 expression in wild populations and that this variation seems to be genetically assimilated in two populations. Furthermore, light-induced cyp27c1 expression exhibited genotype-by-environment interactions in our manipulative experiments. Overall, within-lake variation in cyp27c1 expression was higher and inversely related to variation in opsin gene expression along the photic gradient, emphasizing the key role of cyp27c1 in the visual ecology of cichlid fish.

Biological invasions represent a critical global challenge, profoundly impacting ecosystems and driving environmental change. While the distribution of invasive animal or plant species has received considerable attention, our understanding of the global prevalence of invasive algae and cyanobacteria in continental freshwater ecosystems remains limited. With the aim of studying how much freshwater algae and cyanobacteria are being detected as invaders, we conducted a comprehensive bibliometric analysis. It revealed 72 reported species as invasive, with R. raciborskii, D. geminata, and C. furcoides emerging as principal ones. Only 52% of the reports quantified or analyzed environmental impacts. Among the documented impacts and environmental alterations, changes in phytoplankton structure and diversity were the most frequently reported, followed by toxin production, particularly associated with invasive cyanobacteria species. Geographically, there is a noticeable concentration of reports, with Africa and Asia being underrepresented. Meanwhile, the Czech Republic and Poland emerge as leaders in the number of species classified as invaders. This geographical bias suggests a significant gap in our understanding of the true distribution of invasive freshwater algae and cyanobacteria species.

In recent years, trait-based studies have gained importance as an extension of taxonomic studies to better understanding ecosystem processes. However, these studies are still very limited in Mediterranean freshwaters. The aim of the study was to link functional groups with environmental factors and ecosystem processes for zooplankton in the Lake Iznik, which is an alkaline lake in Türkiye. Morphological, physiological and behavioural categories have been selected as response traits. Physical and chemical variables and trophic state are important predictors of functional traits. A total of 26 zooplankton taxa belonging to four taxonomic groups were classified into five functional groups according to functional traits. It was found that functional groups were significantly affected by seasonally changing environmental conditions, but not by depth. The main predictor of zooplankton functional groups was electrical conductivity. As a result of the alkaline conditions and the deterioration of the trophic state of the lake (meso ~ to eutrophy), the low taxonomic richness, dominance of the microphagous feeding type and small-bodied taxa indicate ecosystem degradation leading to functional depletion (homogenisation). The results showed that temporal variations of environmental variables can affect zooplankton functional groups and that trait-based zooplankton studies will enable a better understanding of ecosystem processes in deep alkaline lakes.