Aquatic Sciences最新文献

The invader density impact model proposes that the impact of an invasive species may increase or decrease linearly or nonlinearly as a function of its density. The Three Gorges Reservoir (TGR), located in the upper Yangtze River Basin, supports high fish diversity, yet non-native fish species have increasingly colonized and expanded their ranges. Pelagic carnivorous Coilia brachygnathus (Engraulidae), native to the middle and lower reaches of the Yangtze River Basin, has colonized and rapidly expanded into the TGR, whereas its density decreases with distance from the dam. Here, we used stable isotopes to investigate similarities in trophic position, niche width, and niche overlap of C. brachygnathus and eight native pelagic species between the lower and upper sections of the TGR. We predicted that in higher density, C. brachygnathus would broaden the trophic niche, while native species would narrow theirs, reducing interspecific niche overlap. We found that C. brachygnathus had a narrower trophic niche in the lower section of the TGR where its density was higher. In contrast, most native species had broader niche widths than those in the upper section where the density of C. brachygnathus was lower. Interestingly, C. brachygnathus has a higher trophic position than those of most native species examined, and the trophic positions of most native species were lower in the lower section. Higher niche overlap was observed between C. brachygnathus and native piscivorous Culter spp. (Cyprinidae) in the upper section. Our findings indicate that C. brachygnathus influences trophic niches of native species, and the density of C. brachygnathus mediates the effects. Under higher density, C. brachygnathus and native species adjust niche width and trophic positions, consequently reducing niche overlap to alleviate competition pressure.

The remineralization of terrestrial dissolved organic carbon (tDOC) plays an important role in coastal carbon and nutrient cycling, and can affect primary productivity and seawater pH. However, the fate of tDOC in the ocean remains poorly understood. Southeast Asia’s Sunda Shelf Sea receives around 10% of global tDOC input from peatland-draining rivers. Here, we performed photodegradation and long-term (2 months to 1.5 years) biodegradation experiments with samples from peatland-draining rivers and from peat tDOC-rich coastal water. We used the resulting photochemical and microbial decay rates to parameterize a 1-dimensional model simulation. This indicates that 24% and 23% of the initial tDOC entering the Sunda Shelf can be remineralized by pure photo- and pure biodegradation, respectively, after 2 years (which represents an upper limit of seawater residence time on the Sunda Shelf). We also show for the first time that the biodegradation rate of Southeast Asian peat tDOC is enhanced by prior photodegradation. Adding photo-enhanced biodegradation to our model simulation causes remineralization of an additional 16% of the initial tDOC. However, the contribution of photo-enhanced biodegradation was likely underestimated because the photo- and biodegradation steps were conducted successively in our experiments. Overall, our results suggest a notably higher contribution of photodegradation compared with other regions, owing to the combination of slow biodegradation, high solar irradiance, long water residence time on the shelf, and the photo-enhancement of the biodegradation rate. Our results are important for informing tDOC modeling studies, and highlight a need for further research on interactive photo–biodegradation of tDOC.

This study investigated the characteristics of dissolved organic matter (DOM) in the Huai River (Bengbu section) in China during wet and dry seasons. The methods included three-dimensional fluorescence spectroscopy (EEMs) combined with parallel factor analysis (PARAFAC) and self-organizing neural networks (SOM) to analyze DOM levels and composition. The results showed that the humus component (C1) of DOM was dominant in the water body, and there were significant seasonal differences. Rainfall and runoff significantly increased the input of humus organic matter in the wet season, and the fluorescence intensity and relative abundance of humic-like components (C1 and C2) were higher in the wet season than in the dry season. The concentration of plankton metabolites (protein-like component, C3) was higher in the dry season, reflecting increased microbial activity in the low water flow environment. Principal component analysis (PCA) revealed the dominant role of plankton metabolism and microbial activity on organic matter distribution, and the contribution of terrestrial organic matter to humus components through soil runoff. In summary, the seasonal variations in the Huai River water DOM were driven by both natural processes and human activities.

Marine caves, often overlooked hotspots of biodiversity, provide unique habitats for specialized species. Located on the Mediterranean coast, Rosh HaNiqra is a midlittoral cave renowned for its vibrant epilithic algal community. In the study reported here, we explored the light environment, algal composition, and ecological dynamics of the Rosh HaNiqra cave. Light measurements revealed that illumination in the cave ranged from 0.5 to 2.5% of the sunlight recorded at the mouth of the cave, with variations across seasons and times of day, peaking during summer, and an increase in red wavelengths towards sunset. Biodiversity assessments, including rbcL gene sequencing studies, identified Hildenbrandia rubra (red alga) as the principal alga, together with Blidingia dawsonii (green alga), cyanobacteria, and mosses, forming a “Balcony of Colors”. The cave's conditions were found to be most favorable for H. rubra in the autumn through early winter, when the cave provides a critical refuge where this alga thrives in stable, low-light conditions, demonstrating high photosynthetic efficiency even in reduced light. Our study of algal distribution showed seasonal fluctuations, with peak coverage during warmer months and a decline in winter. This study not only deepens our understanding of Rosh HaNiqra's cave ecosystem but also provides an essential baseline for future ecological and conservation research in marine caves.

Habitat connectivity is a key spatial attribute influencing biodiversity patterns in river networks by controlling the extent of dispersal in stream metacommunities. Large lake basins within river networks may hinder upstream dispersal of benthic macroinvertebrates to inlet streams, but the effects on biodiversity patterns have not been explicitly explored. We studied the effects of lake-induced variation in connectivity and environmental factors on alpha and beta diversity, and the active aerial dispersal (AAD) trait of stream macroinvertebrate species. Our analysis included data from 19 river-connected (RC) tributary streams and 17 more isolated lake-connected (LC) tributaries, with sampling conducted within approximately 1.5 km upstream of the stream-river confluence or stream-lake transition zone. Generalized additive models (GAM) and partial effects plots were used to assess the associations and the relative importance of connectivity and environmental factors on the community attributes. Species richness and the relative abundance of AAD were positively associated with the connectivity of the sampling site but species richness was also related to environmental factors, whereas the rarefied species richness and exponential of Shannon diversity were solely related to environmental variability. Beta diversity was negatively associated with connectivity but also to variation in pH. The results suggest that environmental factors largely control macroinvertebrate community structure in RC and LC streams, but the connectivity of the site might influence stream macroinvertebrate metacommunity patterns in river networks by enhancing dispersal and the occurrence of rare species. However, large lake basins seem to have a limited barrier effect on stream macroinvertebrate metacommunities, though further research is needed to fully understand this influence.

Metacommunity studies have been gaining in importance in recent decades due to their relevance when interpreting community dynamics. The elements of metacommunity structure (EMS), i.e. coherence, turnover and boundary clumping, are used to assess the assembly of metacommunities. In the present study we analysed the EMS of the Guadiana Hydrographic Demarcation, a prominant seasonal basin located in the southern Iberian Peninsula characterised by a Mediterranean climate, with dry reaches and disconnected pools frequent in streams during the summer. We studied the EMS of the four different taxocoenoses used to assess the ecological status of streams and rivers according to the European Water Framework Directive (diatoms, macrophytes, macroinvertebrates and fishes), both independently of each other and taken together. These analyses were carried out using three different approaches: (1) using a gradient from reciprocal averaging analysis; (2) following a geographical gradient; and (3) following an environmental gradient. We found that the four groups of organisms analysed had either a Clementsian metacommunity structure or a similar structure. When all groups were considered together, the structure of the metacommunity was Clementsian or quasi-Clementsian. Thus, in the framework of the current global change scenario, communities in this basin may be vulnerable to increasing isolation due to more frequent and larger dry periods; consequently, management measures should be considered.

Boreal forests are rich in small rivers, whose primary productivity is limited by tree shading. The diet of benthivorous fish in such rivers is based on a mixture of autochthonous and allochthonous organic matter. Algae produce and aquatic invertebrates accumulate polyunsaturated fatty acids (PUFA) of the n-3 family (n-3 PUFA), including eicosapentaenoic acid, a long-chain PUFA. Terrestrial organisms are poor in these essential nutrients but are rich in n-6 PUFA. Here, we aimed to assess fluxes of biomass and n-3 and n-6 PUFA between aquatic and terrestrial ecosystems of the shaded Krutaya Kacha River. The production of benthic macroinvertebrates in the river was 11.7 mg dry weight (DW) m⁻² day⁻¹, while the export of aquatic insect biomass was 4.28 mg (DW) m⁻² day⁻¹. The import of invertebrate biomass into the river was 56.2 mg (DW) m⁻² day⁻¹, which was 1 order of magnitude higher than the export of aquatic insects and 5 times higher than the production of benthic macroinvertebrates. The import of n-3 PUFA and n-6 PUFA into the river via invertebrates was 0.550 and 0.909 mg (DW) m⁻² day⁻¹, respectively, while the export of these fatty acid groups from the river with emergent insects was lower by factors of 6.7 and 20.7, respectively. Thus, in such rivers, stream consumers feeding on aquatic and terrestrial resources receive food of biochemically differing quality: the amounts of food being equal, fish consuming terrestrial invertebrates receive less n-3 PUFA but more n-6 PUFA than fish consuming aquatic invertebrates. The predominance of allochthonous food towards the base of stream food webs can have cascading effects, which result in lower nutritional quality at higher trophic levels, as previously observed in fish within the Krutaya Kacha River.

Environmental characteristics significantly influence the distribution of fish communities in aquatic ecosystems. This study examined the relationship between fish community structure and ecological characteristics in the Dhansiri River, a tropical river within the Eastern Himalayan ecoregion. Sampling was conducted across three seasons (monsoon, premonsoon, and postmonsoon) at four stations representative of the whole river stretch. The highest number of species was recorded along the upper stretch S1 (54), followed by S2 (45), S3 (41), and S4 (37). Seasonally, the number of species peaked during monsoon (64), decreased in postmonsoon (59), and was lowest in premonsoon (54). The Shannon diversity index (H′) ranged from 3.327 to 3.750, with higher values upstream and gradually declining downstream. Species diversity was lowest at S4, likely owing to poor environmental conditions and high anthropogenic pressure. Cyprinids emerged as the most dominant fish group, with relative family abundance varying from 0% to 5.63%. Nonmetric dimensional scaling indicated a distinct separation of S4 from S1, S2, and S3. Analysis of water quality revealed a pristine nature at S1, with gradual deterioration downstream. Significant relationships were identified between most water quality variables and fish community structure. Principal component analysis showed that pH (20.96%), total alkalinity (13.80%), specific conductivity (9.92%), nitrite (NO₂; 12.19%), and total dissolved solids (TDS; 6.22%) contributed significantly to the first principal component (Dim1), while nitrate (NO₃; 53.43%) and water temperature (6.05%) influenced the second principal component (Dim2). Biota and/or environment matching (BIO-ENV) analysis reflected that ammonia (NH₃), NO₃, carbon dioxide (CO₂), TDS, total alkalinity, pH, specific conductivity, dissolved oxygen (DO), and water temperature significantly correlated with fish abundance and community composition. This study provides critical insights into the role of environmental parameters in shaping the fish community structure in a less-explored tropical river of the Eastern Himalayas and offers valuable information for the sustainable management of riverine fish diversity.

Artificial light at night (ALAN) is a widespread, human-induced alteration of the landscape that affects insect dispersal and potentially contributes to insect decline. We used an experimental area with streetlights installed adjacent to an agricultural drainage ditch to experimentally assess the abundance and diversity of emerging and flying aquatic Diptera over a period of six months in summer and autumn. Emergence was two-fold lower in the lit site, while flying adults were eight-fold more abundant at traps under lights. Results were taxon- and sex-specific. Males of nine taxa were less abundant in lit emergence traps, and females of most taxa were more abundant in lit air-eclector traps than in controls. We developed an empirical model based on emergence and capture rates and used this model to estimate that the majority of the 54 flying Diptera taxa we identified were attracted to light from the adjacent water body, and that a few taxa were attracted from a distance of up to 1800 m. This work provides evidence that artificial light in riparian areas can reduce emergence in aquatic Diptera and hinder dispersal, with effects that vary depending on the taxon. Because many riparian predators rely on adult aquatic insects as prey, these changes can cascade across aquatic-terrestrial ecosystem boundaries. Given the large number of streetlights that are installed along freshwater shorelines, the observed effects are likely to be of relevance to freshwater bodies around the globe.