Aquatic Sciences最新文献

The white-clawed crayfish (Austropotamobius pallipes complex) is a crucial species complex in European freshwater ecosystems, but its population has faced severe declines since the 1860s due to pollution, habitat loss and fragmentation. The introduction of invasive crayfish species that carry the crayfish plague (Aphanomyces astaci), a water mold, has exacerbated this decline. The Avigliana Lakes Nature Park in Piedmont, Italy, which encompasses the Great Lake, Small Lake and Mareschi wetland, has been designated a Natura 2000 site supporting A. pallipes, particularly in the tributaries of the Small Lake. The aim of this study was to assess both the presence and distribution of A. pallipes in the study area and the physicochemical and ecological characteristics of its habitats. We also evaluated the proximity of invasive crayfish Procambarus clarkii populations to A. pallipes to further current understanding of potential health impacts and support management efforts. Macroinvertebrate monitoring was used to gauge overall ecosystem health and habitat suitability for A. pallipes. The results showed that A. pallipes was present at only two out of the six monitored sites, with no visible signs of disease. Macroinvertebrate monitoring indicated good water quality, while significant differences in pH, conductivity, and nutrient levels were found. Canonical correspondence analysis highlighted key environmental factors for A. pallipes, including conductivity, total dissolved solids, and vegetation. The lack of evidence for crayfish plague within the P. clarkii population may enable more effective management strategies and reduce potential health risks to the A. pallipes population. This study emphasises the need for ongoing monitoring and targeted management to mitigate invasive species’ impacts and conserve native crayfish populations.

Anthropogenic activities constitute a major threat to the physical and ecological integrity of freshwater ecosystems. Among the various anthropogenic impacts, alterations in land use and occupation patterns stand out as key drivers of aquatic ecosystem degradation and loss. In this context, agroforestry systems stand out among various land uses as an alternative for reducing environmental impacts. This study evaluated the integrity of streams in the Atlantic Forest under different land use types and their effects on dragonfly larval assemblages. Dragonfly larvae were collected in native forests, pastures, and cocoa cultivation areas, known locally as Cabruca (an agroforestry system in which Atlantic Forest trees are partially preserved, and cacao is planted in the understory). Our results revealed a difference in genus richness among the studied areas, with Cabruca areas showing higher richness and pasture areas exhibiting lower richness. We also observed variations in species composition, with native areas displaying a more homogeneous composition and pasture areas exhibiting a more heterogeneous composition. In addition, our results indicated that dragonfly larvae can serve as excellent indicators of sustainable cultivation areas. Although Cabruca areas represent a model of sustainable agriculture with the potential to contribute to biodiversity preservation, this study emphasizes that such areas cannot fully replace native habitats, reiterating the importance of conserving the remaining forests and their biodiversity.

Exploring the ecological responses of organisms to environmental heterogeneity reveals crucial insights into environmental filtering processes and species distribution patterns, providing a scientific foundation for wetland management and conservation efforts. Macrobenthos play a major role in wetland ecosystem, yet simultaneously, research on biodiversity patterns and their responses to ecological factors remains insufficiently comprehensive. Therefore, we systematically investigated the spatial structure patterns and driving factors of macrobenthic communities in the Yellow River tidal zone (HT) and the Dawenliu tidal zone (DT) of the Yellow River Delta (YRD) wetland using β-diversity analysis, co-occurrence network analysis, and stability analysis. Our findings demonstrate significant differences in community composition and diversity between HT and DT. The HT exhibits higher species richness, dominated by mollusks (51%) and annelids (45%), primarily explained by salinity variations. Conversely, the DT was dominated by arthropods (74%), influenced mainly by sediment sand content. Our findings indicate that environmental heterogeneity intensifies the role of environmental filtering on species distribution. Species turnover dominated biodiversity changes in HT (52%) and DT (80%), driven significantly by sediment properties. Moreover, our research found that high species nestedness enhances the complexity of co-occurrence networks, thereby strengthening the stability of macrobenthic communities. Our study highlights the significance of species coexistence mechanisms in shaping biodiversity patterns. These research findings enhance our understanding of how environmental heterogeneity regulates community composition and sustains biodiversity, underscoring the necessity for diverse conservation strategies.

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.