Aquatic Sciences最新文献

Zooplankton and associated environmental parameters were collected in January and May 2018 to investigate the contrasting taxonomic and functional responses of the zooplankton community to environmental changes in the Strait of Hormuz and its surrounding waters in the Persian Gulf and the Gulf of Oman. Sampling was conducted along three transects perpendicular to the coastline, each transect comprising four stations. Principal component analysis identified temperature, salinity, and dissolved oxygen (DO) as key environmental drivers. Oceanographic conditions were more stable in January, whereas there was pronounced thermal and salinity stratification in May. A total of 72 zooplankton taxa were identified. Community composition differed significantly between months, with Sagitta sp. and Temora sp. dominating in January, and Oikopleura spp. and Penilia sp. being the most abundant taxa in May. Each species was assigned functional traits using six categories based on body length, reproductive mode, feeding strategy, diel vertical migration, gelatinous factor, and trophic group. Species that produce water currents to capture food—referred to as current feeders—were the dominant feeding type during the study. Broadcast spawners, which release their gametes into the water column, were more prevalent in May, whereas sac spawners, which retain their eggs attached to the female’s body, were more abundant in January. Analysis using permutational multivariate analysis of variance (PERMANOVA) revealed significant spatial differences in both taxonomic composition and trait-based structure. The relationship between habitat descriptors and zooplankton functional traits, analyzed using a combined approach of RLQ and fourth-corner analyses, revealed that salinity, temperature, and DO influenced trait composition.

Environmental DNA (eDNA) is a valuable tool for detecting aquatic species, but the efficiency of eDNA recovery is influenced by concentration methods. This study investigated the effectiveness of different eDNA concentration methods to optimise detection protocols for aquatic species in freshwater samples. Using water samples collected from controlled experimental systems, we tested ten types of filters, three pore sizes and an ethanol precipitation protocol to recover eDNA particles. Two invasive aquatic species, the benthic golden mussel (Limnoperna fortunei) and the limnetic Nile tilapia (Oreochromis niloticus), were used as biological models. Differences in DNA concentration were observed among samples from the two tested species. For Nile tilapia, filter materials showed uniform performance without significant differences, whereas cellulose nitrate filters yielded the highest eDNA concentrations for golden mussels. Ethanol precipitation was the least effective method for both species. Filtration time analysis revealed that polytetrafluoroethylene (PTFE) filters had the slowest filtration rates, whereas glass fibre filters had the fastest. A significant negative correlation was observed between filter pore size and eDNA retention for both species, with 0.4-μm and 0.2-μm pore sizes being more effective. These findings highlight the importance of selecting adequate filters and pore sizes to optimise eDNA capture efficiency. This study contributes to standardised protocols, enhancing precision and reproducibility in ecological assessments.

The southwestern Balkans have an exceptional level of freshwater fish endemism, with the Ionian freshwater ecoregion recognized as a key biodiversity hotspot there. In this study, we examined how river Fish Assemblage Types (FATs), identified from 175 electrofished river sampling sites, shape the spatial patterns of β-diversity in this ecoregion. Initially, we used bipartite networks to identify areas of distinct fish assemblages. Subsequently, we used the Ružička index to estimate total β-diversity, decomposing it into the components of replacement and abundance differences. Local (LCBD) and species (SCBD) contributions to β-diversity were calculated. By applying generalized dissimilarity models and generalized additive models, we reveal which regional or local variables shape β-diversity and influence species important to the β–diversity patterns. Six distinct FATs were identified, each exhibiting high levels of β-diversity, but differing in the β-diversity component that contributed the most to the overall dissimilarity pattern. Geographic distance and temperature had the greatest influence on β-diversity, reflecting long-term geographical isolation or past connectivity among river basins, and a longitudinal river zonation pattern. The results provide insights into fish community and biophysical nuances that should be considered when building conservation strategies for this ecoregion. In the headwaters where rheophilic cold water species dominate, conservation actions should focus on protecting specific habitats and cool water conditions. In the middle and lowland areas, mixed methods should address both spatial replacement (endemic species) and abundance differences (widespread species). The findings of this study contribute to the identification of ecologically important water bodies and support conservation efforts by enhancing our understanding of spatial diversity patterns.

Florida manatees (Trichechus manatus latirostris) may affect nutrient cycling through excretion or sediment bioturbation when they migrate from coastal environments to spring-fed ecosystems in the winter for thermal refugia. The combination of exceedingly clear water and migratory manatees associated with these spring-fed ecosystems also attract tourists, which may alter nutrient cycling via bioturbation. We assessed the effects of manatees and humans on benthic and water column nutrient uptake rates (NO₃⁻, NH₄⁺, PO₄³⁻) at Three Sisters Springs and effects of humans alone on uptake rates at Hunters Springs, two spring-fed ecosystems in Kings Bay, FL during October, January, and April. Manatees congregate in high abundances at Three Sisters Springs from November to March when they migrate into Kings Bay, but manatee abundances remain low at Hunters Springs year-round. Manatees are largely absent from Kings Bay by mid-March, but human presence is high at both sites beginning in March due to warming temperatures. We found three overall patterns: (1) large decreases in chl a and nutrient uptake were evident when manatees were present, likely from bioturbation and subsequent sedimentation; (2) humans alone decreased water column nutrient uptake rates and benthic chl a, but changes to benthic nutrient uptake were only evident at one site; (3) the water column could account for a large proportion of nutrient uptake despite having low chl a and suspended material. These results suggest that manatees and humans may function similarly by decreasing benthic chl a, but sediment bioturbation effects of manatees coupled with humans were greater than the effects of humans alone.

Anthropogenic activities in catchments, such as urban and agricultural land use, negatively impact the biogeochemical cycles of carbon, nitrogen and phosphorus in streams by increasing concentrations of these nutrients and altering the composition of dissolved organic matter (DOM). In tropical climates with high temperatures and intense precipitation, streams are particularly vulnerable to high loading from the catchment. The combination of high nutrient loading from the catchment and high processing rates at high temperatures can lead to even higher concentrations and more severe impacts on biogeochemical cycles. However, studies linking human activity to changes in nutrient and DOM composition, and the resulting impacts on stream functions, are still scarce in tropical streams. This study addressed this gap by examining the relationships between land use and water column chromophoric DOM (CDOM), nitrogen and phosphorus across seasons in an Afrotropical watershed. In addition, the effects of nutrient enrichment and changes in DOM composition on stream metabolism were investigated. The results showed that urban land use had the most substantial influence on nutrient concentrations and DOM composition in the studied streams. Streams with a high proportion of urban land use in their riparian zone had high nutrient concentrations and a pronounced autochthonous DOM signal. In contrast, streams with more forest cover in their riparian zone had lower nutrient concentrations and a more allochthonous DOM signal in their water column. Stream metabolism increased with nutrient concentrations and autochthonous organic matter contribution, and these changes were more pronounced in the dry season, pointing to the combined effects of high nutrient loading and processing rates on carbon biogeochemistry. These results confirm that changes in nutrient loading and organic matter composition caused by human activities and seasonal changes will likely impact river ecosystem processes, with implications for food webs and tropical biogeochemical cycles.

In 70 lentic systems across Türkiye, phytoplankton distribution, composition, biovolume, species richness (both alpha and gamma diversity), and Shannon diversity index were determined and environmental variables were measured using samples collected in the spring, summer, and fall of 2017–2019 to determine the impact of altitude (ALT) on phytoplankton assemblages. The lentic systems were categorized into three ALT groups: group I (< 800 m a.s.l.), group II (800–1600 m a.s.l.), and group III (> 1600 m a.s.l.). Changes in species composition and dominant species were observed with increasing ALT, with certain species showing a preference for higher ALT and exhibiting higher ALT optima values. The species composition of group III was markedly different from the other groups. Phytoplankton biovolume, species richness (alpha diversity), and the Shannon diversity index did not show a correlation with ALT. However, group III lentic systems exhibited the lowest biovolume values, while group I systems had the lowest species richness. The total species richness (gamma diversity) of Cryptista (Cryptophytes) and the dominance of flagellate species increased with ALT. While phytoplankton trophic index (PTI) indicated all the systems had only moderate and poor ecological qualities, trophic state index (TSI) did not detect any high-quality lentic systems in group III. In contrast, the PHYTO-TR index demonstrated that group III exhibited a higher proportion of lentic systems classified as good and high quality, providing a more accurate evaluation of the ecological quality of lentic systems. ALT indirectly influenced habitat diversity and the degree of human impact, thereby affecting some parameters, such as temperature, electrical conductivity, alkalinity, pH, total nitrogen, and total phosphorus. Consequently, these parameters were significant determinants of phytoplankton distribution, composition, biovolume, species richness (alpha and gamma diversity), and the ecological quality of these lentic systems.

The effect of estrogenic pollutants on wildlife is a growing concern. Synthetic estrogen, 17α-ethynylestradiol (EE2), is a potent estrogenic pollutant used in birth control that originates in wastewater and ends up in receiving surface waters where it can accumulate in sediments and aquatic organisms. EE2 can reduce growth, gametogenesis, semen quality, fecundity, and embryo viability and promote feminization and skewed sex ratios among different aquatic organisms. Most research on EE2 impacting aquatic life has focused on fish, with less attention paid to invertebrates and algae. We examine the effect of environmentally relevant concentrations of EE2 (0, 1.5, 15, and 150 ng/l) on spawning in males of the aggregating anemone, Anthopleura elegantissima, and density and photosynthetic performance of its zooxanthellae symbiont, Breviolum muscatinei. Exposure to 150 ng/l EE2 significantly increased chlorophyll a content per zooxanthellae cell and photosynthetic efficiency (F_v/F_m) of Photosystem II compared to the negative control. Symbiont density was not significantly associated with EE2 concentration, whereas host clonality was significantly associated. Lastly, EE2 concentration was a significant predictor of whether anemones spawned after being induced. This is the first study to our knowledge to examine the impact of EE2 exposure on anemone spawning and zooxanthellae density and photosynthetic performance.

Streams are essential aquatic ecosystems in the Amazon. The ichthyofauna inhabiting these environments benefits from the available conditions and resources, which act as environmental filters shaping species composition. This study aims to investigate the influence of landscape, local habitat, and spatial distance on the structure of fish communities in streams in the Western Amazon. Research was conducted in the Chico Mendes and Cazumbá-Iracema Extractive Reserves, located in the southwestern part of the State of Acre. A total of 25 streams were sampled, with 15 in the Chico Mendes Extractive Reserve and 10 in the Cazumbá-Iracema Extractive Reserve. To evaluate the effects of landscape variables, local habitat, and space on species richness, we used Generalized Linear Models. To assess the influence of predictor variables on species composition, we utilized Redundancy Analysis. In total, 101species were collected across the two reserves, with 49species in the Chico Mendes Extractive Reserve and 79species in the Cazumbá-Iracema Extractive Reserve. Species richness was influenced by the percentage of forest cover, which varied between reserves, while species composition was shaped by physical habitat variables. These results indicate that environmental variables at different spatial scales are crucial for the structuring of fish assemblages in Amazonian streams. Maintaining the integrity of these environments is essential for preserving habitat characteristics, which in turn support the conservation of these assemblages within and between watersheds.

Littoral-benthic habitats can play a key role in governing whole ecosystem production within lakes. Controls of littoral-benthic production can include light, nutrients, and grazers, although studies examining production across the photic zone in deep lakes are limited. This study investigates the role of nutrient limitation and inhibition from the shallow to deep (lower limit of the photic zone) littoral-benthic habitat of lakes with varying trophic states. We use a combination of nutrient-diffusing substrata (NDS), water column nutrient data, and photosynthetically active radiation (PAR) measurements. We observed that periphyton nutrient limitation and inhibition vary with depth and habitat. Differences were primarily driven by the concentration of dissolved inorganic nitrogen (DIN) and the availability of PAR. Less DIN and more PAR favored N limitation and P inhibition, whereas more DIN and less PAR favored P limitation and N inhibition. Furthermore, we found that differences in nutrient limitation in the shallow littoral-benthic habitat may be driven more by biological factors (e.g., predator density) than by variation in physical habitat heterogeneity. Our findings reveal that periphyton nutrient responses across the littoral-benthic zone for clear lakes are context-dependent. The shifting roles of nitrogen and phosphorus across depth gradients call for a more nuanced understanding of periphyton responses in lakes with extensive photic zones. Considering the importance of littoral-benthic habitat for whole lake function, additional studies exploring the role of nutrient, light, and consumers should occur across depth for clear, deep-water lakes.