Hydrobiologia最新文献

Cyanobacterium Microcoleus anatoxicus, isolated from a coastal stream in northern California, produces both anatoxin-a (ATX) and dihydroanatoxin-a (dhATX), responsible for dog deaths, but its environmental preferences are unknown. We tested the effect of environmentally relevant stressors, e.g., salinity enrichment and nitrogen (N) depletion, on mat formation and toxicity of M. anatoxicus during the stationary growth phase in culture. Microcoleus anatoxicus showed broad salinity tolerance and the potential to enter estuaries and produce toxins in mesohaline conditions. Maximum growth was observed in oligohaline waters with salinity of 4.6 ppt. Moderate salinity stress (up to 7.8 ppt) did not affect dhATX production significantly. In contrast, higher salinity above 9.3 ppt had a detrimental effect on cell growth and significantly suppressed dhATX production. Formation of a common polysaccharide sheath covering multiple filaments was characteristic with increased salinity and may provide protection against osmotic stress. Microcoleus anatoxicus grown for 40 days in N-depleted medium formed mats with significantly elevated dhATX and increased ATX concentrations. Phycobilisome degradation was a possible acclimation response to N-limitation, as indicated by distinctly keritomized and pale cells in these cultures. In both experiments, most of the anatoxins were extracellular, probably due to toxin leaking during the stationary growth phase.

Domestic and industrial effluents contain substantial amounts of micropollutants, such as pharmaceuticals, which may influence the balance of the phytoplankton community. A mesocosm approach was used to determine the effects of different fluoxetine concentrations (20 ng L⁻¹, 20 µg L⁻¹, and 20 mg L⁻¹) on phytoplankton community structure, biochemical composition, antioxidant response, and primary productivity. The total cell density of the phytoplankton community was in the order of control > 20 µg > 20 ng > 20 mg by the 21st day of the experiment. On day 21, the phytoplankton community had chlorophyll a content in the order of 20 mg > 20 µg > 20 ng > control, but these changes were not significant (p > 0.05). Beta diversity results revealed that fluoxetine significantly affected the community structure and dynamics of exposed phytoplankton. Reactive oxygen species, malondialdehyde and peroxidase levels were significantly altered by changes in fluoxetine concentrations. Protein content increased at 20 µg L⁻¹ and decreased at 20 ng L⁻¹ and 20 mg L⁻¹ by day 21 of the experiment. These results suggest that, even in the ng L⁻¹ range, fluoxetine could contribute to the reshaping of phytoplankton community structure and dynamics in aquatic ecosystems.

The goals of this study were to (1) document spatial and temporal variation in diatom species composition across a gradient of northern peatlands and (2) determine how underlying environmental conditions influence diatom species distribution. We sampled three peatlands (a rich, moderate, and poor fen) in interior Alaska during a growing season (May until August). A total of 100 species were observed across all fens, 17 of which were present at > 1% relative abundance, and 15 were selected as indicator species. Based on the differential response of Simpson vs. Shannon diversity metrics, we determined that fen type affected diatom assemblage composition and differences were driven by changes in the most common, but not in the least common species. Diatom species richness declined along a gradient of rich to poor fens. Conductivity, dissolved organic carbon concentration, water temperature, pH, and water depth explained 63% of the total variation in diatom assemblage structure among fens. We identified unique indicator species associated with each fen that either reinforced or expanded current understanding of their environmental thresholds. These results indicate that variation in environmental conditions in boreal fens will be reflected in diatom assemblages, which may be used to monitor biological condition in these ecosystems.

The parasitic copepod Neoergasilus japonicus (Ergasilidae), native to East Asia, has spread rapidly around the world over the past half-century and now represents a clear example of successful parasitic invader. The species is now found in western Asia, Europe, America and Africa, with aquaculture and fish introductions identified as the primary vectors of dispersal. Regional field investigations have revealed surprisingly high number of affected localities, indicating potentially wider distribution than currently recognised. Neoergasilus japonicus exhibits low host specificity, parasitising a diverse range of freshwater fishes. This study updates the global fish host species list to 132, spanning 27 families across 15 orders, with Cypriniformes identified as the most susceptible host species. Under experimental conditions in this study, however, N. japonicus avoided its natural host, topmouth gudgeon Pseudorasbora parva, suggesting a level of resistance to its native parasite. Piscivorous and demersal fish were less infected by copepods than planktivorous, benthivorous, pelagic and benthopelagic species, reflecting the ecology of both the parasite and its hosts. An ability to re-attach to another host, though limited, was confirmed under experimental conditions. Recognising the ecological impacts and potential consequences associated with the introduction of non-native parasites emphasises the need for continuous monitoring and research globally.

The objective of this study was to explore the environmental factors having the greatest influence on the distribution and abundance of epipelic diatom species in different wetlands in southern Spain. We previously defined four groups of conductivity categories: fresh (< 0.8 mS cm⁻¹), oligosaline (< 8 mS cm⁻¹), mesosaline (8–30 mS cm⁻¹) and eusaline (> 30 mS cm⁻¹). A dbRDA analysis performed on a subset of 36 of the 53 wetlands, using a total of 25 environmental variables, showed that five environmental variables (conductivity, pH, wetland area, silicates, and total suspended solids) were the best explanatory variables for the diatom assemblage, with conductivity being the main explanatory variable. Nonmetric multidimensional scaling (nMDS) analysis performed on the set of 53 wetlands revealed significant differences in diatom composition among the four conductivity groups. The key species in the eusaline group were Tryblionella pararostrata, Halamphora sp.1 and Cocconeis euglypta, whereas in the mesosaline and oligosaline group, these were Navicula veneta, Tryblionella hungarica and Nitzschia inconspicua. Finally, in the fresh group dominated Achnanthidium minutissimum, Navicula veneta and Gomphonema exilissimum. This study on epipelic diatoms can therefore contribute to the knowledge of these organisms in a European region with a high diversity of wetland typologies.

Anthropic structures have been deployed in aquatic environments for the most variable purposes. Here, we review the use of artificial aquatic habitats (AAHs) worldwide through a systematic and comprehensive search of peer-reviewed literature. We aimed to synthesize the knowledge on the subject, identify gaps, and propose new perspectives for future research. In total, 460 peer-reviewed papers from 1972 to mid-2016 were included in our systematic review. Field studies carried out in marine temperate environments were predominant, whereas fewer efforts have been made in marine tropical and freshwater ecosystems. Experimental habitats made of concrete were the most common artificial structures. Visual census was the most used sampling method, and there was a dominance of short-term (< 12 months) and shallow waters (< 5 m depth) studies. Fish was the most studied group (18%), whereas tunicates encompassed the large proportion of non-native species associated with AAHs (32.9%). Although idealized for the promotion of biodiversity, AAHs have been serving as stepping stones for non-native invasive species, facilitating biotic homogenization by increasing the connectivity of hard-bottom systems. The scarcity of studies in coastal tropical and freshwater ecosystems, as well as the efforts with reduced temporal scales and restricted depths, calls for future research to better understand the role of artificial habitats, especially in climate change scenarios. In this sense, we provide a conceptual framework exploring major issues regarding AAHs, including biodiversity status, ecosystem services, and climate change, in order to guide future research and assist conservation measures.

Freshwater ecosystems have been severely disturbed in recent years. However, our understanding of the ecosystem-level changes within freshwater food webs under complex disturbances is still limited. To address this knowledge gap, we took Dongting Lake as a case study, which has undergone significant environmental changes. We established Ecopath models for Dongting Lake in 1997, 2013, and 2021, and validated them using stable isotope-determined trophic levels. Our focus was on describing the structure and maturity of the ecosystem, identifying key species, and quantifying energy flows. The verification result showed that the models were acceptable. The model outputs revealed a significant decline in the average energy transfer efficiency of Dongting Lake. The food web maturity of Dongting Lake decreased and subsequently increased in these three representative periods. Simultaneously, the food web structure was successively simplified over time. Moreover, the identification of keystone species revealed the significance of Zooplankton, Other fish, Silurus asotus, and Molluscs within the ecosystem. Overall, our results offer a scientific underpinning for the effective management and conservation of freshwater ecosystems.