Hydrobiologia最新文献

The study of winter in temperate, ice-covered lakes has largely been neglected, creating a major gap in our understanding of annual phytoplankton cycles. We assessed patterns in biovolumes of Asterionella, cf. Synedra, Urosolenia, and total phytoplankton at three depths during the winter of 2014/2015 as estimated using images from an Imaging FlowCytobot (IFCB) moored in Lac (Lake) Montjoie, Quebec (Canada). Even though the use of the IFCB under-ice presented challenges, these were outstripped by its advantages. The IFCB provided unprecedented high temporal and spatial resolution phytoplankton count and biovolume data that allowed patterns of abundance to be observed in detail. Interestingly, the IFCB captured an abundance of Urosolenia, which may be dissolved in standard Lugol's-preserved grab samples. We found Asterionella grew until mid-December and then slowly decreased towards the spring, whereas cf. Synedra diatoms decreased from early December and then rebounded towards late December as light increased before falling again towards the spring. Urosolenia peaked in late December as cf. Synedra diatoms rebounded and then began to decline towards the spring. Total phytoplankton declined towards late December, increased in the beginning of January and then declined towards the spring. The studied diatoms maintained considerable under-ice seed populations and grew when light was sufficient.

Supplementary information: The online version contains supplementary material available at 10.1007/s10750-025-05802-8.

Biotic and abiotic factors that affect the physiology and ecology of scyphozoan polyps are considered to be major drivers of jellyfish blooms, but are rarely studied under field conditions. Here, stable isotopes of carbon and nitrogen were used to investigate feeding ecology in Aurelia aurita polyps from the Beaulieu River, UK (50° 80' 04.55″ N/1° 42' 28.12″ W) in both winter and summer conditions, and compared to laboratory-maintained polyps fed Artemia nauplii at 6 and 20 °C, respectively. In natural conditions, the isotopic composition of A. aurita polyps indicated assimilation of nutrients derived from both benthic and pelagic food pathways, with seasonal switches between benthic-derived nutrients in winter and pelagic-derived nutrients in summer. In laboratory experiments, polyps assimilated Artemia food at 6 °C although metabolic processes were reduced, while at 20 °C, polyps starved as their increased metabolic costs could not be met from the Artemia food. Experiments on growth and asexual reproduction of Artemia-fed polyps of A. aurita may not reflect natural metabolic rates especially at higher temperatures (e.g. 20 °C), because these polyps are not extracting sufficient resources from their Artemia food to fuel the increased metabolic costs associated with high temperatures.

We conducted a study to investigate the potential effects of nutrients released from a fish farm, which fell within the typical range found in oligotrophic offshore waters of the Aegean Sea, on phytoplankton growth. We designed an in situ bioassay experiment at a fish farm and incubated natural phytoplankton assemblages inside dialysis membrane bags for six days. Changes in phytoplankton growth in samples of ambient seawater collected throughout the experiment served as controls and were considered indicative of the net population change rates. Half of the bags were filled with seawater filtered through a 150-µm mesh, while the other half contained unfiltered seawater. The growth rates, estimated based on chlorophyll a concentrations and phytoplankton cell numbers inside the filtered and unfiltered bags, showed no significant differences. While no detectable net phytoplankton growth occurred in the ambient seawater, there was an exponential increase in chlorophyll a content and cell numbers within the bags. Moreover, the species richness within the bags gradually declined throughout the experiment. The findings of the study confirm that continuous nutrient releases from fish farms can promote high population growth rates in oligotrophic environments, provided that phytoplankton losses due to grazing, advection, and sinking are minimized or eliminated.

Dolphins produce narrowband and frequency modulated sounds called whistles during a variety of behavioral contexts. Dolphin species vary in their whistle contour composition, frequency range, modulation, and duration, and these differences can be useful in their identification. Here, we compare the whistle contours of two sympatric dolphin species at La Paz Bay, Gulf of California, the Eastern Tropical Pacific bottlenose dolphin, and the long-beaked common dolphin. Dolphins were recorded (7 h and 1 min recording effort) from the research vessel with the engine off using an over-the-side hydrophone and a broadband recording system. A total of 666 high quality whistles (bottlenose dolphin, n = 415; long-beaked common dolphin, n = 251) were analyzed. A Random Forest Analysis identified duration, ending frequency, and maximum frequency as the most important variables that distinguish the two dolphin species. The most common whistle contour types of bottlenose dolphins were sine and convex, while the long-beaked common dolphins produced mainly upsweep and concave whistles. The results showed that bottlenose dolphins and long-beaked common dolphins differ in their whistle variables and contours facilitating their identification in future passive acoustic studies.

The global demand for affordable animal protein, particularly Nile tilapia, has driven increased adoption of (semi-)intensive farming practices. This intensification poses challenges like fish disease outbreaks, higher parasite loads, increased mortality rates, and environmental degradation. Addressing these issues requires a comprehensive understanding of the biology and ecology of these disrupted equilibria, emphasizing the need to characterize parasites, their pathogenic effects, and the conditions facilitating their emergence. Despite 276 known parasite species infecting Nile tilapia, existing reports are fragmented, often conducted locally or focused on a few species in experimental settings. A timely challenge is summarizing the state of knowledge and presenting links between human, animal, and environmental health. Unfortunately, limited studies focus on these parasites’ actual effects and environmental correlates, indicating little research effort. Comparing the number of parasite species described with few studies documenting their impacts reveals large knowledge gaps. The current information on these parasites lacks practical applicability for stakeholders in production and management. Bridging this knowledge gap requires both descriptive and experimental studies. Adopting the One Health approach in parasitological assessments and conducting further research will ensure aquaculture stakeholders can access valuable information for informed decision-making, prioritizing environmental integrity, fish health and welfare, and consumer well-being.

The Brazilian Cerrado has been experiencing intense land use changes for decades, with large-scale conversion of its natural vegetation to agriculture and livestock grazing. These agents of landscape change also affect the aquatic ecosystems embedded in the biome. Here, we investigated the effects of land use at different scales (catchment, riparian network, and local riparian) on fish assemblages in streams of the Brazilian Cerrado. We hypothesized that increasing agricultural land use (ALU%) reduces fish diversity and the compositional uniqueness of the fish assemblage. We used GLM to evaluate the impact of low-intensity ALU% on fish richness and abundance. Additionally, we employed beta regression to analyze the effect on local contribution to beta diversity (LCBD) and redundancy analysis to assess the impact on species composition. Our results showed that the effects of low-intensity ALU% depend on the spatial scale. While increasing ALU% in the riparian network negatively affected LCBD and altered species composition, ALU% in the catchment had negligible to slightly positive effects on LCDB, within the range of ALU% considered. Our findings reinforce the need to preserve riparian forests to maintain beta diversity in the streams of the Brazilian Cerrado. Also, no evidence was found that low-intense catchment use, without degrading the riparian forest, affects fish assemblages.

The monitoring of phytoplankton is crucial to highlight changes in the marine ecosystems. In the present study, the phytoplankton community of an eLTER station in the Northern Adriatic Sea was analysed combining two approaches, i.e. microscopy and eDNA metabarcoding (targeting V4 and V9 regions of the 18S rRNA gene, and using PR2 and SILVA as reference databases), to highlight the strengths and weaknesses of these two methods. Metabarcoding revealed a so far unknown phytoplankton diversity (99 genera and 151 species), while microscopy detected 14 genera and 44 species not revealed by metabarcoding. Only a small percentage of genera and species were shared by the two methods (microscopy and metabarcoding), 18S regions (V4 and V9) and reference databases (PR2 and SILVA). Metabarcoding showed a community characterized by a higher number of phytoflagellate and dinoflagellate genera and species, in comparison with microscopy where diatom and dinoflagellate taxa were the most represented. Moreover, metabarcoding failed to reveal almost all the coccolithophores. The results confirmed metabarcoding as a powerful tool, but it should still be combined with microscopy to have a more detailed information on the community and to counteract the drawbacks of metabarcoding, such as gaps in the reference databases.

Dissolved organic matter (DOM) influences several physical and chemical drivers of phytoplankton habitat. Increasing variability in lakewater dissolved organic carbon (DOC) concentrations in recent decades has raised uncertainty over temporal responses of phytoplankton communities to changing DOM. We conducted limnological surveys in four lakes with low (~ 2 mg l⁻¹) to moderate (~ 4 mg l⁻¹) DOC in Maine, USA, from February to November 2020 to assess variability in phytoplankton metrics and habitat gradients. Low-DOC lakes had similar thermal structure patterns compared to moderate-DOC lakes, but more stable euphotic depths. While moderate-DOC lakes had greater seasonal heterogeneity of biomass and vertical distribution of chlorophyll-a, the low-DOC lake had greater phytoplankton community turnover (Morisita-Horn Dissimilarity Index), underscored by a shift in dominance from autotrophs in the winter under ice to mixotrophs throughout the open water season. Long-term trends showed DOC concentrations generally increased for one decade beginning in 1995, followed by decreases in all four lakes for 12–15 years until 2020 by rates of 0.02–0.15 mg l⁻¹ year⁻¹, during which time water clarity increased in one lake. Small differences in or changes to DOC elicit greater variability of phytoplankton in lakes with low to moderate DOC concentrations.

Despite the ecological importance of riparian forests to streams, the specific scale at which forest cover most significantly influences fish assemblages remains poorly understood. To address this issue, we measured the percentage of forest cover at 11 spatial scales across 12 streams. These scales were categorized into: “local riparian”, which includes circular buffers around the sampled sections, and “riparian network”, which consists of buffers surrounding the stream network upstream of the sampled sections. We developed linear models using species diversity, based on Hill numbers, and the percentage of forest cover at each scale. Additionally, we included the terrain slope and the dominant type of land use in the watershed (rural or urban) as covariates. The results indicated that the 100-m buffer of the local riparian scale was the most effective for assessing fish diversity. The percentage of forest cover in this buffer had a positive and significant relationship with the diversity metrics, though terrain slope significantly influenced this relationship. Therefore, we recommend that studies evaluating the influence of landscape on fish assemblages in streams adopt a multiscale approach to avoid missing the true impact of the landscape on the assemblages.