Eating Behaviors

Abstract Sensitive and efficient monitoring of species’ distributions is crucial for understanding biodiversity and conserving species. Environmental DNA (eDNA) metabarcoding enables rapid detection of biological communities and its use is increasing in freshwater ecosystems. However, variations in eDNA sampling method may influence results. We compared anuran species richness estimates derived from two eDNA filtration strategies: (i) five Sterivex 0.22 µm filters from five locations per wetland using a manual syringe, and (ii) one Smith-Root 5 µm filter applied to a pooled sample from five locations per wetland using a computer controlled eDNA sampler (halved for analysis). Additionally, we assessed whether the number of sampling locations influenced species richness estimates using a pooled sampling approach and 5 µm filter. There was no difference in the total sample volume of the two filtration methods, yet the likelihood of detecting anuran species was higher when using the 5 µm system compared to 0.22 µm. Species richness also increased with the number of sampling locations, and was higher when using an amphibian-specific assay. These findings demonstrate that eDNA filtration technique can impact anuran detection, and that the use of 5 µm filters enables sample pooling which will be particularly cost-effective for large-scale or long-term applications.

Abstract Predicting effects of rising temperatures on the health and physiology of aquatic organisms is receiving increasing attention, particularly in arid regions with limited freshwater habitat. One approach to estimating energetic health of aquatic ectotherms is scope for growth (SFG)—the net energy available for reproduction and growth after meeting basic maintenance costs. We examined the relationships between temperature, clearance rates, respiration rates, and other physiological parameters to estimate SFG of Popenaias popeii—a federally endangered mussel native to the semi-arid Rio Grande basin of the southwestern USA and Mexico. Scope for growth followed a three-phase pattern with values remaining stable but negative from 16 to 24°C, increasing and becoming positive from 24 to 28°C, and decreasing back down to negative values from 28 to 32°C. In New Mexico’s Black River, a last stronghold for P. popeii, seasonal thermal regimes show that maximum investment in growth and reproduction likely occurs from May to October, when positive SFG values are most common. Within this critical period, mid-summer increases from 28 to 32°C may temporarily dampen or eliminate growth and reproduction in P. popeii as SFG decreases from peak to negative values. Management of flow to minimize thermal stress during mid-summer appears critical to maximizing growth and reproduction of remaining populations.

Abstract Human impacts have led to dramatic declines of the endangered freshwater pearl mussel Margaritifera margaritifera (FPM) and to a shift of its main distribution areas to more undisturbed but colder headwaters. In this study, we investigated whether feeding on high-quality food (i.e. food rich in n-3 polyunsaturated fatty acids) can compensate for growth limitations due to low water temperatures and whether food quality influences the survival rate of juvenile FPM. Therefore, we conducted feeding experiments with juvenile FPM at three different temperatures (11, 15 and 19°C) and with three different food sources. Afterwards, mussels were reared in cages in a stream to analyse survival during the first winter. Our results showed that food quality can compensate to some extent for growth limitations due to low water temperatures, but sufficiently high growth rates of juvenile FPM can only be achieved by the availability of high-quality food in warmer (> 15°C) environments. The availability of high-quality food during the main growing season also improves the survival of FPM over the first winter. Consequently, restoration efforts must aim to restore habitats in the historical main distribution areas of FPM and to create habitat conditions that allow the development of high-quality food.

Abstract Freshwater ecosystems are vital for providing essential services such as water supply and food production. However, increasing human demands have led to significant environmental degradation in these ecosystems. Türkiye, recognized as a global biodiversity hotspot, faces numerous threats from altered flow regimes, land-use changes, pollution, and invasive species. Despite these challenges, Türkiye’s diverse environments support a rich assemblage of zooplankton, with over 662 identified taxa spanning rotifers, cladocerans, and copepods. This study conducted a bibliometric analysis of zooplankton research at both global and national (Türkiye) levels to understand research trends, identify knowledge gaps, and highlight key areas of focus. Globally, stress factors and climate change dominate the research agenda, whereas, in Türkiye, topics such as abundance, diversity, water quality, and bioindicators have gained attention, albeit with relatively low frequency. Since 2013, these themes have shaped the direction of Turkish zooplankton research. The findings of this study emphasize the need for targeted research to better understand the impacts of environmental stressors on zooplankton communities in Türkiye, while also contributing to the global discourse on ecosystem functionality. By using zooplankton as key biotic indicators, this research offers insights into ecosystem health, providing critical information for future conservation and management efforts.

Abstract Freshwater ecosystems receive a constant influx of pollutants affecting all levels of biological organisation. We assessed the impacts of wastewater and the fungicide azoxystrobin on two trophic levels: the shredder Gammarus fossarum and leaf-associated fungal communities. Gammarus fossarum and Fagus sylvatica-leaves were exposed to stream water, wastewater, and both water types spiked with 40 µg/L azoxystrobin. For G. fossarum we determined the feeding rate and the respiratory electron transport system (ETS) activity, while the effects on fungal communities were investigated by measuring biomass, community composition, and sporulation rate, the latter serving as a measure of reproductive output. A significant decrease in feeding rate from stream water to wastewater with azoxystrobin was observed. ETS activity declined over time across all treatments, except in wastewater with azoxystrobin. Fungal biomass and community composition were not affected by azoxystrobin nor by wastewater, but the presence of G. fossarum increased the reproductive output. This study suggests that the combination of two stressors negatively affects G. fossarum, while the shredder itself positively affects the reproduction of leaf-associated fungi. By assessing the impact of fungicides in natural and polluted water, this research expands our understanding of pollutant-driven ecosystem shifts and their cascading effects on different trophic levels.

Abstract Trophic ecology of lacustrine salmonid populations is well-documented in North America and northern Europe, highlighting their role in aquatic ecosystems. However, there is a notable gap in comparative studies on the trophic niches and life-history traits of salmonids in Iberian alpine lakes, which are increasingly impacted by introduced fishes. We compared the trophic ecology and life-history traits of brook trout (Salvelinus fontinalis) and brown trout (Salmo trutta) in two alpine lakes of central Spain, providing insights into their ecological roles and potential responses to environmental pressures. Compared to brown trout, brook trout displayed a broader dietary niche (based on isotopes and stomach contents), higher reliance on terrestrial food resources, higher δ13C values and higher trophic position. Thus, the higher trophic position of top predator salmonids suggests a slightly longer food chain in the lake with brook trout. Brook trout showed a higher trophic plasticity indicated by an ontogenetic dietary shift from zooplanktivory to more generalist foraging on terrestrial prey. Brook trout displayed life-history traits such as early maturation, which likely facilitate successful establishment in alpine lakes. Our study suggests that the trophic plasticity and adaptive life-history traits likely support the successful establishment of non-native salmonids in alpine lake food webs.

Abstract Planktothrix rubescens is a filamentous, freshwater cyanobacterium that has gained outstanding attention due to its ecological significance, toxin production capabilities and potential risks it may pose to human and environmental health. The information related to the species is fragmented in hundreds of scientific articles; thus, our main goal was to connect this knowledge, with the hope that one may uncover information that can be applied widely in the subject. This comprehensive review delves into the taxonomic classification, biogeography, environmental drivers, interaction with other species, toxin production and management strategies related to P. rubescens. The review highlights the outstanding community-forming role of the species in different environments, as well as its very complex biotic relationships, from viruses to organisms at higher trophic levels.

Abstract This study investigates the impact of paleoclimate on the evolutionary history of Coxiella (Tomichiidae), a group of 15 species of aquatic snail in four putative genera that are endemic to Australian salt lakes. It used a time-calibrated phylogeny, based on mitochondrial DNA (COI) sequence variation from 938 individuals from 14 species, to estimate the timing of diversification events in Coxiella. The four putative genera of Coxiella were estimated to have evolved in the late Miocene to late Pliocene, followed by speciation within these genera during late Pliocene to Pleistocene and subsequent divergence within species during the Pleistocene. We also used COI data from 872 individuals to compare the phylogeographic patterns and genetic diversities amongst six species. These species showed three distinctly different phylogeographic patterns, ranging from deep phylogeographic structuring to a very shallow structure in a species that appears to have undergone a range expansion after a severe bottleneck. Overall, the recent evolutionary history of Coxiella shows important parallels with those of many other taxa from southern Australia which implies a common cause, which is usually identified as the trend of increasing aridification of the Australian climate over the last ~ 15 mya.

Abstract Rhopilema nomadica is the most prominent jellyfish species in the eastern Mediterranean, forming huge annual summer swarms. Although planula settlement success is essential in the formation of jellyfish outbreaks, quantitative studies to examine its response to environmental variables have not been performed thus far due to the difficulty in collecting planulae. We concentrated large numbers of R. nomadica planulae to study the effect of substrate type and seawater temperature on planula settlement. In the substrate preferences experiment, two natural substrates (bivalve shells and kurkar rock) and two artificial substrates (concrete and plastic (PVC)) were offered for planula settlement. Settlement success was not different between concrete, PVC, and kurkar substrates, but was significantly lower on the shells. In the temperature experiment, planulae were able to settle and metamorphose into polyps at all five temperatures (16—32 °C) tested, on glass slides, and most settled within three days. Higher temperatures were not only associated with accelerated settlement but also increased settlement success. The anticipated increase in marine infrastructures (potential settlement substrates), and rising seawater temperatures may favor planula settlement success and further enhance outbreaks of R. nomadica in the Mediterranean.

Abstract Aquatic ecosystems in rivers are currently exposed to a large number of stressors, causing a massive decline in abundance and biodiversity. One of these impacts is the wave action induced by inland navigation on riverbanks. The wave impact causes increased remobilization and erosion of the bed substrate and thus a recurring disturbance of the benthic habitats. The focus of this study on impacts of ship waves was on altered near-bed turbulence and its effects on a riverbank on the Danube in Austria. The natural and ship-induced wave action at a well-exposed gravel bar upstream of Vienna was recorded over the course of a year. Near-bed flow velocities were measured, which were used to calculate the turbulence and bed shear stresses. The results of this study reveal differences in the wave impact caused by the different types of ships. Here, the shape of the ship, its speed and the distance to the riverbank have a particular impact on the benthic habitats. To improve the aquatic habitat quality, speed limits and minimum distances to the river banks should be introduced based on further measurements. A possible restriction of recreational boating during ecologically sensitive seasons could also improve the quality of the habitats. The derived data also provide insights into the effects of strong winds compared to the waves caused by inland navigation. The observed wind-induced redistribution of sediments occurs sporadically, whereas the ship-induced resuspension depends on the type of ship and occurs regularly with shipping traffic on the Danube. However, seasonal effects must continue to be investigated and researched in the future. The presented data are also used to discuss the need for research into natural and anthropogenic wave impacts on river morphology and ecology.