Behavioural changes of native freshwater prawn in the presence of a predator fish.

Predation pressure influences animal behaviour in relation to feeding, exposure to predators and habitat use. In the presence of a predator, prey usually decreases feeding and activity, avoiding predation-risk areas. This study evaluated the visual effects of a predator fish (red-bellied piranha Pygocentrus nattereri) on the behaviour and habitat use of Macrobrachium jelskii prawn. It was hypothesized that prawns would modify their behaviour in the presence of a predator, decreasing their general activity (foraging and locomotion) and seeking shelter more frequently. Twenty behavioural tests were carried out without and with the presence of a predator using five different M. jelskii individuals per trial. Behavioural data were collected using scan sampling with instantaneous recording of behaviours every 15 s during 5 min in each trial. The presence of the predator caused prawns to decrease their locomotion and feeding and increase environment exploration and predator inspection. Prawns used the shelter more frequently when the predator was present. Red-bellied piranha elicited anti-predator behaviour in M. jelskii. The patterns observed suggested that the most common anti-predatory behaviours exhibited by M. jelskii are beneficial as they reduce vigilance and active anti-predation strategies, such as escape.

Does the stress axis mediate behavioural flexibility in a social cichlid, Neolamprologus pulcher?

Behavioural flexibility plays a major role in the way animals cope with novel situations, and physiological stress responses are adaptive and highly efficient mechanisms to cope with unpredictable events. Previous studies investigating the role of stress responses in mediating behavioural flexibility were mostly done in laboratory rodents using stressors and cognitive challenges unrelated to the ecology of the species. To better understand how stress mediates behavioural flexibility in a natural context, direct manipulations of the stress response and cognitive tests in ecologically relevant contexts are needed. To this aim, we pharmacologically blocked glucocorticoid receptors (GR) in adult Neolamprologus pulcher using a minimally invasive application of a GR antagonist. GR blockade prevents the recovery after a stressful event, which we predicted to impair behavioural flexibility. After the application of the GR antagonist, we repeatedly exposed fish to a predator and tested their behavioural flexibility using a detour task, i.e. fish had to find a new, longer route to the shelter when the shortest route was blocked. While the latencies to find the shelter were not different between treatments, GR blocked fish showed more failed attempts during the detour tasks than control fish. Furthermore, weak performance during the detour tasks was accompanied by an increase of fear related behaviours. This suggests that blocking GR changed the perception of fear and resulted in an impaired behavioural flexibility. Therefore, our results support a potential link between the capacity to recover from stressors and behavioural flexibility in N. pulcher with potential consequences for an effective and adaptive coping with changing environments.

Development and application of chitosan-urea cotton adsorbent as biomimicry technology inspired by natural predator-prey relationships.

Predator-prey interactions play a crucial role in maintaining ecological balance and possibly provide inspiration for strategies to mitigate environmental changes such as harmful algal blooms (HABs). To this end, this study aims to develop a novel strategy to mitigate HABs based on predator-prey interaction, i.e., Daphnia magna and Microcystis aeruginosa interaction. Bio-compounds (urea and 9-octadecenamide) produced by D. magna when encounter M. aeruginosa, were identified, particularly with urea promoting the aggregation of M. aeruginosa. Then, a novel adsorbent against HABs was synthesized by integrating bio-compounds of urea, and its effectiveness in removing M. aeruginosa was demonstrated. Notably, the adsorbent displayed a high removal efficiency of 99.25 % within 6 h. Our eco-friendly strategy holds promise for controlling HABs, representing the successful application of biomimicry principles.

Naivety dies with the calf: calf loss to human hunters imposes behavioral change in a long-lived but heavily harvested ungulate.

BACKGROUND: In prey, patterns of individual habitat selection and movement can be a consequence of an individuals' anti-predator behavior. Adjustments of anti-predator behavior are important for prey to increase their survival. Hunters may alter the anti-predator behavior of prey. In long-lived animals, experience may cause behavioral changes during individuals' lifetime, which may result in altered habitat selection and movement. Our knowledge of which specific events related to hunting activity induce behavioral changes in solitary living species is still limited. METHODS: We used offspring loss in a solitary and long-lived ungulate species, moose (Alces alces), as our model system. We investigated whether offspring loss to hunters induces behavioral changes in a species subjected to heavy human harvest but free from natural predation. To test for behavioral change in relation to two proxies for experience (calf fate and age), we combined movement data from 51 adult female moose with data on their offspring survival and female age. We tested for adjustments in females' habitat selection and movement following calf harvest using Hidden Markov Models and integrated Step Selection Analysis to obtain behavioral state specific habitat selection coefficients. RESULTS: We found that females with a harvested calf modified habitat selection and movement during the following hunting season. Female moose selected for shorter distance to roads during the night, selected for shorter distance to forests and greater distance to human settlements following calf harvest than females who had not lost a calf. The survival of twins in a given hunting season was related to female age. Older females we more likely to have twins survive the hunting season. CONCLUSIONS: Our findings suggest that losing offspring to human harvest imposes behavioral changes in a long-lived ungulate species, leading to adjustments in females' habitat selection and movement behavior, which may lower the risk of encountering hunters. In our study, female moose that experienced calf loss selected for lower distance to forest and selected for greater distance to human settlements during periods of high hunting pressure compared to females without the experience of calf loss during the previous hunting season. We interpret this as potential learning effects.

The evolution of fear-acquisition strategies under predation.

Fear is a taxonomically widespread behavioral response that functions to keep individuals out of danger. Empirical research has demonstrated that a diverse set of strategies are used in order to acquire a fear response across animals. Animals often use a mixed strategy: fear is acquired both innately and through learning. Despite the ubiquity of the fear response, and its established importance for shaping predator-prey interactions, little is known about why different fear acquisition strategies evolve or why mixed strategies appear common. Here, we model the evolution of fear acquisition (learning versus innate) under predation. We assume a tradeoff where individuals that learn fear are at higher risk from predators initially, but eventually obtain a lower risk as they survive predation attempts. We find that frequent predator encounters, predators that are not very dangerous, and effective learning favor the evolution of learned fear. Only pure strategies of fear acquisition evolve unless individuals suffer from either a cost to fear or, especially, a cost to learning, either of which can lead to the evolution of mixed strategies. Our results thus shed light onto the evolution of mixed fear acquisition strategies and open the door to further research on the evolution of fear acquisition.

Fish couple forecasting with feedback control to chase and capture moving prey.

Predator-prey interactions are fundamental to ecological and evolutionary dynamics. Yet, predicting the outcome of such interactions-whether predators intercept prey or fail to do so-remains a challenge. An emerging hypothesis holds that interception trajectories of diverse predator species can be described by simple feedback control laws that map sensory inputs to motor outputs. This form of feedback control is widely used in engineered systems but suffers from degraded performance in the presence of processing delays such as those found in biological brains. We tested whether delay-uncompensated feedback control could explain predator pursuit manoeuvres using a novel experimental system to present hunting fish with virtual targets that manoeuvred in ways that push the limits of this type of control. We found that predator behaviour cannot be explained by delay-uncompensated feedback control, but is instead consistent with a pursuit algorithm that combines short-term forecasting of self-motion and prey motion with feedback control. This model predicts both predator interception trajectories and whether predators capture or fail to capture prey on a trial-by-trial basis. Our results demonstrate how animals can combine short-term forecasting with feedback control to generate robust flexible behaviours in the face of significant processing delays.

Spatial and seasonal foraging patterns drive diet differences among north Pacific resident killer whale populations.

Highly social top marine predators, including many cetaceans, exhibit culturally learned ecological behaviours such as diet preference and foraging strategy that can affect their resilience to competition or anthropogenic impacts. When these species are also endangered, conservation efforts require management strategies based on a comprehensive understanding of the variability in these behaviours. In the northeast Pacific Ocean, three partially sympatric populations of resident killer whales occupy coastal ecosystems from California to Alaska. One population (southern resident killer whales) is endangered, while another (southern Alaska resident killer whales) has exhibited positive abundance trends for the last several decades. Using 185 faecal samples collected from both populations between 2011 and 2021, we compare variability in diet preference to provide insight into differences in foraging patterns that may be linked with the relative success and decline of these populations. We find broad similarities in the diet of the two populations, with differences arising from spatiotemporal and social variability in resource use patterns, especially in the timing of shifts between target prey species. The results described here highlight the importance of comprehensive longitudinal monitoring of foraging ecology to inform management strategies for endangered, highly social top marine predators.

Variable juvenile growth rates and offspring size: a response to anthropogenic shifts in prey size among populations.

Environmental variables, such as resource quality, shape growth in organisms, dictating body size, an important correlate of fitness. Variation in prey characteristics among populations is frequently associated with similar variation in predator body sizes. Anthropogenic alterations to prey landscapes impose novel ecological pressures on predators that may shift predator phenotypes. Research has focused on determining the adaptability of the phenotypic response by testing its genetic heritability. Here, we asked if anthropogenic shifts in prey size across the landscape correlate with juvenile growth rates among populations of watersnakes with divergent life-history phenotypes. We sought to determine if growth rate variation is the product of genetic adaptation or a non-heritable phenotypic response. Using a common-garden design, we measured growth of neonate snakes from fish farms varying in prey size. We found juvenile growth rates are faster for snakes with larger initial body sizes and from populations with larger average prey sizes. Our data suggest variability in juvenile grow rates within and among populations are not the product of genetic adaptation, but the indirect consequence of initial offspring size variation and prey consumption. We propose larger offspring sizes may favor increased juvenile growth rates, mediated through a larger morphological capacity to consume and process energy resources relative to smaller individuals. This experiment provides evidence supporting the growing body of literature that non-heritable responses may be significant drivers of rapid phenotypic divergence among populations across a landscape. This mechanism may explain the stability and colonization of populations in response to rapid, human-mediated, landscape changes.

Springing into action: Comparing escape responses between bipedal and quadrupedal rodents.

Predation is a fundamental selective pressure on animal morphology, as morphology is directly linked with physical performance and evasion. Bipedal heteromyid rodents, which are characterized by unique morphological traits such as enlarged hindlimbs, appear to be more successful than sympatric quadrupedal rodents at escaping predators such as snakes and owls, but no studies have directly compared the escape performance of bipedal and quadrupedal rodents. We used simulated predator attacks to compare the evasive jumping ability of bipedal kangaroo rats (Dipodomys) to that of three quadrupedal rodent groups-pocket mice (Chaetodipus), woodrats (Neotoma), and ground squirrels (Otospermophilus). Jumping performance of pocket mice was remarkably similar to that of kangaroo rats, which may be driven by their shared anatomical features (such as enlarged hindlimb muscles) and facilitated by their relatively small body size. Woodrats and ground squirrels, in contrast, almost never jumped as a startle response, and they took longer to perform evasive escape maneuvers than the heteromyid species (kangaroo rats and pocket mice). Among the heteromyids, take-off velocity was the only jump performance metric that differed significantly between species. These results support the idea that bipedal body plans facilitate vertical leaping in larger-bodied rodents as a means of predator escape and that vertical leaping likely translates to better evasion success.

Short-term temperature changes affected the predation ability of Orius similis on Bemisia tabaci nymphs.

Bemisia tabaci (Gennadius), a major pest that can adversely affect economies and agriculture globally, is particularly sensitive to climate change-induced temperature fluctuations, which can intensify its outbreaks. Orius similis Zheng, a primary natural predator of B. tabaci, also experiences temperature-related effects that influence its biocontrol efficacy. Thus, understanding the response of O. similis to temperature changes is pivotal for optimizing its biocontrol potential. Herein, our investigations showed that the functional response of O. similis to both high- and low-instar nymphs of B. tabaci adheres to the type II model at temperatures of 19, 22, 25, 28, and 31 °C. At 28 °C, O. similis exhibits the highest instantaneous attack rate (high-instar: 1.1580, low-instar: 1.2112), and the shortest handling time per prey (high-instar: 0.0218, low-instar: 0.0191). The efficacy of O. similis in controlling B. tabaci nymphs follows the sequence: 28 °C > 25 °C > 31 °C > 22 °C > 19 °C. Additionally, search efficiency inversely correlates with prey density. Simulations using the Hessell-Varley interference model indicate that increased density of O. similis under any temperature condition leads to reduced predation rates. Moreover, O. similis shows a predation preference for low-instar nymphs of B. tabaci, with higher predation level observed at the same temperature. In conclusion, for effective control of B. tabaci in field releases, O. similis should be optimally released at temperatures between 25 and 28 °C to preferably target the egg or early nymph stages of B. tabaci and determining the appropriate number of O. similis is important to minimize interference among individuals and enhance biocontrol efficacy.

Effects of long-term fluoxetine exposure on morphology, but not behaviour or metabolic rate, in male guppies (Poecilia reticulata).

Contamination of aquatic ecosystems by pharmaceuticals is a growing threat worldwide. The antidepressant fluoxetine is one such pharmaceutical that is frequently detected in aquatic ecosystems, and has been found to alter the behaviour and physiology of exposed wildlife. Few studies, however, have investigated potential combined effects on behaviour and metabolic rate. In addition, exposures are often short in duration and rarely conducted under ecologically relevant conditions. Here, we examined the impacts of long-term fluoxetine exposure on boldness (exploration, activity, and antipredator behaviour), metabolic rate, and morphology in male guppies (Poecilia reticulata). Specifically, fish were exposed for 8 months (corresponding to approximately two overlapping generations) in semi-natural mesocosms to one of three treatments: an unexposed control (0 ng L-1), or low or high fluoxetine (mean measured concentrations: 30 ng L-1 and 292 ng L-1, respectively). Following exposure, we quantified male exploratory behaviour and activity in a novel environment (maze arena) and antipredator behaviour in the presence or absence of a live predator (spangled perch, Leiopotherapon unicolor), as well as metabolic rate and morphology (mass, standard length, and scaled mass index). Fluoxetine exposure did not significantly alter boldness, metabolic rate, mass, or standard length. However, fluoxetine exposure did alter body condition, whereby fish in the high treatment had a higher scaled mass index than control fish. Our results, considered alongside previous work, underscore the importance of exposure duration in mediating the effects of fluoxetine on fitness-related traits. Continued research under extended exposure periods (i.e., spanning multiple generations) is essential if we are to accurately predict the ecological impacts of fluoxetine on exposed wildlife, and their underlying mechanism(s).

Grazing intensity alters network complexity and predator-prey relationships in the soil microbiome.

Grasslands are recognized as important reservoirs of soil biodiversity. Livestock grazing is implemented as a grassland management strategy to improve soil quality and enhance plant diversity. Soil microbial communities play a pivotal role in grassland ecosystems, so it is important to examine whether grazing practices affect the soil microbiome. Previous studies on grazing have primarily focused on bacteria and fungi, overlooking an important group-protists. Protists are vital in soil microbiomes as they drive nutrient availability and trophic interactions. Determining the impact of grazing on protists and their relationships with bacterial and fungal communities is important for understanding soil microbiome dynamics in grazed ecosystems. In this study, we investigated soil bacterial, fungal, and protist communities under four grazing levels: no grazing, moderate-use grazing, full-use grazing, and heavy-use grazing. Our results showed that heavy grazing led to a greater diversity of protists with specific groups, such as Discoba and Conosa, increasing in abundance. We also found strong associations between protist and bacterial/fungal members, indicating their intricate relationships within the soil microbiome. For example, the abundance of predatory protists increased under grazing while arbuscular mycorrhizal fungi decreased. Notably, arbuscular mycorrhizae were negatively associated with predatory groups. Furthermore, we observed that microbial network complexity increased with grazing intensity, with fungal members playing an important role in the network. Overall, our study reports the impact of temporal grazing intensity on soil microbial dynamics and highlights the importance of considering protist ecology when evaluating the effects of grazing on belowground communities in grassland ecosystems. IMPORTANCE: The significance of this study lies in its exploration of the effects of temporal grazing intensity on the dynamics of the soil microbiome, specifically focusing on the often-neglected role of protists. Our findings provide insights into the complex relationships between protists, bacteria, and fungi, emphasizing their impact on trophic interactions in the soil. Gaining a better understanding of these dynamics is essential for developing effective strategies for grassland management and conservation, underscoring the importance of incorporating protist ecology into microbiome studies in grasslands.

Dynamic primary resources, not just wild prey availability, underpin lion depredation of livestock in a savanna ecosystem.

Because it can lead to retaliatory killing, livestock depredation by large carnivores is among the foremost threats to carnivore conservation, and it severely impacts human well-being worldwide. Ongoing climate change can amplify these human-wildlife conflicts, but such issues are largely unexplored, though are becoming increasingly recognized. Here, we assessed how the availability of primary resources and wild prey interact to shape large carnivore selection for livestock rather than wild prey (i.e., via prey switching or apparent competition). Specifically, we combined remotely sensed estimates of primary resources (i.e., water availability and primary productivity), wild prey movement, and 7 years (2015-2021) of reports for livestock depredation by African lions (Panthera leo) in the Makgadikgadi Pans ecosystem, Botswana. Although livestock depredation did not vary between wet versus dry seasons, analyses at finer temporal scales revealed higher incidences of livestock depredation when primary production, water availability, and wild prey availability were lower, though the effects of wild prey availability were mediated by water availability. Increased precipitation also amplified livestock depredation events despite having no influence on wild prey availability. Our results suggest that livestock depredation is influenced by the diverse responses of livestock, wild prey, and lions to primary resource availability, a driver that is largely overlooked or oversimplified in studies of human-carnivore conflict. Our findings provide insight into tailoring potential conflict mitigation strategies to fine-scale changes in resource conditions to efficiently reduce conflict and support human livelihoods.

Brooding duration does not depend on cat predation risk but is related to weather and phenology in the wandering albatross (Diomedea exulans).

Parental investment increases offspring fitness at the expense of the parent's ability to invest in other offspring. In many animal species, parents guard their offspring after birth. The parental decision over the duration of this period is expected to be triggered by the associated fitness costs and benefits for both offspring and parents. Here, we evaluated the relevance of several intrinsic and environmental variables in determining brooding period duration in the wandering albatross (Diomedea exulans) and questioned whether brooding duration was related to chick subsequent survival and biometry prior to fledging. We used a semi-experimental design to increase the variance in cat abundance, a recent predator of albatross chicks, and predicted that an increased predation risk at the nest scale would trigger longer chick brooding and thus, protection. In addition, we questioned the influence of weather conditions, hatching date, and characteristics of chicks (sex and biometry) and parents (sex and age) on brooding duration. We report no effect of predation risk or parental characteristics on brooding duration. However, the probability for a parent to end brooding decreased with forthcoming unfavorable weather. Our data also revealed reduced brooding duration for late-hatched chicks and a positive association between brooding duration and chick structural size, and between the frequency of shifts between parents and chick structural size. Finally, brooding duration was not associated with chick survival or with chick biometry prior to fledging. We discuss these results in light of pre-existing hypotheses on fitness costs and benefits associated with brooding duration for chicks and parents.

Navigating the landscape of fear: Fruit flies exhibit distinct antipredator and antiparasite defensive behaviors.

Most organisms are at risk of being consumed by a predator or getting infected by a parasite at some point in their life. Theoretical constructs such as the landscape of fear (perception of risk) and nonconsumptive effects (NCEs, costly responses sans predation or infection) have been proposed to describe and quantify antipredator and antiparasite responses. How prey/host species identify and respond to these risks determines their survival, reproductive success and, ultimately, fitness. Most studies to date have focused on either predator-prey or parasite-host interactions, yet habitats and ecosystems contain both parasitic and/or predatory species that represent a complex and heterogenous mosaic of risk factors. Here, we experimentally investigated the behavioral responses of a cactophilic fruit fly, Drosophila nigrospiracula, exposed to a range of species that include parasites (ectoparasitic mite), predators (jumping spiders), as well as harmless heterospecifics (nonparasitic mites, ants, and weevils). We demonstrate that D. nigrospiracula can differentiate between threat and non-threat species, increase erratic movements and decrease velocity in the presence of parasites, but decrease erratic movements and time spent grooming in the presence of predators. Of particular importance, flies could distinguish between parasitic female mites and nonparasitic male mites of the same species, and respond accordingly. We also show that the direction of these NCEs differs when exposed to parasitic mites (i.e., risk of infection) versus spiders (i.e., risk of predation). Given the opposing effects of predation versus infection risk on fly behavior, we discuss potential trade-offs between parasite and predator avoidance behaviors. Our findings illustrate the complexity of risk assessment in a landscape of fear and the fine-tuned NCEs that arise in response. Moreover, this study is the first to examine these behavioral NCEs in a terrestrial system.

Application on power system economic dispatch of marine predator algorithm improved by asymmetric information exchange.

The solution to the economic dispatch (ED) problem for power systems allows the power sector to reduce operating costs. However, the ED problem is a complex nonlinear and nonconvex optimization problem whose solution requires powerful algorithms. We propose a new version of the Marine Predator Algorithm (MPA), called IMPA, for solving complex ED problems. The algorithm introduces an asymmetric information exchange (AIE) mechanism, which not only accelerates to escape of local optima but also enriches the diversity of search. In this work, 12 benchmark functions were used to test the performance of the proposed algorithm IMPA. Then, the IMPA was used to solve the ED engineering problem of power system containing of 6, 13, 40, and complex 140 units. The minimum and average costs searched by IMPA are 1657962.7265$/h and 1657962.7265$/h, and they are much lower than the results of the MPA and NMPA, which means that our proposed improved IMPA improves the performance of MPA for solving the economic dispatch problem of large-scale power systems. The results show that the solutions obtained by IMPA are more competitive than those of MPA and NMPA, which provides an additional solution for cost reduction of the power system.

Trophic cascades regulate arthropods density and plant damage across forest strata.

Research Highlight: Sivault, E., Kollross, J., Jorge, L., Finnie, S., Diez Mendez, D., Fernandez Garzon, S., Maraia, H., Lenc, J., Libra, M., Masashi, M., Nakaji, T., Nakamura, M., Sreekar, R., Sam, L., Abe, T., Weiss, M., & Sam, K. (2024). Insectivorous birds and bats outperform ants in the top-down regulation of arthropods across strata of a Japanese temperate forest. Journal of Animal Ecology. https://doi.org/10.1111/1365-2656.14146. Top-down predators exert strong effects on prey populations. Theoretical and empirical studies investigating the cascading effects of predators on biodiversity dynamics and ecosystem functionality have been central to advancing ecology and conservation biology. Yet, how intraguild predation and niche overlap drive the strength and direction of trophic cascades across forest strata is still barely understood. In a study published in this issue, Sivault et al. (2024) investigated the impacts of excluding vertebrate (birds and bats) and invertebrate (ants) predators on arthropod herbivores and plant damage in understory and canopy forest strata. The study finds that birds and bats (but not ants) have negative impacts on herbivore density, which, in turn, benefits plants by reducing leaf damage. Additionally, the effects of vertebrate predators are similar across strata. The authors also show that herbivore density and herbivory are greater in the understory compared to the canopy strata. Sivault et al. (2024) demonstrate that intraguild predation and niche overlap dictate the strength and direction of trophic cascades in forest ecosystems. In addition, these findings shed new light on forest ecology and conservation, especially considering the potential negative effects of climate change on top predators.

Predator becomes prey: Martial eagle predation of lion cubs in the greater Mara region, Kenya.

In many intact African savannah ecosystems, martial eagles are the top avian predator, while lions are the top terrestrial predator. Here, we report seven records of martial eagle predation or attempted predation of lion cubs in the greater Mara region, Kenya. These events resulted in the death of nine lion cubs, most of which were at least partially consumed, and are the first detailed records of this behaviour to be published. While these observations represent intraguild interactions, we suggest that they reflect neither intraguild predation nor interspecific killing. Rather, the ecology of both species coupled with the details of our records suggest that martial eagles opportunistically kill lion cubs purely to eat them. We hope that by publishing these records we will encourage others to share their observations of raptors predating on large mammalian carnivores, thus improving our understanding of a behaviour that we suspect may be more widespread than the current lack of evidence suggests.

Bottom-up processes drive isotopic variation in the South American sea lion Otaria flavescens across a 2300 km latitudinal gradient.

Spatial differences in the isotope values of widely distributed marine apex consumers may reflect geographical differences in the isotopic composition of basal resources (e.g., phytoplankton) fueling food webs (bottom-up effects) or spatial differences in the trophic ecology of the taxon of interest (top-down effects). We examined spatial variation in δ13C and δ15N values from 264 South American sea lions (SASL, Otaria flavescens) of different age classes (adults, subadults and juveniles), their putative prey consisting of pelagic and benthic coastal fishes, and particulate organic matter (POM) measured from locations situated across >2300 km of the Chilean coast (between 18°42' and 39°17' S). We used generalized least squares (GLS) models to compare the form of the relationship between δ13C and δ15N and latitude between the three functional groups. Our results show that SASL from northern, central, and southern areas were isotopically distinct, with individuals from the north having lower δ13C and higher δ15N values in comparison to individuals from the south. When the relationship for each functional group was modelled individually using GLS, results indicated that for each degree of increasing latitude δ15N decreased on average by 0.12‰ (POM), 0.15‰ (prey), and 0.14‰ (SASL), while δ13C increased by 0.06‰ (POM) and 0.05‰ in both prey and SASL. We suggest that the latitudinal differences observed in SASL δ13C and δ15N values reflect baseline isotopic variation rather than marked differences in trophic ecology of these widely distributed consumers.

Toxic effects of the emerging Alexandrium pseudogonyaulax (Dinophyceae) on multiple trophic levels of the pelagic food web.

The dinoflagellate Alexandrium pseudogonyaulax, a harmful algal bloom species, is currently appearing in increasing frequency and abundance across Northern European waters, displacing other Alexandrium species. This mixotrophic alga produces goniodomins (GDs) and bioactive extracellular substances (BECs) that may pose a threat to coastal ecosystems and other marine resources. This study demonstrated the adverse effects of A. pseudogonyaulax on four marine trophic levels, including microalgae (Rhodomonas salina), microzooplankton (Polykrikos kofoidii) and mesozooplankton (Acartia tonsa), as well as fish gill cells (RTgill-W1, Oncorhynchus mykiss), ultimately leading to enhanced mortality and cell lysis. Furthermore, cell-free supernatants collected from A. pseudogonyaulax cultures caused complete loss of metabolic activity in the RTgill-W1 cell line, indicating ichthyotoxic properties, while all tested GDs were much less toxic. In addition, cell-free supernatants of A. pseudogonyaulax led to cell lysis of R. salina, while all tested GDs were non-lytic. Finally, reduced egg hatching rates of A. tonsa eggs exposed to cell-free supernatants of A. pseudogonyaulax and impaired mobility of P. kofoidii and A. tonsa exposed to A. pseudogonyaulax were also observed. Altogether, bioassay results suggest that the toxicity of A. pseudogonyaulax is mainly driven by BECs and not by GDs, although further research into factors modulating the lytic activity of Alexandrium spp. are needed.