Benthic Predators Research Articles

Effect of Temperature on Black Carp (Mylopharyngodon piceus) Age at Sexual Maturity

ABSTRACTBlack Carp (Mylopharyngodon piceus) is one of the four invasive Asian Carp species (Bighead Carp, Hypophthalmichthys nobilis; Grass Carp, Ctenopharyngodon idella; and Silver Carp, Hypophthalmichthys molitrix) in North America. As benthic predators, Black Carp poses ecological risks to unionids within the Great Lakes and could bring other changes to local benthic communities. One means of assessing invasion risk and potential impact is to determine how critical life history characteristics depend on environmental conditions in new regions. Age at sexual maturity is negatively correlated to the maximum per capita population growth rate and thus can be used to estimate potential population growth for invasive species. Previous studies have found a significant negative relationship between age at maturity and temperature for all three other Asian Carp species, but not for Black Carp. With a more comprehensive dataset, we demonstrate that the same relationship exists for Black Carp. Winter duration is the best predictor of Black Carp age at maturity, followed by average winter air temperature. This significant relationship between age at maturity and temperature was not altered in artificial growing environments. Our results suggested that for Black Carp, temperatures in the winter months are more important for its energy accumulation and maturation and may determine invasion risk in northern locations, such as tributaries of the Great Lakes.

How plastic litter sunk by biofouling recovers buoyancy - The role of benthic predation

Estimates suggest that the amount of plastic litter discarded in the ocean is several times greater than what remains floating at the sea surface, raising questions about the fate of this marine debris. Fouling-induced sinking of plastic litter is one of the proposed mechanisms responsible for this mass difference. While some of this ‘missing’ plastic mass may be explained by the effects of fouling, it has also been hypothesized that sinking litter may return to the surface after benthic organisms consume the biofouling. However, this hypothesis has never been tested. The present study evaluated the structure and biomass of the fouling community in response to benthic predation in both summer and winter seasons. Floating PVC plates were installed during winter and summer in central Chile (36°S) until the growing biofouling community caused them to sink. Plates were then moved to the seabed, where they were exposed to benthic predation, while control plates were maintained in a mesh cage impeding predator access. In summer, all plates recovered their buoyancy, while in the winter only 60 % recovered buoyancy. All caged control samples remained on the bottom in both seasons. The community structure differed both in the treatments and across the seasons, with plates that recovered buoyancy initially being dominated by Ulva sp. and Ciona robusta. Conversely, plates that did not refloat were mainly covered by species resistant to predation such as Pyura chilensis, Austromegabalanus psittacus, and Balanus laevis. Thus, fouling community structure influences how predation facilitates buoyancy recovery, because not all epibionts can be consumed by predators. While previous studies had shown how fouling organisms cause sinking of floating litter, this is the first study to provide experimental evidence that predation can reverse this process and allow litter to resurface and become again available as dispersal vectors for native and invasive species.

Using sea lion-borne video to map diverse benthic habitats in southern Australia

Across the world’s oceans, our knowledge of the habitats on the seabed is limited. Increasingly, video/imagery data from remotely operated underwater vehicles (ROVs) and towed and drop cameras, deployed from vessels, are providing critical new information to map unexplored benthic (seabed) habitats. However, these vessel-based surveys involve considerable time and personnel, are costly, require favorable weather conditions, and are difficult to conduct in remote, offshore, and deep marine habitats, which makes mapping and surveying large areas of the benthos challenging. In this study, we present a novel and efficient method for mapping diverse benthic habitats on the continental shelf, using animal-borne video and movement data from a benthic predator, the Australian sea lion (Neophoca cinerea). Six benthic habitats (between 5-110m depth) were identified from data collected by eight Australian sea lions from two colonies in South Australia. These habitats were macroalgae reef, macroalgae meadow, bare sand, sponge/sand, invertebrate reef and invertebrate boulder habitats. Percent cover of benthic habitats differed on the foraging paths of sea lions from both colonies. The distributions of these benthic habitats were combined with oceanographic data to build Random Forest models for predicting benthic habitats on the continental shelf. Random forest models performed well (validated models had a >98% accuracy), predicting large areas of macroalgae reef, bare sand, sponge/sand and invertebrate reef habitats on the continental shelf in southern Australia. Modelling of benthic habitats from animal-borne video data provides an effective approach for mapping extensive areas of the continental shelf. These data provide valuable new information on the seabed and complement traditional methods of mapping and surveying benthic habitats. Better understanding and preserving these habitats is crucial, amid increasing human impacts on benthic environments around the world.

Behavioral responses of benthic and nektonic tadpoles to the presence of a benthic predator

Behavioral responses of benthic and nektonic tadpoles to the presence of a benthic predator

Responses of Gross's stinkfish, Callionymus grossi (Ogilby 1910) to perceived threats

AbstractPredator avoidance is critical to fish survival and yet multiple types of predator response are rarely recorded at the level of individuals let alone studied in detail. Behaviour of an individual adult male dragonet, Gross's stinkfish Callionymus grossi (Ogilby 1910) (Family Callionymidae) was observed over the course of four consecutive daily snorkelling sessions on high tides in the Maroochy River estuary, Queensland, Australia. On two occasions, the dragonet buried in the sand in the presence of a great barracuda, Sphyraena barracuda, whereas, smaller benthic predators or competitors and the observer sometimes provoked dorsal fin raising and fleeing responses of the dragonet. The dragonet, therefore, demonstrates multiple responses to potential predators and competitors seemingly depending on the likely severity of interaction. Further research of dragonet fishes is recommended to disentangle the functionality of fin display in this group, with the anti‐predator function of fin displays and honest signalling of chemical defence a promising aspect for investigation.

Water column-based assays underestimate benthic predation pressure in mid-latitude systems

Water column-based assays underestimate benthic predation pressure in mid-latitude systems

Combined effects of climate warming and pharmaceuticals on a tri-trophic freshwater food web

Multiple anthropogenic stressors influence the functioning of lakes and ponds, but their combined effects are often little understood. We conducted two mesocosm experiments to evaluate the effects of warming (+4 °C above ambient temperature) and environmentally relevant concentrations of a mixture of commonly used pharmaceuticals (cardiovascular, psychoactive, antihistamines, antibiotics) on tri-trophic food webs representative of communities in ponds and other small standing waters. Communities were constituted of phyto- and zooplankton and macroinvertebrates (molluscs and insects) including benthic detritivores, grazers, omnivorous scrapers, omnivorous piercers, water column predators, benthic predators, and phytophilous predators. We quantified the main and interactive effects of warming and pharmaceuticals on each trophic level in the pelagic community and attributed them to the direct effects of both stressors and the indirect effects arising through biotic interactions. Warming and pharmaceuticals had stronger effects in the summer experiment, altering zooplankton community composition and causing delayed or accelerated emergence of top insect predators (odonates). In the summer experiment, both stressors and top predators reduced the biomass of filter-feeding zooplankton (cladocerans), while warming and pharmaceuticals had opposite effects on phytoplankton. In the winter experiment, the effects were much weaker and were limited to a positive effect of warming on phytoplankton biomass. Overall, we show that pharmaceuticals can exacerbate the effects of climate warming in freshwater ecosystems, especially during the warm season. Our results demonstrate the utility of community-level studies across seasons for risk assessment of multiple emerging stressors in freshwater ecosystems.

Predators Induce Phenotypic Plasticity in Echinoderms across Life History Stages.

AbstractMarine invertebrates with biphasic life cycles feature life history transitions that coincide with habitat changes from benthic adults to planktonic embryos and larvae, then a return to the benthos as a juvenile at metamorphosis. The metamorphic transition exposes animals to a new suite of benthic predators, and high mortality often occurs in the hours and days following settlement. Juvenile invertebrates may produce phenotypically plastic morphological defenses when predator cues are detected. However, time lags inherent to phenotypic plasticity may delay the production of defenses until after the period of highest vulnerability. It should, therefore, be beneficial for planktonic larvae approaching settlement to detect waterborne cues from benthic predators and produce juvenile phenotypes appropriate for postmetamorphic survival. Echinoderms are useful models for testing transhabitat and trans-life history stage phenotypic plasticity because many species have larvae that construct their juvenile phenotype while still in the water column. In this study, we tested whether planktonic echinoderm larvae exposed to cues from benthic predators modified their juvenile phenotypes at settlement. Green urchin (Strongylocentrotus droebachiensis) and Pacific sand dollar (Dendraster excentricus) larvae were exposed to predatory green crab (Carcinus maenus) or red rock crab (Cancer productus) cues, respectively, from their early-stage juvenile rudiment formation through settlement. Green urchin larvae exposed to predator cues settled with significantly more juvenile spines compared to unexposed controls. Sand dollars exhibited earlier settlement, larger disk area, fewer spines, and shorter spines when exposed to benthic predator cues. Sand dollar larvae were also exposed to cues from planktonic crab larvae and in response settled sooner and larger, with even fewer and shorter spines than those exposed to benthic predator cues. These results suggest that echinoderm larvae alter their juvenile phenotype in response to predator cues, but the response varies between species, and responses to planktonic threats may be prioritized over benthic ones.

Neustonic tadpoles do not detect and respond to insect predator

ABSTRACT Prey animals use various signals to detect their predators and respond accordingly to enhance their survival. Since responding to a predator is costly, prey species may cut cost by using other strategies such as behavioural tactics, morphological changes, seeking natural refuge or unique habitat acquisition. Tadpoles of Microhyla nilphamariensis have a transparent body and live in a neustonic environment, which provides them protection against benthic predators. As a result, we investigated the predator detection mechanism in M. nilphamariensis tadpoles using different cues from an insect predator, dragonfly larvae, to determine if the presence of natural shelter and unique habitat acquisition influences the chemo-ecology of predator recognition in this species. We also exposed these tadpoles to active caged predators and a stress hormone, corticosterone (CORT) to study physiological mechanism underlying their behavioural anti-predator responses toward alarm cues. In the predator avoidance assay, M. nilphamariensis tadpoles did not respond to the predator using visual or chemical signals. The tadpoles did not change their activity in response to alarm, heterospecific, kairomones, and dietary cues released from the predator. Pre-conditioning of M. nilphamariensis tadpoles with caged predator and different concentrations of CORT also did not alter their activity in response to alarm cues. These results clearly demonstrated that neustonic tadpoles of M. nilphamariensis do not detect and respond to co-existing insect predator. We discuss these results in the context of unique habitat occupied by these prey tadpoles, the presence of alternate prey, and inherent factors such as transparent body.

Biofouling assemblages on anthropogenic structures reflect seafloor access for benthic predators

The design of anthropogenic marine structures can have unintended consequences for ecological communities. We describe differences in biofouling assemblages between two primary anthropogenic habitats—pontoons and pilings—in a marina in British Columbia, Canada, using multiple measures of diversity (i.e., richness, evenness, and Shannon indices) and multiple metrics of variability in taxonomic composition (i.e., Jaccard and modified Gower methods) using two complementary surveys. First, a video-transect survey revealed abundances of crawling benthic predators to be 19 times greater on pilings than on pontoons. Second, a photo-quadrat survey of sessile invertebrates revealed moderate differences in diversity but differences of 86% in taxonomic composition and 88% in non-indigenous species (NIS), owing largely to the dominance of mussels (Mytilus species complex) on pontoons and their absence on pilings. We discuss several environmental factors associated with the design of anthropogenic infrastructure and propose that contact with the seafloor is the key driver of observed differences between the biofouling assemblages at this site. Contact with the seafloor permits access to crawling predators and thereby drives the abundances of ecosystem-engineering taxa. Patterns of taxonomic composition and assemblage dispersion indicate that biofouling organisms are affected by these phenomena according to their roles either as prey or as competitors with mussels and not whether they are native or NIS. Finally, we consider how the growing body of ecological studies on biofouling communities such as ours can inform the implementation of infrastructure for the purposes of enhancing biotic diversity and resilience.

Sclerochronological records of environmental variability and bivalve growth in the Pacific Arctic

The Pacific Arctic region has experienced, and is projected to continue experiencing, rapid climate change. Large uncertainties exist in our understanding of the impact these physical changes have on the region’s ecology. This is, in part, due to the lack of long-term data. Here we investigate bivalve mollusc growth increment width chronologies (sclerochronologies) to develop a long-term biological data series in an Arctic species and address the hypothesis that benthic production in the Pacific Arctic region is in decline with implications for predators (e.g., walrus, whales, seals, and sea ducks). Growth increments formed in the shells of two bivalve mollusc species, Astarte borealis and Liocyma fluctuosa, were examined using conventional sclerochronological techniques. The A. borealis and L. fluctuosa samples exhibited measured longevities of >148 and >18 years, respectively, in the coastal waters of Alaska’s Chukchi Sea. Dendrochronology crossdating techniques facilitated the development of two robust (expressed population signal > 0.85) independent growth increment width chronologies. These chronologies provide evidence of the growth conditions through time for each species (1985–2015 for A. borealis and 1997–2014 for L. fluctuosa). Linear regression analyses identified that both species grew more rapidly in years with warmer sea surface temperature and lower sea ice concentration. The results provide evidence that benthic ecosystems are benefiting from the warmer conditions and reduced sea ice that have accompanied recent Arctic climate trends. This result is encouraging for benthic predators in the eastern Chukchi Sea as it alleviates the concern that their benthic prey has already become food limited by weakened pelagic-benthic coupling. More broadly, this initial A. borealis chronology is among the longest biological data series for any Arctic species and highlights the feasibility of multicentennial biological data for the Arctic.

First Molecular Characterization of the Elusive Marine Protist Meteora sporadica

Meteora sporadica is a protist species first described by Hausmann et al. (2002) in deep-sea sediments from the Sporades Basin, Eastern Mediterranean Sea. Due to its unusual morphology and locomotion, very different from those of other high-rank eukaryotic taxa, it was classified as an incertae sedis species. Unfortunately, its morphological characterization was not accompanied by the generation of molecular data, preventing its placement in molecular phylogenetic trees including other protist lineages. Here, we report the observation of protist cells in sediments from a shallow marine lagoon in the Mediterranean Sea with morphological characteristics indistinguishable from those of Meteora sporadica. Given this similarity and the geographical proximity to the type location, we consider that the organism that we observed likely corresponded to the type species, M. sporadica, which seems to be a benthic predator spanning from shallow to deep-sea habitats. We determined the 18S rRNA gene sequence of M. sporadica from micromanipulated cells. Searches in sequence databases did not yield closely related hits, suggesting that Meteora is a rare organism. Phylogenetic analyses did not show any close affinity with other eukaryotic groups, supporting its initial incertae sedis status and suggesting that it may define a new high-rank level eukaryotic lineage.

Assessment of endangered freshwater pearl mussel populations in the Northern Iberian Plateau in relation to non–native species: xenodiversity as a threat

In the last two decades, small populations of freshwater pearl mussels, Margaritifera margaritifera, have been recorded in Mediterranean rivers of the Iberian Northern Plateau. A survey was carried out in Castilla and León in 2018 to assess the development of populations of this species in all the rivers of known distribution and to update the threat classification. Thirty sections in the rivers Negro, Tera, Alberche and Águeda were positive for its presence, and another 50 stretches of seven rivers were negative. The species is currently distributed over about 22.5 km. Águeda and Tera populations have decreased dramatically in the last 14 years and are on the threshold of extinction. The Negro river supports the largest population, although the species has now disappeared in at least 61 % of the stretches that were inhabited in 2004. All populations showed very low densities and an ageing population structure, with no recruitment for decades. The presence of non-native invasive alien species (NIS) was higher than in a previous regional survey, with the signal crayfish representing the greatest threat. We observed changes in benthic microhabitats and direct predation of adults and glochidia conglutinates. In the Alberche River, in strict syntopy with M. margaritifera and two other mussel species, 10 NIS were detected. The current hydrological and ecological conditions in the Duero watershed support the settlement of exotic species to the disadvantage of native mollusks, which are more demanding in terms of microhabitats.

Diet Metabarcoding Reveals Extensive Dietary Overlap between Two Benthic Stream Fishes (Zingel asper and Cottus gobio) and Provides Insights into Their Coexistence

Niche partitioning studies are essential to understand the mechanisms that allow ecologically similar species to coexist. The Rhone streber (Zingel asper) and the European bullhead (Cottus gobio) are both benthic riverine fishes that consume macroinvertebrates. Both species are protected under European legislature. We focused on trophic niche partitioning between these species, as sufficient access to trophic resources is an important requirement for long-term coexistence. We used a combination of faeces metabarcoding dietary data and prey community data to evaluate dietary overlap, trophic niche variation and dietary preferences. Sampling was performed in three sites along the Durance River (France). Both species consumed a wide range of macroinvertebrates but neither C. gobio nor Z. asper selected the most abundant taxa (chironomids and simuliids). Both species selected larger mayfly (Baetis and Ecdyonurus) and caddisfly (Hydropsyche) taxa. Dietary overlap was generally high but declined when large mayflies were rare. Contrasting secondary prey preferences and trophic niche variation may allow these species to exploit the same preferred mayflies in periods of abundance and to avoid competition during resource scarcity. We propose that dietary partitioning may support the coexistence of these two ecologically similar, benthic predators.

Protection effectiveness and sea urchin predation risk: The role of roving predators beyond the boundaries of a marine protected area in the Western Mediterranean Sea

Abstract Effective marine protected areas (MPAs) increase top predator density. Accordingly, a large abundance of predatory fish potentially increases predation risk for sea urchins inside an MPA. Intensity of predation was investigated for the sea urchin Paracentrotus lividus at a Mediterranean MPA. Predation rates were estimated for three levels of protection (full, partial, and absent) and two habitats (rocky reefs and Posidonia oceanica meadows). The natural density of sea urchins was correlated with predator biomass (fish sparids Diplodus spp. and Sparus aurata and the gastropod Hexaplex trunculus), and predation risk was evaluated through a tethering experiment. Significantly higher fish predation was found on the rocky reefs of the fully and non‐protected areas than in the partially protected area. These findings are consistent with the sparid biomass estimated in the fully and partially protected areas. However, a discrepancy between high predation risk and low sparid biomass was detected outside of the MPA's northern boundary, where marine farms (fish and mussels) are present. Benthic predator biomass also increased significantly across the northern boundary, but its predation activity was negligible. The low predatory fish biomass and low sea urchin density suggest a top‐down control by roving predatory fish on the rocky reefs of the non‐protected area, in proximity to the fish farms. Similarly, a significant gradient of benthic predator biomass and low sea urchin density suggest potential predation interactions inside the P. oceanica meadows across the northern MPA boundary near the mussel farms. This study highlights deviations from the expected trophic interactions outside the MPA that could be caused by aquaculture activities. Our understanding of the potential synergies between the MPAs and the nearby human activities needs to be broadened to improve the effectiveness of both ecosystem conservation and resource management.

PREVALENCE OF THE Anguillicola crassus PARASITE IN THE INTERNATIONAL MINHO RIVER

The European eel, Anguilla anguilla (Linnaeus, 1758), is vulnerable to infections by the parasitic nematode Anguillicola crassus Kuwahara, Niimi & Itagaki, 1974, mainly in freshwater ecosystems. The eel is a bioindicator species due to its benthic behaviour, predator, and life cycle. The parasite feeds on blood from the eel's swim bladder, causing damage to the walls and deterioration of this organ, reducing energy reserves, and affecting its migratory capacity for reproduction. Eels were captured at different sampling points divided into 4 areas of the international section of the Minho River in the following time periods: 1995-96, 2008-2011 and 2017-2021, through fyke nets and electric fishing sampling techniques. The objectives of this work were to analyze the dispersion and prevalence of A. crassus in the Minho River basin over time, infection rates and the eels condition. The prevalence levels found reach values ​​close to 75% in some sampled locations and 99% of eels shown pathological signs of swim bladder infection. The nematode dispersal area increased since the early 1990s when its presence in the Minho River was first recorded.

The smaller, the most delicious: Differences on vulnerability to predation between juvenile and adult of invasive ascidians

Ascidians are one of the most important taxa in fouling communities of artificial structures. These organisms can establish new populations and successfully invade new areas, spreading outside the region where they were initially introduced, due to their high reproductive and growth rates and their broad tolerance to environmental conditions. Predation pressure has also an influence on the colonization success of ascidians, with variations depending on their life stage, the fluctuations of the abundance of predators and their identity. Among these factors, the consequences of invasive and native predators on different life stages of invasive ascidians have been poorly evaluated. Thus, the goal of this work is to assess the survival of different life stages (juveniles and adults) of the two most successful invasive ascidians in the presence of different benthic predators in a cold temperate port. To evaluate this, we performed experiments offering juvenile and adult ascidians to different native and exotic benthic predators, under controlled aquarium conditions. We observed that juvenile ascidians were more vulnerable to predation than adults. Moreover, adult vulnerability differed between ascidian species probably because of different physical and chemical defences. Our results evidence the importance of evaluating the effects of predation through different stages of the life cycle of the preys, and the role of both native and exotic predators. Therefore, we hypothesize that juvenile ascidians depend on the use of different refuges, such as mussel beds and adult ascidians, to escape from predation until they reach a less vulnerable adult size. Understanding the differential effects of predation through different stages of life-history of the preys, and the interaction between native and exotic species helps to comprehend the causes of success in the establishment of invasive species.

Trade-offs between foraging reward and mortality risk drive sex-specific foraging strategies in sexually dimorphic northern elephant seals.

Sex-specific phenotypic differences are widespread throughout the animal kingdom. Reproductive advantages provided by trait differences come at a cost. Here, we link sex-specific foraging strategies to trade-offs between foraging reward and mortality risk in sexually dimorphic northern elephant seals (Mirounga angustirostris). We analyse a decadal dataset on movement patterns, dive behaviour, foraging success and mortality rates. Females are deep-diving predators in open ocean habitats. Males are shallow-diving benthic predators in continental shelf habitats. Males gain six times more mass and acquire energy 4.1 times faster than females. High foraging success comes with a high mortality rate. Males are six times more likely to die than females. These foraging strategies and trade-offs are related to different energy demands and life-history strategies. Males use a foraging strategy with a high mortality risk to attain large body sizes necessary to compete for females, as only a fraction of the largest males ever mate. Females use a foraging strategy with a lower mortality risk, maximizing reproductive success by pupping annually over a long lifespan. Our results highlight how sex-specific traits can drive disparity in mortality rates and expand species' niche space. Further, trade-offs between foraging rewards and mortality risk can differentially affect each sex's ability to maximize fitness.

The scent of fear makes sea urchins go ballistic

BackgroundClassic ecological formulations of predator–prey interactions often assume that predators and prey interact randomly in an information-limited environment. In the field, however, most prey can accurately assess predation risk by sensing predator chemical cues, which typically trigger some form of escape response to reduce the probability of capture. Here, we explore under laboratory-controlled conditions the long-term (minutes to hours) escaping response of the sea urchin Paracentrotus lividus, a key species in Mediterranean subtidal macrophyte communities.MethodsBehavioural experiments involved exposing a random sample of P. lividus to either one of two treatments: (i) control water (filtered seawater) or (ii) predator-conditioned water (with cues from the main P. lividus benthic predator—the gastropod Hexaplex trunculus). We analysed individual sea urchin trajectories, computed their heading angles, speed, path straightness, diffusive properties, and directional entropy (as a measure of path unpredictability). To account for the full picture of escaping strategies, we followed not only the first instants post-predator exposure, but also the entire escape trajectory. We then used linear models to compare the observed results from control and predators treatments.ResultsThe trajectories from sea urchins subjected to predator cues were, on average, straighter and faster than those coming from controls, which translated into differences in the diffusive properties and unpredictability of their movement patterns. Sea urchins in control trials showed complex diffusive properties in an information-limited environment, with highly variable trajectories, ranging from Brownian motion to superdiffusion, and even marginal ballistic motion. In predator cue treatments, variability reduced, and trajectories became more homogeneous and predictable at the edge of ballistic motion.ConclusionsDespite their old evolutionary origin, lack of cephalization, and homogenous external appearance, the trajectories that sea urchins displayed in information-limited environments were complex and ranged widely between individuals. Such variable behavioural repertoire appeared to be intrinsic to the species and emerged when the animals were left unconstrained. Our results highlight that fear from predators can be an important driver of sea urchin movement patterns. All in all, the observation of anomalous diffusion, highly variable trajectories and the behavioural shift induced by predator cues, further highlight that the functional forms currently used in classical predator–prey models are far from realistic.

Female Pacific walruses (Odobenus rosmarus divergens) show greater partitioning of sea ice organic carbon than males: Evidence from ice algae trophic markers.

The expected reduction of ice algae with declining sea ice may prove to be detrimental to the Pacific Arctic ecosystem. Benthic organisms that rely on sea ice organic carbon (iPOC) sustain benthic predators such as the Pacific walrus (Odobenus rosmarus divergens). The ability to track the trophic transfer of iPOC is critical to understanding its value in the food web, but prior methods have lacked the required source specificity. We analyzed the H-Print index, based on biomarkers of ice algae versus phytoplankton contributions to organic carbon in marine predators, in Pacific walrus livers collected in 2012, 2014 and 2016 from the Northern Bering Sea (NBS) and Chukchi Sea. We paired these measurements with stable nitrogen isotopes (δ15N) to estimate trophic position. We observed differences in the contribution of iPOC in Pacific walrus diet between regions, sexes, and age classes. Specifically, the contribution of iPOC to the diet of Pacific walruses was higher in the Chukchi Sea (52%) compared to the NBS (30%). This regional difference is consistent with longer annual sea ice persistence in the Chukchi Sea. Within the NBS, the contribution of iPOC to walrus spring diet was higher in females (~45%) compared to males (~30%) for each year (p < 0.001), likely due to specific foraging behavior of females to support energetic demands associated with pregnancy and lactation. Within the Chukchi Sea, the iPOC contribution was similar between males and females, yet higher in juveniles than in adults. Despite differences in the origin of organic carbon fueling the system (sea ice versus pelagic derived carbon), the trophic position of adult female Pacific walruses was similar between the NBS and Chukchi Sea (3.2 and 3.5, respectively), supporting similar diets (i.e. clams). Given the higher quality of organic carbon from ice algae, the retreat of seasonal sea ice in recent decades may create an additional vulnerability for female and juvenile Pacific walruses and should be considered in management of the species.