Structure Of Marine Food Webs Research Articles

Impacts of Aggregation Methods and Trophospecies Number on the Structure and Function of Marine Food Webs

Impacts of Aggregation Methods and Trophospecies Number on the Structure and Function of Marine Food Webs

Potential impacts of ocean warming on energy flow and fisheries production in an overexploited ecosystem: Implication for effective fisheries management

The influences of ocean warming on marine lives have accelerated over the 21st century, greatly altering the structure and function of marine food webs and causing distributional shifts, species invasions, and changes in productivity. It is imperative to clarify the overall ecosystem responses to ocean warming and develop fisheries management strategies adaptive to the ecosystem changes. In this study, the potential impacts of ocean warming on trophic structure, energy flows, and fisheries production of an overexploited ecosystem were examined, and the effectiveness of fisheries management in mitigating warming impacts were also evaluated. We constructed a mass-balance food web model in Haizhou Bay and simulated three climate scenarios (RCPs 2.6, 4.5, and 8.5) along with different levels of fishing pressure, in order to examine the ecosystem responses to the combined changes in fishing and climate changes. Results showed that the total biomass of commercial species and fisheries catches would decline with rising temperature, especially under the RCP8.5 scenario. Ocean warming could induce lower trophic transfer efficiency and decrease energy recycling capacity within the food web, leading to large losses in total biomass and total production. Reducing fishing intensity could help mitigate the negative effects of ocean warming on fisheries productivity, but was insufficient to maintain ecological properties. Moreover, the effectiveness of such alternative measures would be diminished with increased greenhouse gas emissions, especially under the climate scenario of RCP8.5. The findings of this study highlight the need to slow the rise of sea temperature and implement climate-adaptive fisheries management in the future.

Changing environmental conditions have altered the feeding ecology of two keystone Arctic marine predators

Environmental change in the Arctic has impacted the composition and structure of marine food webs. Tracking feeding ecology changes of culturally-valued Arctic char (Salvelinus alpinus) and ringed seals (Pusa hispida) can provide an indication of the ecological significance of climate change in a vulnerable region. We characterized how changes in sea ice conditions, sea surface temperature (SST), and primary productivity affected the feeding ecology of these two keystone species over a 13- and 18-year period, respectively, in northern Labrador, Canada. Arctic char fed consistently on pelagic resources (δ13C) but shifted over time to feeding at a higher trophic level (δ15N) and on more marine/offshore resources (δ34S), which correlated with decreases in chlorophyll a concentration. A reduction in Arctic char condition factor and lipid content was associated with higher trophic position. Ringed seals also shifted to feeding at a higher trophic level, but on more pelagic resources, which was associated with lower SST and higher chlorophyll a concentrations. Years with abnormally high SSTs and reduced sea ice concentrations resulted in large isotopic niche sizes for both species, suggesting abrupt change can result in more variable feeding. Changes in abundance and distribution of species long valued by the Inuit of Labrador could diminish food security.

Amino acid carbon isotope fingerprints are unique among eukaryotic microalgal taxonomic groups

AbstractEukaryotic microalgae play critical roles in the structure and function of marine food webs. The contribution of microalgae to food webs can be tracked using compound‐specific isotope analysis of amino acids (CSIA‐AA). Previous CSIA‐AA studies have defined eukaryotic microalgae as a single functional group in food web mixing models, despite their vast taxonomic and ecological diversity. Using controlled cultures, this work characterizes the amino acid δ13C (δ13CAA) fingerprints—a multivariate metric of amino acid carbon isotope values—of four major groups of eukaryotic microalgae: diatoms, dinoflagellates, raphidophytes, and prasinophytes. We found excellent separation of essential amino acid δ13C (δ13CEAA) fingerprints among four microalgal groups (mean posterior probability reclassification of 99.2 ± 2.9%). We also quantified temperature effects, a primary driver of microalgal bulk carbon isotope variability, on the fidelity of δ13CAA fingerprints. A 10°C range in temperature conditions did not have significant impacts on variance in δ13CAA values or the diagnostic microalgal δ13CEAA fingerprints. These δ13CEAA fingerprints were used to identify primary producers at the base of food webs supporting consumers in two contrasting systems: (1) penguins feeding in a diatom‐based food web and (2) mixotrophic corals receiving amino acids directly from autotrophic endosymbiotic dinoflagellates and indirectly from water column diatoms, prasinophytes, and cyanobacteria, likely via heterotrophic feeding on zooplankton. The increased taxonomic specificity of CSIA‐AA fingerprints developed here will greatly improve future efforts to reconstruct the contribution of diverse eukaryotic microalgae to the sources and cycling of organic matter in food web dynamics and biogeochemical cycling studies.

Tracing carbon flow and trophic structure of a coastal Arctic marine food web using highly branched isoprenoids and carbon, nitrogen and sulfur stable isotopes

Climate-driven alterations of the marine environment are most rapid in Arctic and subarctic regions, including Hudson Bay in northern Canada, where declining sea ice, warming surface waters and ocean acidification are occurring at alarming rates. These changes are altering primary production patterns that will ultimately cascade up through the food web. Here, we investigated (i) the vertical trophic structure of the Southampton Island marine ecosystem in northern Hudson Bay, (ii) the contribution of benthic and pelagic-derived prey to the higher trophic level species, and (iii) the relative contribution of ice algae and phytoplankton derived carbon in sustaining this ecosystem. For this purpose, we measured bulk stable carbon, nitrogen and sulfur isotope ratios as well as highly branched isoprenoids in samples belonging to 149 taxa, including invertebrates, fishes, seabirds and marine mammals. We found that the benthic invertebrates occupied 4 trophic levels and that the overall trophic system went up to an average trophic position of 4.8. The average δ34S signature of pelagic organisms indicated that they exploit both benthic and pelagic food sources, suggesting there are many interconnections between these compartments in this coastal area. The relatively high sympagic carbon dependence of Arctic marine mammals (53.3 ± 22.2 %) through their consumption of benthic invertebrate prey, confirms the important role of the benthic subweb for sustaining higher trophic level consumers in the coastal pelagic environment. Therefore, a potential decrease in the productivity of ice algae could lead to a profound alteration of the benthic food web and a cascading effect on this Arctic ecosystem.

Bioregionalization of the coastal and open oceans of British Columbia and Southeast Alaska based on Sentinel-3A satellite-derived phytoplankton seasonality

Classifying the ocean into regions with distinct biogeochemical or physical properties may enhance our interpretation of ocean processes. High-resolution satellite-derived products provide valuable data to address this task. Notwithstanding, no regionalization at a regional scale has been attempted for the coastal and open oceans of British Columbia (BC) and Southeast Alaska (SEA), which host essential habitats for several ecologically, culturally, and commercially important species. Across this heterogeneous marine domain, phytoplankton are subject to dynamic ocean circulation patterns and atmosphere-ocean-land interactions, and their variability, in turn, influences marine food web structure and function. Regionalization based on phytoplankton biomass patterns along BC and SEA’s coastal and open oceans can be valuable in identifying pelagic habitats and representing a baseline for assessing future changes. We developed a two-step classification procedure, i.e., a Self-Organizing Maps (SOM) analysis followed by the affinity propagation clustering method, to define ten bioregions based on the seasonal climatology of high-resolution (300 m) Sentinel-3 surface chlorophyll-a data (a proxy for phytoplankton biomass), for the period 2016-2020. The classification procedure allowed high precision delineation of the ten bioregions, revealing separation between off-shelf bioregions and those in neritic waters. Consistent with the high-nutrient, low-chlorophyll regime, relatively low values of phytoplankton biomass (< 1 mg/m3) distinguished off-shelf bioregions, which also displayed, on average, more prominent autumn biomass peaks. In sharp contrast, neritic bioregions were highly productive (>> 1 mg/m3) and characterized by different phytoplankton dynamics. The spring phytoplankton bloom onset varied spatially and inter-annually, with substantial differences among bioregions. The proposed high-spatial-resolution regionalization constitutes a reference point for practical and more extensive implementation in understanding the spatial dynamics of the regional ecology, data-driven ocean observing systems, and objective regional management.

The microbiome of the pelagic tunicate Dolioletta gegenbauri: Apotential link between the grazing and microbial food web.

Bloom-forming gelatinous zooplankton occur circumglobally and significantly influence the structure of pelagic marine food webs and biogeochemical cycling through interactions with microbial communities. During bloom conditions especially, gelatinous zooplankton are keystone taxa that help determine the fate of primary production, nutrient remineralization, and carbon export. Using the pelagic tunicate Dolioletta gegenbauri as a model system for gelatinous zooplankton, we carried out a laboratory-based feeding experiment to investigate the potential ecosystem impacts of doliolid gut microbiomes and microbial communities associated with doliolid faecal pellets and the surrounding seawater. Metabarcoding targeting Bacteria and Archaea 16S rRNA genes/Archaea) and qPCR approaches were used to characterize microbiome assemblages. Comparison between sample types revealed distinct patterns in microbial diversity and biomass that were replicable across experiments. These observations support the hypothesis that through their presence and trophic activity, doliolids influence the structure of pelagic food webs and biogeochemical cycling in subtropical continental shelf systems where tunicate blooms are common. Bacteria associated with starved doliolids (representative of the resident gut microbiome) possessed distinct low-biomass and low-diversity microbial assemblages, suggesting that the doliolid microbiome is optimized to support a detrital trophic mode. Bacterial genera Pseudoalteromomas and Shimia were the most abundant potential core microbiome taxa, similar to patterns observed in other marine invertebrates. Exploratory bioinformatic analyses of predicted functional genes suggest that doliolids, via their interactions with bacterial communities, may affect important biogeochemical processes including nitrogen, sulphur, and organic matter cycling.

Climate change negates positive CO2 effects on marine species biomass and productivity by altering the strength and direction of trophic interactions

One of the biggest challenges in more accurately forecasting the effects of climate change on future food web dynamics relates to how climate change affects multi-trophic species interactions, particularly when multiple interacting stressors are considered. Using a dynamic food web model, we investigate the individual and combined effect of ocean warming and acidification on changes in trophic interaction strengths (both direct and indirect) and the consequent effects on biomass structure of food web functional groups. To do this, we mimicked a species-rich multi-trophic-level temperate shallow-water rocky reef food web and integrated empirical data from mesocosm experiments on altered species interactions under warming and acidification, into food-web models. We show that a low number of strong temperature-driven changes in direct trophic interactions (feeding and competition) will largely determine the magnitude of biomass change (either increase or decrease) of high-order consumers, with increasing consumer biomass suppressing that of prey species. Ocean acidification, in contrast, alters a large number of weak indirect interactions (e.g. cascading effects of increased or decreased abundances of other groups), enabling a large increase in consumer and prey biomass. The positive effects of ocean acidification are driven by boosted primary productivity, with energy flowing up to higher trophic levels. We show that warming is a much stronger driver of positive as well as negative modifications of species biomass compared to ocean acidification. Warming affects a much smaller number of existing trophic interactions, though, with direct consumer-resource effects being more important than indirect effects. We conclude that the functional role of consumers in future food webs will be largely regulated by alterations in the strength of direct trophic interactions under ocean warming, with ensuing effects on the biomass structure of marine food webs.

Sifting environmental DNA metabarcoding data sets for rapid reconstruction of marine food webs

AbstractMarine ecosystems are changing rapidly due to ocean warming, overfishing and a raft of other anthropogenic impacts. Such changes are expected to disrupt productivity dynamics and alter marine food webs, with likely negative consequences for ecosystem services. It is, therefore, essential to devise and implement methods that can rapidly and inexpensively monitor changes in the marine food web structure. Unfortunately, conventional methods for surveying marine food webs are typically laborious, expensive and often destructive, resulting in only a small fraction of marine ecosystems being well studied, and an even smaller subset of them being studied through time. Here, we pilot a low‐cost approach to reconstructing trophic networks of marine tropical, temperate and polar regions, using taxonomical inventories arising from published environmental DNA (eDNA) metabarcoding studies, and building trophic links based on primary literature information. Although the trophic webs obtained are a simplified approximation of those constructed with traditional methods, they generate realistic networks that fit with expectations, and allow ecological inference over time scales and costs that are orders of magnitude smaller than that traditionally achieved. We show the potential of a new application of environmental DNA analysis that promises to offer a rapid and scalable approach to gather vital information on ecosystem structure, hence boosting marine monitoring at a time of increasingly rapid environmental changes.

Feeding habits and trophic interactions of four sympatric hammerhead shark species reveal trophic niche partitioning

Knowledge of the ecological roles of species within food webs and how their trophic interactions affect food web structure is critical to model management and conservation scenarios for species that are suffering high levels of anthropogenic pressure, such as hammerhead sharks. In this paper, we analyze the diet and trophic relationships of 4 sympatric hammerhead shark species using a combination of stomach content and stable isotope analyses. These species showed trophic similarities by sex and trophic dissimilarities by maturity stage. We found that the trophic niche of hammerhead species tends to be more similar within species than among them. This suggests that competitive interactions are more likely to occur between conspecifics than between congeneric individuals and highlights the potential different roles that these species can play within the food web structure. The intermediate to high trophic positions observed inSphyrna corona,S.media,S.tiburoandS.lewinijuveniles indicate mesopredator roles, whereasS. lewinisubadults could be considered top predators. Our findings revealed multiple trophic interactions between hammerhead sharks and prey from different trophic levels, which could be critical for the structure and function of marine food webs.

Latitudinal changes in the trophic structure of benthic coastal food webs along the Antarctic Peninsula

Stable isotopes of C and N have been used to assess the effect of the duration of the sea ice season on the structure of benthic, Antarctic coastal food webs. Samples of suspended particulate organic matter, macroalgae and macroinvertebrates were collected at five subtidal rocky sites across a latitudinal gradient along the western Antarctic Peninsula and among the South Shetland Islands. We tested the hypotheses that trophic positions of omnivores decrease, and food web structure becomes more redundant at higher latitudes. A latitudinal shift in the isotope baseline was detected for both δ13C and δ15N, but the trophic positions of macroinvertebrates and their relative positions along the δ13C axis and were basically constant across sites, even after rescaling stable isotope ratios to account for shifts in the baseline. Although the northernmost and southernmost study sites differed significantly in most of the metrics of the food web structure, changes with latitude and the duration of the sea ice season were non-monotonic. Highly productive phytoplankton blooms during the ice-free season at Esperanza Bay and Rothera Point may explain the observed pattern, as they result in a massive supply of planktonic organic matter to the detritus bank in the seabed and, hence, shorten the C range and increase trophic redundancy. If this hypothesis is correct, the intensity of the summer phytoplankton bloom can be as relevant for the structure of the benthic marine food web as the duration of the sea ice season.

Links between Phenology of Large Phytoplankton and Fisheries in the Northern and Central Red Sea

Phytoplankton phenology and size structure are key ecological indicators that influence the survival and recruitment of higher trophic levels, marine food web structure, and biogeochemical cycling. For example, the presence of larger phytoplankton cells supports food chains that ultimately contribute to fisheries resources. Monitoring these indicators can thus provide important information to help understand the response of marine ecosystems to environmental change. In this study, we apply the phytoplankton size model of Gittings et al. (2019b) to 20-years of satellite-derived ocean colour observations in the northern and central Red Sea, and investigate interannual variability in phenology metrics for large phytoplankton (>2 µm in cell diameter). Large phytoplankton consistently bloom in the winter. However, the timing of bloom initiation and termination (in autumn and spring, respectively) varies between years. In the autumn/winter of 2002/2003, we detected a phytoplankton bloom, which initiated ~8 weeks earlier and lasted ~11 weeks longer than average. The event was linked with an eddy dipole in the central Red Sea, which increased nutrient availability and enhanced the growth of large phytoplankton. The earlier timing of food availability directly impacted the recruitment success of higher trophic levels, as represented by the maximum catch of two commercially important fisheries (Sardinella spp. and Teuthida) in the following year. The results of our analysis are essential for understanding trophic linkages between phytoplankton and fisheries and for marine management strategies in the Red Sea.

Characterizing niche differentiation among marine consumers with amino acid δ13C fingerprinting.

Marine food webs are highly compartmentalized, and characterizing the trophic niches among consumers is important for predicting how impact from human activities affects the structuring and functioning of marine food webs. Biomarkers such as bulk stable isotopes have proven to be powerful tools to elucidate trophic niches, but they may lack in resolution, particularly when spatiotemporal variability in a system is high. To close this gap, we investigated whether carbon isotope (δ13C) patterns of essential amino acids (EAAs), also termed δ13CAA fingerprints, can characterize niche differentiation in a highly dynamic marine system. Specifically, we tested the ability of δ13CAA fingerprints to differentiate trophic niches among six functional groups and ten individual species in the Baltic Sea. We also tested whether fingerprints of the common zooplanktivorous fishes, herring and sprat, differ among four Baltic Sea regions with different biochemical conditions and phytoplankton assemblages. Additionally, we investigated how these results compared to bulk C and N isotope data for the same sample set. We found significantly different δ13CAA fingerprints among all six functional groups. Species differentiation was in comparison less distinct, due to partial convergence of the species' fingerprints within functional groups. Herring and sprat displayed region‐specific δ13CAA fingerprints indicating that this approach could be used as a migratory marker. Niche metrics analyses showed that bulk isotope data had a lower power to differentiate between trophic niches than δ13CAA fingerprinting. We conclude that δ13CAA fingerprinting has a strong potential to advance our understanding of ecological niches, and trophic linkages from producers to higher trophic levels in dynamic marine systems. Given how management practices of marine resources and habitats are reshaping the structure and function of marine food webs, implementing new and powerful tracer methods are urgently needed to improve the knowledge base for policy makers.

1H NMR Metabolic Profile of Scyphomedusa Rhizostoma pulmo (Scyphozoa, Cnidaria) in Female Gonads and Somatic Tissues: Preliminary Results.

The Mediterranean basin is one of the regions heavily affected by jellyfish bloom phenomena, mainly due to the presence of scyphozoans, such as Rhizostoma pulmo. The jellyfish have few natural predators, and their bodies represent an organic-rich substrate that can support rapid bacterial growth with great impact on the structure of marine food webs. In Asiatic countries, jellyfish are widely studied for their health benefits, but their nutritional and nutraceutical values still remain poorly characterized. In this study, the differences in the 1H NMR spectroscopy metabolic profiles of R. pulmo female gonads and body fractions (including umbrella and oral arms), in different sampling periods, were studied. For each body compartment both lipid and aqueous extracts were characterized and their 1H NMR metabolic profiles subjected to multivariate analysis. From a statistical analysis of the extracts, a higher contents of ω-3 polyunsaturated fatty acids (PUFAs), amino acid and osmolytes (homarine, betaine, taurine) with important roles in marine invertebrates were observed in female gonads, whereas umbrella and oral arms showed similar metabolic profiles. These results support a sustainable exploitation of the jellyfish for the extraction of bioactive compounds useful in nutraceutical, nutricosmetics, and functional food fields.

Using chemical language to shape future marine health

“Infochemicals” (information‐conveying chemicals) dominate much of the underwater communication in biological systems. They influence the movement and behavior of organisms, the ecological interactions between and across populations, and the trophic structure of marine food webs. However, relative to their terrestrial equivalents, the wider ecological and economic importance of marine infochemicals remains understudied and a concerted, cross‐disciplinary effort is needed to reveal the full potential of marine chemical ecology. We highlight current challenges with specific examples and suggest how research on the chemical ecology of marine organisms could provide opportunities for implementing new management solutions for future “blue growth” (the sustainable use of ocean resources) and maintaining healthy marine ecosystems.

Changes in the population structure of Calanus sinicus during summer-autumn in the southern Yellow Sea

Calanus sinicus is a calanoid copepod widely distributed in coastal waters of China and Japan, and oversummering strategies may have major impacts on their population dynamics which in turn affect local marine food web structure. The abundance, stage composition, and sex composition of the planktonic copepod C. sinicus were studied from August to October 2002 in the southern Yellow Sea to understand how its population recovers from the over-summering state. Results showed that C. sinicus had low reproduction in August due to high temperature, except in waters near the Cheju Island with rich food and moderate bottom temperature, but the reproduction rates here decreased in September-October as food availability declined. When temperature dropped in September-October, C. sinicus actively propagated in coastal shallow waters. However, reproduction rates of C. sinicus individuals inhabiting the Yellow Sea Cold Water Mass (YSCWM) remained low during the three months of the study. The percentage of C. sinicus females was high during the reproductive period, which suggests that the sex composition of adult C. sinicus may reflect whether or not the population is in the reproductive mode. Numerous fifth copepodite stage (CV) C. sinicus aggregated in the YSCWM in a suspended developmental stage during the three months of this study, and they potentially served as the parental individuals for population development when conditions became optimal for reproduction later in the year.

Alternative energy pathways in Southern Ocean food webs: Insights from a balanced model of Prydz Bay, Antarctica

In recent years, there has been a shift away from the long-standing paradigm in which a short, krill-dominated food chain was considered to be the central element in Southern Ocean food webs. Instead, there is now increasing recognition that alternative energy pathways through mid-trophic level groups (mesopelagic fish and squid) may be equally (if not more) important than the krill pathway in many regions. Ecosystem models are a valuable tool to synthesise existing data on the structure of marine food webs and to visualise and quantify alternative energy pathways. In this study we develop a static mass balance food web model for the southern Kerguelen Axis region (Prydz Bay and Princess Elizabeth Trough) to evaluate the importance of alternative energy pathways through mid-trophic level groups, including fish, squid and krill, in maintaining energy flow to top predators within East Antarctica. Our model reveals several major trophic pathways distinct from, and equally important to the Antarctic krill (Euphausia superba) pathway. Using simple scenarios of reductions in krill biomass, we investigate how the system might switch to a state dominated by fish and squid pathways with the response of krill-reliant predators strongly dependent on their ability to switch to other prey sources. We conclude by discussing what these findings might suggest for the future vulnerability of East Antarctic food webs and the implications for future modelling work in the region.

Reconstructing hyperdiverse food webs: Gut content metabarcoding as a tool to disentangle trophic interactions on coral reefs

Abstract Anthropogenic stressors have strong impacts on ecosystems. To understand their influence, detailed knowledge about trophic relationships among species is critical. However, this requires both exceptional resolution in dietary assessments and sampling breadth within communities, especially for highly diverse, tropical ecosystems. We used gut content metabarcoding across a broad range of coral reef fishes (8 families, 22 species) in Mo'orea, French Polynesia, to test whether this technique has the potential to capture the structure of a hyperdiverse marine food web. Moreover, we explored whether taxonomic groups (families) and traditional, broad‐scale trophic assignments explained fish diet across four different metrics of quantifying predator–prey interactions. Metabarcoding yielded a large number (4,341) of unique operational taxonomic units (i.e. prey) with high‐resolution taxonomic assignments (i.e. often to the level of genus or species). We demonstrate that across multiple metrics, taxonomic group at the family level is a consistently better, albeit still weak, predictor of empirical trophic relationships than frequently used, broad‐scale functional assignments. Our method also reveals a complex trophic network with fine‐scale partitioning among species, further emphasizing the importance of examining fish diets beyond broad trophic categories. We demonstrate the capacity of metabarcoding to reconstruct diverse and complex food webs with exceptional resolution, a significant advancement from traditional food web reconstruction. Furthermore, this method allows us to pinpoint the trophic niche of species with niche‐based modelling, even across hyperdiverse species assemblages such as coral reefs. In conjunction with complementary techniques such as stable isotope analysis, applying metabarcoding to whole communities will provide unparalleled information about energy and nutrient fluxes and inform their susceptibility to disturbances even in the world's most diverse ecosystems.

The seasonal succession of optimal diatom traits

AbstractDiatoms are a successful taxon of primary producers in the world's oceans with significant impact both on biogeochemical cycles and the structure of marine food webs. We present a trait‐based model that captures key physical characteristics of diatoms: a silica exoskeleton and a large centric vacuole. We examine how these unique features contribute to the success of diatoms compared to similar‐sized, nonvacuolated, shell‐less phytoplankton with identical photosynthetic and nutrient uptake machinery. Our predicted seasonal succession of optimal diatom traits and growth rates are consistent with observed annual time series. The respective environmental conditions where the diatom attributes of shell and vacuole confer an advantage over nonvacuolated, shell‐less phytoplankton are typical during the transition phases of seasonal cycles—during the early phase when vacuolation provides an advantage in terms of light affinity and protection against protist grazers and late phase when specific nutrient affinity and protection from metazoan grazers are of benefit. Although the model reproduces high light and nutrient affinities as well as observed seasonal patterns of diatom dominance, it fails to predict the high growth rates generally observed in diatoms compared to other phytoplankton taxa. This exposes a conundrum in our mechanistic understanding of phytoplankton trade‐offs; namely, if the high growth rate of diatoms is independent of their physical attributes (shell and/or vacuole), why has it not been exploited by nondiatom taxa?

Back to the future? Late Holocene marine food web structure in a warm climatic phase as a predictor of trophodynamics in a warmer South-Western Atlantic Ocean.

Stable carbon and nitrogen isotope ratios in the skeletal elements of both ancient and modern marine species from the Beagle Channel were used to compare the structure of Late Holocene and modern food webs, and predict potential changes as a result of a Sea Surface Temperature (SST) increase in the region. Complementary, ancient and modern shells of limpets and mussels were isotopically analysed to explore changes in the isotopic baseline and compare marine food webs through time after an appropriate correction for baseline shifts. Results confirmed a declining pattern of marine primary productivity during the Late Holocene in the Beagle Channel. In general, the isotopic niches overlapped largely in the ancient food web in comparison to the current marine one, with the exception of that of cormorants (Phalacrocorax sp.). Our data suggest that all the species that have undergone intense human exploitation (Arctocephalus australis, Otaria flavescens and Merluccius sp.) significantly increased their trophic levels. The most important finding of this work was the very high isotopic overlap between snoek (Thyrsites atun) and hake (Merluccius sp.) during the Late Holocene. Increasing SST as a result of global warming could favour the recolonization of the southern South-Western Atlantic Ocean by snoek from the South-Eastern Pacific Ocean, with a potential impact on the landings of the economically important Argentine and Austral hake. These findings highlight the relevance of using zooarchaeological remains for providing predictions about marine food webs changes in the near future.