References of "Lepoint, Gilles"
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See detailFacultative paedomorphosis as a mechanism promoting intraspecific niche differentiation
Lejeune, Benjamin ULiege; Sturaro, Nicolas ULiege; Lepoint, Gilles ULiege et al

in Oikos (in press)

Organisms with complex life cycles are characterized by a metamorphosis that allows for a major habitat shift and the exploitation of alternative resources. However, metamorphosis can be bypassed in some ... [more ▼]

Organisms with complex life cycles are characterized by a metamorphosis that allows for a major habitat shift and the exploitation of alternative resources. However, metamorphosis can be bypassed in some species through a process called paedomorphosis, resulting in the retention of larval traits at the adult stage and is considered important at both micro- and macroevolutionary scales. In facultatively paedomorphic populations of newts, some individuals retain gills and a fully aquatic life at the adult stage (paedomorphs), while others undergo complete metamorphosis (metamorphs), allowing for a terrestrial life-stage. Because facultative paedomorphosis affects trophic structures and feeding mechanism of newts, one hypothesis is that it may be maintained as a trophic polymorphism, with the advantage to lessen intraspecific competition during the shared aquatic life-stage. Here, we tested this hypothesis combining stomach content data with stable isotope techniques, using carbon and nitrogen stable isotopes, in facultatively paedomorphic alpine newts Ichthyosaura alpestris. Both stomach content and stable isotope analyses showed that paedomorphs had smaller trophic niches and were more reliant on pelagic resources, while metamorphs relied more on littoral resources, corresponding to a polyphenism along the littoral-pelagic axis and the extension of the population's trophic niche to otherwise ‘underused’ pelagic resources by paedomorphs. Interestingly, stable isotopes revealed that the trophic polyphenism was less marked in males than in females and potentially linked to sexual activity. Although paedomorphosis and metamorphosis are primarily seen as results of tradeoffs between the advantages of using aquatic versus terrestrial habitats, this study provides evidence that additional forces, such as intraspecific trophic niche differences between morphs and trophic niche expansion, may play an important role in the persistence of this dimorphism in heterogeneous environments. Moreover, the different patterns found in males and females show the importance of considering sex to understand the evolutionary ecology of trophic polymorphisms. [less ▲]

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See detailUse of multi-element stable isotope ratios to investigate ontogenetic movements of Micropogonias furnieri in a tropical Brazilian estuary
Pizzochero, Ana Carolina; Michel, Loïc ULiege; Chenery, Simon et al

in Canadian Journal of Fisheries & Aquatic Sciences (in press)

The whitemouth croaker, Micropogonias furnieri, is a long-lived fish of high commercial importance in the Western Atlantic Ocean. Here, we used stable isotope ratios of carbon, sulfur and nitrogen and ... [more ▼]

The whitemouth croaker, Micropogonias furnieri, is a long-lived fish of high commercial importance in the Western Atlantic Ocean. Here, we used stable isotope ratios of carbon, sulfur and nitrogen and isotopic niche metrics (SIBER) to study feeding habits and track habitat use by whitemouth croakers in Guanabara Bay, an estuary in Rio de Janeiro state, Brazil. Our results highlighted size-related habitat segregation, with small juvenile (< 30 cm) fishes residing mostly inside estuaries, while large adult (> 60 cm) fishes feed mainly in Continental Shelf (CS) waters. Medium adult fishes (30-60 cm) appear to feed in multiple coastal and CS habitats. Moreover, their feeding ecology showed strong temporal differences, linked with seasonal and, to a lesser extent, inter-annual variation in oceanographic features of the ecosystem in which they live. Overall, these differences in ecological features suggest that (1) adult and juvenile whitemouth croakers should be treated as different components of the food web and (2) the conservation of these habitats should be prioritized to better manage and sustain the coastal fisheries in Guanabara Bay. [less ▲]

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See detailEffects of fluid preservation on sea star stable isotope compositions: How useful can museum collections be for trophic ecology studies?
Le Bourg, Baptiste ULiege; Lepoint, Gilles ULiege; Michel, Loïc

Poster (2017, November 23)

Stable isotope analyses (SIA) of carbon (δ13C) and nitrogen (δ15N) are a common tool to investigate the trophic ecology of animals. After field sampling, animal tissues are usually preserved dried or ... [more ▼]

Stable isotope analyses (SIA) of carbon (δ13C) and nitrogen (δ15N) are a common tool to investigate the trophic ecology of animals. After field sampling, animal tissues are usually preserved dried or frozen before subsequent analysis. However, museum samples, or samples not initially collected for SIA are often fixed in preservative solutions. These preservation methods may alter stable isotope ratios in animal tissues, and those effects should be quantified. Here, we investigated long-term effects (one year) of four preservation methods (freezing, alcohol, formaldehyde, drying) on δ13C and δ15N values of sea stars. We show that only formaldehyde preservation significantly affects δ13C values. However, after being altered, the mean δ13C value remained stable over time, suggesting that a correction factor may be used regardless of preservation time. δ15N values change across time for all methods except freezing but this may be the result of a higher intra-individual variability of δ15N values. The influence of preservation methods on estimation of isotopic niches size (parameterised as standard ellipse area) was also investigated. Bayesian estimations of standard ellipse areas (SEAB) of preserved samples were not different from those of fresh samples except for the samples preserved 6 months in alcohol. These preliminary results suggest that samples stored during one year in preservative fluids may be used for SIA in order to investigate the trophic ecology of sea stars. Future results will also help to determine whether the findings can be generalised to sea stars preserved for a longer time, such as those in museum collections. [less ▲]

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See detailMorphological diversification of the endemic Antarctic fishes Trematominae (Notothenioidei, Teleostei)
Frederich, Bruno ULiege; Heindler, Franz Maximilian; Christiansen, Henrik et al

Poster (2017, November 23)

Adaptive radiation involves the early, rapid ecological and morphological diversification of multiple lineages from a common ancestor into new, diverging adaptive zones. Regarding this definition with ... [more ▼]

Adaptive radiation involves the early, rapid ecological and morphological diversification of multiple lineages from a common ancestor into new, diverging adaptive zones. Regarding this definition with emphasis on the tempo of diversification, Antarctic notothenioids represent one of the very few examples of adaptive radiation in marine fishes. Time-calibrated phylogenies suggest that the diversification of most speciose notothenioid lineages occured between 20 and 15 Ma. The subfamily Trematominae is one of those diverse subclades showing a large range of ecological niches. In the present study, we aim to describe the evolutionary history of Trematomus species. By combining a consensus time-tree and a geometric morphometric dataset, we first illustrate their pattern of cephalic shape diversification in a phylomorphospace and we infer the morphology of their common ancestor. We also explore whether the cephalic shape data shows a phylogenetic signal, which is defined as the statistical dependence among species trait values due to their phylogenetic relatedness. The combination of phylogenetic signal test and exploration of the phylomorphospace allows us to assess whether Trematomus rapidly diverged in various adaptive zones as expected under a classic scenario of adaptive radiation. [less ▲]

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See detailTrophic ecology of icefishes (Notothenioidei, Perciformes) in a context of climate change
Peignot, Quentin; Frederich, Bruno ULiege; Lepoint, Gilles ULiege et al

Poster (2017, November 23)

The Southern Ocean currently undergoes major environmental modifications related to climate change. When faced with environmental changes, all organisms are expected to have some intrinsic capacity to ... [more ▼]

The Southern Ocean currently undergoes major environmental modifications related to climate change. When faced with environmental changes, all organisms are expected to have some intrinsic capacity to adapt their ecological habits to their new life conditions. Currently, biological traits of many Antarctic species are still unknown and we need such information to assess their capacity to adapt to natural and anthropogenic perturbations. Notothenioidei (Perciformes), or icefishes, are endemic to the Southern Ocean and they are an important trophic component of these marine ecosystems. Here we used stable isotopes ratios of carbon (δ13C) and nitrogen (δ15N) of two well represented genera of icefishes (Trematomus and Lepidonotothen) sampled in 2002/2004 and/or in 2015/2016 to better understand their resources partitioning and the influence of environmental changes on their trophic ecology. Isotopic niches (which are a proxy of the realized ecological niches) were modeled using the SIBER (Stable Isotope Bayesian Ellipses in R) R-package. Our results revealed a great variation in isotopic compositions among icefishes, suggesting that they exploit a wide array of resources. The overlap between the isotopic niches of Trematomus and Lepidonotothen genera in 2002/2004 highlights a possible past competition for resources. Moreover, temporal evolution of niches suggests taxon-specific ecological plasticity in response to variation in environmental parameters and/or in prey availability. An increase in resources partitioning between the two genera was observed over the studied period. In the future, it would be interesting to use mixing models including isotopic composition of potential preys to identify possible changes in their trophic ecology. [less ▲]

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See detailFurther insight into the iterative ecological radiation of damselfishes (Pomacentridae)
Gajdzik, Laura ULiege; Lepoint, Gilles ULiege; Michel, Loic et al

Conference (2017, October 05)

The evolutionary history of Pomacentridae (damselfishes) is a rare example of the occurrence of an iterative ecological radiation in the ocean. Damselfishes have experienced many repeated convergences ... [more ▼]

The evolutionary history of Pomacentridae (damselfishes) is a rare example of the occurrence of an iterative ecological radiation in the ocean. Damselfishes have experienced many repeated convergences wherein subclades radiated across similar trophic strategies (i.e. pelagic foragers, benthic feeders, and an intermediate group) and similar morphologies. The presence of evolutionary convergences in damselfishes was recently highlighted by the combination of ecological and morphological data, and the use of phylogenetic comparative methods. Nevertheless, many other aspects of these replicated sets of lineages remain unexplored. For example, little is known about the functional diversity of assemblages including convergent lineages that emerged from iterative processes of ecological radiation, or which of the niche-related processes and phylogenetic conservatism are the major factors shaping these assemblages. Here, we conducted a quantitative comparison of these processes in damselfish assemblages that belong to three distinct Indo-Pacific coral reefs differing in taxonomic composition, morphology and degree of human disturbance. Using various metrics, we compared the functional diversity (based on a dataset of eight functional traits) and the isotopic diversity (a proxy of trophic diversity) among assemblages, grasping many aspects of the eco-functional diversity of Pomacentridae. We also tested whether these eco-functional traits displayed some evolutionary conservatism. Our results demonstrate that the eco-functional diversity of damselfishes follows similar patterns among Indo-Pacific coral reefs. The trophic space remains equivalent despite gradient in species richness, whereas the number of functional entities occupied by taxa dictates the size of the functional space. In each assemblage, eco-functional niches are highly differentiated and evenly distributed in spaces of similar size. The inconsistent phylogenetic structure of eco-functional traits suggests that the similarity in the diversity of damselfish assemblages is mainly driven by niche-based processes and not by phylogenetic relatedness. We suggest that a broader application of our approach will help to uncover the mechanisms of reef fish community assembly over space and time. [less ▲]

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See detaila journey through stable isotopes applications in trophic ecology
Lepoint, Gilles ULiege

Learning material (2017)

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See detailEffects of an experimental resource pulse on the macrofaunal assemblage inhabiting seagrass macrophytodetritus
Remy, François ULiege; Gobert, Sylvie ULiege; Lepoint, Gilles ULiege

in Belgian Journal of Zoology (2017), 147(1), 1-15

Physical disturbances and resource pulses are major structuring drivers of terrestrial and aquatic ecosystems. The accumulations of exported dead leaves from the Neptune grass, Posidonia oceanica (L ... [more ▼]

Physical disturbances and resource pulses are major structuring drivers of terrestrial and aquatic ecosystems. The accumulations of exported dead leaves from the Neptune grass, Posidonia oceanica (L.) Delile are ephemeral and highly dynamic detrital habitats offering food sources and shelter for vagile macrofauna community. These habitats are frequently subject to wind and storms which can add “new” detrital material to previous accumulations; these can be defined as resource pulses and could potentially impact the associated macrofauna. This study assesses the impact of an experimental resource pulse on the macrofauna associated with exported P. oceanica litter accumulations. The experimental design consisted of two pulse treatments (the addition of dead leaves with and without the associated fauna), and two controls (one procedural, and one total control), where the added material was left underwater for 14 days. Invertebrates then present in the sampled detritus were all identified and counted. Our data suggest that the responses of these invertebrates to resource pulses present intermediate characteristics between aquatic and terrestrial ecosystems responses. Inputting a moderate amount of dead P. oceanica leaves into experimental mesocosms had a non-negligible impact and rapidly affected the macrofauna community. Specialist detritivores species were boosted while herbivore/detritivore species dramatically decreased. Predators also showed a modest but significant density increase, demonstrating the fast propagation of the pulse response throughout the entire community and through several trophic levels. Strict hypoxia-tolerant species were also only observed in the treated mesocosms, indicating the strong influence of resource pulses on physico-chemical conditions occurring inside litter accumulations. [less ▲]

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See detailInfluence of environmental conditions on trophic niche partitioning among sea stars assemblages
Le Bourg, Baptiste ULiege; Blanchard, Alice; Danis, Bruno et al

Conference (2017, July 10)

The Southern Ocean undergoes intense and contrasted impacts linked to climate change. The Western Antarctic Peninsula is one of the most rapidly warming regions of the world (Meredith and King, 2005 ... [more ▼]

The Southern Ocean undergoes intense and contrasted impacts linked to climate change. The Western Antarctic Peninsula is one of the most rapidly warming regions of the world (Meredith and King, 2005), resulting in sharp sea ice cover decrease (Parkinson and Cavalieri, 2012). In contrast, surface temperature and sea ice cover remain stable in other regions such as the Weddell Sea. Sea stars (Echinodermata: Asteroidea) are a key group of the Southern Ocean benthos, thought to be quite resistant to seawater temperature changes (Peck et al., 2008). Other, more indirect environmental changes, might induce important shifts in food web structure and fluxes, that may affect sea stars trophic ecology. In this context, the aim of this study was to use stable isotopes ratios of C, N and S to study sea stars trophic ecology to characterise their trophic diversity and plasticity regarding food web changes. Sea stars were sampled during the austral summer in the South Georgia (sub-Antarctic) in 2011 and in the South Shetland (2006) and South Orkney Islands (2016), as well as in the Weddell Sea (2015-2016). Trophic diversity, i.e. differences of trophic ecology between sea star species, and variability, i.e. differences of trophic ecology between individuals of the same species, were investigated in each region by investigating isotopic dispersion and isotopic niche (proxy of the trophic niche) areas and overlap. Difference in niche width and overlap between the regions may be the result of different environmental conditions, including sea ice coverage and dynamics. For example, in the South Shetland, sea stars had small and poorly differentiated isotopic niches. This result indicate that they may exploit the same benthic communities relying on few common food sources such as organic matter released during sea ice melting (Isla et al., 2006) or sinking phytoplankton (Mincks et al., 2008). Whether this situation leads to competition or not depends on the resources availability. In contrast, isotopic niches were larger and better separated for sea stars from South Georgia. South Georgia is an oligotrophic environment with no sea ice (Korb et al., 2008). As available food items are more limited but, perhaps, more diversified, a higher trophic segregation may appear between species. Ultimately, this project will help delineating processes determining trophic ecology of Southern Ocean sea stars. This research was funded by the Belgian Federal Science Policy Office (BELSPO) in the framework of the vERSO and RECTO project (rectoversoprojects.be). [less ▲]

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See detailIncreased sea ice cover disrupts food web structure in Antarctic coastal benthic ecosystem
Michel, Loïc ULiege; Danis, Bruno; Dubois, Philippe et al

Conference (2017, July 10)

Antarctica currently undergoes strong and contrasted impacts linked to climate change. While the West Antarctic Peninsula is one of the most rapidly warming regions in the world, resulting in sea ice ... [more ▼]

Antarctica currently undergoes strong and contrasted impacts linked to climate change. While the West Antarctic Peninsula is one of the most rapidly warming regions in the world, resulting in sea ice cover decrease, the sea ice cover of East Antarctica unexpectedly tends to increase. Here, we studied shallow (0-20 m) benthic food web structure on the coasts of Petrels Island (Adélie Land, East Antarctica) during an event of unusually high spatial and temporal (two successive austral summers without seasonal break-up) sea ice cover. Using time-tested integrative trophic markers (stable isotope ratios of carbon, nitrogen and sulfur) and state-of-the-art data analysis tools (Bayesian ecological models), we studied the structure of the food web associated to benthic macroinvertebrates communities. In total, 28 taxa spanning most present animal groups (sponges, sea anemones, nemerteans, nematods, sipunculids, sessile and mobile polychaetes, gastropods, bivalves, pycnogonids, crustaceans, sea stars, sea urchins, brittle stars and sea cucumbers) and functional guilds (grazers, deposit feeders, filter feeders, predators, scavengers) were investigated. Our results indicate that the absence of seasonal sea ice breakup deeply influences coastal benthic food webs. We recorded marked differences from literature data, both in terms of horizontal (i.e. primary producers and resources supporting animal populations) and vertical (i.e. trophic level of the studied consumers) structure of the food web. Overall, sympagic algae dominated the diet of many key consumers, and the trophic levels of invertebrates were low, suggesting omnivore consumers relied less on predation and/or scavenging than in normal environmental conditions. Surprisingly, few animals seemed to feed on the extremely abundant benthic biofilm, whose exceptional development was also presumably linked with the peculiar sea ice conditions. Comparison of data obtained in the austral summers of 2013-2014 (first year without seasonal breakup) and 2014-2015 (second year without seasonal breakup) clearly showed that the observed trends were linked to actual temporal changes in invertebrate feeding habits rather than with other potential ecological drivers. Our results provide insights about how Antarctic benthic consumers, which have evolved in an extremely stable environment, might adapt their feeding habits in response to sudden changes in environmental conditions and trophic resource availability. They also show that local and/or global trends of sea ice increase in Antarctica have the potential to cause drastic changes in food web structure and therefore impact benthic communities. This research was funded by the Belgian Federal Science Policy Office (BELSPO) in the framework of the vERSO project (http://www.versoproject.be). [less ▲]

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See detailIn Search for Marine Antarctic Cyanobacteria
Lara, Yannick ULiege; Stelmach Pessi, Igor ULiege; Durieu, Benoit ULiege et al

Poster (2017, July)

Cyanobacteria are among the most ancient prokaryotic phyla present on the planet. They are thought to be responsible of two major geological changes and evolutionary process, the Great Oxygenation Event ... [more ▼]

Cyanobacteria are among the most ancient prokaryotic phyla present on the planet. They are thought to be responsible of two major geological changes and evolutionary process, the Great Oxygenation Event and the Endosymbiosis, which supported modern Life. In Polar freshwater and terrestrial ecosystems, cyanobacteria often constitute the major carbon fixers and the base of the food web. They are present in a wide range of habitat from hypersaline lakes to cryoconites. Nevertheless, their presence between the Polar front and Antarctic coast remains enigmatic. For a long time, it has been accepted that they were not present in Antarctic waters (Wilkins et al., 2012). However, they were found in low abundances in two publications, which were investigated the water column (Wilmotte et al., 2002; Wilkins et al., 2013). There is still a lack of information regarding their presence and role in Antarctic coastal waters. In order to investigate the presence of cyanobacteria in Antarctic marine benthos, samples were collected by scuba diving during two expeditions (2015, 2016) in the Lion’s channel, (Terre Adélie, Antarctica). Samples were directly frozen, dried or fixed with formaldehyde. DNA was extracted from one frozen sample and two dried samples. Then, 16S rRNA V3-V4 region was amplified using cyanobacteria-specific primers. Amplicons were sequenced using MiSeq Illumina technology. In parallel, fixed and frozen samples were scrutinized by microscopy. We obtained 14 558 reads, which were related to Cyanobacteria. They clustered into 97 OTUs and belong to six orders (Chroococcales, Nostocales, Oscillatoriales, Pseudanabaenales, Stigonematales, Synechococcales) with a large dominance of Pseudanabaenales. Thirty-one of the cyanobacterial OTUs were 100% identical to sequences of strains isolated from freshwater environment, and air samples from both temperate and Polar regions. Microscope observations revealed the presence of at least 3 cyanobacterial morphotypes including thin filaments, large Oscillatoriales, and a potential symbiotic or opportunist Nostocales. Albeit the low abundance of reads attributed to cyanobacteria, it remains necessary to assess their ecological role in Antarctic coastal waters. [less ▲]

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See detailStable isotopes reveal effects of environmental changes on ecological niches of Iphimediidae amphipods
Michel, Loïc ULiege; d'Udekem d'Acoz, Cédric; Frederich, Bruno ULiege et al

Poster (2017, July)

When faced with environmental changes, organisms are expected to have some intrinsic ability to adapt through ecological plasticity. However, this process is still poorly understood in many Antarctic ... [more ▼]

When faced with environmental changes, organisms are expected to have some intrinsic ability to adapt through ecological plasticity. However, this process is still poorly understood in many Antarctic invertebrates. Here, we focused on Iphimediidae amphipods, as this widely distributed family shows important ecological diversity. In total, 248 amphipods (19 species) from two widely different zones (the West Antarctic Peninsula, or WAP, and Adélie Land, AL) were studied to elucidate how environment can influence ecological niche parameters. Ecological niches were explored using stable isotope ratios of carbon and nitrogen and the SIBER approach (Jackson et al., 2011). The isotopic niche of the whole amphipod assemblage was wider in WAP than in AL. This was true for both total (proxy of the whole range of resources exploited by animals) and the core (proxy of the most commonly used resources) isotopic niches. The ratio between total and core isotopic niches was smaller in WAP than in AL (4.13 vs. 5.74), suggesting that in WAP, animals commonly use a greater relative percentage of the resources to which they have access. Niche modelling at the specific level revealed that this trend was not found in all taxa. For example, niches of Gnathiphimedia sexdentata and Iphimediella microdentata were bigger in WAP than in AL, following the general pattern. On the other hand, niches of Echiniphimedia echinata and E. hodgsoni had the same width in both areas. Moreover, relative niche overlap between these two species was much higher in WAP (42%) than in AL (20%). Our results indicate that the widely different environmental conditions encountered by the animals in these two zones clearly influence their ecology. Overall, Iphimediidae amphipods tend to exploit more resources in WAP, i.e. in the zone where impacts of global change (temperature increase, sea ice cover decrease) are the strongest. Niche overlap between some closely related (i.e. congeneric) species was also more important in WAP. Ultimately, environmental changes in this region might reinforce these trends, which might lead to competition and perturb amphipod community structure. This research was funded by the Belgian Federal Science Policy Office (BELSPO) in the framework of the vERSO and RECTO projects. [less ▲]

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See detailComparative Feeding Ecology of Cardinalfishes (Apogonidae) at Toliara Reef, Madagascar
Frederich, Bruno ULiege; Michel, Loïc ULiege; Zaeytydt, Esther et al

in Zoological Studies (2017), 56(10), 1-14

Despite their importance in coral reef ecosystem function and trophodynamics, the trophic ecology of nocturnal fishes (e.g. Apogonidae, Holocentridae, Pempheridae) is by far less studied than diurnal ones ... [more ▼]

Despite their importance in coral reef ecosystem function and trophodynamics, the trophic ecology of nocturnal fishes (e.g. Apogonidae, Holocentridae, Pempheridae) is by far less studied than diurnal ones. The Apogonidae (cardinalfishes) include mostly carnivorous species and evidence of trophic niche partitioning among sympatric cardinalfishes is still limited. The present study combines stomach contents and stable isotope analyses to investigate the feeding ecology of an assemblage of eight cardinalfishes from the Great Reef of Toliara (SW Madagascar). δ13C and δ15N of fishes ranged between -17.49‰ and -10.03‰ and between 6.28‰ and 10.74‰, respectively. Both stomach contents and stable isotopes showed that they feed on planktonic and benthic animal prey in various proportions. Previous studies were able to group apogonids in different trophic categories but such a discrimination is not obvious here. Large intra-specific variation in the stomach contents and temporal variation in the relative contribution of prey to diet support that all apogonids should be considered as generalist, carnivorous fishes. However the exploration of the isotopic space revealed a clear segregation of isotopic niches among species, suggesting a high level of resource partitioning within the assemblage. According to low inter-specific variation in stomach content compositions, we argue that the differences in isotopic niches could be driven by variation in foraging locations (i.e. microhabitat segregation) and physiology among species. Our temporal datasets demonstrate that the trophic niche partitioning among cardinalfishes and the breadth of their isotopic niches are dynamic and change across time. Factors driving this temporal variation need to be investigated in further studies. [less ▲]

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See detailThe use of stable isotopes in marine animal trophic ecology
Sturaro, Nicolas ULiege; Lepoint, Gilles ULiege; Frederich, Bruno ULiege et al

Conference (2017, May 05)

Stable isotope analysis has been recognised as a useful tool for studying animal diet, identifying trophic relationships, and delineating food web structures as well as their alteration by human ... [more ▼]

Stable isotope analysis has been recognised as a useful tool for studying animal diet, identifying trophic relationships, and delineating food web structures as well as their alteration by human activities. Over the past decade, the number of studies using stable isotopes of carbon and nitrogen in marine trophic ecology has increased rapidly as technological advancements greatly facilitate their use. This tool is now among the most popular in ecology and several fields of investigations have developed, including the extension of analyses to more ‘difficult’ stable isotope ratio measurements such as sulfur, the use of isotope mixing models, and the creation of compound-specific stable isotope analysis. Here, we present three case studies taken from our own investigations and previously published literature. The first investigates seagrass detritus ecosystem in which the coexistence of a rich number of species of crustacean raises the question of whether trophic diversity exist among these species. The second examines the feeding habits of coral reef fish and explores whether habitat choice on the reef and their behaviour emerges as good predictors of diet. The third presents the potential use of stable isotope analysis in studying the nutrition of scleractinian corals, which are complex symbiotic organisms that usually present both autotrophic and heterotrophic pathways. This tool has enhanced our understanding of coral species biology, yet it remains underused. Overall, we aim to provide initial insights into stable isotope analysis for illustrating their utility and potential applications to better understand food web structures and species diet in the waters around Taiwan. [less ▲]

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See detailUnusually high sea ice cover influences resource use by benthic invertebrates in coastal Antarctica
Michel, Loïc ULiege; Dubois, Philippe; Eleaume, Marc et al

Conference (2017, May 04)

Antarctica currently undergoes strong and contrasted impacts linked with climate change. While the West Antarctic Peninsula is one of the most rapidly warming regions in the world, resulting in sea ice ... [more ▼]

Antarctica currently undergoes strong and contrasted impacts linked with climate change. While the West Antarctic Peninsula is one of the most rapidly warming regions in the world, resulting in sea ice cover decrease, the sea ice cover of East Antarctica unexpectedly tends to increase, possibly in relation with changes in atmospheric circulation. Changes in sea ice cover are likely to influence benthic food web structure through modifications of benthic-pelagic coupling, disruption of benthic production and/or modifications of benthic community structure (i.e. resource availability for benthic consumers). Here, we studied shallow (0-20 m) benthic food web structure on the coasts of Petrels Island (Adélie Land, East Antarctica) during an event of unusually high spatial and temporal (two successive austral summers without seasonal break-up) sea ice cover. Using stable isotope ratios of C and N and the SIAR mixing model, we examined importance of 4 organic matter sources (benthic macroalgae, benthic biofilm, sympagic algae, suspended particulate organic matter) for nutrition of dominant primary consumers and omnivores. 14 invertebrate taxa including sessile and mobile polychaetes, gastropods, bivalves, sea stars, sea urchins and sea cucumbers were studied. Our results indicate that most benthic invertebrates predominantly relied on sympagic algae. Despite its very high abundance, trophic role of benthic biofilm seemed limited. However, interpretation of data was complicated by the peculiar ecophysiological features of Antarctic invertebrates, whose very low metabolic rates could be associated to low isotopic turnover and long time to reach isotopic equilibrium with their food items. Resource use by consumers from Adélie Land markedly differed from literature data about invertebrate diet in coastal Antarctica, suggesting 1) important influence of increased sea ice cover on benthic food web structure and 2) high spatial and/or temporal variation in the feeding habits of studied organisms, likely linked with a high degree of trophic plasticity. Our results provide insights about how Antarctic benthic consumers, which have evolved in an extremely stable environment, might adapt their feeding habits in response to sudden man-driven changes in environmental conditions and trophic resource availability. [less ▲]

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See detailIsotopic half-life and enrichment factor in two species of European freshwater fish larvae: an experimental approach
Latli, Adrien; Sturaro, Nicolas ULiege; Dujardin, Nelson et al

in Rapid Communications in Mass Spectrometry (2017), 31(8), 685-692

RATIONALE: Stable isotope ratios of carbon and nitrogen are valuable tools for field ecologists to use to analyse animal diets. However, the application of these tools requires knowledge of the tissue ... [more ▼]

RATIONALE: Stable isotope ratios of carbon and nitrogen are valuable tools for field ecologists to use to analyse animal diets. However, the application of these tools requires knowledge of the tissue enrichment factor (TEF) and half-life (HL). We experimentally compared TEF and HL in two freshwater fish larvae. We hypothesised that chub had a better growth/tissue replacement ratio than roach, due to the use of a food closer to their natural diet. METHODS: We determined the isotopic HL, the TEF and the contribution of growth or metabolic tissue replacement to dynamic isotopic incorporation. After yolk sac resorption, larvae were fed for 5 weeks with prey similar to their natural diet (Artemia nauplii) up to the isotopic equilibrium followed by Chironomid larvae. Stable isotope measurements were carried out using a continuous flow isotope ratio mass spectrometer coupled to an elemental analyser. RESULTS: Changes in isotopic composition strongly followed the predictions of exponential growth and time-dependent models. The isotopic HL varied between 8.2 and 12.6 days and the TEF of nitrogen and carbon ranged from 1.7 to 2.1‰ and from –0.9 to 1.2 ‰, respectively. The incorporation of dietary 13C was due more to the production of new tissue (between 56 and 79%) than to the metabolic process. Chub allocated more energy to growth than roach and the Chironomidae diet contributed more to the consumers’ growth than the Artemia diet. CONCLUSIONS: Metabolic rates seemed lower for chub than for roach, especially when they were fed with Chironomidae. A Chironomidae-based diet would be more profitable to chub, and the high associated growth rate could increase the development of the fish larvae. The HL and TEF were in the range of those reported in the literature. These results will be helpful for field-based studies, because they can help to increase the accuracy of models. [less ▲]

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See detailThe role of natural hazards and human activities on change of sedimentation patterns: The case of Lake Yamanaka (Fuji Five Lakes, Japan)
Lamair, Laura ULiege; Hubert, Aurelia ULiege; El Ouahabi, Meriam ULiege et al

Conference (2017, April 10)

The last eruption of Mt Fuji (Japan) occurred in A.D. 1707. The eruption lasted 16 days from 16 December 1707 to 1 January 1708 (Tsuya, 1955) and 1.8 km3 of volcanic materials were ejected in total ... [more ▼]

The last eruption of Mt Fuji (Japan) occurred in A.D. 1707. The eruption lasted 16 days from 16 December 1707 to 1 January 1708 (Tsuya, 1955) and 1.8 km3 of volcanic materials were ejected in total (Miyaji et al., 2011). Lake Yamanaka, a very shallow lake (max. 14. 3 m depth) located at the foot of the east-north-eastern flank of Mt Fuji, was heavily impacted by the eruption. A thick scoria layer entirely covered the catchment of Lake Yamanaka. The thickness of the deposit varies from 5 to 37 cm around Lake Yamanaka and reaches up to 149 cm at the south-west extremity of the catchment (Miyaji et al., 2011). In order to study the influence of Hoei eruption on Lake Yamanaka, 5 gravity cores were taken during the 2014 QuakeRecNankai campaign. The Hoei scoria was present at the bottom of the one core and in the core catcher of the four other cores. High resolution magnetic susceptibility, XRD, XRF, LOI, C/N and 210Pb/137Cs analyses were performed on the gravity cores. The results shows three distinct periods of sedimentation: (1) From Hoei eruption to A.D. 1900; (2) From A.D. 1900 to A.D. 1990; (3) From A.D. 1990 to A.D. 2014. The first period is characterized by a very low sedimentation rate (~0.07 cm/yr). During this period, the sediments of the catchment were trapped below the thick Hoei scoria layer. However, peaks of terrigenous input are recorded. We link such detrical signals with violent typhoons that hit the Fuji Five Lakes region. The water from the heavy rains percolated through the porous thick scoria layer and saturated it. As a result, surface runoffs carried the sediments from the catchment into Lake Yamanaka. The second period (from A.D. 1900 to A.D. 1990) is defined by an increase of the sedimentation rate (~0.16 cm/yr). The development of soil and the agriculture (e.g. pastureland, rice field, mulberry plantations) reduced the impact of Hoei scoria. The terrigenous inputs are higher than previously but remained more or less constant during this period of time. As the thickness of the scoria layer is partially reduced or covered by new soil, rains triggered by smaller typhoons could drain the sediments from watershed and transport them into the lake. The most recent period representing the last 27 years is characterized by a very high sedimentation rate (~1.036 cm/yr). The transition between period 2 and period 3 corresponds to the development of mass tourism and the urbanization around Lake Yamanaka. It is marked by an increasing of atmospheric pollution (Pb, Zn). In the upper part of the cores, a peak of 137Cs is observed. Such peak is related to cesium fall-out after Fukushima incident in 2011. In addition to the fingerprint of human impact, the lake also record a terrigenous signal related to the 2007 Fitow typhoon which provoked damage in the area. This study highlights the influence of eruptions and typhoons on the sedimentation of Lake Yamanaka. In the present day, the sedimentation recovery after a major eruption is accelerated by human activity. References: Miyaji N., Kan'no A., Kanamaru T., Mannen K. 2011. High-resolution reconstruction of the Hoei eruption (AD 1707) of Fuji volcano, Japan. Journal of Volcanology and Geothermal Research 207, 113–129. Tsuya, H. 1955. Geological and petrological studies of volcano, Fuji, V.: 5. on the 1707 eruption of Volcano Fuji. Bulletin of the Earthquake Research Institute 33, 341–383. [less ▲]

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See detailTectonic, human and climate signal over the last 4000 years in the Lake Amik record (southern Turkey)
El Ouahabi, Meriam ULiege; Hubert, Aurelia ULiege; Vander Auwera, Jacqueline ULiege et al

Poster (2017, April)

This study investigates the upper sediments infilling the central part of the Amik Basin in Southern Turkey. The Amik Basin is located in a tectonically active area: it is crossed by the Dead Sea Fault, a ... [more ▼]

This study investigates the upper sediments infilling the central part of the Amik Basin in Southern Turkey. The Amik Basin is located in a tectonically active area: it is crossed by the Dead Sea Fault, a major neotectonic structure in the Middle East extending from the Red Sea in the South to the East Anatolian Fault Zone in the North. Continuous human occupation is attested since 6000-7000 BC in the Amik Basin. The study focuses on the sedimentary record of the Lake Amik occupying the central part of the Basin. Our objective is to constrain major paleo-environmental changes over the last 4000 years. The lake has been drained and progressively dried up since the mid-50s. The absence of water column during the summer season allows to collect lacustrine samples along a 5 meter depth trench with a sampling resolution of 1 to 2 cm. Diverse complementary methods were applied to characterize the sedimentary record: i.e. magnetic susceptibility, grain size, organic and inorganic matter by loss-of-ignition, mineralogy by X-ray diffraction and core scanner X-ray fluorescence (XRF) geochemistry. The age of the record is constrained combining radionuclide and radiocarbon datings. Structural disturbances observed in the lacustrine sediments record are linked with major historical earthquakes from the 6th to the 9th century AD due to the Hasipasa Fault rupture. In addition to the tectonic influence, the sedimentary record clearly shows two periods indicating strong soil erosion in the lake catchment: (1) the most recent erosion phase occurs over the Roman period to Present; (2) the oldest one would have occurred during the Late Bronze period. Such changes are most probably related to change in land use. In term of climate influences, the mineralogical and geochemical results allow to evidence variations in chemical weathering conditions in the watershed and lake water level fluctuations, respectively. The clay mineral assemblages attest for significant pedogenesis transformations, especially during the Islamic/Ottoman period. Based on XRF results, an increase in potassium is attributed to a lake development phase during a wet phase An overflow of the Orontes River would be responsible for clay deposition. By contrast, increased calcium and strontium rather correspond to a low lacustrine level and a drier period. The Bronze and Iron/Hellenistic periods are both characterized by low lake level with limited contribution from the watershed. To conclude, our multiproxy study of the Lake Amik allows to decipher between tectonic, human and climate influences over the last 4000 years. Further step would be to compare the Amik record with other regional archives to evidence local and regional events. [less ▲]

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