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

in Belgian Journal of Zoology (in press)

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 detailReconstitution des paléoenvironnements et des activités humaines à partir de l’étude de sédiments prélevés dans le Cap Corse (Corse, France)
Fagel, Nathalie ULg; Fontaine, François ULg; Pleuger, Elisa ULg et al

in Ghilardi, Mathieu (Ed.) La géoarchéologie des îles de Méditerranée (in press)

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See detailComparative Feeding Ecology of Cardinalfishes (Apogonidae) at Toliara Reef, Madagascar
Frederich, Bruno ULg; Michel, Loïc ULg; 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 ULg; Lepoint, Gilles ULg; Frederich, Bruno ULg 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 ULg; 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 ULg; 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 ULg; Hubert, Aurelia ULg; El Ouahabi, Meriam ULg 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 ULg; Hubert, Aurelia ULg; Vander Auwera, Jacqueline ULg 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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See detailA meta-analysis of isotopic compositions of North Sea marine mammals
Damseaux, France ULg; Lepoint, Gilles ULg; Das, Krishna ULg

Conference (2017, March 03)

For over a decade, the North Sea has been undergoing significant changes due to global changes and overfishing. We conducted meta-analyses of previously published data on marine mammals sampled in the ... [more ▼]

For over a decade, the North Sea has been undergoing significant changes due to global changes and overfishing. We conducted meta-analyses of previously published data on marine mammals sampled in the North Sea to test the competition for food sources and spatial variations. The overall objective of this study was to assess the potential trophic changes of the grey seal, the harbour seal and the harbour porpoise. Data included δ13C and δ15N values measured in blood cells and muscles from the three species. SIBER, a trophic niche overlap quantification approach, highlighted potential competition between marine mammal species. The ellipse drawn for harbour seal data showed the highest δ15N values, reflecting its trophic position at the top of the food web. But the ellipse overlapping between the harbour seal and the grey seal of Germany was very important, showing a potential strong competition for food sources may be due to the overfishing. The harbour porpoise displayed a lower trophic position and a wide range of δ13C and δ15N values compared to harbour seal and grey seal as seen from its extended ellipse size. This may be due to a more opportunistic behaviour following the decline of some fish population in the North Sea. Surprisingly a group of grey seals sampled in Scotland present a very small ellipse size, presumably more selective in their prey choice, and showed the lowest δ15N values. Caution should be taken before comparing the trophic position of the groups of grey seals as the baseline differed between the two sampling areas. Low nitrates concentrations, higher latitudes, colder temperatures, deeper waters and rocky soils of the Scotland’s coasts of the North Sea cause a stratification phenomenon of the water column explaining the lower δ15N baseline in this area and so the spatial variation between these two groups of grey seals living in the North Sea. [less ▲]

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See detailIncreased sea ice cover disrupts food web structure in coastal Antarctica
Michel, Loïc ULg; Dubois, Philippe; Eleaume, Marc et al

Conference (2017, March 03)

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. Sea ice is a major environmental driver in Antarctica, and changes in sea ice cover are likely to influence benthic food web structure through several processes (modifications of benthic-pelagic coupling, disruption of benthic production and/or modifications of benthic community structure and therefore resource availability for benthic consumers). To date, regions where sea ice cover is decreasing have received more attention than regions where it is increasing. Here, on the other hand, 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 macroinvertebrate 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 in Antarctica. 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 (sea-ice associated) algae dominated the diet of many important 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. Interpretation of data was complicated by the peculiar ecophysiological features of Antarctic invertebrates, whose very low metabolic rates could be associated to low tissue turnover. However, 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 with 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 man-driven changes in environmental conditions and trophic resource availability. They also show that local and/or global trends of sea ice increase in Antarctica could cause strong changes in food web structure and therefore impact zoobenthic communities. This reinforces the view that, no matter their overall direction (i.e. increase or decrease), fluctuations in sea ice cover are likely to influence Antarctic benthic ecosystems' structure and functioning. [less ▲]

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See detailLinking pollutant exposure of humpback whales breeding in the Indian Ocean to their feeding habits and feeding areas off Antarctica
Das, Krishna ULg; Malarvannan, Govindan; Dirtu, Alin et al

in Environmental Pollution (2017), 220

Humpback whales, Megaptera novaeangliae, breeding off la Reunion Island (Indian Ocean) undergo large-scale seasonal migrations between summer feeding grounds near Antarctica and their reproductive winter ... [more ▼]

Humpback whales, Megaptera novaeangliae, breeding off la Reunion Island (Indian Ocean) undergo large-scale seasonal migrations between summer feeding grounds near Antarctica and their reproductive winter grounds in the Indian Ocean. The main scope of the current study was to investigate chemical exposure of humpback whales breeding in the Indian Ocean by providing the first published data on this breeding stock concerning persistent organic pollutants (POPs), namely polychlorinated biphenyls (PCBs), hexachlorobenzene (HCB), hexachlorocyclohexanes (HCHs), DDT and its metabolites (DDTs), chlordane compounds (CHLs), polybrominated diphenyl ethers (PBDEs), and methoxylated PBDEs (MeO-PBDEs). Analyses of stable isotopes δ13C and δ15N in skin resulted in further insight in their feeding ecology, which was in agreement with a diet focused mainly on low trophic level prey species, such as krill from Antarctica. POPs were measured in all humpback whales in the order of HCB > DDTs > CHLs > HCHs > PCBs > PBDEs > MeO-BDEs. HCB (median: 24 ng.g-1 lw) and DDTs (median: 7.7 ng.g-1 lw) were the predominant compounds in all whale biopsies. Among DDT compounds, p,p’-DDE was the major organohalogenated pollutant, reflecting its long-term accumulation in humpback whales. Significantly lower concentrations of HCB and DDTs were found in females than in males (p<0.001). Other compounds were similar between the two genders (p>0.05). Differences in the HCB and DDTs suggested gender-specific transfer of some compounds to the offspring. POP concentrations were lower than previously reported results for humpback whales sampled near the Antarctic Peninsula, suggesting potential influence of their nutritional status and may indicate different exposures of the whales according to their feeding zones. Further investigations are required to assess exposure of southern humpback whales throughout their feeding zones. [less ▲]

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See detailImpact of food type on respiration, fractionation and turnover of carbon and nitrogen stable isotopes in the marine amphipod Gammarus aequicauda (Martynov, 1931).
Remy, François ULg; Darchambeau, François ULg; Melchior, Aurélie et al

in Journal of Experimental Marine Biology & Ecology (2017), 486

This study experimentally determined the impact of food source type on turnover rate and trophic enrichment factors (TEFs or ∆) of δ13C and δ15N, as well as on respiration rate, in captive populations of ... [more ▼]

This study experimentally determined the impact of food source type on turnover rate and trophic enrichment factors (TEFs or ∆) of δ13C and δ15N, as well as on respiration rate, in captive populations of the marine amphipod Gammarus aequicauda. Gammarus aequicauda (318 individuals) were fed ad libitum with three food sources animal, algae, and dead Posidonia oceanica leaves (also called “litter”), varying in palatability, digestibility, nutritional qualities and isotopic compositions, for between four and six weeks in a controlled feeding experiment. The resulting death rate was lower for the amphipods fed with animal treatment (30.9%) than for individuals fed with algal (65.9%) or litter treatment (64.4%), indicating a better fitness of the individuals fed with the animal food source. Respiration rates also differed highly among the treatments. Animal treatment showed higher respiration rates than algal and litter treatments, potentially due to the toxicity of the algae and the very low nutritional quality of the litter. Amphipods fed with these treatments might have entered in a “low activity state” to cope with these unsuitable food sources, inducing low respiration rates. Due to the very low assimilation and toxicity of the algae source, turnover rate for δ13C was impossible to determine. Turnover rate for δ13C was much faster (half-life = 12.55 days) for amphipods fed with the animal food source than for amphipods fed with litter (half-life = 51.62 days), showing the faster assimilation of the most nutritionally optimal food sources by G. aequicauda. Turnover for δ15N was impossible to determine because the amphipods were already at isotopic equilibrium at the beginning of the experiment. Despite the detritus feeder status of Gammarus aequicauda, TEFs for the animal treatments were in accordance with values generally found for carnivorous organisms (∆13C = 0.9 ± 0.7‰; ∆15N = 2.9 ± 0.6‰). TEFs for the litter treatment were in accordance with values generally corresponding to detritivorous organisms (∆13C = 1.2‰; ∆15N = 1.0 ± 0.4‰). SIAR mixing model outputs obtained with these new TEF values were more constrained and coherent than outputs obtained with general literature TEFs. This study thus demonstrated the non-negligible impact of the food source on Gammarus aequicauda physiological status, fitness and turnover rates, but also on TEFs—highlighting the importance of TEF experimental calculations for every potential food source of a given organism to ensure more robust isotopic data interpretation. [less ▲]

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See detailSoil erosion in relation to land use changes in the Amik Lake sediments near the Antioch antique city during the last 4kyr
El Ouahabi, Meriam ULg; Hubert, Aurelia ULg; Lebeau, Héléne et al

in The Holocene (2017)

The Amik Basin in the Eastern Mediterranean region occupied since 6000-7000 BC has sustained a highly variable anthropic pressure culminating during the Late Roman Period when the Antioch city reached its ... [more ▼]

The Amik Basin in the Eastern Mediterranean region occupied since 6000-7000 BC has sustained a highly variable anthropic pressure culminating during the Late Roman Period when the Antioch city reached its golden age. The present 6m long sedimentary record of the Amik Lake occupying the central part of the Basin constrains major paleo-environmental changes over the last 4000 years using a multi-proxy analyses (grain-size, magnetic susceptibility and XRF geochemistry). An age model is provided by combining short-lived radionuclides with radiocarbon dating. A lake/marsh prevailed during the last 4kyrs with a level increase at the beginning of the Roman Period possibly related to optimum climatic condition and water channelling. The Bronze/Iron Ages are characterized by a strong terrigenous input linked to deforestation, exploitation of mineral resources and the beginning of upland cultivation. The Bronze/Iron Age transition marked by the collapse of the Hittite Empire is clearly documented. Erosion continues during the Roman Period and nearly stopped during the Early Islamic Period in conjunction with a decreasing population and soil depletion on the calcareous highland. The soil-stripped limestone outcrops triggered an increase in CaO in the lake water, and a general decrease in ZrO2 released in the landscape that lasts until the present day. During the Islamic Period, pastoralism on the highland sustained continued soil erosion of the ophiolitic Amanus Mountains. The modern Period is characterized by a higher pressure particularly on the Amanus Mountains linked to deforestation, road construction, ore exploitation and the drying of the lake for agriculture practices. [less ▲]

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See detailInhibition of ethylene synthesis reduces salt-tolerance in tomato wild relative species Solanum chilense
Gharbi, E.; Martínez, J.-P.; Benahmed, H. et al

in Journal of Plant Physiology (2017), 210

Exposure to salinity induces a burst in ethylene synthesis in the wild tomato halophyte plant species Solanum chilense. In order to gain information on the role of ethylene in salt adaptation, plants of ... [more ▼]

Exposure to salinity induces a burst in ethylene synthesis in the wild tomato halophyte plant species Solanum chilense. In order to gain information on the role of ethylene in salt adaptation, plants of Solanum chilense (accession LA4107) and of cultivated glycophyte Solanum lycopersicum (cv. Ailsa Craig) were cultivated for 7 days in nutrient solution containing 0 or 125 mM NaCl in the presence or absence of the inhibitor of ethylene synthesis (aminovinylglycine (AVG) 2 μM). Salt-induced ethylene synthesis in S. chilense occurred concomitantly with an increase in stomatal conductance, an efficient osmotic adjustment and the maintenance of carbon isotope discrimination value (Δ13C). In contrast, in S. lycopersicum, salt stress decreased stomatal conductance and Δ13C values while osmotic potential remained higher than in S. chilense. Inhibition of stress-induced ethylene synthesis by AVG decreased stomatal conductance and Δ13C in S. chilense and compromised osmotic adjustment. Solanum chilense behaved as an includer and accumulated high amounts of Na in the shoot but remained able to maintain K nutrition in the presence of NaCl. This species however did not stimulate the expression of genes coding for high-affinity K transport but genes coding for ethylene responsive factor ERF5 and JREF1 were constitutively more expressed in S. chilense than in S. lycopersicum. It is concluded that ethylene plays a key role in salt tolerance of S. chilense. © 2016 [less ▲]

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See detailExtreme intra-clutch egg size dimorphism is not coupled with corresponding differences in antioxidant capacity and stable isotopes between eggs
Poisbleau, Maud; Beaulieu, Michaël; Dehnhard, Nina et al

in Comparative Biochemistry and Physiology Part A : Molecular & Integrative Physiology (2017), 205

Oviparous females need to allocate resources optimally to their eggs in order to maximize their fitness. Among these resources, dietary antioxidants, acquired by females and transferred to the eggs during ... [more ▼]

Oviparous females need to allocate resources optimally to their eggs in order to maximize their fitness. Among these resources, dietary antioxidants, acquired by females and transferred to the eggs during egg formation, can greatly affect the development and survival of the embryo and chick. In crested penguins, incubation starts after the second and last egg is laid and, as opposed to many other bird species, this egg hatches first, thereby enhancing the survival of the chick. Here, we assessed whether antioxidant and isotopic composition could underlie these differences between eggs within clutches of southern rockhopper penguins (Eudyptes chrysocome chrysocome). The second-laid egg had higher total antioxidant capacity than the first-laid egg, although this was not due to higher antioxidant concentration but to its higher mass. This suggests that resources are allocated by females at a constant rate in both eggs within clutches. Accordingly, we found a strong correlation for isotopic compositions between eggs suggesting that resources were allocated similarly to each egg within the clutch. Overall, we found little evidence for a significant role of antioxidant and isotopic compositions to explain differences in terms of embryo/chick development between eggs in crested penguins. However, since our results suggest a constant rate of antioxidant transfer from females to eggs, limiting the mass of the first-laid egg might represent a strategy for females to spare antioxidant defences and preserve self-maintenance. [less ▲]

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See detailTrophic ecology of Southern Ocean sea stars inferred from stable isotopes ratios of C and N
Le Bourg, Baptiste ULg; Blanchard, Alice; Danis, Bruno et al

Conference (2016, December 17)

The Southern Ocean undergoes strong and contrasted impacts of climate change. Increasing seawater temperature and sea ice cover reduction in Western Antarctic Peninsula and associated regions will likely ... [more ▼]

The Southern Ocean undergoes strong and contrasted impacts of climate change. Increasing seawater temperature and sea ice cover reduction in Western Antarctic Peninsula and associated regions will likely impact food web structure and function. Sea stars (Echinoderms: Asteroidea) are an important group of the Southern Ocean benthos. They typically have highly variable feeding habits and are potentially more resistant than other organisms to temperature changes. Consequently, they will likely be impacted by modifications of the food web rather than by direct warming. Investigating their trophic ecology is therefore necessary to infer how climate change will impact them. In this context, the aim of this study was to use stable isotopes ratios of C, N and S to infer sea stars trophic ecology. During austral summers 2006 and 2009, sea stars were sampled in Subantarctic and Antarctic locations, with most of the samples coming from South Shetland Islands and South Georgia. The isotopic niche (proxy of the trophic niche) associated to each sea star population was explored through SIBER (Stable Isotope Bayesian Ellipses in R) metrics. Stable isotope ratios of sea stars were clearly different between South Shetland Islands and South Georgia. Sea stars of South Shetland Islands had smaller isotopic niches than sea stars of South Georgia. The overlap between the isotopic niches of sea star species was also important in South Shetland Islands, while isotopic niches of South Georgia were well separated. Difference of niche width and overlap between the two regions may be the result of different environmental conditions. In South Shetland Islands, sea star species may exploit a common benthic community relying on organic matter released during sea ice summer melting. In contrast, South Georgia is an oligotrophic environment with no sea ice. As resources are more limited, a higher trophic segregation between sea stars may appear to limit competition. Ultimately, this project highlighted the importance of sea ice in the trophic ecology of Antarctic sea stars. Our results suggest that future reduction of sea ice extent in Western Antarctica may have deleterious effect on sea star populations. [less ▲]

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See detailHead shape disparity of the cod icefishes Trematominae (Notothenioidei, Teleostei)
Frederich, Bruno ULg; Heindler, Franz M.; Dettai, Agnès et al

Poster (2016, December 16)

The suborder Notothenioidei (Teleostei) has undergone a remarkable adaptive radiation in the Southern Ocean. Within this suborder, the subfamily Trematominae is endemic to Antarctic waters and represents ... [more ▼]

The suborder Notothenioidei (Teleostei) has undergone a remarkable adaptive radiation in the Southern Ocean. Within this suborder, the subfamily Trematominae is endemic to Antarctic waters and represents a dominant component of the shelf fish fauna. After recent advances in molecular phylogenetics, 14 species of Trematomus are currently recognized (including Pagothenia and Cryothenia spp.) comprising both considerable morphological and ecological diversity. Here, we aim to illustrate the main axes of shape variation in Trematomus and explore the evolution of their morphology. A dataset of 96 specimens representing 10 species of Trematomus from the collection of the Natural History Museum of Paris was assembled, and landmark-based geometric morphometrics was applied to quantify head shape disparity. Regular regression analysis revealed significant interspecific allometry while a low percentage of shape variation was explained by size (R2 = 0.11; P < 0.001). Main shape variation across species was explored using a principal component (PC) analysis on shape variables. Two groups diverged along PC1: (1) T. bernacchii, T. hansoni, T. pennellii and T. tokarevi have short cephalic profiles with larger cheeks (lowest values along PC1); and (2) T. lepidorhinus, T. eulepidotus and T. newnesi show lengthened cephalic profiles with larger eyes (highest values along PC1). Trematomus scotti differed from all other species mainly along PC3 indicating more elongated cheeks. Phenogram based on Procrustes shape distances will be compared to molecular phylogenetic trees and morphometric data will be mapped onto phylogenetic trees in order to illustrate the mode of phenotypic diversification of Trematomus during evolution. [less ▲]

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See detailWho would want to live in there? A history of Posidonia oceanica detritus accumulations, the associated invertebrate community, and its food web…
Remy, François ULg; Michel, Loïc ULg; Darchambeau, François ULg et al

Conference (2016, December 16)

Most seagrasses are rarely consumed directly by herbivore organisms. The "detrital pathway" thus represents a potentially important way of transfer of the seagrasses production to the coastal food webs ... [more ▼]

Most seagrasses are rarely consumed directly by herbivore organisms. The "detrital pathway" thus represents a potentially important way of transfer of the seagrasses production to the coastal food webs. The case of Posidonia oceanica is particularly interesting since up to 90% of its foliar primary production may constitute extensive and highly dynamic exported litter accumulations. Preliminary studies concerning these detritus accumulations suggest that an abundant community of vagile macro invertebrates (size > 500μm) lives inside them. We characterized for the first time this community in an exhaustive way (multi-site, seasonal and multi-year study), we linked the observed density and diversity variations to environmental parameters, but also described the trophic web these invertebrates compose. We sampled an abundant (up to 5000 organisms/m²) community composed of 115 species. We showed that crustaceans were massively dominant, followed by annelids and mollusks, and that one single amphipod species Gammarella fucicola represented from 20 to 85% of the whole sampled community. Observed variations appeared to be mostly linked to litter oxygen water concentration in a very species specific way. Most species were linked to no measured environmental parameter at all, but several dominant species were demonstrated (observation and in situ experimentation) to be linked positively or negatively to litter oxygen concentration. The described food web was composed of more than 3 trophic levels, indicating the presence of a trophic web composed of primary consumers/detritivore species, of omnivore species, but also of first and second order predators, each level occupying a distinct isotopic niche. From a specific point of view, we highlighted several different feeding preferences, with SIAR mixing model runs indicating that some species feed mostly on detrital material, other species feed on a mixture of detrital and algal material, other species feed on both animal and vegetal material and finally predator species feed exclusively on animal material. The fact that P. oceanica detritus constituted a non-negligible food source for some dominant species confirmed the importance of this macrofauna community as a key transfer link of seagrass organic matter from P. oceanica to the coastal food webs. [less ▲]

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See detailFeeding ecology of metamorphic and paedomorphic palmate newts (Lissotriton helveticus) in Larzac
Didaskalou, Emilie; Lejeune, Benjamin ULg; Lepoint, Gilles ULg et al

Poster (2016, December 16)

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