The interaction between warming and enrichment accelerates food-web simplification in freshwater systems.

Nutrient enrichment and climate warming threaten freshwater systems. Metabolic theory and the paradox of enrichment predict that both stressors independently can lead to simpler food-webs having fewer nodes, shorter food-chains and lower connectance, but cancel each other's effects when simultaneously present. Yet, these theoretical predictions remain untested in complex natural systems. We inferred the food-web structure of 256 lakes and 373 streams from standardized fish community samplings in France. Contrary to theoretical predictions, we found that warming shortens fish food-chain length and that this effect was magnified in enriched streams and lakes. Additionally, lakes experiencing enrichment exhibit lower connectance in their fish food-webs. Our study suggests that warming and enrichment interact to magnify food-web simplification in nature, raising further concerns about the fate of freshwater systems as climate change effects will dramatically increase in the coming decades.

Local adaptation in trait-mediated trophic cascades.

Predator-induced changes in prey foraging can influence community dynamics by increasing the abundance of basal resources via a trait-mediated trophic cascade. The strength of these cascades may be altered by eco-evolutionary relationships between predators and prey, but the role of basal resources has received limited attention. We hypothesized that trait-mediated trophic cascade strength may be shaped by selection from trophic levels above and below prey. Field and laboratory experiments used snails (Nucella lapillus) from two regions in the Gulf of Maine (GoM) that vary in basal resource availability (e.g. mussels), seawater temperature, and contact history with the invasive green crab, Carcinus maenas. In field and laboratory experiments, Nucella from both regions foraged on mussels in the presence or absence of green crab risk cues. In the field, Nucella from the northern GoM, where mussels are scarce, were less responsive to risk cues and more responsive to seawater temperature than southern Nucella. In the lab, however, northern Nucella foraged and grew more than southern snails in the presence of risk, but foraging and growth were similar in the absence of risk. We suggest that adaptation to basal resource availability may shape geographical variation in the strength of trait-mediated trophic cascades.

Species motif participation provides unique information about species risk of extinction.

Loss of species in food webs can set in motion a cascade of additional (secondary) extinctions. A species' position in a food web (e.g. its trophic level or number of interactions) is known to affect its ability to persist following disturbance. These simple measures, however, offer only a coarse description of how species fit into their community. One would therefore expect that more detailed structural measures such as participation in three-species motifs (meso-scale structures which provide information on a species' direct and indirect interactions) will also be related to probability of persistence. Disturbances affecting the basal resources have particularly strong effects on the rest of the food web. However, how disturbances branch out and affect consumer persistence depends on the structural pattern of species interactions in several steps. The magnitude, for example, the proportion of basal resources lost, will likely also affect the outcome. Here, we analyse whether a consumer's risk of secondary extinction after the removal of basal resources depends on the consumer's motif participation and how this relationship varies with the severity of disturbance. We show that consumer species which participate more frequently in the direct competition motif and less frequently in the omnivory motif generally have higher probability of persistence following disturbance to basal resources. However, both the strength of the disturbance and the overall network structure (i.e. connectance) affect the strength and direction of relationships between motif participation and persistence. Motif participation therefore captures important trends in species persistence and provides a rich description of species' structural roles in their communities, but must be considered in the context of network structure as a whole and of the specific disturbance applied.

Trophic transfer, bioaccumulation and translocation of microplastics in an international listed wetland on the Montreux record.

Microplastics (MPs) are concerning emerging pollutants. Here, MPs in four edible aquatic species of different trophic levels (between ∼2 and 4), including fish species Esox lucius (Esocidae: Esocinae); Cyprinus carpio (Cyprinidae: Cyprininae); and Luciobarbus caspius (Cyprinidae: Barbinae); and the swan mussel Anodonta cygnea (Unionidae), were assessed in the Anzali freshwater ecosystem. It is a listed wetland in the Montreux record. MPs were extracted from gastrointestinal tracts (GI), gills, muscles, and skin. All the studied fish and mussels (n = 33) had MPs. MP fibres, fragments and sheets were detected in every GI examined, however, fibres were the only type of MPs in skins, muscles and gills and were the most abundant MP. The MPs found in the fish and mussels were mainly made of nylon (35% of the total MPs), polypropylene-low density polyethylene (30%), and polycarbonate (25%). The average numbers of MPs found in every fish specimen, expressed per wet body mass, had a moderate negative correlation with the condition factor (K) (MP/g - K: Pearson correlation r = -0.413, p = 0.049), and there was no significant relation with the growth factor (b) (r = -0.376; p = 0.068). Importantly, Luciobarbus caspius (with trophic level 2.7-2.8) bioaccumulated MPs and presented a strong correlation between their MP contamination and age (r = 0.916 p < 0.05). Greater gill mass (or related factors) played an important role in the accumulation of MPs, and there was a strong correlation between these factors for Esox lucius and Cyprinus carpio (r = 0.876; r = 0.846; p < 0.05 respectively). The highest MP/g gills (1.91 ± 2.65) were in the filter feeder Anodonta cygnea inhabiting the benthic zone. Esox lucius (piscivorous, trophic level 4.1) was the most contaminated species overall (a total of 83 MPs in 8 individuals, with 0.92 MP/g fish), and their gills where MPs mainly accumulated. Cyprinus carpio was the most contaminated specimen (MPs in specimens), while the number of MPs per mass unit increased with the trophic level. Their feeding and ecological behavior in the aquatic habitat affected the level of accumulation. This work includes evidence of translocation of MPs within the aquatic organisms.

Effects of water replenishment on lake water quality and trophic status: An 11-year study in cold and arid regions.

Water replenishment is an important measure for maintaining and improving the aquatic environmental quality of lakes. The problems of water quality deterioration and water shortage can be alleviated by introducing water of higher quality. However, the mechanism of water replenishment in the improvement of the water quality and trophic status of lakes remains unclear. This study investigated water replenishment in Wuliangsuhai Lake (WLSHL) from 2011 to 2021 by collecting seasonal water samples and conducting laboratory analyses. Water replenishment was found to be capable of significantly improving lake water quality and alleviating eutrophication. It is worth noting that single long-term water replenishment measures have limitations in improving the water quality and trophic status. The whole process was divided into three stages according to the water quality and trophic status, namely the buffer period, decline period, and stable period. During the buffer period, the water quality and trophic status showed only slight improvement because of the small amount of water replenishment and the low proportion of higher-quality water from the Yellow River. In the decline period, with increasing water replenishment, the proportion of higher-quality water from the Yellow River gradually increased, leading to the most significant and stable degree of improvement. In the stable period, increases in the amount of water replenishment had little effect on improving the water quality and trophic status, which is attributable to the balance between internal pollutants (lake water-sediment), and the balance between internal-external pollutants (lake water-irrigation return flow + Yellow River water). On the premise of stable water quality, with eutrophication control as the management goal, the optimal water replenishment would be approximately 10.58 ×108 m3. Further necessary measures for solving aquatic environmental problems include the combination of sediment dredging, optimization of the water replenishment route, and implementation of quality management in water replenishment.

Dental topographic proxies for ecological characteristics in carnivoran mammals.

Form-function relationships in mammalian feeding systems are active topics of research in evolutionary biology. This is due principally to their fundamental importance for understanding dietary adaptations in extinct taxa and macro-evolutionary patterns of morphological transformations through changing environments. We hypothesize that three-dimensional dental topographic metrics represent stronger predictors for dietary and other ecological variables than do linear measurements. To test this hypothesis, we measured three dental topographic metrics: Relief Index (RFI), Dirichlet Normal Energy (DNE), and Orientation Patch Count Rotated (OPCR) in 57 extant carnivoran species. Premolar and molar dental topographic indices were regressed against activity, diet breadth, habitat breadth, terrestriality, and trophic level variables within a phylogenetic framework. The results of this study showed significant correlations between RFI and the ecological variables diet breadth and trophic level. Weaker correlations are documented between OPCR and activity and between DNE and trophic level. Our results suggest that cusp height is strongly reflective of dietary ecology in carnivorans as a whole, and represents a proxy mainly for different degrees of hypercarnivory observed within this group of predatory mammals.

Herbivory and elevated levels of CO2 and nutrients separately, rather than synergistically, impacted biomass production and allocation in invasive and native plant species.

Large parts of the Earth are experiencing environmental change caused by alien plant invasions, rising atmospheric concentration of carbon dioxide (CO2 ), and nutrient enrichments. Elevated CO2 and nutrient concentrations can separately favour growth of invasive plants over that of natives but how herbivory may modulate the magnitude and direction of net responses by the two groups of plants to simultaneous CO2 and nutrient enrichments remains unknown. In line with the enemy release hypothesis, invasive plant species should reallocate metabolites from costly anti-herbivore defences into greater growth following escape from intense herbivory in the native range. Therefore, invasive plants should have greater growth than native plants under simultaneous CO2 and nutrient enrichments in the absence of herbivory. To test this prediction, we grew nine congeneric pairs of invasive and native plant species that naturally co-occurred in grasslands in China under two levels each of nutrient enrichment (low-nutrient vs. high-nutrient), herbivory (with herbivory vs. without herbivory) and under ambient (412.9 ± 0.6 ppm) and elevated (790.1 ± 6.2 ppm) levels of CO2 concentrations in open top chambers in a common garden. Elevated CO2 and nutrient enrichment separately increased total plant biomass, while herbivory reduced it regardless of the plant invasive status. High-nutrient treatment caused the plants to allocate a significantly lower proportion of total biomass to roots, while herbivory induced an opposite pattern. Herbivory suppressed total biomass production more strongly in native plants than invasive plants. The plants exhibited significant interspecific and intergeneric variation in their responses to the various treatment combinations. Overall, these results suggest that elevated CO2 and nutrients and herbivory may separately, rather than synergistically, impact productivity of the invasive and co-occurring native plant species in our study system. Moreover, interspecific variation in resource-use strategies was more important than invasive status in determining plant responses to the various treatment combinations.

Analysis of Toxic Metals Found in Shark Fins Collected from a Global Trade Hub.

As human activities release increasingly more fossil fuel-derived emissions directly into the atmosphere, terrestrial, aquatic, or marine ecosystems, the biomagnification and bioaccumulation of toxic metals in seafood is an ever more pressing concern. As apex predators, sharks are particularly susceptible to biomagnification and bioaccumulation. The consumption of shark fin is frequent throughout Asia, and their ingestion represents a pathway through which human exposure to potentially unsafe levels of toxic metals can occur. Shark fins processed for sale are difficult, if not impossible to identify to the species level by visual methods alone. Here, we DNA-barcoded 208 dried and processed fins and in doing so, identified fourteen species of shark. Using these identifications, we determined the habitat of the shark that the fin came from and the concentrations of four toxic metals (mercury, arsenic, cadmium, and lead) in all 208 samples via inductively coupled plasma mass spectrometry. We further analyzed these concentrations by habitat type, either coastal or pelagic, and show that toxic metal concentrations vary significantly between species and habitat. Pelagic species have significantly higher concentrations of mercury in comparison to coastal species, whereas coastal species have significantly higher concentrations of arsenic. No significant differences in cadmium or lead concentrations were detected between pelagic or coastal species. Our results indicate that a number of analyzed samples contain toxic metal concentrations above safe human consumption levels.

Trace elements, dioxins and PCBs in different fish species and marine regions: Importance of the taxon and regional features.

Chemical contaminant concentrations in wild organisms are used to assess environmental status under the European Marine Strategy Framework Directive. However, this approach is challenged by the complex intra- and inter-species variability, and the different regional features. In this study, concentrations in trace elements (As, Cd, Hg and Pb), polychlorinated biphenyls (PCBs), polychlorodibenzo-para-dioxines (PCDDs) and polychlorodibenzofuranes (PCDFs) were monitored in 8 fish species sampled on the continental shelf of three French regions: the Eastern English Channel (EEC) and Bay of Biscay (BoB) in the Northeast Atlantic Ocean, and the Gulf of Lions (GoL) in Western Mediterranean Sea. Our objectives were to identify species or regions more likely to be contaminated and to assess how to take this variability into account in environmental assessment. While concentrations were higher in benthic and demersal piscivores, PCB and PCDD/F concentrations (lipid-weight) were similar in most teleost species. For Cd, Hg and Pb, the trophic group accumulating the highest concentrations depended on the contaminant and region. Concentrations in Hg, PCBs and PCDD/Fs were higher in the EEC and/or GoL than in BoB. Cadmium and Pb concentrations were highest in the BoB. Lipid content accounted for 35%-84% of organic contaminant variability. Lipid normalisation was employed to enhance robustness in the identification of spatial patterns. Contaminant patterns in chondrichthyans clearly differed from that in teleosts. In addition, trophic levels accounted for ≤1% and ≤33% of the contaminant variability in teleost fishes in the EEC and BoB, respectively. Therefore, developing taxa-specific thresholds might be a more practical way forward for environmental assessment than normalisation to trophic levels.

Community-scale relationships between body shape and trophic ecology in tropical demersal marine fish of northeast Brazil.

Functional morphology investigates the relationships between morphological characters and external factors, such as environmental, physical and ecological features. Here, we evaluate the functional relationships between body shape and trophic ecology of a tropical demersal marine fish community using geometric morphometrics techniques and modelling, hypothesizing that shape variables could partially explain fish trophic level. Fish were collected over the continental shelf of northeast Brazil (4-9°S). Analysed fish were distributed into 14 orders, 34 families and 72 species. Each individual was photographed in lateral view, and 18 landmarks were distributed along the body. A principal component analysis (PCA) applied on morphometric indices revealed that fish body elongation and fin base shape were the main axes of variation explaining the morphology. Low trophic levels (herbivore and omnivore) are characterized by deep bodies and longer dorsal and anal fin bases, while predators present elongated bodies and narrow fin bases. Fin position (dorsal and anal fins) on the fish body is another important factor contributing to (i) body stability at high velocity (top predators) or (ii) manoeuvrability (low trophic levels). Using multiple linear regression, we verified that 46% of trophic level variability could be explained by morphometric variables, with trophic level increasing with body elongation and size. Interestingly, intermediate trophic categories (e.g., low predators) presented morphological divergence for a given trophic level. Our results, which can likely be expanded to other tropical and nontropical systems, show that morphometric approaches can provide important insights into fish functional characteristics, especially in trophic ecology.

Ingestion of microplastics in commercially important species along Thoothukudi coast, south east India.

Microplastics pollute the marine environment and pose a greater risk to marine organisms. The microplastics were observed in the guts of the 12 species, which varied from 0.00 to 1.80 ± 1.19 particles /individual. Most of the microplastics were fibre shaped, 0.5-1 mm sized, blue-coloured, and polyethylene polymers. The abundance of the microplastics was higher for benthic species (0.66 ± 0.13 particles/ individual) than the pelagic species (0.53 ± 0.11 particles/individual), with no significant difference (p > 0.05). According to their feeding habits and trophic level, significantly the microplastics were abundant in the herbivores (1.23 ± 0.61 particles/individual) and quaternary consumers (0.76 ± 0.16 particles/individual), respectively. The present study suggests that microplastic ingestion in commercially important species was influenced by their feeding habits irrespective of their habitat and length and weight. In addition to this, biomagnification of the microplastics (Trophic Magnification Factor, TMF = 1.02) was also observed in the commercially important species with increasing trophic level. This further indicates that the trophic level can serve as the pathway for the transfer of microplastics from lower trophic level organisms to higher trophic level organisms. The present study concludes that the occurrence of biomagnification of microplastics and the pollutants absorbed by them might harm the commercially important species from the Thoothukudi region.

Trophic fingerprinting of a pristine but rapidly deteriorating downstream region of a Western Ghats River.

Chalakudy River is renowned for its pristine waters and rich ichthyofaunal biodiversity. The downstream area of the river is confronting a series of risks, including pollution, saline water ingression, sand mining, illegal and intensified fishing practices, and invasion of exotic and alien species. A mass balanced ecosystem model was constructed for the downstream region of Chalakudy River (DCR) using Ecopath with Ecosim (EWE), incorporating 12 functional groups to delineate the food web and network flow indices for the period 2020 to 2021. The trophic level (TL) of the ecosystem network ranged from TL-1 (detritus) to TL-3.4 (birds). High fishing pressure is one possible cause for the high ecotrophic efficiency values as evidenced by the fish groups. Both the grazing food chain and detritus food chain (detritivory: herbivory ratio 0.94) contributed more or less equal to the energy transfer between TL. Network analysis of the model indicated a mean transfer efficiency of 12%, with shares from primary producers (14%) and detritus (11%). A mixed trophic impact analysis demonstrated a strong positive impact of primary producers and detritus groups on most of the other ecological groups at higher trophic levels. The DCR model showed a high system throughput (32,464.7 t km-2 year-1), low system omnivory (0.09), low connectance index (0.36), low Finn's cycling index (4.9), and mean path length (2.8), low relative ascendency (37.5%), and high system overhead (62.5%). These indices propound that DCR is an immature and developing ecosystem with moderate strength in reserve to resist external perturbations.

Eutrophication assessment in Pannonian Basin (the case of Ludas Lake Special Nature Reserve and Palic Nature Park).

Agricultural, industrial, and human activities in general threaten water quality, as well as the biotic integrity of aquatic ecosystems. The increased concentration of total nitrogen (TN) and phosphorus (TP) affects high concentrations of chlorophyll (Chl-a) in freshwater ecosystems, which causes the process of eutrophication of the waters of shallow lakes. Eutrophication, as an alarming threat to the global quality of surface waters, affects environmental degradation. This research assesses the risk of eutrophication caused by chemical oxygen demand (COD), TN, TP, Secchi disk (SD), and Chl-a using the trophic level index (TLI) in Palic and Ludas lakes. Both lakes have been nominated as potential Natura 2000 areas in 2021 because they belong to important bird areas, and Ludas Lake has the status of Ramsar site 3YU002. In the research period from 2011 to 2021, the results showed that the lake is in an extremely eutrophic state. Laboratory analyses indicate an increased concentration of Chl-a during autumn. In the paper, the normalized difference chlorophyll index (NDCI) was calculated using the Google Earth Engine platform, and the result indicates the loading of the lake throughout the year, with an emphasis on winter, summer, and autumn. By using satellite images and remote sensing, it is possible to determine the most degraded spots, which is a help to the researchers in choosing the places where the samples will be taken and thus act more efficiently on the most endangered parts, as well as reduce the costs of standard in situ methods.

The relationship between dietary trophic level, parasites and the microbiome of Pacific walrus (Odobenus rosmarus divergens).

Arctic species are likely to experience rapid shifts in prey availability under climate change, which may alter their exposure to microbes and parasites. Here, we describe fecal bacterial and macroparasite communities and assess correlations with diet trophic level in Pacific walruses harvested during subsistence hunts by members of the Native Villages of Gambell and Savoonga on St Lawrence Island, Alaska. Fecal bacterial communities were dominated by relatively few taxa, mostly belonging to phyla Fusobacteriota and Firmicutes. Members of parasite-associated phyla Nematoda, Acanthocephala and Platyhelminthes were prevalent in our study population. We hypothesized that high versus low prey trophic level (e.g. fish versus bivalves) would result in different gut bacterial and macroparasite communities. We found that bacterial community structure correlated to diet, with nine clades enriched in walruses consuming higher-trophic-level prey. While no parasite compositional differences were found at the phylum level, the cestode genus Diphyllobothrium was more prevalent and abundant in walruses consuming higher-trophic-level prey, probably because fish are the intermediate hosts for this genus. This study suggests that diet is important for structuring both parasite and microbial communities of this culturally and ecologically important species, with potential implications for population health under climate change.

The Matthew effect: Common species become more common and rare ones become more rare in response to artificial light at night.

Artificial light at night (ALAN) has been and still is rapidly spreading and has become an important component of global change. Although numerous studies have tested its potential biological and ecological impacts on animals, very few studies have tested whether it affects alien and native plants differently. Furthermore, common plant species, and particularly common alien species, are often found to benefit more from additional resources than rare native and rare alien species. Whether this is also the case with regard to increasing light due to ALAN is still unknown. Here, we tested how ALAN affected the performance of common and rare alien and native plant species in Germany directly, and indirectly via flying insects. We grew five common alien, six rare alien, five common native, and four rare native plant species under four combinations of two ALAN (no ALAN vs. ALAN) and two insect-exclusion (no exclusion vs. exclusion) treatments, and compared their biomass production. We found that common plant species, irrespective of their origin, produced significantly more biomass than rare species and that this was particularly true under ALAN. Furthermore, alien species tended to show a slightly stronger positive response to ALAN than native species did (p = .079). Our study shows that common plant species benefited more from ALAN than rare ones. This might lead to competitive exclusion of rare species, which could have cascading impacts on other trophic levels and thus have important community-wide consequences when ALAN becomes more widespread. In addition, the slightly more positive response of alien species indicates that ALAN might increase the risk of alien plant invasions.

Transfer of Microplastics in Terrestrial and Aquatic Food Webs: The Impact of E-Waste Debris and Ecological Traits.

Factors affecting the trophic transfer of microplastics (MPs) in aquatic and terrestrial ecosystems remain to be clarified. Here, we determined the abundances of MPs in multiple terrestrial and aquatic species, including insects, snails, crustaceans, fishes, snakes, birds, and voles, from an abandoned e-waste recycling site. Approximately 80% of MPs were within the size range 20-50 µm. In wildlife, the MP abundances per individual and per body weight were found to be positively and negatively correlated with body weight, respectively. Herein, terrestrial vertebrates, primarily birds, exhibited more complex compositions of polymer types than other organisms owing to the wide foraging areas and diverse food sources. However, according to the MPs modeled and the observed results in bird food chains, MPs do not appear to be preferentially retained in the bird gastrointestinal tract. The species-specific polymer types identified indicate the influences of habitat on MP pollution in organisms, which is further supported by significant correlations between the abundance of MPs and δ13C in the terrestrial food web (p < 0.05). In the analyzed bird species, the low MP abundance detected in birds compared with the amount of food ingested indicates that MPs constitute a negligible factor in the bioaccumulation of chemical pollutants.

Are cysteine, glutathione and phytochelatins responses of Myriophyllum alterniflorum to copper and arsenic stress affected by trophic conditions?

The aim of this article is to study the impact of both copper (Cu2+) and arsenic (As (V)) at 100 µg/L, with each element being combined with trophic conditions at the level of glutathione, cysteine and phytochelatins in the aquatic macrophyte Myriophyllum alterniflorum, whose potential for bioindication and phytoremediation of metal/metalloid pollution has already been demonstrated. To achieve this goal, a synthetic medium, of a composition similar to the water found in the Vienne River in France's Limousin Region and modified for eutrophic or oligotrophic conditions, is prepared. The analysis of cysteine, glutathione and phytochelatins is performed at 0, 3, 7, 14 and 21 days. Our results indicate that the eutrophic medium without contaminant only induces a significant increase in the glutathione level when compared to the oligotrophic medium. However, the joint presence of As (V) and Cu is able to increase the synthesis of cysteine, glutathione and phytochelatins (PC2 and PC3) under both eutrophic and oligotrophic conditions, with a significant increase in the eutrophic medium compared to the oligotrophic one. Phytochelatins (PC2 and PC3) are induced after as little as 3 days of exposure to copper and arsenic under both trophic conditions. Copper induces the synthesis of more PC3 than PC2, unlike arsenic. Our results confirm the potential use of phytochelatins as a specific biochemical biomarker for metal/metalloid stress. In conclusion, the eutrophic condition combined with copper or arsenic does change the response of Myriophyllum alterniflorum by enhancing its antioxidative defense. Thus, M. alterniflorum phytochelatins represent a potential dedicated biomarker to monitor water quality in terms of metal/metalloid stress regardless of the trophic level.

Assessing microplastic ingestion and occurrence of bisphenols and phthalates in bivalves, fish and holothurians from a Mediterranean marine protected area.

Microplastic (MP) ingestion, along with accumulated plasticizers such as bisphenol A (BPA), bisphenol F (BPF), and bisphenol S (BPS), and phthalates represented by diethyl phthalate (DEP), dibutyl phthalate (DBP) and bis (2-ethylhexyl) phthalate (DEHP), were quantified in bivalves, fish, and holothurians collected from a coastal pristine area at the western Mediterranean Sea. MP ingestion in sediment-feeders holothurians (mean value 12.67 ± 7.31 MPs/individual) was statistically higher than ingestion in bivalves and fish (mean 4.83 ± 5.35 and 3 ± 4.44 MPs/individual, respectively). The main ingested polymers were polyethylene, polypropylene, and polystyrene. The levels of BPS, BPF, and DEHP were highest in bivalves' soft tissue; BPA and DBP had the highest levels in the holothurians' muscle. In addition, the levels of all plasticizers assessed were lowest in fish muscle; only BPA levels in fish were higher than in bivalves, with intermediate values between those of bivalves and holothurians. This study provides data on exposure to MPs and plasticizers of different species inhabiting Cabrera Marine Protected Area (MPA) and highlights the differences in MP ingestion and levels of plasticizers between species with different ecological characteristics and feeding strategies.

Effect of trophic position on mercury concentrations in bottlenose dolphins (Tursiops truncatus) from the northern Gulf of Mexico.

Marine species from the Gulf of Mexico often have higher mercury (Hg) concentrations than conspecifics in the Atlantic Ocean. Spatial differences in Hg sources, environmental conditions, and microbial communities influence both Hg methylation rates and the bioavailability of Hg to organisms at the base of the food web. Mercury bioaccumulates within organisms and biomagnifies in marine food webs, and therefore reaches the greatest concentrations in long-lived marine carnivores, such as dolphins. In this study, we explored whether differences in trophic position and foraging habitat among bottlenose dolphins (Tursiops truncatus) from the northern Gulf of Mexico (nGoM) contributed to the observed variation in skin total Hg (THg) concentrations. Using the δ13C and δ34S values in dolphin skin, we assigned deceased stranded dolphins from Florida (FL; n = 29) and Louisiana (LA; n = 72) to habitats (estuarine, barrier island, and coastal) east and west of the Mississippi River Delta (MRD). We estimated the mean trophic position of dolphins from each habitat using δ15N values from stranded dolphin skin and tissues of primary consumers taken from the literature following a Bayesian framework. Finally, we compared trophic positions and THg concentrations among dolphins from each habitat, accounting for sex and body length. Estimated marginal mean THg concentrations (µg/g dry weight) were greatest in dolphins assigned to the coastal habitat and estuarine habitats east of the MRD (range: 2.59-4.81), and lowest in dolphins assigned to estuarine and barrier island habitats west of the MRD (range: 0.675-0.993). On average, dolphins from habitats with greater THg concentrations also had higher estimated trophic positions, except for coastal dolphins. Our results suggest that differences in trophic positions and foraging habitats contribute to spatial variability in skin THg concentrations among nGoM bottlenose dolphins, however, the relative influence of these factors on THg concentrations are not easily partitioned.

Exploring diet shifts and ecology in modern sharks using calcium isotopes and trace metal records of their teeth.

Sharks occupy all living environments of the marine realm as well as some freshwater systems. They display varied and flexible feeding behaviours, but understanding their diet remains challenging due to their elusive ecology and the invasiveness of stomach content analyses in regard of their threatened status. As a potential alternative, we discuss the variability in δ44/42 Ca values recorded in the tooth enamel of size-graded individuals belonging to three species of large sharks with distinct diets (Isurus oxyrinchus, Hexanchus griseus and Carcharodon carcharias). The preliminary results highlight shifts in diet linked to ontogeny (I. oxyrinchus and H. griseus) and spatial distribution (C. carcharias) characterizing feeding behaviour in these species at individual and population level. These outcomes agree with the results of traditional stomach analyses supporting that nontraditional stable isotopes thus represent new perspectives for the study of modern and extinct shark ecology. In addition, for the first time, the Sr/Ca elemental ratios measured in H. griseus reflect sexual differences that could be interpreted in terms of spatial segregation or physiological heterogeneities.