Trophic Markers Research Articles

Trophic ecology of squids in the Benguela Upwelling System elucidated by combining stomach content, stable isotope and fatty acid analyses

Squids occur worldwide in marine ecosystems and play a major role in pelagic food webs by connecting lower and higher trophic levels. Their high feeding intensities and pronounced diel vertical migrations make squids important components of nutrient cycles in marine ecosystems. This study assessed the trophic position and nutritional ecology of a squid species assemblage in the Benguela Upwelling System (BUS) by combining stomach content, stable isotope and fatty acid trophic marker analyses. Samples were collected in the northern (nBUS) and southern (sBUS) BUS in austral spring 2021. A total of 20 squid species from eleven families were identified. Stomach content analyses showed that squid species preyed on a variety of organisms ranging from crustaceans to lanternfishes (Myctophidae) and flying squids (Ommastrephidae). Stable isotope analyses revealed significant differences in δ15N values of small squids (dorsal mantle length < 10 cm) between the two subsystems, but none in those of large squids (dorsal mantle length > 10 cm). Trophic levels ranged from 2.2 to 5.0. Isotopic niche width was widest in the families Ommastrephidae and Cranchiidae. Principal component analyses of fatty acid compositions displayed distinct clusters separating squid families and different prey taxa. This study shows that nBUS and sBUS squids exploit a large variety of pelagic prey organisms and that trophic differences are primarily dependent on squid species and size. The results emphasize the squids’ importance as interlinking element in pelagic food webs and their key function in energy transfer between epi- and mesopelagic layers.

Benthic marine invertebrate herbivores diversify their algal diets in winter

AbstractChanges in the seasonal environment substantially influence organisms. Understanding how species respond to such changes, such as in their feeding interactions and physiology, is key to predicting their resilience to both seasonal and longer term climate changes. The Sitka Sound in Southeast Alaska, USA, is an attractive natural laboratory for studying change, as the marine environment experiences substantial seasonal fluctuations in parameters such as temperature, pH, and productivity between summer and winter. By sampling a suite of dominant macrophyte algae and their benthic herbivores in winter (January) and summer (July) 2019, we investigated how producers and their primary consumers may respond to seasonal change inferred through fatty acid trophic markers. We used a fatty acid logratio selection and analysis approach to ask the following: (1) Do fatty acid biomarkers for algae differ between seasons? (2) Do the same fatty acid biomarkers differ between seasons when applied to herbivores, with herbivore fatty acids tracking the presumed trophic resources? (3) Do fatty acid biomarkers for herbivores differ between seasons, when considered independently from algae? Comparing logratio sets selected each for the algae and the herbivore fatty acids, we found that algae fatty acids were different between our sampling seasons, but the algae‐selected fatty acid logratios did not clearly separate most herbivores by season. In contrast, the herbivore‐selected logratios strongly distinguished herbivore species between the January and June samplings. Further, dispersions of fatty acid logratios were greater within herbivore species in the winter than in the summer, potentially due to the utilization of more diverse resources when preferred algae are less abundant. In total, results suggest that herbivores are not simply tracking the seasonal fatty acid changes in the dominant algae as trophic resources; instead, herbivore fatty acid seasonal changes may occur largely through some other nonexclusive mechanisms, such as omnivory, reductions or shifts in dietary composition, and/or endogenous physiological responses. Thus, the benthic herbivores in our study appear not to be locked into their diets when faced with seasonal change and may use a range of strategies, including diet diversification, to cope with environmental variation.

Ontogeny of foraging behaviour in an opportunistic gull inhabiting urban marine ecosystems

Urbanization affects ecosystems by reducing biodiversity and displacing species from native habitats. While some suffer, others, like urban wildlife, adapt through innovative feeding and behaviours that improve their fitness in human‐altered settings. Despite research on wildlife in urban areas, the development of foraging behaviour in urban species is still understudied. Here, we examined the age‐related differences in the foraging behaviour of yellow‐legged gulls Larus michahellis in Barcelona (Spain), a densely populated coastal urban ecosystem. Using biologging technologies and trophic markers, we compared the foraging strategies, habitat use, human interactions, and trophic niches of juvenile, immature, and adult yellow‐legged gulls over three breeding seasons. The results showed age‐related differences in spatial distribution and foraging behaviour in this opportunistic species. Juveniles and immatures mainly foraged in ports and at sea, while adults favoured urban habitats. These patterns likely stem from reproductive constraints in adults and lower foraging efficiency in younger birds. Adults' primary use of urban habitats also explains their higher trophic niche. Furthermore, fishing activity significantly influenced yellow‐legged gull foraging across age groups, with strong associations between gulls and fishing vessels. By studying how age and life stage influence habitat use and behaviour, this research provides insights to guide targeted management strategies for this species.

Foraging in contrasting oceanographic regions impacts the fatty acid profile of two closely related pelagic seabirds

Coastal urbanisation negatively affects marine ecosystems through habitat degradation and pollution. Cory’s (Calonectris borealis) and Scopoli’s (C. diomedea) shearwaters are closely related species inhabiting the Northeast Atlantic Ocean and the Mediterranean Sea, respectively. This study assesses the fatty acid profile, with the trophic and foraging ecology, of Cory’s and Scopoli’s shearwaters breeding at Berlenga (Atlantic Ocean) and Chafarinas (Mediterranean Sea) Islands. The diet quality of Scopoli’s shearwaters is expected to be generally lower, characterised by reduced levels of ω-3 fatty acids. Additionally, higher concentrations of specific fatty acid trophic markers are anticipated, reflecting the Mediterranean's semi-enclosed environment, low productivity, and pollution challenges. These markers include oleic acid, vaccenic acid, trans fatty acids (indicative of urban and industrial discharges), and odd-chain fatty acids (indicative of bacterial presence). This study supported these predictions, with Scopoli’s shearwaters foraging in the Mediterranean having higher concentrations of oleic and vaccenic acids, odd-chain fatty acids, and trans-palmitoleic acid in their plasma. Yet, concentrations of ω-3 were also higher in Scopoli’s shearwaters. This may result from diverse prey availability and selection, and different habitat exploitation, partially supported by differences in the trophic ecology and foraging patterns of both species; or from an enhanced immunological basal response of Scopoli’s shearwaters to cope with higher anthropogenic pressure in the western Mediterranean Sea. Further studies including specific diet and contaminant analyses are crucial to understand differences in fatty acid profiles of seabirds inhabiting both oceanic basins and the implications of diet quality for seabird populations.

13C-enrichment NMR spectroscopy: a tool to identify trophic markers and linkages

Current climate change, particularly ocean warming, will induce shifts in marine species distribution and composition, affecting the marine food web and, thus, trophic interactions. Analyses of the stable isotopes 13C and 15N are commonly used to detect trophic markers for food web analyses. With the current standard methods used in food web ecology, it is still challenging to identify potential changes in the uptake and utilization of trophic markers. In this work, we present a 13C-enrichment analysis by NMR spectroscopy to track the uptake and utilization of dietary carbon in a simple laboratory experiment of a primary producer and its consumer (algae and bivalve). In particular, we tested the hypothesis of a temperature-dependent use of dietary carbon by tracing the incorporation of 13C-atoms. Unicellular phytoplankton, Phaeodactilum tricornutum, was reared in a medium containing 13C-labeled bicarbonate. The accompanying 13C-NMR spectra of labeled P. tricornutum showed a specific profile of 13C-labeled compounds, including typical trophic markers such as the polyunsaturated omega-3 fatty acid eicosapentaenoic acid (EPA). Afterwards, 13C-labeled P. tricornutum was fed to King scallops, Pecten maximus, kept at two different temperatures (15°C and 20°C). Tissue-specific NMR spectra of P. maximus revealed elevated 13C-NMR signals, particularly of the fatty acid EPA in the digestive gland, which was not evident in muscle tissue. The comparison between the two temperatures indicated a change in trophic markers. At the higher temperature, less unsaturated fatty acids were detected in the digested gland, but increased 13C-labels in sugars were detected in the adductor muscle. This might indicate a change in the uptake and utilization of the trophic marker EPA in P. maximus due to a shift in energy conversion from favored beta-oxidation at colder temperatures to conversion from carbohydrates in the warmth. Our approach indicates that besides the accumulation of trophic markers, their incorporation and conversion are additional important factors for the reliable interpretation of trophic linkages under climate change.

A dataset of individual wet weights of benthic macroinvertebrates

AbstractBiomass estimates are crucial for modeling and understanding energy flow through ecosystems. Many modeling frameworks rely on published body weights of organisms to convert density estimates to biomass. However, published body weight data are limited to few taxa in a limited number of systems. Here we present mean individual weights for common benthic macroinvertebrates of the Laurentian Great Lakes from over 2000 benthic samples and 8 yr of data collection. We also compiled wet to dry weight conversions to facilitate data reuse for researchers interested in dry weight. We compared our benthic invertebrate weights to other lakes, demonstrating when weight measurements may be applied outside the Great Lakes. Sensitivity analyses supported the robustness of our calculations. Our dataset is applicable to food web energy flow models, calculation of secondary production, interpretation of trophic markers, and for understanding how biomass distribution varies by benthic invertebrate species in the Great Lakes.

Spatial and cumulative organochlorine and mercury exposure assessments in Steller Sea lions of Alaska: Emphasizing pups

Steller sea lions (SSL) are sentinels for monitoring environmental contaminants in remote areas of the Aleutian Islands, Alaska. Therefore, concentrations of several organochlorines (OCs) were measured in blood from 123 SSL pups sampled from 3 regions; the western Aleutian Islands (WAI), central Aleutian Islands (CAI), and the central Gulf of Alaska. Blood, blubber, and milk from 12 adult female SSL from WAI, CAI and southeast Alaska also were analyzed. Findings included the following. SSL pups had higher concentrations of some OCs and mercury (Hg) on rookeries in the WAI than those more easterly. Pups had significantly higher blood concentrations of many OC classes than adult females sampled within the same region; some pups had PCB concentrations exceeding thresholds of concern (∑PCBs >8600 ng/g lw). ∑PCB concentration in pup whole blood was positively correlated with the trophic marker, δ15N within the regions sampled, along with two PCB congeners (PCB138 and PCB153). This suggests that the dams of pups with higher ∑PCBs, PCB138, and PCB153 concentrations were feeding on more predatory prey. Adult female blubber ∑DDT and hexachlorocyclohexane concentrations were also positively correlated with δ15N values. Several pups (mostly from WAI) had blood Hg concentrations and/or blood PCB concentrations (surrogate for overall OC exposures) of concern. The finding that WAI SSL pups have been exposed to multiple contaminants calls for future investigation of their cumulative exposure to a mixture of contaminants especially their transplacental and then transmammary exposure routes.

Seasonal variation in fatty acid profiles of Holothuria poli (Delle Chiaje, 1823) from Monastir Bay (Tunisia): implications for trophic markers and lipid nutritional quality assessment

ABSTRACT This study investigated the seasonal variations in the proximate composition, fatty acid profile, lipid nutritional quality, and diet composition of Holothuria poli collected from Monastir Bay. Our findings revealed significant seasonal variations in protein, lipids, and ash contents, with the highest protein levels recorded during the summer and peak lipid levels observed in winter. Total monounsaturated fatty acids peaked in both winter and summer, while total saturated fatty acids reached their maximum in autumn. These variations in biochemical compositions were closely linked to the sea cucumber's dietary preferences. Our results demonstrated that H. poli exhibits a diverse diet, consuming bacteria, detritus, diatoms, zooplankton, and algae, with notable seasonal fluctuations. Moreover, the EPA + DHA content and the atherogenic (AI), thrombogenic (TI), and hypocholesterolemic/hypercholesterolemic (H/H) indexes align with the ranges characteristic of high-quality seafood, though marked variations are evident among seasons. A principal component analysis illuminated the dynamic seasonal shifts in Holothuria poli's dietary habits and lipid nutritional characteristics, offering valuable insights into its ecological adaptations and potential repercussions for marine food webs. These findings underscore the intriguing interplay between fatty acid composition, lipid nutritional quality, dietary preferences, and environmental factors in sea cucumbers.

The impact of advection on a Subarctic fjord food web dominated by the copepod Calanus finmarchicus

Fjord and shelf food webs are frequently supplemented by the advection of external biomass, which in high-latitude seas often comes in the form of lipid-rich copepods that can support a wide range of fish species, including Northeast Arctic cod (Gadus morhua). A seasonal match or mismatch at the lower trophic levels (phytoplankton and zooplankton) is central in determining how much energy and biomass is available for higher trophic levels (fish). Here, we quantify the inflow of the copepod Calanus finmarchicus into the Vestfjorden fjord system using high-resolution measurements of ocean currents and zooplankton (laser optical plankton counter). We evaluate a spatio-temporal match/mismatch between the phytoplankton bloom and Calanus and assess the input of advected copeods at the lower trophic level fjord and shelf food web based on an integrative approach employing stable isotope analyses (C, N), fatty acid trophic marker analyses, and biovolume spectrum analyses. Our results suggest two different sources of the Calanus population in the fjord/shelf system: one fraction overwintered locally and started ascending early to feed on the phytoplankton bloom that peaked around April 11. The other fraction had only recently (end of April) been and still was being advected from the oceanic overwintering habitats. Ca. 119 g C/s of Calanus were advected into the fjord, comparable to the biomass of Calanus advected into an Arctic fjord, and the mesozooplankton community was dominated by the copepod. The fjord food web was tightly coupled between the phytoplankton spring bloom, the local part of the Calanus population (trophic level 1.8–2.4) and cod larvae (high levels of wax esters). On the shelf, our results suggest that the impact of advected Calanus in the food web is at its starting point (low trophic level, large difference of δ13C of POM and Calanus). We highlight important factors that can contribute to the successful spawning of Northeast Arctic cod: an extended phytoplankton bloom that can support both locally and advected Calanus, which in turn can supply the essential nauplii prey for first-feeding cod larvae.

Resource partitioning in hammerhead shark species out-migrating from coastal ecosystems in the Gulf of California

Juveniles of large hammerhead shark species occupy coastal nurseries before migrating offshore to reproduce. In the central Gulf of California, artisanal elasmobranch fisheries have reported catches of juvenile scalloped Sphyrna lewini and smooth S. zygaena hammerhead sharks, but their local foraging habits are yet to be fully understood. In this study, the trophic niches of both hammerhead species as well as of sympatric Pacific sharpnose sharks Rhizoprionodon longurio were investigated using stable isotope values (δ13C, δ34S and δ15N) and fatty acid compositions in whole blood and muscle tissues. Despite interspecific similarities among trophic niches, smooth hammerheads were characterized by lower δ13C, higher δ34S and greater proportion of docosahexaenoic acid (DHA) in both tissues, suggesting they were already partly relying on offshore pelagic resources. For scalloped hammerheads, muscle reflected coastal dietary resources, while offshore trophic markers were detected in blood integrating prey signal over shorter time periods, indicating their more recent initiation of ontogenetic migration. Multidimensional niche calculation revealed low overlap between hammerhead shark trophic niches, implying that potential fine-scale differences in habitat use could reduce competition between these morphologically and ecologically similar species. In the meantime, the isotopic niches of juvenile scalloped and smooth hammerheads were smaller than that of Pacific sharpnose sharks, suggesting they could be more specialized consumers. Overall, the identification of foraging grounds for juvenile hammerhead sharks calls for a future characterization of their residency time in coastal ecosystems to further understand their interactions with fishing pressure in the Gulf of California.

Early prey intake of a short-finned pilot whale (Globicephala macrorhynchus Gray, 1846, Cetacea: Delphinidae) in the Canary Islands.

This study reveals early prey eating by a short-finned pilot whale (Globicephala macrorhynchus Gray, 1846, Cetacea: Delphinidae) in the Canary Islands. Stomach contents, trophic markers, skin isotopic ratios of nitrogen (δ15N:15N/14N) and carbon (δ13C:13C/12C), and fatty acid profiles of the blubber of a short-finned pilot whale of 213 cm size euthanized in free-ranging conditions were analyzed. A total of 15 species of oegopsid squids, mostly diel vertical mesopelagic migrant species of the families Enoploteuthidae, Ommastrephidae, and Histioteuthidae, as well as mother's milk, were identified in the stomach contents. Asperoteuthis acanthoderma (Lu, 1977, Cephalopoda: Chiroteuthidae) was found as first time in this area, suggesting the possibility of its presence on both sides of the subtropical Atlantic, extending its current known distribution. The δ15N value (11.55‰) was higher than expected based on the size range of squid ingested, but lower than that of adult pilot whales, suggesting that mother's milk intake has a significant effect on these values in calves. Similarly, the δ13C values (-17.99‰) were shifted to those of adult pilot whales rather than the ingested squids, also due to the ingestion of high-fat breast milk. The fatty acid (FA) composition of blubber showed a clear stratification. Long-chain polyunsaturated fatty acids (LC-PUFA) were mainly present in the inner layer, while most relevant ≤C20 monounsaturated fatty acids (MUFA) were more abundant in the outer layer.

Food preferences of two nudibranch species from the South China Sea revealed by fatty acid trophic markers

AbstractNudibranchs are mostly predators preying on a variety of invertebrates. The dietary preferences of tropical nudibranchs were studied by the method of fatty acid trophic markers (FATM) in order to for better understanding of their trophic ecology. For this, the fatty acid profiles of two nudibranch species from the South China Sea, Doriprismatica atromarginata (Cuvier, 1804) and Jorunna funebris (Kelaart, 1859), were analyzed and trophic markers were identified. The high level of very long chain fatty acids (from C24 to C28), which are characteristic of sponges, in nudibranchs was evidence of their predation on sponges. However, the distribution of these components differed significantly between the species. The acids 24:2Δ5,9, 25:2Δ5,9, 26:2Δ9,19, and especially 26:2Δ5,9 dominated in D. atromarginata, but were not found in J. funebris that was rich in 28:2Δ5,9 and 28:3Δ5,9,19. The significant differences in the profile of these demospongic acids indicate that these nudibranchs consumed different species of sponges. The similarity between the FATMs of J. funebris and its potential prey, the sponge Xestospongia, confirmed their predator–prey relationship. Doriprismatica atromarginata from different sites along the Vietnam coast had different FATM profiles, which showed this nudibranch as having no any strict food specialization and feeding on various Demospongiae species. The abundance of bacterial FATMs in the nudibranchs suggests the importance of bacteria in their diet. Thus, the FATM method has proven to be useful for identifying the feeding specialization and assessing the effect of food availability on the diet of these tropical nudibranch species.

The yellow mullet fish oil from the Banc d’Arguin Imrâguens in Mauritania: an example of polyunsaturated fatty acids transfer from diatoms to the fish within the alimentary chain

The Banc d’Arguin National Park (PNBA) in Mauritania is listed by the UNESCO World Heritage. It is characterized by an exceptionnal marine biodiversity with numerous endemic species and it provides a major site of reproduction for western Africa fish. The Imrâguens form fisherman communities established at Banc d’Arguin, who live upon fishing the yellow mullet (Mugil cephalus) during its migration and derived products. The fish oil produced by Imrâguens from mullet heads is rich in omega 3 polyunsaturated fatty acids (37.7 % of total fatty acids). The main fatty acid is eicosapentaenoic fatty acid (EPA ; 20.18 ± 0.01 %). This fatty acid is particularly abundant in diatoms, that contribute to 20- 30% of mullet feeding. The identification of 16:4n-1 also provide a good trophic marker for yellow mullet feeding on diatoms. The lipases potentially involved in the mobilization of these fatty acids in the course of digestion of diatoms were identified from the analysis of Mugil cephalus genome. Genes encoding a lipase homologous to gastric lipase and four lipases homologous to pancreatic carboxylester hydrolase or bile-salt stimulated lipase were identified. These later could be involved in the lipolysis of galactolipids, the main lipids present in diatom photosynthetic membranes which are rich in EPA. These data provide an added value to the traditional fishing practice of Imrâgens and highlight the nutritional value of the fish oil they produce.

Lipid biomarkers reveal trophic relationships and energetic trade‐offs in contrasting phenotypes of the cold‐water coral Desmophyllum dianthus in Comau Fjord, Chile

Abstract Benthic suspension feeders like corals and sponges are important bioengineers in many marine habitats, from the shallow tropics to the depth of polar oceans. While they are generally considered opportunistic, little is known about their actual in situ diet. To tackle this limitation, fatty acid trophic markers (FATMs) have been employed to gain insights into the composition of their diet. Yet, these in situ studies have not been combined with physiological investigations to understand how physiological limitations may modulate the biochemistry of these organisms. Here, we used the cold‐water coral (CWC) Desmophyllum dianthus in its natural habitat in Comau Fjord (Northern Patagonia, Chile) as our model species to assess the trophic ecology in response to contrasting physico‐chemical conditions (variable vs. stable) and ecological drivers (food availability) at three shallow sites and one deep site. We took advantage of the expression of two distinct phenotypes with contrasting performance (growth, biomass, respiration) coinciding with the differences in sampling depth. We analysed the corals' fatty acid composition to evaluate the utility of FATM profiles to gain dietary insights and assess how performance trade‐offs potentially modulate an organism's FATM composition. We found that 20:1(n‐9) zooplankton markers dominated the deep high‐performance phenotype, while 20:5(n‐3) and 22:6(n‐3) diatom and flagellate markers, respectively, are more prominent in shallow low‐performance phenotype. Surprisingly, both energy stores and performance were higher in the deep phenotype, in spite of measured lower zooplankton availability. Essential FA concentrations were conserved across sites, likely reflecting required levels for coral functioning and survival. While the deep high‐performance phenotype met with these requirements, the low‐performance phenotype appeared to need more energy to maintain functionality in its highly variable environment, potentially causing intrinsic re‐allocations of energy and enrichment in certain essential markers (20:5(n‐3), 22:6(n‐3)). Our analysis highlights the biological and ecological insights that can be gained from FATM profiles in CWCs, but also cautions the reliability of FATM as diet tracers under limiting environmental conditions that may also be applicable to other marine organisms. Read the free Plain Language Summary for this article on the Journal blog.

Are Upwelling Systems an Underestimated Source of Long Chain Omega‐3 in the Ocean? The Case of the Southern Benguela Upwelling System

AbstractThe Benguela upwelling system (BUS) is one of the world's most productive ecosystems, supporting globally relevant fisheries. The BUS marine community is modulated by the availability of nutrients and omega‐3 long chain polyunsaturated fatty acid (hereafter, LC omega‐3). Phytoplankton growth in the BUS can be supported by upwelled nitrate, a new nitrogen (N) source to the surface, or by recycled N such as ammonium. Preferential assimilation of one N source over another may yield differences in LC omega‐3 production between high and low food‐quality species. To evaluate how upwelling and the N source(s) consumed by phytoplankton influence LC omega‐3 production, we sampled a BUS anchor station daily for 10 days. Upwelling on days 5–7 supplied high concentrations of nutrients to the surface, while pre‐ and post‐upwelling, surface waters were stratified and nutrient concentrations were low. LC omega‐3 and phytoplankton concentrations were near‐zero during upwelling, and elevated pre‐ and post‐upwelling. Throughout our sampling, nanoplankton (2.7–10 µm) dominated primary production (30–95%), relying mainly on nitrate to support their growth. Surface LC omega‐3 concentrations reached peaks of 215 and 175 µg L−1 pre‐ and post‐upwelling, up to 10 times higher than previous measurements from the BUS (&lt;5 µg L−1). Pre‐upwelling, non‐diatom trophic markers (18:1n − 9, 18:4n − 3, 18:5n − 3) were dominant, with a switch over just two days to diatom trophic markers post‐upwelling (16:1n − 7, 16:2n − 4, 16:2n − 7, 16:3n − 4, 16:4n − 1). This study reveals the key role of upwelling in promoting phytoplankton LC omega‐3 production, which is tightly coupled to the supply of new nitrate. Additionally, the high observed LC omega‐3 concentrations suggest that global LC omega‐3 production is underestimated.

Isotopic and biochemical trophic markers reveal the complexity of interactions at the base of pelagic food webs (Mediterranean sea)

To gain insight into the impact of bottom-up changes in the plankton community on planktivorous fish in the context of the decline of small pelagic fisheries in the Northwestern Mediterranean Sea, we have conducted an extensive year-long study. The investigation combined biochemical analyses (proteins, carbohydrates, and lipids) with C and N stable isotope analyses (SIA) to simultaneously study phytoplankton, zooplankton, and eight planktivorous fish species (Engraulis encrasicolus, Sardina pilchardus, Sardinella aurita, Sprattus sprattus, Cepola macrophthalma, Chromis chromis, Boops boops, and Spicara maena). This study is the first to analyze both stable isotope and biochemical compositions in coastal particulate organic matter (POM) size classes (0.7–2.7 μm, 2.7–20 μm, and 20–200 μm), zooplankton size classes (200–300 μm, 300–500 μm, 500–1000 μm, 1000–2000 μm, and >2000 μm), and taxonomic groups.We demonstrated that: (1) POM stable isotope compositions varied based on its spatial origin, the taxonomic composition of its biota, and its biochemical content; (2) δ15N values increased with zooplankton size classes and groups, indicating different trophic levels; (3) Phytoplankton exhibited a lipid-rich composition (∼55%), while zooplankton and fish muscles were protein-rich (∼61% and ∼66%, respectively).Bayesian stable isotope mixing models revealed that, on average: (1) POM from oceanic waters contributed the most to the POM in the bay (>51%), with a dominance of pico-POM (∼43%); (2) The 200–1000 μm zooplankton primarily consumed nano-POM, the 1000–2000 μm zooplankton mostly consumed micro-POM (∼64%), and the >2000 μm zooplankton also mostly consumed micro-POM; (3) Mesozooplankton (200–2000 μm) constituted the main portion (∼42%) of the diet for planktivorous fish species, while macrozooplankton organisms (>2000 μm) were the primary food resource (∼43%) for both B. boops and S. sprattus.Our study underscores the complexity of the pelagic food web and highlights the bottom-up transfer of organic matter from the smallest phytoplankton size fractions to planktivorous fish.

Multiple-biomarkers show the importance of blue carbon to commercially important fishery species

Coastal blue carbon ecosystems (BCE) support nearshore food webs and provide habitat for many commercially important fish and crustacean species. However, the complex links between catchment vegetation and the carbon food-base of estuarine systems are difficult to disern. We employed a multi-biomarker approach (stable isotope ratios - δ13C and δ15N, fatty acid trophic markers – FATMs and metabolomics – central carbon metabolism metabolites) to test links between estuarine vegetation and the food sources available to commercially important crabs and fish occurring within the river systems of the near-pristine eastern coastline of the Gulf of Carpentaria, Australia. Stable isotope analysis confirmed the dietary importance of fringing macrophytes to consumer diet, but showed that this is modulated by their dominance along the riverbank. FATMs indicative of specific food sources further confirmed the differences among upper intertidal macrophytes (driven by concentrations of 16: 1ω7, 18:1ω9, 18:2ω6, 18:3ω3 & 22.0) and seagrass (driven by 18:2ω6, 18:3ω3). These dietary patterns were also reflected in the concentration of central carbon metabolism metabolites. Overall, our study demonstrates the congruence of different biomarker approaches to resolve biochemical links between blue carbon ecosystems and important nekton species, and provides fresh insights into the pristine tropical estuaries of northern Australia.

Terrestrial fatty acids from feed oil in feed for farmed salmonids are transferred to the liver, gonads, and muscle of wild Atlantic cod (Gadus morhua)

Abstract Wild fish attracted to salmon farms feed on waste feed that presently contain high levels of fatty acids of terrestrial origin. This study examines whether mature Atlantic cod (Gadus morhua) caught at spawning grounds has eaten salmon waste feed. Cod were caught at four spawning grounds around Smøla (Norway), an area with multiple salmon farms, during the spawning season in 2018 (n = 327) and 2019 (n = 488). The fatty acid (FA) profile of their livers, gonads (ovary and testis), and muscles (2019) were determined. Multivariate k-mean cluster analysis of liver FA profiles revealed three main clusters, which could be allocated to trophic niches using known fatty acid trophic markers (FATMs). Of the sampled cod in 2018 and 2019, 13 % and 20 % respectively had high liver concentrations of terrestrial FATMs (18:1n-9, 18:2n-6, and 18:3n-3), indicating waste feed feeding. The remaining cod could be assigned to either the pelagic or benthic food chain. The cod identified as feeding on waste feed had large, fatty livers. The terrestrial FAs were also transferred to the muscle and gonad lipids. It is postulated that the latter may result in gametes with sub-optimal lipid composition, potentially impacting fitness, which warrants further investigation.

Autochthonous production sustains food webs in large perialpine lakes, independent of trophic status: Evidence from amino acid stable isotopes

Abstract Lakes are recipients of allochthonous organic matter and nutrients. However, the importance of these subsidies for food webs and how they vary with lake trophic status remains unclear, especially for large lakes. We assessed the source and fate of organic matter and nutrients in seven perialpine lakes across a gradient of trophic status. We measured carbon and nitrogen stable isotopes of amino acids of lake‐residing Atlantic trout, Salmo trutta, to determine the source of primary production (i.e., how carbon is fixed in the ecosystem) and how it is transferred through food webs, respectively. Based on essential amino acid carbon fingerprinting, we estimated the probability of organic carbon originating from autochthonous (algal), allochthonous (terrestrial plant), and recycled (bacterial) sources. In addition, we used amino acid δ15N to track how this primary production is transferred to consumers in general, and by using different trophic amino acids (glutamic acid and alanine), identify the trophic pathways involving either metazoan or protozoans. We found a high likelihood of autochthonous origin of organic carbon (86 ± 9%) in trout that contrasted with allochthonous origins of particulate organic matter and some sediments. We showed that those estimates are good proxies of source reliance. Our results also highlighted the importance of bacterial origin of organic carbon in fish (12%). The likely autochthonous origin of this carbon was supported by trophic markers (Ala δ15N) that suggest the role of protists in transferring recycled organic carbon up the food web. While the sources of nitrogen sustaining food webs varied among lakes, we found a conserved carbon fingerprinting of fish. Overall, this suggests an uncoupling between the source of nutrients and organic carbon in large perialpine lakes. Across a wide range of trophic status (c. 2 orders of magnitude range of phosphorus concentration), several lines of evidence suggested that perialpine lake food webs shared a common reliance on autochthonous and bacterial production. Our study is the first to quantify the dependence on allochthonous organic carbon in lake food webs based on new amino acid stable isotope markers (carbon fingerprinting and Ala δ15N) and shows promise for estimating the source of carbon fixation in ecosystems. Our results support previous suggestions that terrestrial organic carbon is a relatively minor source for aquatic consumers despite contributing to the pool of organic matter, and more importantly, its contribution does not vary substantially with trophic status in perialpine lakes.

Size‐based changes in trophic ecology and nutritional quality of moon jellyfish (Aurelia labiata)

AbstractDespite their seemingly watery constitution, jellyfish are eaten by a diverse range of predators. However, while the role of jellyfish in marine food webs is gaining attention, the nutritional value of these gelatinous organisms and how it varies remain poorly understood. In this study, we aimed to connect jellyfish food web biology and nutrition by determining the relationship between jellyfish size, diet, and nutritional quality. We measured stable isotope (SI) and fatty acid (FA) profiles of particulate organic matter (POM), plankton size classes, and gelatinous zooplankton collected from a coastal site in British Columbia, Canada, in July and September 2019. Gelatinous zooplankton comprised 152 Aurelia labiata collected across both months (bell diameters = 19–225 mm), and 2 Aequorea victoria and approximately 30 Pleurobrachia bachei collected in July for comparison. According to FA trophic markers and chlorophyll a concentrations, the POM was a mix of phytoplankton, microzooplankton, bacteria, and detritus. According to δ15N, POM was ~1 trophic level lower than plankton. All gelatinous zooplankton had low FA content (5–6 μg/mg dry mass) compared with zooplankton (43–65 μg/mg dry mass). A Bayesian mixing model (MixSIAR) was used to assess the contributions of POM and plankton to A. labiata diet, which demonstrated a size‐based shift from 40% plankton at 19 mm to 70%–75% at 225 mm. Similarly, both δ13C and δ15N increased with size and A. labiata of 19 mm were ~1 trophic level lower than A. labiata of 225 mm. We also documented size‐based changes in nutritional quality of A. labiata, where C:N decreased with A. labiata size, and essential FAs arachidonic acid (ARA) and docosahexaenoic acid (DHA) increased with size while eicosapentaenoic acid (EPA) did not change. A. labiata were elevated in ARA compared with other zooplankton, ranging from 1% to 9%. The changes in C:N and DHA of A. labiata with size mirrored the changes in their diet, but changes in ARA and EPA did not. Overall, these findings emphasize the importance of considering jellyfish size and taxonomy when evaluating nutritional pathways through jellyfish in marine food webs, and support that diet is one important driver of jellyfish biochemical composition.