Low redundancy among caddisflies sharing a mid‐mountain stream

Traceability of organic fish – Authenticating the production origin of salmonids by chemical and isotopic analyses

Samples of kelp Laminaria hyperborea, various species of red algae, phytoplankton, material from sediment traps, invertebrates, fish and seabirds were collected on the west coast of Norway and the abundance of stable isotopes was analyzed. Canopy plants of L. hyperborea were most 13 C depleted in spring and there was a significant difference between the basal (δ 13 C: -16.65‰) and distal (δ 13 C: -18.67‰) parts of the lamina. Young kelp plants were more 13 C depleted (-23.59‰). The red algae fell into 2 groups: one in the same range as kelp plants (δ 13 C: -18.93 to -22.27‰) and the other highly depleted (δ 13 C: -32.85 to -34.38‰). Phytoplankton showed an average δ 13 C value of -24.44 ‰. δ 15 N values from L. hyperborea differed between the basal (δ 15 N: 5.54 ‰) and distal (δ 15 N: 3.54 ‰) part of lamina. δ 15 N values for all primary producers values were in the range of 3.52 to 5.78 ‰. Among the gastropods, Helcion pellucida proved to be a kelp plant grazer, Lacuna vincta probably fed on both kelp and various species of red algae, whereas Aplysia punctata grazed exclusively on the most 13 C-depleted red algae. δ 15 N values for 2 other gastropods, Gibbula sp. and Calliostoma zizyphinum (8.64 and 10.30%o, respectively), suggest that they belong to higher trophic levels. Filter feeders occupied lower trophic levels and received variable carbon inputs from kelp. The only group of animals with δ 13 C signals in the same range as phytoplankton were amphipods. Based on δ 15 N values, the fish varied from intermediate to top consumers (trophic level: 2.6 to 3.3). Two species of seabirds were included in the study and their δ 15 N values suggested 2 different trophic levels, which correspond to their known feeding preferences. A mixing model suggests that kelp-derived carbon plays an important role in this nearshore system and that kelp may serve as a carbon source for marine animals with several different types of feeding strategies.

Viking Haithabu and its successor, the medieval town of Schleswig, were important international trade centres. Human skeletal finds spanning a period of approximately 400 years represent the bodily relics of the former inhabitants, who witnessed the rise and fall of these trade centres. Analysis of δ13C and δ15N from bone collagen was performed to reconstruct and detect changes in dietary preferences over time. A comparison with the respective isotopic data obtained from a large archaeofaunal sample resulted in a classic ‘mixing muddle’ that could only be deciphered using isotope mass balance mixing models applied on an individual basis. It was found that the overall subsistence economy shifted over time from a focus on fishing to one based predominantly on farming. The move to utilizing a new main source of protein did not impair overall protein supply. In addition, changing living conditions experienced by the inhabitants of Schleswig may have led to a change in infant nursing strategy.

Feeding behaviour of a serpulid polychaete: Turning a nuisance species into a natural resource to counter algal blooms?

Isotopic signatures of carbon and nitrogen are widely used for analysis of the structure of food webs in aquatic ecosystems. The study of animals raises a number of methodological questions, including choice of representative tissues and organs for sampling as well as storage of the studied organisms. Furthermore, the impacts of preservation methods can be tissue-specific, age-specific, and even taxon-specific; thus, studies of these impacts on particular taxa are necessary. We focused on the C and N isotope composition of the common toad (Bufo bufo), one of the most widespread European anuran amphibians. We hypothesized that its different tissues and organs may vary in isotopic composition, and ethanol and freezing may have different effects on isotopic values. Our results showed that both “tissue” and “storage method” factors significantly affected the δ13C values of tadpoles and postmetamorphic juveniles, whereas only the “tissue” factor had a significant effect on the δ15N values. The two stages, tadpoles and postmetamorphs, should be analyzed separately despite the brief postmetamorphic period of the juveniles. The skin, legs, muscles, and tail in tadpoles and legs, muscles and heart in juveniles can be used for δ13C and δ15N analysis regardless of the method of storage. The results will serve for the optimization of future study designs in isotopic ecology.

We previously showed the first clear evidence of aggregate hierarchy in an Andisol by comparing the particle-size fractions released upon different levels of dispersion energy up to the maximum dispersion – sonication at 5 kJ mL−1 following sodium saturation. While smaller particles (< 2 μm) appeared to act as major binding agents, the variation in organic matter (OM) chemistry among the size fractions remains unstudied. Here, we focused on comparing the carbon structure and carbon and nitrogen stable isotope ratio (δ13C and δ15N) among the particle-size fractions isolated by limited dispersion (mechanical shaking) and by the maximum dispersion treatments for the allophanic Andisol previously examined. Both solid-state carbon-13 nuclear magnetic resonance (13C NMR)and stable isotope ratios showed clear differences among the size fractions after the maximum dispersion but not after the limited dispersion. From 2–53 μm toward the < 0.2 μm fraction, we observed a progressive decline in the proportion of aromatic-C and an increase in that of O-alkyl-C. Similarly, the enrichment of 13C and 15N toward the smaller particle size fractions was observed after the maximum dispersion. While δ15 N had progressive enrichment from 3.6‰ (53–4000 μm) to 6.4‰ (< 0.2 μm fraction), δ13C showed a 2.5–3.0‰ enrichment from the 53–4000 μm fraction (−24.0‰) to 2–53 μm fraction and remained largely constant between 0.2–2 μm and < 0.2 μm fractions. The sonication-induced redistribution and chemical alternation of OM appeared to be minor due to the small pool sizes of low-density materials (e.g., plant litter) and microbial biomass. The emergence of the size-dependent changes in C chemistry after the maximum dispersion was consistent with the Andisol aggregate hierarchy model we previously proposed. The observed difference in C/N ratio and isotopic ratios as well as C composition implies that the OM present in the sonication-resistant particles of < `2 μm sizes (that account for roughly 70% of total C and N) are highly recycled by and/or largely originated from soil microbes. The applicability of current findings to other samples (e.g., non-allophanic Andisols) should be examined to establish the unique role of OM-enriched, micron to submicron particles in the aggregate hierarchy of Andisols.

Despite the Southern Hemisphere’s high proportion of endemic diadromous fish, the trophic role of upstream migrating forage fish in freshwater ecosystems remains unquantified. We combined food web δ13C and δ15N analyses with fish biomass estimates to quantify estuarine resource contribution (from the ecologically significant Waituna lagoon) to the diet and growth of the apex predators, longfin eels (Anguilla dieffenbachii) and brown trout (Salmo trutta) in Waituna Creek, Southland, Aotearoa (New Zealand) during 2019 and 2021. Our results demonstrated that exceptionally high biomasses of large predatory fishes (610–830 kg km−1) were maintained in a degraded agricultural catchment through connectivity to a near-pristine estuarine lagoon. Īnanga (Galaxias maculatus) migrating upstream from the lagoon supported 60%–80% of longfin eel and 40%–90% of brown trout biomass over the two years sampled. Mass-balance modelling suggested that large predatory fish in the Waituna Creek consume about two tonnes of migrating whitebait annually. These findings highlight the wider role of estuarine/marine subsidies in structuring New Zealand freshwater food webs and challenge the orthodoxy of ‘restoring streams from the headwaters down’. Estuarine ecosystems may be more important than headwater areas for sustaining large predatory fish, such as longfin eels, when they are food limited.

Re-investigating fish consumption in Greek antiquity: results from δ13C and δ15N analysis from fish bone collagen

1. Littoral biota in boreal lakes are known to assimilate epilithon. Being able to predict the stable isotopic composition of these alga will help to identify those systems in which δ13C and δ15N analysis can be used in foodweb investigations of allochthony and biomagnification.2. In a survey of 15 boreal lakes, the concentration of dissolved organic carbon (DOC) explained 76% of the variation in epilithon δ13C, and 86% of the variation in epilithon δ15N.3. Because both δ13C and δ15N values were depressed and similar to terrestrial values in humic (high DOC) lakes, it will be more difficult to successfully employ stable isotopic techniques for estimating allochthony in such systems. Lower δ15N values in humic lakes also indicate that trophic positions estimated by stable isotopes are not directly comparable to those of similar biota inhabiting clearwater lakes, unless autochthonous baseline corrections are made.

Isotopes of amino acids give novel insights on nitrogen sources partitioning and trophic position of invertebrates in a subtropical mangrove

Habitat use, feeding habits and trophic level were estimated for four shark species, Caribbean sharpnose shark Rhizoprionodon porosus, bull shark Carcharhinus leucas, juveniles of silky shark Carcharhinus falciformis and scalloped hammerhead shark Sphyrna lewini, based on stable isotope analysis (SIA) of δ15N and δ13C in three tissues (muscle, liver and blood) with different turnover rates. The δ15N values of R. porosus and C. leucas did not differ by sex/maturity stage or time scale. At the same time, juveniles of C. falciformis and S. lewini showed the loss of maternal isotopic signal that decreased based on the tissue scale time. The δ13C values indicated a shared habitat for three species: R. porosus, C. falciformis and S. lewini, the latter two with possible regional movements between coastal waters and open waters in their juvenile stage, whereas C. leucas prefers coastal waters because of a higher isotopic enrichment. The mixing model suggests that R. porosus and C. falciformis shared the most abundant prey in the ecosystem (small pelagic fish). Reef fish had a higher percentage contribution for C. leucas, whereas diet contribution of S. lewini was not clearly distinguished. All four species have trophic levels between 3.5 and 4.5, fulfilling meso- and top-predator roles, with generalist, opportunist or specialist behaviours based on isotopic niche breadth and variance comparisons.

The impact of anthropogenic food subsidies on a generalist seabird during nestling growth

This study aimed to understand changes in the biogeochemical processing of organic matter (OM) in response to multiple stressors (e.g., littoral area expansion, wastewater input, and hydrological regulation) in East Dongting Lake (Central China) over the past 60 years, using analyses of total organic carbon (TOC), total nitrogen (TN), C/N ratios, δ13C, δ15N, and diatoms from 2 sediment cores collected from the littoral and central parts of the lake. OM mainly originated from phytoplankton and C3 plant‐derived soil OM based on the ranges of C/N ratios (from 7 to 11) and δ13C (between −27‰ and −23‰). Littoral area expansion due to siltation caused an increasing influx of terrestrial soil OM in the 1980s and the 1990s, subsequently lowering δ13C values and rising C/N ratios in both sediment cores. Meanwhile, higher δ15N was linked to a high influx of isotopically heavy nitrate from urban and agricultural wastewaters. After 2000, slight decreases in TOC and TN in the littoral area were attributable to reducing inputs of external OM, likely linked to declining sediment influx from the upper reaches resulting from the Three Gorges Dam impoundment. Contrasting increases in TOC, TN, and C/N ratios in the central part indicated a high influx of terrestrial soil OM due to the declining distance from the shoreline with littoral area expansion. Declining δ15N values after 2000 indicated an increase in N2‐fixing cyanobacteria with eutrophication. Changes in diatom assemblages in both the littoral and central zones reflected nutrient enrichment and hydrological alterations. These results indicate that littoral expansion, declining riverine influx, and anthropogenic nutrient inputs are potential driving forces for the biogeochemical processing of OM in floodplain lakes. This study provides sedimentary biogeochemical clues for tracking past limnological conditions of floodplain lakes that are subjected to increasing disturbances from hydrological regulation and eutrophication.

The feeding behaviour of Peringia ulvae was studied with the aim of assessing its preferential feeding niche (habit) as well as its potential role in controlling or preventing the occurrence of macroalgal blooms. Both these aspects were studied in the Mondego estuary because of the clear long-lasting eutrophication process that favours the growth of two opportunistic macroalgae, Gracilaria spp. and Ulva spp., over the local beds of the macrophyte Zostera nolteii, which is another potential food source. All three species, both with and without periphyton, were used as a single food source in feeding experiments to assess different feeding parameters of the gastropod. Sediment with microphytobenthos was used together with the latter three species in feeding niche preference experiments. None of the food types provided were resistant to grazing. Higher levels of grazing occurred on Ulva spp. (apical parts) and Z. nolteii, both with periphyton. The presence of periphyton did not change grazing rates. When a choice between each food type was offered, the sediment was clearly the feeding niche preferred by the snails. As P. ulvae spent more time on the sediment (preferred feeding niche), the hypothesis that it has a role in preventing macroalgal blooms was not supported.

ABSTRACTSedentary filter-feeders such as the razor clam (Solen cylindraceus) are believed to indiscriminately exploit a carbon source derived from particulate organic matter (POM). POM demonstrates a high degree of spatial and temporal variability in composition, which may result in intraspecific dietary variation. This study aimed to investigate seasonal ontogenetic shifts in the feeding ecology of S. cylindraceus using dual stable isotopic (δ13C and δ15N) analyses in the oligotrophic temperate permanently open Kariega Estuary, South Africa. Mixing model results demonstrate that the different size classes of S. cylindraceus had a diet comprised mainly of POM. However, size grouping did have a significant effect on carbon and nitrogen signatures. Specifically, during winter, carbon isotopic signatures became more depleted with a decrease in size, while both winter and summer δ15N values became more nitrogen enriched with an increase in size. The observed trend in the ratios can likely be ascribed to the hydrodynamics of the system. Data from this study suggest that there may be some degree of variation among the different size cohorts, although this needs further investigation.