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Reservoir construction promotes many environmental impacts, including the enhancement of mercury concentrations in fish. The processes that can influence mercury concentrations in fish in Amazonian reservoirs are still little explored in depth, especially when we consider the possible particularities of the ecosystems in question. This study aims to investigate how mercury concentrations in fish could be influenced by the Tucuruí dam, considering possible changes in their feeding and trophic position according to the dam position (up or downstream). Fish were sampled upstream and downstream of the Tucuruí reservoir, and total mercury (THg) and stable isotopes of carbon and nitrogen (δ15N and δ13C) were measured in muscles. We observed three different Hg bioaccumulation patterns influenced by the dam. These differences occurred due to species trophic niche changes corroborated by the isotope analysis. Higher THg concentrations downstream compared to those upstream ones were only observed for Geophagus proximus. On the contrary, Plagioscion squamosissimus, from downstream, presented lower concentrations than upstream ones. The isotopic niche of these two species presented different changes according to the sampled site. THg biomagnification was higher upstream compared to downstream, considering that the regression slope was approximately two times higher upstream versus downstream. THg concentrations in fish were explained by the differences in their feeding habits according to their location in relation to the dam. The difference in THg biomagnification was able to reflect differences in structure of the food web chain in ecosystems under the dam's influence. [ABSTRACT FROM AUTHOR]

Abstract Upwellings are important oceanographic processes that induce several changes in marine ecosystems, including in the benthic-pelagic coupling (BPC) that plays a major role in coastal areas. However, there is little available information about the possible effects of coastal upwellings on the trophic role of predators and in the BPC. Thus, here we investigate possible seasonal and ontogenetic changes in the trophic interaction of a demersal predator, the Brazilian flathead Percophis brasiliensis, from an upwelling ecosystem. Sampling was carried out for one year during two coastal upwelling events. Based on stomach content analysis (SCA) were recorded seasonal diet shifts, probably driven by coastal upwellings, leading to an increase in pelagic prey and changing the trophic coupling pathways. Stable isotope analysis revealed that isotopic niche decreased with the body size, as well as the values of the Levins’ index. Also, significant, and positive relationships were observed between δ13C and δ15N versus total length. Our results showed that the demersal predator has a relevant trophic role in the BPC which is probably influenced by coastal upwellings.

Inter-annual variation in the feeding habits and food sources of Japanese sardine and mackerel at age-0 and age-1+ caught in the Kuroshio-Oyashio transition zone of the Western North Pacific were investigated based on analyses of bulk stable isotopes (δ13C, δ15N) and amino acid nitrogen isotopes (δ15NAA). Differences in δ13C and δ15N between Japanese sardine and mackerel were small for age-0, and inter-annual variation trends were similar, suggesting they depend on similar food sources in the same food web at this age. In contrast, inter-annual variation in δ13C and δ15N were significantly different between both species at age-1+, and both δ15N of phenylalanine (δ15NPhe: an indicator of nitrogen source) and trophic position estimated from δ15NAA (TPAA) were higher in mackerel, suggesting that the two species depend on distinct food webs as they age. Inter-annual variations in δ15NPhe were considered to have different causes for the two species; differences in food web structure due to the degree of southward intrusion of the Oyashio Current for Japanese sardine, compared to a shift in migration area and depth for mackerel. Furthermore, competition for food due to the recent increases in the population densities of both fishes appeared to be reflected in increased TPAA of mackerel. Although they are caught in the same region, the mechanism of variation in food sources differs because of differences in migration area, depth, and feeding habits. Differences in the feeding habits of Japanese sardine and mackerel may affect trophic status and spawning characteristics, potentially leading to different shifts in stock abundances. [ABSTRACT FROM AUTHOR]

Fish belonging to the Nototheniidae family are considered to be the most significant members of the Notothenioids family and are essential to the Antarctic marine ecology. However, the trophic dynamics of some unexploited species, including semi-pelagic painted notothen Lepidonotothen larseni , remains unknown. This study used fatty acids (FAs) and stable isotope indicators to examine the shift in diet from early juvenile to adult stages at South Georgia throughout winter in order to improve our understanding of the dietary diversity and trophic niche of L. larseni. Thirty different types of fatty acids were found in the muscular tissues of early juveniles (4.10–4.85 cm) and adults (8.7–14.9 cm), yet there was a notable variation in the composition of FAs between the two groups. FAs including C22:6n3, C22:2n6, C16:1n7, and C20:5n3 were found in high amounts in both early juveniles and adults. Both the δ15N and δ13C values of adults were significantly higher than those of early juveniles, suggesting an ontogenetic shift in L. larseni 's diet and trophic niche separation between the two stages of development. Significant separation in marker FAs was also observed between early juveniles and adults. Early juvenile L. larseni primarily fed on pelagic algae or copepods, whereas adults predominantly fed on Antarctic krill (Euphausia superba) on the seafloor and in the water column. • Diet of Lepidonotothen larseni during winter at the South Georgia was investigated. • Significant difference in fatty acids composition occurred between early juveniles and adults. • Stable carbon and nitrogen isotopes in adults higher significantly than early juveniles. • Trophic niche separation and ontogenetic dietary shift presented between early juveniles and adults. [ABSTRACT FROM AUTHOR]

Recent studies showed the potential of stable isotopes of the macronutrient calcium (δ44/40Ca) and nonessential strontium (δ88/86Sr) as new trophic level indicators in terrestrial vertebrates and marine teleost fishes. In this study, we tested whether similar Ca and Sr isotopic fractionation trends existed in macroinvertebrate‐dominated stream food webs compared to vertebrates despite their physiological differences. We have determined the δ44/40Ca and δ88/86Sr values as well as the 87Sr/86Sr ratios of stream macroinvertebrates and small gobies and their potential metal sources (stream water, periphyton, and terrestrial plant litter) in upper and lower reaches of two streams in the Lake Biwa catchment, central Japan. The 87Sr/86Sr ratios revealed that stonefly nymphs, crustacea, and gobies mostly relied on aquatic Sr sources. Higher 87Sr/86Sr ratios of some crane fly and caddisfly larvae, mayfly, dobsonfly, and dragonfly nymphs indicated greater terrestrial contributions via plant litter. Positive correlations between the δ44/40Ca and δ88/86Sr values implied that similar Ca and Sr sources existed, and that Ca and Sr stable isotopes underwent similar fractionation trends although Sr was not essential. The δ44/40Ca and partly the δ88/86Sr values were positively correlated with Sr/Ca ratios and negatively with δ15N values indicating trophic effects on Ca and Sr stable isotopes. The enrichment of 44Ca and 88Sr in large filter‐feeding caddisfly larvae was a notable exception from these trophic trends. Our data confirm that the trophic 44Ca and 88Sr depletion observed for marine teleost fishes and terrestrial vertebrates also applied to macroinvertebrate‐dominated stream food webs despite their different physiologies indicating that shared mechanisms of Ca and Sr isotopic fractionation may exist at the cellular or molecular level between these taxa. [ABSTRACT FROM AUTHOR]

The proliferation of native, alien, invasive and domestic species offers enough novel and abundant food resources for the common vampire bat, Desmodus rotundus, to potentially alter preferences for prey. By reference to a stable-isotope analysis for carbon and nitrogen, we report here on the choices of introduced mammal prey made by D. rotundus residing on Anchieta Island — a tropical land-bridge island from which domestic animals were removed and 100 individuals of 15 mammal species were introduced intentionally. Our analysis shows that the studied individuals of D. rotundus were more likely to prey upon species of open habitats (mean value of δ13C = -14.8‰), that is, animals with high δ13C values characterising the consumption of C4 resources. The δ15N values for D. rotundus were higher than expected, most likely similar to apex predator species (mean value of 8.2‰) and overlapped the isotopic niche with capybaras (Hydrochoerus hydrochaeris) on the island. Values were in turn distant from those noted for coatis, as well as other potential prey from a preserved area on the mainland (capybaras included), indicating that, from among all the potential mammalian prey species, the studied bats were feeding exclusively on capybaras, which also represent the species with the greatest mammalian biomass on the island. Previous information regarding the time of human occupation suggests that the domestic animals then present on Anchieta Island might have been the main prey of D. rotundus and responsible for maintaining a viable population. As capybaras were introduced only 36 years ago, this suggests a rapid shift in predation preference induced by anthropogenic disturbances that have allowed D. rotundus to exploit these rodents successfully. Records in the literature further show that common vampire bats were not captured in preserved areas of the mainland close to Anchieta Island, indicating that the rate of capture characterising D. rotundus is usually low in natural forested habitats where potential prey are scattered. As three individuals of the introduced population of capybaras were confirmed to have died from bat rabies virus (RABV) in 2020, we advocate periodic monitoring for bat rabies viruses in the D. rotundus population on Anchieta Island (as well as nearby areas), so that the magnitude of the outbreak may be determined and control strategies developed. Such actions are all the more important given that both the island and nearby areas are frequented by tourists. We highlight that the prey choice indicated here is context-dependent, and possibly influenced by the removal of domestic animals, as well as the explosive population growth achieved by the introduced capybaras, in combination with the predictability of their foraging behaviour. [ABSTRACT FROM AUTHOR]

We investigated inter-species dietary variation and potential cellulose digestion of 12 macroinvertebrate taxa collected from two locations in the estuarine Idoura Lagoon, Sendai Bay. All taxa exhibited cellulase activity (CA), which was higher among surface-deposit feeders (bivalve Macoma contabulata, polychaete Tylorrhynchus osawai, and ocypodid crabs) and obligatory suspension feeders (bivalves Corbicula japonica and Nuttallia japonica) (0.108 to 0.764 μmol min-1 mg-protein-1). In contrast, CA was lower among facultative suspension-feeding and deep-deposit feeding polychaetes (Hediste spp. and Heteromastus sp., respectively), and was lowest in the deep-deposit feeding polychaete Notomastus sp. The stable isotope ratios of the macroinvertebrates differed among feeding groups. A d13C-based isotope mixing model revealed that the major dietary component of the surface-deposit feeders was microphytobenthos (34-50%), regardless of their high CAs. Although CAs of obligatory and facultative suspension feeders were comparable to or lower than those of surface-deposit feeders, they were highly dependent on river-derived materials at the station near the freshwater input (38-59%). These results indicate that CA is a common physiological characteristic of macroinvertebrates in estuarine soft-bottom habitats, but the dietary contribution of riverine detritus is not correlated with enzymatic activity. Our findings indicate that several factors affect the realized dietary components of macroinvertebrates, including feeding mode, the selectivity of ingestion, and digestive enzyme activity. [ABSTRACT FROM AUTHOR]

Bulk carbon and nitrogen stable isotope (SI) ratios (δ 13C and δ 15N) were analysed to investigate the feeding habits of six taxa of mesopelagic fish larvae inhabiting the Kuroshio waters of the northeastern East China Sea. Large variation in tissue SI during early larval periods suggested maternal effects from parent fishes, and non-selective feeding on a variety of plankton species due to poor swimming ability. The similarity between SI ratios measured in larval tissues and those estimated for eggs of an "income breeder" in the spawning area support an "income breeder" strategy in Diaphus slender type and Vinciguerria nimbaria, while Lipolagus ochotensis seemed to show "capital breeder"-like characteristics. SI ratios of the fish larvae studied became relatively constant at species-specific body dry-weights (0.5–1.0 mg), probably due to the commencement of selective feeding, meaning SI ratios during late larval periods could be used for trophic position analysis. There was great overlap (44.6–76.5%) in trophic niche among the larval fishes within the same taxonomic family of Myctophidae. Even if principal diet components cannot be identified with gut contents analyses, diet information from other fish species occupying a similar isotopic niche can thus improve our understanding of the diets of larval fishes. [ABSTRACT FROM AUTHOR]

The article focuses on the trophic ecology of temperate reef fish on the rocky reefs of southern California. In southern California's kelp beds and rock beds, the California sheephead Semicossyphus pulcher are the common predators of benthic invertebrates. The study done by the authors found difference in population in terms of proportion of sessile filter/suspension feeders. They also claim that larger mobile invertebrates like sea urchins are likely to the prey of California sheephead as they double their size and change their diet.

Release-recapture experiments were conducted to examine temporal changes of the carbon and nitrogen stable isotope (δ13C and δ15N) ratios in the muscle tissue of artificially produced Japanese flounder Paralichthys olivaceus, juveniles. About 9000 juveniles (mean ± s.d. 43·3 ± 5·2 mm in standard length and 1·07 ± 0·37 g, n = 15) were released in each of three coastal areas: Chojagasaki, Arasaki and Jogashima with different geographical conditions, along Sagami Bay, Pacific coast of central Japan. Recapture efforts were made on 4, 11, 18, 40 and 55 days after the release. The stable isotope ratios, RNA:DNA ratio, stomach content mass (per body mass Msc) and condition factor ( K) of recaptured individuals were measured. The mean ± s.d. δ13C and δ15N values ( n = 15) were −18·3 ± 0·2‰ and 12·2 ± 0·2‰, respectively at the release. Wild Japanese flounder juveniles were captured only in Chojagasaki, and the δ13C and δ15N values ( n = 6) were −14·0 ± 0·4‰ and 13·2 ± 0·7‰, respectively; these values were considered to represent the wild diet. Nutritional conditions of the released and recaptured juveniles as determined by the RNA : DNA ratio, MSC and K were indicated to be the best in Chojagasaki, in which the stable isotope ratios gradually shifted towards and reached the wild values within 40 days. This result along with stomach content analyses suggested that the released juveniles had acquired a wild feeding habit. In Arasaki and Jogashima, nutritional conditions of the recaptured juveniles were poorer, with no clear changes in the stable isotope ratios. Greatly varied stable isotope ratio values were observed in the juveniles recaptured in Chojagasaki 11 days after the release, ranging from the release levels to the wild levels. The extent of changes in the stable isotope ratios had a positive correlation to the RNA : DNA ratio and K of these juveniles ( r = 0·87, n = 10 and r = 0·83, n = 18, respectively). The analyses of stable isotope ratios coupled with nutritional condition were considered to be an effective tool to examine post-release feeding adaptation of Japanese flounder juveniles. [ABSTRACT FROM AUTHOR]

The trophic ecology of xenophyophores (Foraminifera, Rhizaria) was examined during a 2-day in situ feeding experiment on the seafloor (water depths of 5370 m) off the east coast of Torishima Island, Japan. Both 13C-labeled glucose (as an example of labile dissolved organic matter) and 15N-labeled diatoms (as an example of labile particulate organic matter sinking from the ocean surface) were supplied to the specimens captured in in - situ incubation cores using the manned submersible Shinkai 6500. We found that xenophyophores took up both dissolved and particulate organic matter during the 2 days of incubation in situ. The higher concentrations of 15N-labeled diatoms in the xenophyophores than in the surrounding sediments suggest efficient collection and use of food resources by xenophyophores, and may support their rapid growth. It is likely that the agglutinated test of xenophyophores, which forms a contorted plate-like structure with upper open fan-like and funnel-like elements, also contributes to their ability to collect phytodetritus derived from the ocean surface. [Display omitted] • We conducted an in situ experiment on xenophyophores at abyssal depths using isotope-labeled food. • Xenophyophores respond rapidly to the presence of organic matter – particulate or dissolved. • They ingest both particulate and dissolved organic matter in a short period of time. • In abyssal depths, the contribution to material cycling by xenophyophores is high. [ABSTRACT FROM AUTHOR]