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The alien invasive silver carpHypophthalmichthys molitrixestablished a self-sustaining feral population in an oligotrophic impoundment, Flag Boshielo Dam, in South Africa. The ability of this population to persist in a dam with low algal biomass (median annual suspended chlorophylla= 0.08 µg l−1), and limited access to rivers considered large enough for successful spawning, has implications for their invasive potential in other systems. Stomach content and stable isotope analysis were used to assess the trophic ecology ofH. molitrix, which was then compared with indigenous Mozambique tilapiaOreochromis mossambicus, on a seasonal basis during 2011.Hypophthalmichthys molitrixare generalist filter feeders, with a diet consisting primarily of sediment, vegetative detritus, dinoflagellates and diatoms. The dominance of sediments in their stomachs suggests occasional benthic scavenging. However,H. molitrixoccupied a higher trophic level (TL = 2.8) than expected, suggesting that this population subsidised their diet with an unidentified dietary constituent, characterised by enriched nitrogen values. Although the stomach contents indicated dietary overlap betweenH. molitrixandO. mossambicus, stable isotopes revealed fine-scale resource partitioning, despite both species occupying the same trophic level. Nonetheless, the persistence of this feralH. molitrixpopulation in an oligotrophic impoundment highlights their phenotypic plasticity. [ABSTRACT FROM PUBLISHER]

The Southern Ocean is a major sink of anthropogenic CO 2 and an important foraging area for top trophic level consumers. However, iron limitation sets an upper limit to primary productivity. Here we report on a considerably dense late summer phytoplankton bloom spanning 9000 km 2 in the open ocean of the eastern Weddell Gyre. Over its 2.5 months duration, the bloom accumulated up to 20 g C m -2 of organic matter, which is unusually high for Southern Ocean open waters. We show that, over 1997-2019, this open ocean bloom was likely driven by anomalies in easterly winds that push sea ice southwards and favor the upwelling of Warm Deep Water enriched in hydrothermal iron and, possibly, other iron sources. This recurring open ocean bloom likely facilitates enhanced carbon export and sustains high standing stocks of Antarctic krill, supporting feeding hot spots for marine birds and baleen whales., (© 2023. The Author(s).)

The measurement of bulk tissue nitrogen (δ 15 N) and carbon isotope values (δ 13 C) chronologically along biologically inert tissues sampled from offspring can provide a longitudinal record of their mothers' foraging habits. This study tested the important assumption that mother-offspring stable isotope values are positively and linearly correlated. In addition, any change in the mother-offspring bulk tissues and individual amino acids that occurred during gestation was investigated. Whiskers sampled from southern elephant seal pups ( Mirounga leonina ) and temporally overlapping whiskers from their mothers were analyzed. This included n  = 1895 chronologically subsampled whisker segments for bulk tissue δ 15 N and δ 13 C in total and n  = 20 whisker segments for amino acid δ 15 N values, sampled from recently weaned pups ( n  = 17), juvenile southern elephant seals (SES) < 2 years old ( n  = 23) and adult female SES ( n  = 17), which included nine mother-offspring pairs. In contrast to previous studies, the mother-offspring pairs were not in isotopic equilibrium or linearly correlated during gestation: the Δ 15 N and Δ 13 C mother-offspring offsets increased by 0.8 and 1.2‰, respectively, during gestation. The foetal bulk δ 15 N values were 1.7 ± 0.5‰ (0.9-2.7‰) higher than mothers' δ 15 N values before birth, while the foetal δ 13 C increased by ~1.7‰ during gestation and were 1.0 ± 0.5‰ (0.0-1.9‰) higher than their mothers' δ 13 C at the end of pregnancy. The mother-offspring serine and glycine Δ 15 N differed by ~4.3‰, while the foetal alanine δ 15 N values were 1.4‰ lower than that of their mothers during the third trimester of pregnancy. The observed mother-offspring δ 15 N differences are likely explained by shuttling of glutamate-glutamine and glycine-serine amongst skeletal muscle, liver, placenta and foetal tissue. Foetal development relies primarily on remobilized endogenous maternal proteinaceous sources. Researchers should consider foetal physiology when using offspring bulk tissue isotope values as biomarkers for the mother's isotopic composition as part of monitoring programmes., (© The Author(s) 2020. Published by Oxford University Press and the Society for Experimental Biology.)

Changes in the nutritional status of free-ranging animals have a strong influence on individual fitness, yet it remains challenging to monitor longitudinally. Nitrogen (δ 15 N) and carbon (δ 13 C) isotope values measured chronologically along the length of metabolically inert keratinous tissues can be used as a nutritional biomarker to retrospectively reconstruct the foraging ecology and eco-physiology of consumers. We quantitatively describe the physiological effects of fasting on amino acid metabolism using sequentially measured bulk tissue and amino acid δ 15 N values along the length of whiskers sampled from free-ranging juvenile, subadults, adult female, and male southern elephant seals (SES; Mirounga leonina) on Marion Island in the Southern Ocean. For both juveniles and adult females, whisker segments representing fasting had significantly higher bulk tissue δ 15 N values of 0.6 ± 0.5‰ and 1.3-1.8‰, respectively, in comparison to segments unaffected by fasting. We also found a large increase (2-6‰) in δ 15 N values for most glucogenic amino acids and a simultaneous depletion (2-3‰) of alanine in segments reflecting fasting, which enabled us to accurately predict (74%) the nutritional status of our model species. We hypothesize that the glucose-alanine cycle is the mechanism driving the observed depletion of alanine δ 15 N values during fasting. We demonstrated that keratinaceous tissues can be used as a longitudinal nutritional biomarker to detect changes in the nitrogen balance of an individual. Moreover, it is evident that physiological factors have an important influence on tissue δ 15 N values and can lead to erroneous bulk tissue or amino acid isotope-based reconstructions of foraging habits.

Obtaining longitudinal endocrinological data from free-ranging animals remains challenging. Steroid hormones can be extracted sequentially from non-invasively sampled biologically inert keratinous tissues, such as feathers, nails, hair and whiskers. However, uncertainty regarding the type and levels of steroids incorporated into such tissues complicates their utility in wildlife studies. Here, we developed a novel, comprehensive method to analyze fourteen C 19 and fourteen C 21 steroids deposited chronologically along the length of seal whiskers in a single, 6-minute chromatographic step, using ultra-performance convergence chromatography-tandem mass spectrometry. The limits of detection and quantification ranged from 0.01 to 2 ng/mL and from 0.1 to 10 ng/mL, respectively. The accuracy and precision were within acceptable limits for steroids at concentrations ≥2 ng/mL. The recovery (mean = 107.5% at 200 ng/mL), matrix effect and process efficiency of steroids evaluated, using blanked whisker matrix samples, were acceptable. The method was applied to the analysis of steroid hormone levels in adult female whisker segments obtained from southern elephant seals (Mirounga leonina), n = 10, and two fur seal species, Antarctic fur seals (Arctocephalus gazella; n = 5) and subantarctic fur seals (Arctocephalus tropicalis; n = 5), sampled between 2012 and 2017. In the whisker subsamples analyzed (n = 71), the median concentration of steroid hormones detected above the LOQ ranged from 2.0 to 273.7 pg/mg. This was the first extraction of multiple C 19 and C 21 steroids, including their C11-oxy metabolites, from the whiskers of mammals. Measuring hormones sequentially along the whisker lengths can contribute to our understanding of the impact of stress associated with environmental/climate changes that affect the health, survival of organisms, as well as to delineate the reproductive cycles of free-living mammals with cryptic life stages., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)