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2. Bidirectional energy subsidies for fish in river mouths of a large lake as revealed by stable isotopes and fatty acids.

Author

Eglite, Elvita, Stein, Sarah R., Turschak, Benjamin A., Bowen, Gabriel J., and Höök, Tomas O.

Subjects
*ENERGY subsidies, *STABLE isotopes, *ESSENTIAL fatty acids, *FATTY acids, *NUTRITIONAL assessment, *BIVALVE shells
Abstract

Freshwater river mouths may facilitate cross‐habitat resource use and bidirectional subsidization through (a) active cross‐habitat movement by consumers like fish and (b) water and material movement both downstream, from tributary to nearshore lake, and in the opposite direction due to backflow processes. Despite potential importance of freshwater river mouths, relative contributions of lentic and tributary energy sources to fishes along these ecotones remain understudied, in part because measuring cross‐habitat subsidization is not straightforward. We assessed cross‐habitat subsidization of three fish consumers round goby (Neogobius malanostomus), yellow perch (Perca flavescens), and alewife (Alosa psuedoharengus) in three river mouths of Lake Michigan, USA. Specifically, we (a) measured stable isotope ratios (δ13C, δ15N, δ2H, δ18O) in ambient water, bivalve shells, potential invertebrate prey, and fish soft tissue, and we assessed fish nutritional status based on essential fatty acid composition, and (b) estimated Bayesian ellipses and mixing models including either two (δ13C‐δ15N) or three (δ13C‐δ15N‐δ2H) isotope ratios. Results revealed evidence of bidirectional habitat subsidies for all fishes, but energy subsidies varied by species and across river mouths; likely related to differences in species‐specific behavior and hydrologic differences among river mouths. Relative to nearshore oligotrophic Lake Michigan, fish in productive tributary environments contained relatively low essential fatty acid content, suggesting a possible trade‐off between prey quantity and quality across habitats. This study advances our understanding of resource connectivity in lake ecosystems and the combined use of multiple stable isotopes (including mixing models) and fatty acids to document cross‐habitat subsidies along freshwater ecotones. [ABSTRACT FROM AUTHOR]

Published
2024
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6. Report on tools and concepts to support the Baltic food web research of the future

Author

Dierking, Jan, Winder, M., Lindegren, M., Temming, A., Neuenfeldt, Stefan, Eglite, Elvita, Mohm, Clarissa, Tomkiewicz, Jonna, Reusch, Thorsten B. H., Nordstroem, M. C., Dierking, Jan, Winder, M., Lindegren, M., Temming, A., Neuenfeldt, Stefan, Eglite, Elvita, Mohm, Clarissa, Tomkiewicz, Jonna, Reusch, Thorsten B. H., and Nordstroem, M. C.

Published
2020

7. Metabolism and foraging strategies of mid‐latitude mesozooplankton during cyanobacterial blooms as revealed by fatty acids, amino acids, and their stable carbon isotopes

Author

Eglite, Elvita, Graeve, Martin, Dutz, Jörg, Wodarg, Dirk, Liskow, Iris, Schulz‐Bull, Detlef, Loick‐Wilde, Natalie, Eglite, Elvita, Graeve, Martin, Dutz, Jörg, Wodarg, Dirk, Liskow, Iris, Schulz‐Bull, Detlef, and Loick‐Wilde, Natalie

Abstract

Increasing sea surface temperatures (SST) and blooms of lipid‐poor, filamentous cyanobacteria can change mesozooplankton metabolism and foraging strategies in marine systems. Lipid shortage and imbalanced diet may challenge the build‐up of energy pools of lipids and proteins, and access to essential fatty acids (FAs) and amino acids (AAs) by copepods. The impact of cyanobacterial blooms on individual energy pools was assessed for key species temperate Temora longicornis and boreal Pseudo‐/Paracalanus spp. that dominated field mesozooplankton communities isolated by sea‐sonal stratification in the central Baltic Sea during the hot and the cold summer. We looked at (a) total lipid and protein levels, (b) FA trophic markers and AA composition, and (c) compound‐specific stable carbon isotopes (δ13C) in bulk mesozooplankton and in a subset of parameters in particulate organic matter. Despite lipid‐poor cyanobacterial blooms, the key species were largely able to cover both energy pools, yet a tendency of lipid reduction was observed in surface animals. Omni‐ and car‐nivory feeding modes, FA trophic makers, and δ13C patterns in essential compounds emphasized that cyanobacterial FAs and AAs have been incorporated into meso‐zooplankton mainly via feeding on mixo‐ and heterotrophic (dino‐) flagellates and detrital complexes during summer. Foraging for essential highly unsaturated FAs from (dino‐) flagellates may have caused night migration of Pseudo‐/Paracalanus spp. from the deep subhalocline waters into the upper waters. Only in the hot summer (SST>19.0°C) was T. longicornis submerged in the colder subthermocline water (~4°C). Thus, the continuous warming trend and simultaneous feeding can eventually lead to competition on the preferred diet by key copepod species below the thermocline in stratified systems. A comparison of δ13C patterns of essential AAs in surface meso‐zooplankton across sub‐basins of low and high cyanobacterial biomasses revealed the potential of δ13C‐AA

Published
2019

12. De novo amino acid synthesis and turnover during N2 fixation.

Author

Loick‐wilde, Natalie, Weber, Sarah C., Eglite, Elvita, Liskow, Iris, Schulz‐bull, Detlef, Wasmund, Norbert, Wodarg, Dirk, and Montoya, Joseph P.

Subjects
AMINO acid synthesis, NITROGEN fixation, CYANOBACTERIA, AUTOTROPHS, PHOSPHATES & the environment
Abstract

Abstract: Cyanobacteria are the main autotrophs and N2‐fixing (diazotrophic) organisms in large parts of the oligotrophic global ocean, where generally all heterotrophic production depends on their activity. Amino acids (AAs) from cyanobacteria are essential macronutrients for these heterotrophic food webs, yet little is known about the de novo synthesis of AAs during N2 fixation. Through a combination of bulk and amino acid nitrogen (AAN) specific analyses of field based N2 fixation experiments, we demonstrate that the de novo synthesis of 13 AAs accounted for the majority of bulk N2 fixation rates at four stations in the central Baltic Sea in July 2015. Slow AA turnover times of 87 ± 14 d coincided with low phosphate concentrations and high cell‐carbon biomasses of unicellular cyanobacteria. Very fast turnover times of 17 ± 3 d coincided with high phosphate concentrations and undecayed Nodularia spumigena cells, but unexpectedly also with phosphate depletion and decayed N. spumigena cells. In a decayed bloom, volumetric N2 fixation rates into AAN provided a much better estimate of the net incorporation of N2 into biomass than fixation into bulk nitrogen that rather reflected gross N2 fixation. In an undecayed bloom, the turnover times of 13 AAs can be predicted from a single bulk N2 fixation rate. This is the first direct evidence that the very late, decayed stage of a cyanobacteria bloom can be a flashpoint of very fast AA turnover during N2 fixation with hitherto uncharacterized consequences for heterotrophic food webs and diazotroph N inputs to the global ocean. [ABSTRACT FROM AUTHOR]

Published
2018
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13. Nutrient turnover at the hypoxic boundary : flux measurements and model representation for the bottom water environment of the Gulf of Riga, Baltic Sea

Author

Eglite, Elvita, Lavrinovics, Aigars, Muller-Karulis, Bärbel, Aigars, Juris, Poikane, Rita, Eglite, Elvita, Lavrinovics, Aigars, Muller-Karulis, Bärbel, Aigars, Juris, and Poikane, Rita

Abstract

Experimental studies of intact sediment cores from the Gulf of Riga, Baltic Sea, were conducted to estimate the response of sediment nutrient fluxes to various near-bottom water oxygen conditions. The experiment was performed in the laboratory using a batch-mode assay type system on the sediment cores held at 4 degrees C and oxygen concentrations maintained at 1, 2, 3, 4 and 5 mg l(-1). The results from the experiment were subsequently used to optimise the fit of the sediment denitrification sub-model of the Gulf of Riga basin. Sedimentwater fluxes of phosphate were low and directed out of the sediments under all treatments, demonstrating a general decreasing tendency with increasing near-bottom water oxygen concentration. The sediment-water fluxes of ammonium and nitrate + nitrite demonstrated opposing trends: ammonium fluxes decreased whereas nitrate + nitrite fluxes increased with rising near-bottom water oxygen concentration. The modelled fluxes agreed well with the measured ones, with correlation coefficients of 0.75, 0.63 and 0.88 for ammonium, nitrate + nitrite and phosphate fluxes respectively. The denitrification rate in sediments was simulated at oxygen concentrations from -2 to 10 mg l(-1). At oxygen concentrations < 2 mg l(-1) the modelled denitrification was sustained by nitrate transport from water overlying the sediments. With increasing oxygen concentrations the simulated denitrification switched from the process fuelled by nitrates originating from the overlying water (D-w) to one sustained by nitrates originating from the coupled sedimentary nitrification - denitrification (D-n). D-n reached its maximum at an oxygen concentration of 5 mg l(-1)., AuthorCount:5

Published
2014
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14. Trophic dynamics of fishes in the Great Lakes: a cross-lake comparison using stable isotopes data.

Author

Eglite, Elvita, Scofield, Anne E., Hook, Tomas O., and Collingsworth, Paris D.

Subjects
ISOTOPES
Abstract

Stable isotope ratios of nitrogen (δ15N) and carbon (δ13C) are valuable tools for identifying basal energy sources for fish production and describing trophic complexity, but cross-lake comparisons are often limited by the challenges associated with standardizing study design and isotopic baselines. Using studies conducted in collaboration with the bi-national Cooperative Science and Monitoring Initiative, as well as other research efforts across the Great Lakes, we assembled δ15N and δ13C data for zooplankton and fish muscle tissue across all Great Lakes from 2002 to 2018. We aimed to detect differences in food web structures by estimating trophic positions (TP) and the ratio of benthic to pelagic δ13C contributions for planktivorous Rainbow Smelt (Osmerus mordaX) and piscivorous Lake Trout (Salvelinus namaycush). To account for variable baselines in the lower food web, we used averaged bulk zooplankton δ15N values by lake, month, year. Despite high variation in the zooplankton, we identified a robust pattern in TP across lakes for both species. Consistent with predator-prey interactions, mean TPs of Lake Trout (4.1-5.9) were greater than Rainbow Smelt (3.1-4.6) in all lakes. TPs were lower in Superior, Huron and Michigan, and greater in Ontario and Erie. The proportion of benthic/pelagic contributions to fish diets also differed among lakes, with Lake Huron having the highest benthic reliance. Overall, TPs increased with the lake productivity and suggest that both food web complexity and resource use by these fish species differs across lakes. [ABSTRACT FROM AUTHOR]

Published
2023

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