δ13C Values Of Zooplankton Research Articles

δ13C and δ15N zooplankton isoscapes as trace of water masses and mesoscale activity in the Pacific Tropical-Subtropical Convergence off Mexico during June 2010

This research analyzes for the first time in the Pacific Tropical-Subtropical Convergence off Mexico during June 2010 the relationships among the δ13C and δ15N signal distribution in the bulk zooplankton, water masses, and mesoscale structures. The environmental analysis showed that the California Current Water (CCW) and Transitional Water (TrW) converge where the 22 °C isotherm and 34.6 g kg−1 isohaline were observed (22°N). Two cyclonic eddies were detected: one in CCW at 24°N about 70 km in diameter, the other one located in TrW at 21°N with 150 km in diameter. A cluster analysis defined three zooplankton isoscapes with significant differences. Isoscape 1, immerses in CCW – the lowest δ13C (−22.37 ± 0.89 ‰) and δ15N (9.89 ± 1.32 ‰) – showed temperature (19.86 ± 1.97 °C), salinity (34.08 ± 0.37 g kg−1) values, the deepest thermocline (77.93 ± 25.51 m) and oxygen minimum zone (164.78 ± 44.96 m). The CCW was relatively oligotrophic without important mesoscale features in the sampled time within the sampled area. Isoscape 2, a cyclonic eddy in CCW – relatively enriched zooplankton δ13C values (−16.78 ± 1.95 ‰) due to the entry of enriched coastal biota– reflected in high chlorophyll a and subsequently assimilated into zooplankton tissues. Isoscape 3, a cyclonic eddy immerses in TrW – the highest δ15N (13.14 ± 1.60 ‰), salinity (34.76 ± 0.19 g kg−1) and temperature (19.90 ± 2.27 °C) values and shallowest thermocline (32.27 ± 18.63 m), and oxygen minimum zone (66.82 ± 37.68 m) in depth. Likely, this 15N-enriched recycled nitrate was pumped from the deoxygenated subsurface to the surface, reflected in the zooplankton bulks. The results showed that the isotopic signals in bulk zooplankton may be a good water mass and mesoscale activity tracer.

Response of stable isotopes (δ2H, δ13C, δ15N, δ18O) of lake water, dissolved organic matter, seston, and zooplankton to an extreme precipitation event

Lake ecosystems process and cycle organic substrates, thus serving as important bioreactors in the global carbon cycle. Climate change is predicted to increase extreme weather and precipitation events that can flush nutrients and organic matter from soils to streams and lakes. Here we report changes in stable isotopes (δ2H, δ13C, δ15N, or δ18O) of water, dissolved organic matter (DOM), seston, and zooplankton in a subalpine lake at short time resolution following an extreme precipitation event between early July to mid-August 2021. Water from excess precipitation and runoff remained in the lake epilimnion and coincided with increasing δ13C values of seston (−30 ‰ to −20 ‰), due to the input of carbonates and terrestrial organic matter. Particles settled into deeper lake layers after two days and contributed to the uncoupling of C and N cycling as the lake responded to this extreme precipitation event. Following the event, there was an increase in bulk δ13C values of zooplankton (from −35 ‰ to −32 ‰). Throughout this study, δ13C values of DOM remained stable throughout the water column (−29 ‰ to −28 ‰), while large isotopic fluctuations in DOM δ2H (−140 ‰ to −115 ‰) and δ18O (+9 ‰ to +15 ‰) values suggested DOM relocation and turnover. Integrating isotope hydrology, ecosystem ecology, and organic geochemistry offers an element-specific, detailed approach to investigating the impact of extreme precipitation events on freshwater ecosystems and particularly aquatic food webs.

Reduced efficiency of pelagic–benthic coupling in the Arctic deep sea during lower ice cover

Pelagic–benthic coupling describes the connection between surface-water production and seafloor habitats via energy, nutrient and mass exchange. Massive ice loss and warming in the poorly studied Arctic Chukchi Borderland are hypothesized to affect this coupling. The strength of pelagic–benthic coupling was compared between 2 years varying in climate settings, 2005 and 2016, based on δ13C and δ15N stable isotopes of food-web end-members and pelagic and deep-sea benthic consumers. Considerably higher isotopic niche overlap and generally shorter isotopic distance were found between pelagic and benthic food web components in 2005 than in 2016, suggesting weaker coupling in the latter, low-ice year. δ15N values indicated more refractory food consumed by benthos in 2016 and fresher food reaching the seafloor in 2005. Higher δ13C values of zooplankton indirectly suggested a higher contribution of ice algae in 2005 than 2016. The difference in pelagic–benthic coupling between these years is consistent with higher energy retention within the pelagic system, perhaps due to strong stratification in the Amerasian Basin in the recent decade. Weaker coupling to the benthos can be expected to continue with ice loss in the study area, perhaps reducing benthic biomass and remineralization capacity; monitoring of the area is needed to confirm this prediction.

Spatial Heterogeneity of Food Webs in A River-Lake Ecotone under Flow Regulation – A Case Study in Northern China

The river–lake ecotone supports diverse aquatic life, but its food web structure and topology are poorly understood. Baiyangdian Lake, northern China’s largest shallow lake, depends on external environmental flows, of which the Fu River provides the most stable water supply. Here, we used stable isotopes and topological analysis to explore the food web structure along a spatial gradient using data from field surveys from 2018 to 2019. Carbon and nitrogen stable isotopes and the food web structure were associated with environmental factors for four ecosystem types (river, river mouth, lake mouth, lake). Detritus, phytoplankton, and zooplankton δ13C values became more depleted along the gradient from the river to the lake, whereas δ13C of submerged macrophytes was enriched in the ecotones compared to the river and lake. Higher δ15N values for basal resources and zooplankton occurred at the lake mouth and river mouth. The top consumers were omnivorous fish: Hemiculter leucisculus (trophic level [TL] = 3.85 ± 0.89) in the river and Pseudorasbora parva (TL = 4.54 ± 0.58) in the river mouth. Carnivorous Erythroculter dabryi occupied the highest TL (3.61 ± 0.36 and 4.46 ± 0.36, respectively) in the lake mouth and lake. These results together led to a change from a detritus-based to phytoplankton-based food web along the gradient from the river to the lake. The species richness, number of trophic links, link density, and mean food chain length all are greatest in the lake, followed by the lake mouth, and the lowest were in the river. Our results provide a holistic view of the ecotone ecosystem and its food web, suggesting that it supports a more diverse species assemblage and more complex food web structure than the adjacent river ecosystem, rather than the adjacent lake ecosystem. Therefore, management should emphasize the combined effects of altered hydrological regimes and poor water quality on the ecotone food webs to manage the river and lake more sustainably.

Plankton population dynamics and methylmercury bioaccumulation in the pelagic food web of mine-impacted surface water reservoirs

Thermal stratification of reservoirs can lead to anaerobic conditions that facilitate the microbial conversion of mercury (Hg) to neurotoxic and bioaccumulative methylmercury (MeHg). But MeHg production is just the first step in a complex set of processes that affect MeHg in fish. Of particular relevance is uptake into suspended particulate matter (SPM) and zooplankton at the base of the pelagic food web. We assessed plankton dynamics and Hg uptake into the pelagic food web of four Hg-impaired California water reservoirs. Combining water chemistry, plankton taxonomy, and stable carbon (C) and nitrogen (N) isotope values of SPM and zooplankton samples, we investigated differences among the reservoirs that may contribute to differing patterns in MeHg bioaccumulation. Methylmercury accumulated in SPM during the spring and summer seasons. Percent MeHg (MeHg/Hg*100%) in SPM was negatively associated with δ15N values, suggesting that “fresh” algal biomass could support the production and bioaccumulation of MeHg. Zooplankton δ13C values were correlated with SPM δ13C values in the epilimnion, suggesting that zooplankton primarily feed in surface waters. However, zooplankton MeHg was poorly associated with MeHg in SPM. Our results demonstrate seasonal patterns in biological MeHg uptake and how multiple data sources can help constrain the drivers of MeHg bioaccumulation.

Can the stable isotope variability in a zooplankton time series be explained by its key species?

Stable isotope (SI) analysis is a standard tool to study marine food webs, usually based on the measurement of a few individuals from a small list of subjectively pre-defined species. The main objective of this study was to find out which species are significantly associated with the temporal variability of the SI composition of zooplankton in a tropical marine ecosystem. We investigated this by means of a novel species-biomass-isotopes-mixture (SBIM) approach that uses a relative biomass matrix to explain the SI signature of the zooplankton community. Furthermore, SBIM was applied to detect key taxa that can be considered bioindicators for important descriptors of ecosystem state (e.g., oligotrophy, carbon sources, mean trophic level). Plankton samples (64 μm mesh size) were obtained in Tamandaré Bay (northeastern Brazil) from June 2013 to August 2019. One aliquot of each sample was taken for stable isotope measurements and one for taxonomic identification and estimation of size and relative biomass. Total zooplankton biomass differed significantly between years, seasons and stations. Total zooplankton δ13C values ranged from −21.0 to −18.2‰ (mean ± standard deviation: −19.7 ± 0.7‰ in the dry season, and −19.4 ± 0.8‰ in the rainy season). Total zooplankton δ15N values ranged from 3.8 to 9.0‰ (7.0 ± 1.0‰ in the dry season, and 6.5 ± 1.2‰ rainy season). Total zooplankton C/N ratios ranged from 3.5 to 5.0 (4.2 ± 0.4 in the dry season and 4.2 ± 0.3 in the rainy season). The sparsely abundant and relatively large-sized copepod Pseudodiaptomus acutus was the most important species for explaining the variability in δ15N (22% of the total variability). Relative biomass (%) of P. acutus showed a strong positive correlation with δ15N, indicating a high trophic level (TL). Our results highlight the importance of less abundant taxa for marine food webs. Small-sized invertebrate larvae were negatively correlated with δ15N, indicating a TL below average. The copepod Dioithona oculata was the most important organism in explaining the δ13C of zooplankton (17.7% of the total variability, positive correlation with δ13C), indicating possible selective use of a13C-enriched food source (e.g., diatoms) by this cyclopoid copepod. Oithona spp. juveniles showed a negative relationship with zooplankton C/N ratio, which can be indicators of an oligotrophic ecosystem state and lipid-poor zooplankton. The tintinnid F. ehrenbergii showed a positive correlation with C/N, being an indicator for turbid “green waters'', during the rainy season, when the ecosystem was in a eutrophic state, with high lipid contents in the zooplankton community. The proposed SBIM approach opens up a novel pathway to understanding the factors and species that shape the temporal variability of food webs.

Spatial and Seasonal Variations in the Stable Isotope Values and Trophic Positions of Dominant Zooplankton Groups in Jiaozhou Bay, China

The spatial and seasonal distributions of stable carbon and nitrogen isotopes (δ13C and δ15N) in dominant zooplankton groups were investigated in Jiaozhou Bay. Zooplankton δ13C values ranged from −22.89‰ to −15.86‰, and δ15N values ranged from 3.18‰ to 13.57‰, respectively. The δ13C and δ15N values generally followed the order of small zooplankton < large calanoids < small Sagitta < large Sagitta. Spatial distribution patterns of zooplankton δ13C and δ15N values varied in different seasons. Our results suggested that the spatial variation of δ13C was mainly controlled by terrigenous organic matter (OM) input and phytoplankton biomass, but water temperature may have played a key role in the seasonal variation of δ13C. In spring, the high phytoplankton biomass might increase the δ13C value of small zooplankton in the inner bay. During other seasons, the δ13C values of zooplankton generally increased from the inner bay to the outer bay, which might be associated with the influence of 13C-depleted terrigenous OM carried by the river discharge. Small zooplankton stable isotope values were significantly correlated with that of particulate organic matter (POM). The influence of anthropogenic nutrient input on isotopic baseline can be cascaded to the zooplankton, and the effect might be weak at higher trophic levels. The Bayesian standard ellipse areas of dominant zooplankton groups were generally smallest in the winter, suggesting a narrow niche width during that time. The niche partition between small zooplankton, large calanoids, and Sagitta was most distinct in winter, and followed by summer. The relative trophic level of Sagitta ranged from 2.23 to 4.01, which generally declined from the inner bay to the outer bay during the spring, autumn, and winter seasons. High anthropogenic nutrient loading might reduce the difference in trophic niches among zooplankton groups. This study provided detailed information on the distribution of zooplankton δ13C and δ15N in a coastal bay, which will be useful for understanding the anthropogenic influence on the ecosystem structure and function.

Spatial distributions of zooplankton stable isotopes and their trophic positions in a bay under serious anthropogenic influences: Daya Bay, China

Trophic structure of zooplankton community can effectively reflect the ecosystem health and the influence of anthropogenic disturbances. The Daya Bay is a semi-closed coastal bay under intensive anthropogenic impacts in northern South China Sea. Spatial variations of stable isotope values (δ13C and δ15N) and trophic positions of dominant zooplankton groups were investigated in Daya Bay during winter. The δ13C values of zooplankton ranged from −22‰ to −15.59‰, and the δ15N ranged from 4.19‰ to 12.65‰, respectively. Generally, the δ13C values of zooplankton were higher in the inner bay. This distribution pattern was determined by the less terrestrial organic matter input and high nutrient loading in Daya Bay. An abnormally lower δ15N value of zooplankton occurred near the Dan’ao River estuary. It suggested that the 15N-depleted signature of food source can be transferred to the zooplankton along the food chain. The isotopic Bayesian ellipses of dominant zooplankton groups were generally larger in the inshore region, suggesting a wider food source. In the offshore region, the isotopic ellipses of these dominant zooplankton groups were relatively separate. Our results suggested that eutrophication can increase the trophic overlap between zooplankton groups. The δ15N value indicated large Sagitta was the top predator in zooplankton community. Excluding the abnormal estuarine station, the relative trophic level of large Sagitta was generally lower in the inner bay, suggesting a shorter food chain in eutrophic waters. In addition, our results showed that the stable isotopic signatures of mysids were significantly different from other zooplankton groups. It can be speculated that the mysids might migrate from the open sea in a short time. This study provided detail information on the δ13C and δ15N values of different zooplankton groups in Daya bay, which will be useful for understanding the anthropogenic influence on the ecosystem structure and function.

Use of epidermal mucus in elasmobranch stable isotope studies: a pilot study using the giant manta ray (Manta birostris)

Stable isotope analysis of tissues with different turnover rates allows for a broader temporal view of a species’ feeding habits. Epidermal mucus is a rapid to medium turnover ‘tissue’ in teleost fish, but its use in elasmobranch dietary studies is unknown. In the present study, we conducted stable isotope analysis on mucus and muscle from the giant manta ray Manta birostris. Mucus δ13C values were depleted and closer to surface zooplankton δ13C values compared with muscle, whereas there was no significant difference in δ15N values between these two tissue types. Using diet tissue discrimination factors from the literature, there was no significant difference in the expected prey profile between muscle and epidermal mucus. However, a broader range in δ13C values of expected prey was shown for mucus compared with muscle. The results suggest that if M. birostris mucus is indicative of recent dietary intake, resource use during aggregative behaviour off Ecuador is broader, but with no obvious resource switching. The present study is the first example of using bulk stable isotope analysis to evaluate mucus to investigate feeding ecology in elasmobranchs. However, the time course for the change in mucus isotope signature still needs to be determined through controlled feeding studies in an aquarium setting.

Land Use Affects Carbon Sources to the Pelagic Food Web in a Small Boreal Lake.

Small humic forest lakes often have high contributions of methane-derived carbon in their food webs but little is known about the temporal stability of this carbon pathway and how it responds to environmental changes on longer time scales. We reconstructed past variations in the contribution of methanogenic carbon in the pelagic food web of a small boreal lake in Finland by analyzing the stable carbon isotopic composition (δ13C values) of chitinous fossils of planktivorous invertebrates in sediments from the lake. The δ13C values of zooplankton remains show several marked shifts (approx. 10 ‰), consistent with changes in the proportional contribution of carbon from methane-oxidizing bacteria in zooplankton diets. The results indicate that the lake only recently (1950s) obtained its present state with a high contribution of methanogenic carbon to the pelagic food web. A comparison with historical and palaeobotanical evidence indicates that this most recent shift coincided with agricultural land-use changes and forestation of the lake catchment and implies that earlier shifts may also have been related to changes in forest and land use. Our study demonstrates the sensitivity of the carbon cycle in small forest lakes to external forcing and that the effects of past changes in local land use on lacustrine carbon cycling have to be taken into account when defining environmental and ecological reference conditions in boreal headwater lakes.

Lake zooplankton δ13C values are strongly correlated with the δ13C values of distinct phytoplankton taxa

AbstractAnalyses of carbon stable isotopes are often used to estimate the contributions of allochthonous and autochthonous dietary resources to aquatic consumers. Most pelagic food web studies assume that all phytoplankton taxa have a similar δ13C value. We studied pelagic food web compartments (dissolved inorganic carbon [DIC], phytoplankton, bacteria, seston, cladoceran zooplankton) in 12 small (< 0.1 km2) lakes in southern Finland. These lakes were classified as oligotrophic, mesotrophic, eutrophic, and dystrophic based on their concentrations of total phosphorus and dissolved organic carbon. Additionally, we studied phytoplankton photosynthetic carbon fractionation (εp) in laboratory conditions. The photosynthetic fractionation in 28 phytoplankton cultures from nine different phytoplankton classes varied significantly at the class level, and fractionation correlated significantly with the DIC concentration of the growth media. In small boreal lakes, the δ13C values of different phytoplankton taxa, as directly measured or estimated from the δ13C values of biomarker fatty acids, varied greatly (−18‰ to −44.5‰). Phytoplankton δ13C values varied significantly by lake type and were most depleted in dystrophic lakes even though the δ13C values of the DIC was similar to mesotrophic lakes. Further within‐taxa variation was found between lakes and between different depths within a lake. Vertical samples from dystrophic lakes also showed lower εp in the phytoplankton from meta‐ and hypolimnion, possibly as a result of reduced light intensity. Altogether, in nine of the 10 sampled lakes, the δ13C values of cladoceran zooplankton were between the minimum and the maximum phytoplankton δ13C value of each lake, and thus, phytoplankton alone could explain zooplankton δ13C values. We conclude that stable isotope mixing models should take into account carbon variation among different phytoplankton taxa.

ABUNDANCE AND ISOTOPIC COMPOSITION OF PLANKTONIC MICROCRUSTACEANS IN A CENTRAL AMAZON FLOODPLAIN LAKE: IMPLICATIONS FOR THE TROPHIC DYNAMICS OF THE PLANKTON COMMUNITY

<p>During the hydrological year from December 2007 to November 2008, monthly samplings in the pelagic, littoral and macrophytes zones were conducted in the Lago Catalão, a floodplain lake receiving a mixture of water from Negro and Solimões Rivers, in front of Manaus city. Taxonomic composition and their relative abundance of the planktonic microcrustaceans community was studied. Natural abundances of carbon (C) and nitrogen (N) stable isotopes were measured to indicate energy sources. Cladocerans were the most abundant, with a relative abundance of 60%, followed by the calanoid and cyclopoid copepods with relative abundances of 29% and 11%, respectively. Diaphanosoma spp. was the dominant cladoceran group during all the sampling periods. Cladocerans were also represented by Moina spp., Ceriodaphnia spp. and Daphnia gessneri. Three genera of calanoid copepods were found: Notodiaptomus spp, Rhacodiaptomus spp., and Argyrodiaptomus spp. The genus Mesocyclops spp. was identified among the cyclopoid copepods. Zooplankton δ13C values indicated that the aquatic macrophyte zone was distinct, with a mean of -27.31‰, which was more enriched than zooplankton in the pelagic and littoral zones, where they had mean δ13C values of -33.11 and -34.66‰, respectively. Overall, analysis of stable isotopes showed that regardless of the pathways, the initial source of carbon for the zooplankton was phytoplankton, with a minimal participation of heterotrophic bacteria.</p>

The effect of summer monsoon on pelagic and littoral food webs in a large regulated reservoir (Lake Paldang, Korea): A stable isotope approach

To investigate the effect of summer monsoon-derived inputs of particulate organic matter (POM) on patterns of stable isotopes in the food web in a reservoir, we traced dietary sources of carbon and nitrogen in pelagic zooplankton and herbivorous littoral zoobenthos following a monsoonal disturbance in Lake Paldang, a large regulated reservoir in Korea. Carbon and nitrogen stable isotopes were analyzed in POM, zooplankton, sedimentary organic matter, zoobenthos, and piscivorous fishes in pre- and post-summer monsoon periods. Sharp depletion of 13C and enrichment of 15N of POM along with elevated POC/Chl a ratios occurred following the summer monsoon period, reflecting the rapid reduction of phytoplankton biomass and a pulsed supply of terrestrial organic detritus. Herbivorous zooplankton δ13C values, which were initially similar to POM δ13C values in the pre-summer monsoon period, decreased to nearly that of terrestrial organic matter, providing isotopic evidence of allochthonous contribution to zooplankton in the post-summer monsoon period. In contrast, herbivorous zoobenthos in the littoral area and higher fishes appeared to have a similar stable isotope composition between the pre- and post-summer monsoon period. Our findings indicate that although monsoon storms dramatically decrease phytoplankton biomass, the augmented allochthonous material after the summer monsoon offsets this effect temporarily by subsidizing pelagic zooplankton production. Allochthonous subsidies to herbivorous littoral zoobenthos and piscivorous fishes are relatively limited.

Spatial patterns in zooplankton communities and stable isotope ratios (δ13C and δ15N) in relation to oceanographic conditions in the sub-Arctic Pacific and western Arctic regions during the summer of 2008

We define the biogeographic status quo of zooplankton communities sampled during the summer of 2008 in the sub-Arctic Pacific and western Arctic regions and examine spatial patterns of stable isotopes in the context of regional oceanography. Eight zooplankton assemblages were identified and corresponded to these regions: Gulf of Alaska, Bering Sea Slope, St-Lawrence Island, Western Bering Strait, Eastern Bering Strait, Barrow Canyon, Beaufort Gyre and Beaufort Shelf. Neocalanus spp., Eucalanus bungii and Metridia pacifica were abundant in the warmer and saltier waters of the Gulf of Alaska and on the Bering Sea Slope, whereas Calanus hyperboreus, Calanus glacialis and Metridia longa were abundant in the cold and fresher Arctic waters on the Beaufort Shelf and in the Beaufort Gyre. Salinity, nitrate and temperature, all of which were strongly correlated with latitude, and water column depth were the main factors influencing variation of zooplankton composition and spatial distribution. The δ15N values were less enriched in the Gulf of Alaska and on the Bering Sea Slope and more enriched in the eastern portion of Bering Strait and in Barrow Canyon. The δ13C values of zooplankton were more depleted in the Gulf of Alaska and in the Beaufort Sea regions and were more enriched in Western Bering Strait. The level of carnivory in the zooplankton community appeared highest in the Beaufort Gyre decreasing on the Beaufort Shelf and lowest in Western Bering Strait and in the Gulf of Alaska. Our results highlight the existence of large intra- and inter-specific differences in zooplankton isotopic signatures in relation to community composition and environmental conditions.

Seasonal shifts between autochthonous and allochthonous carbon contributions to zooplankton diets in a subarctic lake

We addressed the extent to which autochthonous and allochthonous carbon sources contribute to zooplankton diet throughout the year in oligotrophic subarctic Lake Saanajärvi. Optical measures of dissolved organic matter (DOM) indicated high water discharge and associated terrestrial DOM during winter and low inputs in summer. Bulk particulate organic matter (POM) showed δ13C values consistent with allochthonous inputs of DOM. The most positive POM δ13C values (−27‰) occurred during winter, when heterotrophic bacteria and nanoflagellates peaked in abundance; the isotopically lighter autotrophic phytoplankton shifted the POM δ13C to −29‰ in summer. The δ13C values of zooplankton were up to 4‰ more negative than those of POM, most likely because detritus and other nonliving material with higher δ13C values comprised 45–90% of POM. The δ13C of the cladoceran Daphnia umbra mirrored the trend of POM δ13C, indicating a dietary shift from heavy dependence on autochthonous carbon in summer to allochthonous or heterotrophic food in winter. The δ13C of the most abundant zooplankton in Lake Saanajärvi, Eudiaptomus graciloides and Cyclops abyssorum, remained low and constant in winter, suggestive of little or no food intake during the 8 months of winter. There are significant differences in the zooplankton utilization of nonphytoplankton carbon in different seasons and among species. Although autochthonous carbon seemed to be mainly responsible for the growth of zooplankton, the ability to utilize allochthonous carbon‐fueled microorganisms explains the survival of Daphnia through winter in northern lakes.

Zooplankton, lipids and stable isotopes: importance of seasonal, latitudinal, and taxonomic differences

We found considerable seasonal, latitudinal, and taxonomic differences in zooplankton lipid content and concurrent δ13C values of zooplankton. We collected cladoceran as well as cyclopoid and calanoid copepod zooplankton from boreal and subarctic lakes throughout a year, allowing us to study zooplankton likely subjected to different isotopic fractionation processes and with highly variable lipid contents. Considerable seasonal variation was observed in the difference between bulk and lipid-extracted zooplankton δ13C values, indicating that seasonally changing lipid content introduced notable variation in zooplankton δ13C values. The difference between bulk and lipid-extracted material was most amplified in lipid-rich subarctic zooplankton in winter, δ13C difference being >5 units. Significant differences were also observed among zooplankton taxa, with copepods showing a greater lipid impact on δ13C than cladocerans. Published lipid correction models failed to produce satisfying fits to our data, and considerable variation was left even after recalibrating the model parameters. This was likely due to taxonomic differences in lipid effects on δ13C values. We therefore produced separate mass balance-based lipid correction models for cladocerans and also cyclopoid and calanoid copepods. We conclude that arithmetic lipid correction models perform well with zooplankton samples, but taxonomic differences need to be considered.

Benthic algae support zooplankton growth during winter in a clear‐water lake

We used stable carbon (δ13C) and nitrogen (δ15N) isotopes to assess the importance of benthic algae for the zooplankton individual growth in winter in a shallow, clear subarctic lake. The δ13C values of calanoid (Eudiaptomus graciloides) and cyclopoid (Cyclops scutifer) zooplankton in autumn suggest a food resource of pelagic origin during the ice‐free period. The zooplankton δ13C values were high in spring compared to autumn. E. graciloides did not grow over winter and the change in δ13C was attributed to a decrease in lipid content during the winter. In contrast, the increase in δ13C values of C. scutifer over the winter was explained by their growth on organic carbon generated by benthic algae. The δ15N of the C. scutifer food resource during winter was low compared to δ15N of the benthic community, suggesting that organic matter generated by benthic algae was mainly channelled to zooplankton via 15N‐depleted heterotrophic bacteria. The results demonstrate that benthic algae can sustain zooplankton metabolic demands and growth during long winters, which, in turn, may promote zooplankton growth on pelagic resources during the summer. Such multi‐chain omnivory challenges the view of zooplankton as mainly dependent on internal primary production and stresses the importance of benthic resources for the productivity of plankton food webs in shallow lakes.