Editorial: Essential Biomolecules Caught in the Food Web?

Peer Reviewe

Climate change drives widespread shifts in lake thermal habitat

Lake surfaces are warming worldwide, raising concerns about lake organism responses to thermal habitat changes. Species may cope with temperature increases by shifting their seasonality or their depth to track suitable thermal habitats, but these responses may be constrained by ecological interactions, life histories or limiting resources. Here we use 32 million temperature measurements from 139 lakes to quantify thermal habitat change (percentage of non-overlap) and assess how this change is exacerbated by potential habitat constraints. Long-term temperature change resulted in an average 6.2% non-overlap between thermal habitats in baseline (1978–1995) and recent (1996–2013) time periods, with non-overlap increasing to 19.4% on average when habitats were restricted by season and depth. Tropical lakes exhibited substantially higher thermal non-overlap compared with lakes at other latitudes. Lakes with high thermal habitat change coincided with those having numerous endemic species, suggesting that conservation actions should consider thermal habitat change to preserve lake biodiversity

Widespread deoxygenation of temperate lakes

The concentration of dissolved oxygen in aquatic systems helps to regulate biodiversity, nutrient biogeochemistry, greenhouse gas emissions, and the quality of drinking water. The long-term declines in dissolved oxygen concentrations in coastal and ocean waters have been linked to climate warming and human activity, but little is known about the changes in dissolved oxygen concentrations in lakes. Although the solubility of dissolved oxygen decreases with increasing water temperatures, long-term lake trajectories are difficult to predict. Oxygen losses in warming lakes may be amplified by enhanced decomposition and stronger thermal stratification8,9 or oxygen may increase as a result of enhanced primary production. Here we analyse a combined total of 45,148 dissolved oxygen and temperature profiles and calculate trends for 393 temperate lakes that span 1941 to 2017. We find that a decline in dissolved oxygen is widespread in surface and deep-water habitats. The decline in surface waters is primarily associated with reduced solubility under warmer water temperatures, although dissolved oxygen in surface waters increased in a subset of highly productive warming lakes, probably owing to increasing production of phytoplankton. By contrast, the decline in deep waters is associated with stronger thermal stratification and loss of water clarity, but not with changes in gas solubility. Our results suggest that climate change and declining water clarity have altered the physical and chemical environment of lakes. Declines in dissolved oxygen in freshwater are 2.75 to 9.3 times greater than observed in the world’s oceans and could threaten essential lake ecosystem services

Global data set of long-term summertime vertical temperature profiles in 153 lakes

Climate change and other anthropogenic stressors have led to long-term changes in the thermal structure, including surface temperatures, deepwater temperatures, and vertical thermal gradients, in many lakes around the world. Though many studies highlight warming of surface water temperatures in lakes worldwide, less is known about long-term trends in full vertical thermal structure and deepwater temperatures, which have been changing less consistently in both direction and magnitude. Here, we present a globally-expansive data set of summertime in-situ vertical temperature profiles from 153 lakes, with one time series beginning as early as 1894. We also compiled lake geographic, morphometric, and water quality variables that can influence vertical thermal structure through a variety of potential mechanisms in these lakes. These long-term time series of vertical temperature profiles and corresponding lake characteristics serve as valuable data to help understand changes and drivers of lake thermal structure in a time of rapid global and ecological change

Global data set of long-term summertime vertical temperature profiles in 153 lakes

Measurement(s) : temperature of water, temperature profile Technology Type(s) : digital curation Factor Type(s) : lake location, temporal interval Sample Characteristic - Environment : lake, reservoir Sample Characteristic - Location : global Machine-accessible metadata file describing the reported data: https://doi.org/10.6084/m9.figshare.14619009Climate change and other anthropogenic stressors have led to long-term changes in the thermal structure, including surface temperatures, deepwater temperatures, and vertical thermal gradients, in many lakes around the world. Though many studies highlight warming of surface water temperatures in lakes worldwide, less is known about long-term trends in full vertical thermal structure and deepwater temperatures, which have been changing less consistently in both direction and magnitude. Here, we present a globally-expansive data set of summertime in-situ vertical temperature profiles from 153 lakes, with one time series beginning as early as 1894. We also compiled lake geographic, morphometric, and water quality variables that can influence vertical thermal structure through a variety of potential mechanisms in these lakes. These long-term time series of vertical temperature profiles and corresponding lake characteristics serve as valuable data to help understand changes and drivers of lake thermal structure in a time of rapid global and ecological change

Evidence that a highly unsaturated fatty acid limits Daphnia growth in nature

This study relates measured sestonic food parameters to growth rates of Daphnia galeata. Daphnia growth rates were obtained from standardized laboratory experiments feeding the animal natural lake seston. The experimental period spanned one season. Elemental (carbon, nitrogen, phosphate) and biochemical (fatty acids) food parameters of this natural food source were compared. The correlation between growth rates and sestonic phosphorus was very weak (r-2 = 0.08). The regressions with the nitrogen (r-2 = 0.42) and carbon (r-2 = 0.62) content were significantly better but still exhibited the usual considerable scatter around the regression line. In contrast, a very tight correlation (r-2 = 0.93) was found between Daphnia growth rates and the sestonic content of eicosapentaenoic acid (2Q:5-omega-3), an essential, highly unsaturated fatty acid. This relationship exhibited a normal asymptotic curve with a distinct plateau above concentrations of 0.8 mu-g 20:5-omega-3/L. In contrast, a plateau was not observed for particulate organic carbon, nitrogen or phosphate. Carbon, nitrogen and other essential fatty acids were not only moderately correlated to Daphnia's growth rates but also to 20:5-omega-3. Thus, the modest suitability of carbon and nitrogen as food parameters seems to be due to co-occurrence with 20:5-omega-3. This shows, that the sestonic 20:5-omega-3 content is a parameter for natural food quantity including its food quality. High 20:5-omega-3 concentrations within the plateau region occurred mostly during spring. These results suggest that Daphnia was limited by the 20:5-omega-3 concentration during most of the summe

Essential Biomolecules in Food Webs

We here review the ecological role of essential nutritional biomolecules [fatty acids (FA), amino acids (AA), sterols, vitamins] in aquatic and terrestrial food webs, encompassing the forces behind their environmental distribution. Across ecosystems, mutualistic relationships frequently ensure exchanges of vitamins between producer and demander, especially between B12 and other B vitamins as well as the AA methionine. In contrast, FA, sterols and most AA are transferred up the food chain via classical predatorprey interactions, and therefore have good biomarker potential for trophic interactions. As biomass-flow depends on the absolute amounts of potential limiting resources, considering solely the relative share in the respective biochemical group may underor overestimate the availability to consumers. Moreover, if not accounted for, “hidden” trophic channels, such as gut symbionts as well as metabolic conversion of precursor molecules, can hamper food web analyses. Fundamental differences exist between aquatic and terrestrial ecosystems: Vitamin B12 produced by ammonium oxidizing Archaea is essential to many aquatic algae, whereas terrestrial plants escaped this dependency by using B12 independent enzymes. Long-chain &3 polyunsaturated FA (LC-&3PUFA) in aquatic systemsmainly originate fromplanktonic algae, while in terrestrial systems, belowground invertebrates can well be a source, also supporting aboveground biota. Interlinks from terrestrial to aquatic ecosystems are of a biochemically totally different nature than vice versa. While biomass rich in proteins and LC-&3PUFA is transferred to land, e.g., by trophic relationships, the link from terrestrial to aquatic ecosystems provides recalcitrant plant carbon, mainly devoid of essential nutrients, fuelling detrital food chains. Recent global changes influence food webs via altered input and transfer of essential biomolecules, but separating the effects of nutrients, CO2, and warming is not trivial. Current evolutionary concepts (e.g., Black Queen, relaxed selection) considering the costs of metabolic production partly explain food web dynamics, especially for vitamins, whereas adaptations to potential oxidative stress seemto bemore important for LC-PUFA. Overall, the provision with essential biomolecules is precious for both heterotrophs and auxotrophs. These nutritional valuable molecules often are kept unaltered in consumer metabolism, including their stable isotope composition, offering a great advantage for their use as trophic markers.Peer Reviewe

Bioactive Compounds Offered in Microcapsules to Determine the Nutritional Value of Copepods’ Natural Diet

Experiments were performed, feeding Calanus pacificus seston and a food consisting of seston and microcapsules (μ-caps), i.e., protein and lipid μ-caps to test for potential biochemical limitation. Seston was collected off Scripps Pier (La Jolla, CA, USA). Whereas protein μ-caps were too small to be efficiently ingested, lipid μ-caps rich in ω3-highly-unsaturated fatty acids (ω3-HUFA) were ingested similarly to natural seston and lipids were assimilated. However, egg production experiments exhibited that animals fed with lipid μ-caps didn’t produce significantly more eggs than with seston of equal carbon concentration and egg production even declined when the diet consisted of 50% lipid μ-caps. Thus, the content of certain ω3-HUFA seemed to have been sufficiently high in seston to prevent limitation. Algal counts revealed that seston consisted mainly of plankton rich in those fatty acids, such as cryptophytes, dinoflagellates, diatoms, and ciliates in the edible size range. This might be characteristic for upwelling systems like the area off Southern California which are known for high trophic transfer efficiency

Seasonal patterns of food limitation in Daphnia galeata: separating food quantity and food quality effects

Food limitation for the cladoceran Daphnia galeata was measured growing them with natural lake seston for one growing season under standardized conditions in the laboratory. Growth rates were related to several measures of food quantity. Particulate organic carbon (POC) <30 mu m was the best predictor of total food availability measured. It was better than chlorophyll-a (Chi-a) of the same size fraction, algal volume calculated from cell counts or total particle volume from Coulter Counter measurements. Daphnids were also grown with Scenedesmus acutus under the same conditions and their growth rates were compared. Sestonic carbon concentrations were related to Scenedesmus carbon concentrations, that provided equal growth rates. The ratio of the carbon concentrations of both food types (seston, Scenedesmus) represented the food quality of seston. Thus, the nutritional quality of natural lake seston relative to a standard alga was determined over one growing season. Growth rates of seston fed animals revealed that they were food limited during long periods of the year. This was also ascertained by standard clutch sizes of field animals. However, the causes of food limitation varied within the duration of the studied period. Whereas during the clear water phase the food quantity was limiting (while the quality was high; 100% Scenedesmus). shortly after on 10 June and 17 June food conditions were close to threshold concentrations due to low food quality. For the remainder of the summer, a POC of 0.3-0.6 mg C l(-1) with a quality of similar to 50% Scenedesmus, resulted in moderate food limitation of Daphni