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Your search keyword '"Strandberg, U."' showing total 2 results
Start Over Author "Strandberg, U." Publisher ecological society of america
2 results on '"Strandberg, U."'

1. Inferring phytoplankton community composition with a fatty acid mixing model

Author

Strandberg, U., Taipale, Sami, Hiltunen, M., Galloway, A. W. E., Brett, M. T., and Kankaala, P.

Subjects
zooplankton, FASTAR, seasonality, fungi, chemotaxonomic marker, Bayesian mixing model, food quality, freshwater phytoplankton, levät, polyunsaturated fatty acid
Abstract

The taxon specificity of fatty acid composition in algal classes suggests that fatty acids could be used as chemotaxonomic markers for phytoplankton composition. The applicability of phospholipid-derived fatty acids as chemotaxonomic markers for phytoplankton composition was evaluated by using a Bayesian fatty acid-based mixing model. Fatty acid profiles from monocultures of chlorophytes, cyanobacteria, diatoms, euglenoids, dinoflagellates, raphidophyte, cryptophytes and chrysophytes were used as a reference library to infer phytoplankton community composition in five moderately humic, large boreal lakes in three different seasons (spring, summer and fall). The phytoplankton community composition was also estimated from microscopic counts. Both methods identified diatoms and cryptophytes as the major phytoplankton groups in the study lakes throughout the sampling period, together accounting for 54–63% of the phytoplankton. In addition, both methods revealed that the proportion of chlorophytes and cyanobacteria was lowest in the spring and increased towards the summer and fall, while dinoflagellates peaked in the spring. The proportion of euglenoids and raphidophytes was less than 8% of the phytoplankton biomass throughout the sampling period. The model estimated significantly lower proportions of chrysophytes in the seston than indicated by microscopic analyses. This is probably because the reference library for chrysophytes included too few taxa. Our results show that a fatty acid-based mixing model approach is a promising tool for estimating the phytoplankton community composition, while also providing information on the nutritional quality of the seston for consumers. Both the quantity and the quality of seston as a food source for zooplankton were high in the spring; total phytoplankton biomass was ~ 56µgCL 1, and the physiologically important polyunsaturated fatty acids 20:5n-3 and 22:6n-3 comprised ~ 22% of fatty acids. peerReviewed

Published
2015

2. Differing Daphnia magna assimilation efficiencies for terrestrial, bacterial, and algal carbon and fatty acids.

Author

Taipale SJ, Brett MT, Hahn MW, Martin-Creuzburg D, Yeung S, Hiltunen M, Strandberg U, and Kankaala P

Subjects
Animals, Carbon chemistry, Cryptophyta metabolism, Fatty Acids chemistry, Nitrogen, Phosphorus, Phytoplankton, Sterols, Bacteria chemistry, Carbon metabolism, Cryptophyta chemistry, Daphnia metabolism, Energy Metabolism physiology, Fatty Acids metabolism
Abstract

There is considerable interest in the pathways by which carbon and growth-limiting elemental and biochemical nutrients are supplied to upper trophic levels. Fatty acids and sterols are among the most important molecules transferred across the plant-animal interface of food webs. In lake ecosystems, in addition to phytoplankton, bacteria and terrestrial organic matter are potential trophic resources for zooplankton, especially in those receiving high terrestrial organic matter inputs. We therefore tested carbon, nitrogen, and fatty acid assimilation by the crustacean Daphnia magna when consuming these resources. We fed Daphnia with monospecific diets of high-quality (Cryptomonas marssonii) and intermediate-quality (Chlamydomonas sp. and Scenedesmus gracilis) phytoplankton species, two heterotrophic bacterial strains, and particles from the globally dispersed riparian grass, Phragmites australis, representing terrestrial particulate organic carbon (t-POC). We also fed Daphnia with various mixed diets, and compared Daphnia fatty acid, carbon, and nitrogen assimilation across treatments. Our results suggest that bacteria were nutritionally inadequate diets because they lacked sterols and polyunsaturated omega-3 and omega-6 (omega-3 and omega-6) fatty acids (PUFAs). However, Daphnia were able to effectively use carbon and nitrogen from Actinobacteria, if their basal needs for essential fatty acids and sterols were met by phytoplankton. In contrast to bacteria, t-POC contained sterols and omega-6 and omega-3 fatty acids, but only at 22%, 1.4%, and 0.2% of phytoplankton levels, respectively, which indicated that t-POC food quality was especially restricted with regard to omega-3 PUFAs. Our results also showed higher assimilation of carbon than fatty acids from t-POC and bacteria into Daphnia, based on stable-isotope and fatty acids analysis, respectively. A relatively high (>20%) assimilation of carbon and fatty acids from t-POC was observed only when the proportion of t-POC was >60%, but due to low PUFA to carbon ratio, these conditions yielded poor Daphnia growth. Because of lower assimilation for carbon, nitrogen, and fatty acids from t-POC relative to diets of bacteria mixed with phytoplankton, we conclude that the microbial food web, supported by phytoplankton, and not direct t-POC consumption, may support zooplankton production. Our results suggest that terrestrial particulate organic carbon poorly supports upper trophic levels of the lakes.

Published
2014
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