Nutritional constraints at the cyanobacteria—Daphnia magna interface: The role of sterols

Abstract

In past decades, a considerable amount of research has been conducted to elucidate the factors that affect the carbon transfer across the cyanobacteria-Daphnia interface. It is well accepted that cyanobacteria are a nutritionally inadequate food source for cladocerans, but the underlying mechanisms are still controversial. Morphological properties, toxicity, and the absence of essential lipids, i.e., polyunsaturated fatty acids (PUFAs) and sterols, are discussed as the most important factors that account for this nutritional inadequacy. Here, we conducted standardized growth experiments with the herbivore Daphnia magna feeding on coccal, filamentous, and putatively toxic cyanobacterial strains comprising the genera Synechococcus, Anabaena, Aphanizomenon, and Microcystis and on a cyanobacterial mixture containing strains of these genera. The relative importance of PUFAs and sterols in determining the food quality of cyanobacteria for Daphnia was assessed by supplementation of eicosapentaenoic acid-and/or cholesterol-containing liposomes to the cyanobacterial carbon. We provide evidence that somatic growth of daphnids on coccal as well as on filamentous cyanobacteria is primarily constrained by the absence of sterols, provided that the cyanobacterial carbon is readily ingested and nontoxic. The absence of PUFAs in cyanobacteria appears to be of minor importance for somatic growth but potentially affects egg production in Daphnia. Thus, the absence of sterols has to be considered a major food-quality constraint that potentially affects the efficiency of carbon transfer across the cyanobacteria-Daphnia interface.

Water fleas require microbiota for survival, growth and reproduction

“…Bacteria alone cannot meet the nutritional requirements of Daphnia because they lack sterols and polyunsaturated fats that are required by Daphnia for somatic growth and reproduction (Martin-Creuzburg and Von Elert, 2004;Martin-Creuzburg et al, 2008Taipale et al, 2012). In our study, Daphnia from all treatments were fed equal amounts of Scenedesmus, an alga that typically sustains growth and reproduction in Daphnia.…”

Light, nutrients, and food-chain length constrain planktonic energy transfer efficiency across multiple trophic levels

“…In contrast, cyanobacteria, which were most abundant in 3-level systems with high light and low nutrients, have low fatty acid and sterol concentrations, represent the lowest food quality of any taxonomic group, and were associated with high C/P. In addition to the low fatty acid content of cyanobacteria, recent studies indicate that the absence of sterols in cyanobacteria may contribute to their low quality as food for zooplankton (17). Chlorophytes are generally of intermediate quality in terms of these indicators (18).…”

“…Algal cell carbon/nitrogen (C/N) and carbon/phosphorus (C/P) ratios decrease with increasing nutrients and decreasing light intensity (10,12,13), and the ecological efficiency of aquatic herbivores is often higher under low light and/or high nutrient conditions, when algal C/P is relatively low (14)(15)(16). However, other aspects of algal food quality may also covary with stoichiometry, such as morphological features (e.g., size, shape, presence of gelatinous sheaths) and biochemicals (e.g., essential fatty acid and sterol concentrations) (11,17). Because algal species differ in these characteristics, phytoplankton taxonomic identity may be a surrogate of food quality.…”

Spatial avoidance of Microcystis aeruginosa by Daphnia: Fitness consequences and evolutionary implications

“…There is much less information on how food conditions alter the spatial distribution of zooplankton populations, and most studies have focused on the response of zooplankton to edible and nutritional foods (Haney 1993;Larsson 1997;Lampert et al 2003). Cyanobacteria are often poor food for Cladocera, interfering with filter feeding (Hawkins and Lampert 1989;Gliwicz and Lampert 1990), providing inadequate nutrition (Martin-Creuzburg et al 2008), and producing toxic secondary metabolites (Ibelings and Havens 2008). Regularly occurring blooms of cyanobacteria in the warm epilimnetic waters of lakes may last for days or months, representing a major potential threat to zooplankton grazers such as Daphnia.…”

“…Concerning cyanobacteria, the different mechanisms rendering them poor food for filter feeders may be relevant for the behavioral response. Reichwaldt (2008) looked at vertical distributions of Daphnia in gradients of Scenedesmus and the cyanobacterium Synechococcus, lacking sterols (Martin-Creuzburg et al 2005). A similar study by Reichwaldt and Abrusan (2007) tested the effect of filamentous Planktothrix interfering with the filtering process.…”