Growth and reproduction of Daphnia galeata in response to changes in fatty acids, phosphorus, and nitrogen in Chlamydomonas reinhardtii

Abstract

The importance of changes in elemental and fatty acid composition of the algal food for Daphnia galeata was investigated. The green alga Chlamydomonas reinhardtii was grown under nitrogen or phosphorus limitation to modify its elemental and biochemical composition. Both N-and P-limited slgae exhibited similar fatty acid compositions but differed from algae grown under N and P saturation. Nutrient iimitation of algae caused the amounts of saturated fatty acids, monounsaturated, and diunsaturated fatty acids to ncrease, but those of polyunsaturated fatty acids to decrease markedly. Life-history experiments with D. galeatu, carried out to examine the effects of the varying N and P regimes to the food quality of Chlamydomonas, revealed that N-limited and N+P-saturated algae were of a comparable quality. In contrast, P-limited alga was a very poor food; that is, both population growth and somatic growth rate were much lower than with N-and N+P-saturated algae. Differences of algal fatty acid composition did not explain the differences in algal food quality as N+P-saturated and N-limited Chlamydomonas were both similar in quality despite differences in fatty acid composition. P limitation of daphnid growth is more consistent with the observed differences in growth and reproduction. The low growth rates of the daphnids when fed P-limited alga, however, may also be a result of indirect effects because P limitation may induct changes in algal morphology or biochemical compounds other than fatty acids.

Phosphorus limitation in Daphnia: Evidence from a long term study of three hypereutrophic Dutch lakes

“…Therefore, our results do not directly rule out the possibility that fatty acids, digestion resistance, or another factor influencing food quality covaried with the seston C : P ratio. However, several recent laboratory studies provide support for the elemental limitation hypothesis and/or evidence against alternative hypotheses for mechanisms underlying the poor food quality of P-deficient algae for Daphnia (e.g., Sundbom and Vrede 1997;Urabe et al 1997;Weers and Gulati 1997;DeMott 1998;DeMott et al 1998). These studies also point to methods for manipulating the quality of natural seston to provide direct experimental tests of the mechanism(s) by which food quality may constrain Daphnia growth and abundance.…”

Nutritional quality of seston for the freshwater herbivore Daphnia galeata × hyalina: biochemical versus mineral limitations

“…If the phosphorus concentration of algae is low, nutritional quality of the food is low (Urabe et al 1997;DeMott et al 1998). On the other hand, several studies have indicated the importance of highly unsaturated fatty acids (HUFAs), such as eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) for herbivorous zooplankton (Müller-Navarra 1995; Brett and Müller-Navarra 1997;Sundbom and Vrede 1997;Weers and Gulati 1997b). The empirical support comes mainly from laboratory experiments with algal monocultures grown under different conditions (e.g.…”

The nutritional quality of P‐limited algae for Daphnia

“…The discussion on mineral versus biochemical limitations has triggered a series of studies on the nature of food-quality constraints on zooplankton growth (DeMott and Müller-Navarra 1997;Lürling and van Donk 1997;Sundbom and Vrede 1997;Urabe et al 1997;Weers and Gulati 1997b;Weers and Gulati 1997a;DeMott et al 1998). Thus far, most of the published reports seem to conclude that, direct phosphorus-limitation plays a role, with other unknown differences also of potential importance.…”

“…However, in some field studies the correlation of daphniid growth and the phosphorus content of the seston was low (Hessen 1989;Müller-Navarra 1995b), which has lead to alternative explanations for the distinct effect of nutrient limitation in food on the growth of zooplankters in laboratory experiments. Nutrient-limited algae contain a different fatty acid spectrum when compared to non-limited algae (Müller-Navarra 1995a; Weers and Gulati 1997b), making them potentially less nutritious (Müller-Navarra 1995b). Although nutrient-limited algae contain higher absolute amounts of fatty acids, they seem to be lacking in highly unsaturated fatty acids, such as eicosapentaenoic acid (EPA,20:53), or docosahexaenoic acid (DHA, 22:63) (Reitan et al 1994;Müller-Navarra 1995a), which are essential for animal growth (e.g., Reitan et al 1997).…”