Sundbom, M., T. Vrede
Abstract:
Although the beneficial effects of w3-polyunsaturated fatty (w3-PUFA) acids have been extensively studied within health sciences and aquaculture, little is known about their role in aquatic food webs. Recent studies have however indicated a strong relationship between w3-PUFA in food items and zooplankton production. On the other hand it has been suggested that nutrients, in particular phosphorus (P), may limit the secondary production in lakes. This controversy arising from different studies employing a correlative approach may partly be explained by a natural covariation between w3-PUFA and P-contents in phytoplankton; previous studies have in many cases only focused on one of these two parameters. Moreover have algae of different taxe, potentially differing in size, toxicity and digestability, been compared regarding food quality and fatty acid composition.
Using microencapsulation techniques and a single algal species (Scenedesmus quadricauda) at different levels of P-deficiency we here present an experimental design that allows estimation of the relative importance of P and different w3-PUFA for Daphnia. Results show that algal nutrient stress has large negative impact on food quality. Additions of w3-PUFA did however also stimulate Daphnia production; eicosapentaenoic acid tended to exceed linolenic acid which in turn exceeded oleic acid (non-w3) in quality.
Different hypothesis and predictions are discussed. We suggest that w3-PUFA limit Daphnia production and that nutrient stress highly decreases digestibility of S. quadricauda.
(Uppsala University, Institute of Limnology, Norbyv. 20, 752 36 Uppsala, Sweden)
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