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Imbalance of fatty acids in the base of the Baltic Sea food web — a mesocosm study

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A reproductive disturbance in Baltic Sea Atlantic salmon (Salmo salar), the M74 syndrome, has been reported since early 1970s and has occasionally caused up to 90% mortality for newborn fry. Previous research has revealed that the M74 syndrome may be due to reduced levels of the vitamin thiamin, the carotenoid astaxanthin, and elevated ratios of 3/6 fatty acids in salmon eggs. Using mesocosm experiments, we compared the quantity (µg·L–1) and quality (mg·g–1 C) of fatty acids in microalgae and copepods in the southern Baltic Sea where the M74 syndrome is common with those in a habitat in the Norwegian Sea where the syndrome has not been observed. Daily additions were made of the nutrients N and P or N, P, and Si, copepods were added after 6–7 days, and nutrient additions were stopped after 9–10 days. Flagellates dominated completely in the Baltic Sea, whereas higher phytoplankton diversity was found in the Norwegian Sea. We found elevated 3/6 ratios in phytoplankton and abnormally high docosahexaenoic acid/arachidonic acid ratios (22:63/20:46) in copepods in the Baltic Sea mesocosms compared with those in the Norwegian Sea. Our results suggest that imbalance in fatty acid composition may prevail in the basic food web of the Baltic Sea.

On a signalé depuis le début des années 1970 une perturbation de la reproduction, le syndrome M74, chez le saumon atlantique (Salmo salar) de la Baltique qui, à l’occasion, cause une mortalité pouvant atteindre 90 % chez les alevins néonates. Les études antérieures ont montré que le syndrome M74 peut être dû à des concentrations faibles de la vitamine thiamine et du caroténoïde l’astaxanthine et à des rapports élevés des acides gras 3/6 dans les oeufs de saumons. Dans des expériences de mésocosmes, nous avons comparé la quantité (µg·L–1) et la qualité (mg·g–1 C) des acides gras dans les microalgues et les copépodes dans le sud de la Baltique où le syndrome M74 est répandu à celles d’un habitat de la mer de Norvège où le syndrome n’a pas été observé. Nous avons ajouté quotidiennement les nutriments N et P ou alors N, P et Si, introduit des copépodes au bout de 6–7 jours et arrêté les additions de nutriments après 9–10 jours. Dans la Baltique, les flagellés sont dominants, alors que, dans la mer de Norvège, le phytoplancton est plus diversifié. Dans les mésocosmes de la Baltique, les rapports 3/6 du phytoplancton sont élevés et les rapports acide docosahexanoïque/acide arachidonique (22:63/20:46) anormalement grands chez les copépodes, par comparaison aux mésocosmes de la mer de Norvège. Nos résultats laissent croire qu’il peut y avoir un déséquilibre dans la composition en acides gras dans le réseau alimentaire de base de la Baltique.

Document Type: Research Article

Publication date: October 1, 2005

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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